TODOs for later

Fixes #37708
Bug 1 part of the issue

src/compiler/diagnosticMessages.json

@@ -4473,6 +4473,10 @@
         "category": "Message",
         "code": 6235
     },
+    "Resolving type reference directive for program with typeRoots, skipping lookup in 'node_modules' folder.": {
+        "category": "Message",
+        "code": 6236
+    },
 
     "Projects to reference": {
         "category": "Message",

src/compiler/moduleNameResolver.ts

@@ -250,7 +250,7 @@ namespace ts {
         }
 
         if (currentDirectory !== undefined) {
-            return getDefaultTypeRoots(currentDirectory, host);
+            return getDefaultTypeRoots(currentDirectory);
         }
     }
 
@@ -258,19 +258,11 @@ namespace ts {
      * Returns the path to every node_modules/@types directory from some ancestor directory.
      * Returns undefined if there are none.
      */
-    function getDefaultTypeRoots(currentDirectory: string, host: { directoryExists?: (directoryName: string) => boolean }): string[] | undefined {
-        if (!host.directoryExists) {
-            return [combinePaths(currentDirectory, nodeModulesAtTypes)];
-            // And if it doesn't exist, tough.
-        }
-
+    function getDefaultTypeRoots(currentDirectory: string): string[] | undefined {
         let typeRoots: string[] | undefined;
         forEachAncestorDirectory(normalizePath(currentDirectory), directory => {
             const atTypes = combinePaths(directory, nodeModulesAtTypes);
-            if (host.directoryExists!(atTypes)) {
-                (typeRoots || (typeRoots = [])).push(atTypes);
-            }
-            return undefined;
+            (typeRoots || (typeRoots = [])).push(atTypes);
         });
         return typeRoots;
     }
@@ -343,15 +335,15 @@ namespace ts {
                     trace(host, Diagnostics.Resolving_with_primary_search_path_0, typeRoots.join(", "));
                 }
                 return firstDefined(typeRoots, typeRoot => {
-                    const candidate = combinePaths(typeRoot, typeReferenceDirectiveName);
-                    const candidateDirectory = getDirectoryPath(candidate);
-                    const directoryExists = directoryProbablyExists(candidateDirectory, host);
-                    if (!directoryExists && traceEnabled) {
-                        trace(host, Diagnostics.Directory_0_does_not_exist_skipping_all_lookups_in_it, candidateDirectory);
-                    }
                     return resolvedTypeScriptOnly(
-                        loadNodeModuleFromDirectory(Extensions.DtsOnly, candidate,
-                            !directoryExists, moduleResolutionState));
+                        nodeLoadModuleByRelativeName(
+                            Extensions.DtsOnly,
+                            combinePaths(typeRoot, typeReferenceDirectiveName),
+                            /*onlyRecordFailures*/ false,
+                            moduleResolutionState,
+                             /*considerPackageJson*/ true
+                        )
+                    );
                 });
             }
             else {
@@ -363,20 +355,25 @@ namespace ts {
 
         function secondaryLookup(): PathAndPackageId | undefined {
             const initialLocationForSecondaryLookup = containingFile && getDirectoryPath(containingFile);
-
             if (initialLocationForSecondaryLookup !== undefined) {
-                // check secondary locations
-                if (traceEnabled) {
-                    trace(host, Diagnostics.Looking_up_in_node_modules_folder_initial_location_0, initialLocationForSecondaryLookup);
-                }
+                // Do not resolve auto types from secondary location
                 let result: Resolved | undefined;
-                if (!isExternalModuleNameRelative(typeReferenceDirectiveName)) {
-                    const searchResult = loadModuleFromNearestNodeModulesDirectory(Extensions.DtsOnly, typeReferenceDirectiveName, initialLocationForSecondaryLookup, moduleResolutionState, /*cache*/ undefined, /*redirectedReference*/ undefined);
-                    result = searchResult && searchResult.value;
+                if (!options.typeRoots || !endsWith(containingFile!, inferredTypesContainingFile)) {
+                    // check secondary locations
+                    if (traceEnabled) {
+                        trace(host, Diagnostics.Looking_up_in_node_modules_folder_initial_location_0, initialLocationForSecondaryLookup);
+                    }
+                    if (!isExternalModuleNameRelative(typeReferenceDirectiveName)) {
+                        const searchResult = loadModuleFromNearestNodeModulesDirectory(Extensions.DtsOnly, typeReferenceDirectiveName, initialLocationForSecondaryLookup, moduleResolutionState, /*cache*/ undefined, /*redirectedReference*/ undefined);
+                        result = searchResult && searchResult.value;
+                    }
+                    else {
+                        const { path: candidate } = normalizePathAndParts(combinePaths(initialLocationForSecondaryLookup, typeReferenceDirectiveName));
+                        result = nodeLoadModuleByRelativeName(Extensions.DtsOnly, candidate, /*onlyRecordFailures*/ false, moduleResolutionState, /*considerPackageJson*/ true);
+                    }
                 }
-                else {
-                    const { path: candidate } = normalizePathAndParts(combinePaths(initialLocationForSecondaryLookup, typeReferenceDirectiveName));
-                    result = nodeLoadModuleByRelativeName(Extensions.DtsOnly, candidate, /*onlyRecordFailures*/ false, moduleResolutionState, /*considerPackageJson*/ true);
+                else if (traceEnabled) {
+                    trace(host, Diagnostics.Resolving_type_reference_directive_for_program_with_typeRoots_skipping_lookup_in_node_modules_folder);
                 }
                 const resolvedFile = resolvedTypeScriptOnly(result);
                 if (!resolvedFile && traceEnabled) {
@@ -944,6 +941,7 @@ namespace ts {
                 if (traceEnabled) {
                     trace(host, Diagnostics.Loading_module_0_from_node_modules_folder_target_file_type_1, moduleName, Extensions[extensions]);
                 }
+                // TODO:: resolve type ference directive
                 const resolved = loadModuleFromNearestNodeModulesDirectory(extensions, moduleName, containingDirectory, state, cache, redirectedReference);
                 if (!resolved) return undefined;
 
@@ -1473,7 +1471,8 @@ namespace ts {
                 }
                 if (extensions === Extensions.TypeScript) {
                     // If we didn't find the file normally, look it up in @types.
-                    return loadModuleFromNearestNodeModulesDirectoryTypesScope(moduleName, containingDirectory, state);
+                    // TODO type referecnce like resolution
+                    return resolveTypeReferenceDirective(moduleName, containingFile,  containingDirectory, state);
                 }
             }
             else {

src/compiler/resolutionCache.ts

@@ -869,26 +869,28 @@ namespace ts {
 
         function createTypeRootsWatch(typeRootPath: Path, typeRoot: string): FileWatcher {
             // Create new watch and recursive info
-            return resolutionHost.watchTypeRootsDirectory(typeRoot, fileOrDirectory => {
-                const fileOrDirectoryPath = resolutionHost.toPath(fileOrDirectory);
-                if (cachedDirectoryStructureHost) {
-                    // Since the file existence changed, update the sourceFiles cache
-                    cachedDirectoryStructureHost.addOrDeleteFileOrDirectory(fileOrDirectory, fileOrDirectoryPath);
-                }
+            return canWatchTypeRootPath(typeRootPath) ?
+                resolutionHost.watchTypeRootsDirectory(typeRoot, fileOrDirectory => {
+                    const fileOrDirectoryPath = resolutionHost.toPath(fileOrDirectory);
+                    if (cachedDirectoryStructureHost) {
+                        // Since the file existence changed, update the sourceFiles cache
+                        cachedDirectoryStructureHost.addOrDeleteFileOrDirectory(fileOrDirectory, fileOrDirectoryPath);
+                    }
 
-                // For now just recompile
-                // We could potentially store more data here about whether it was/would be really be used or not
-                // and with that determine to trigger compilation but for now this is enough
-                hasChangedAutomaticTypeDirectiveNames = true;
-                resolutionHost.onChangedAutomaticTypeDirectiveNames();
+                    // For now just recompile
+                    // We could potentially store more data here about whether it was/would be really be used or not
+                    // and with that determine to trigger compilation but for now this is enough
+                    hasChangedAutomaticTypeDirectiveNames = true;
+                    resolutionHost.onChangedAutomaticTypeDirectiveNames();
 
-                // Since directory watchers invoked are flaky, the failed lookup location events might not be triggered
-                // So handle to failed lookup locations here as well to ensure we are invalidating resolutions
-                const dirPath = getDirectoryToWatchFailedLookupLocationFromTypeRoot(typeRoot, typeRootPath);
-                if (dirPath) {
-                    scheduleInvalidateResolutionOfFailedLookupLocation(fileOrDirectoryPath, dirPath === fileOrDirectoryPath);
-                }
-            }, WatchDirectoryFlags.Recursive);
+                    // Since directory watchers invoked are flaky, the failed lookup location events might not be triggered
+                    // So handle to failed lookup locations here as well to ensure we are invalidating resolutions
+                    const dirPath = getDirectoryToWatchFailedLookupLocationFromTypeRoot(typeRoot, typeRootPath);
+                    if (dirPath) {
+                        scheduleInvalidateResolutionOfFailedLookupLocation(fileOrDirectoryPath, dirPath === fileOrDirectoryPath);
+                    }
+                }, WatchDirectoryFlags.Recursive) :
+                noopFileWatcher;
         }
 
         /**
@@ -906,7 +908,7 @@ namespace ts {
 
             // we need to assume the directories exist to ensure that we can get all the type root directories that get included
             // But filter directories that are at root level to say directory doesnt exist, so that we arent watching them
-            const typeRoots = getEffectiveTypeRoots(options, { directoryExists: directoryExistsForTypeRootWatch, getCurrentDirectory });
+            const typeRoots = getEffectiveTypeRoots(options, { getCurrentDirectory });
             if (typeRoots) {
                 mutateMap(
                     typeRootsWatches,
@@ -922,12 +924,11 @@ namespace ts {
             }
         }
 
-        /**
-         * Use this function to return if directory exists to get type roots to watch
-         * If we return directory exists then only the paths will be added to type roots
-         * Hence return true for all directories except root directories which are filtered from watching
-         */
-        function directoryExistsForTypeRootWatch(nodeTypesDirectory: string) {
+        function canWatchTypeRootPath(nodeTypesDirectory: string) {
+            // If type roots is specified, watch that path
+            if (resolutionHost.getCompilationSettings().typeRoots) return true;
+
+            // Otherwise can watch directory only if we can watch the parent directory of node_modules/@types
             const dir = getDirectoryPath(getDirectoryPath(nodeTypesDirectory));
             const dirPath = resolutionHost.toPath(dir);
             return dirPath === rootPath || canWatchDirectory(dirPath);

src/compiler/types.ts

@@ -7748,7 +7748,6 @@ namespace ts {
     }
 
     export interface GetEffectiveTypeRootsHost {
-        directoryExists?(directoryName: string): boolean;
         getCurrentDirectory?(): string;
     }
 

src/server/project.ts

@@ -2278,10 +2278,6 @@ namespace ts.server {
             return !!this.externalProjectRefCount;
         }
 
-        getEffectiveTypeRoots() {
-            return getEffectiveTypeRoots(this.getCompilationSettings(), this.directoryStructureHost) || [];
-        }
-
         /*@internal*/
         updateErrorOnNoInputFiles(fileNameResult: ExpandResult) {
             updateErrorForNoInputFiles(fileNameResult, this.getConfigFilePath(), this.configFileSpecs!, this.projectErrors!, this.canConfigFileJsonReportNoInputFiles);

src/services/types.ts

@@ -250,6 +250,7 @@ namespace ts {
         readFile?(path: string, encoding?: string): string | undefined;
         realpath?(path: string): string;
         fileExists?(path: string): boolean;
+        directoryExists?(directoryName: string): boolean;
 
         /*
          * LS host can optionally implement these methods to support automatic updating when new type libraries are installed

src/testRunner/unittests/reuseProgramStructure.ts

@@ -210,6 +210,18 @@ namespace ts {
         checkCache("resolved type directives", program, fileName, expectedContent, f => f.resolvedTypeReferenceDirectiveNames, checkResolvedTypeDirective);
     }
 
+    type Traces = [subScenario: string, program: ProgramWithSourceTexts][];
+    function baselineTrace(scenario: string, traces: Traces) {
+        const actual: MapLike<string[]> = {};
+        for (const [subScenario, program] of traces) {
+            actual[subScenario] = program.host.getTrace().map(Utils.sanitizeTraceResolutionLogEntry);
+        }
+        Harness.Baseline.runBaseline(
+            `reuseProgramStructure/${scenario.split(" ").join("-")}.trace.json`,
+            JSON.stringify(actual, undefined, 4)
+        );
+    }
+
     describe("unittests:: Reuse program structure:: General", () => {
         const target = ScriptTarget.Latest;
         const files: NamedSourceText[] = [
@@ -455,34 +467,11 @@ namespace ts {
             const options: CompilerOptions = { target: ScriptTarget.ES2015, traceResolution: true, moduleResolution: ModuleResolutionKind.NodeJs };
             const rootFiles = [file1Ts, file2Ts];
             const filesAfterNpmInstall = [file1Ts, file2Ts, indexDTS];
+            const traces: Traces = [];
 
             const initialProgram = newProgram(rootFiles, rootFiles.map(f => f.name), options);
             {
-                assert.deepEqual(initialProgram.host.getTrace(),
-                    [
-                        "======== Resolving module 'a' from 'file1.ts'. ========",
-                        "Explicitly specified module resolution kind: 'NodeJs'.",
-                        "Loading module 'a' from 'node_modules' folder, target file type 'TypeScript'.",
-                        "File 'node_modules/a/package.json' does not exist.",
-                        "File 'node_modules/a.ts' does not exist.",
-                        "File 'node_modules/a.tsx' does not exist.",
-                        "File 'node_modules/a.d.ts' does not exist.",
-                        "File 'node_modules/a/index.ts' does not exist.",
-                        "File 'node_modules/a/index.tsx' does not exist.",
-                        "File 'node_modules/a/index.d.ts' does not exist.",
-                        "File 'node_modules/@types/a/package.json' does not exist.",
-                        "File 'node_modules/@types/a.d.ts' does not exist.",
-                        "File 'node_modules/@types/a/index.d.ts' does not exist.",
-                        "Loading module 'a' from 'node_modules' folder, target file type 'JavaScript'.",
-                        "File 'node_modules/a/package.json' does not exist.",
-                        "File 'node_modules/a.js' does not exist.",
-                        "File 'node_modules/a.jsx' does not exist.",
-                        "File 'node_modules/a/index.js' does not exist.",
-                        "File 'node_modules/a/index.jsx' does not exist.",
-                        "======== Module name 'a' was not resolved. ========"
-                    ],
-                    "initialProgram: execute module resolution normally.");
-
+                traces.push(["initialProgram: execute module resolution normally.", initialProgram]);
                 const initialProgramDiagnostics = initialProgram.getSemanticDiagnostics(initialProgram.getSourceFile("file1.ts"));
                 assert.lengthOf(initialProgramDiagnostics, 1, `initialProgram: import should fail.`);
             }
@@ -491,25 +480,12 @@ namespace ts {
                 f[1].text = f[1].text.updateReferences(`/// <reference no-default-lib="true"/>`);
             }, filesAfterNpmInstall);
             {
-                assert.deepEqual(afterNpmInstallProgram.host.getTrace(),
-                    [
-                        "======== Resolving module 'a' from 'file1.ts'. ========",
-                        "Explicitly specified module resolution kind: 'NodeJs'.",
-                        "Loading module 'a' from 'node_modules' folder, target file type 'TypeScript'.",
-                        "File 'node_modules/a/package.json' does not exist.",
-                        "File 'node_modules/a.ts' does not exist.",
-                        "File 'node_modules/a.tsx' does not exist.",
-                        "File 'node_modules/a.d.ts' does not exist.",
-                        "File 'node_modules/a/index.ts' does not exist.",
-                        "File 'node_modules/a/index.tsx' does not exist.",
-                        "File 'node_modules/a/index.d.ts' exist - use it as a name resolution result.",
-                        "======== Module name 'a' was successfully resolved to 'node_modules/a/index.d.ts'. ========"
-                    ],
-                    "afterNpmInstallProgram: execute module resolution normally.");
-
+                traces.push(["afterNpmInstallProgram: execute module resolution normally.", afterNpmInstallProgram]);
                 const afterNpmInstallProgramDiagnostics = afterNpmInstallProgram.getSemanticDiagnostics(afterNpmInstallProgram.getSourceFile("file1.ts"));
                 assert.lengthOf(afterNpmInstallProgramDiagnostics, 0, `afterNpmInstallProgram: program is well-formed with import.`);
             }
+
+            baselineTrace("fetches imports after npm install", traces);
         });
 
         it("can reuse ambient module declarations from non-modified files", () => {
@@ -519,78 +495,19 @@ namespace ts {
             ];
             const options = { target: ScriptTarget.ES2015, traceResolution: true };
             const program = newProgram(files, files.map(f => f.name), options);
-            assert.deepEqual(program.host.getTrace(),
-                [
-                    "======== Resolving module 'fs' from '/a/b/app.ts'. ========",
-                    "Module resolution kind is not specified, using 'Classic'.",
-                    "File '/a/b/fs.ts' does not exist.",
-                    "File '/a/b/fs.tsx' does not exist.",
-                    "File '/a/b/fs.d.ts' does not exist.",
-                    "File '/a/fs.ts' does not exist.",
-                    "File '/a/fs.tsx' does not exist.",
-                    "File '/a/fs.d.ts' does not exist.",
-                    "File '/fs.ts' does not exist.",
-                    "File '/fs.tsx' does not exist.",
-                    "File '/fs.d.ts' does not exist.",
-                    "File '/a/b/node_modules/@types/fs/package.json' does not exist.",
-                    "File '/a/b/node_modules/@types/fs.d.ts' does not exist.",
-                    "File '/a/b/node_modules/@types/fs/index.d.ts' does not exist.",
-                    "File '/a/node_modules/@types/fs/package.json' does not exist.",
-                    "File '/a/node_modules/@types/fs.d.ts' does not exist.",
-                    "File '/a/node_modules/@types/fs/index.d.ts' does not exist.",
-                    "File '/node_modules/@types/fs/package.json' does not exist.",
-                    "File '/node_modules/@types/fs.d.ts' does not exist.",
-                    "File '/node_modules/@types/fs/index.d.ts' does not exist.",
-                    "File '/a/b/fs.js' does not exist.",
-                    "File '/a/b/fs.jsx' does not exist.",
-                    "File '/a/fs.js' does not exist.",
-                    "File '/a/fs.jsx' does not exist.",
-                    "File '/fs.js' does not exist.",
-                    "File '/fs.jsx' does not exist.",
-                    "======== Module name 'fs' was not resolved. ========",
-                ], "should look for 'fs'");
+            const traces: Traces = [];
+            traces.push(["should look for 'fs'.", program]);
 
             const program2 = updateProgram(program, program.getRootFileNames(), options, f => {
                 f[0].text = f[0].text.updateProgram("var x = 1;");
             });
-            assert.deepEqual(program2.host.getTrace(), [
-                "Module 'fs' was resolved as ambient module declared in '/a/b/node.d.ts' since this file was not modified."
-            ], "should reuse 'fs' since node.d.ts was not changed");
-
+            traces.push(["should reuse 'fs' since node.d.ts was not changed", program2]);
             const program3 = updateProgram(program2, program2.getRootFileNames(), options, f => {
                 f[0].text = f[0].text.updateProgram("var y = 1;");
                 f[1].text = f[1].text.updateProgram("declare var process: any");
             });
-            assert.deepEqual(program3.host.getTrace(),
-                [
-                    "======== Resolving module 'fs' from '/a/b/app.ts'. ========",
-                    "Module resolution kind is not specified, using 'Classic'.",
-                    "File '/a/b/fs.ts' does not exist.",
-                    "File '/a/b/fs.tsx' does not exist.",
-                    "File '/a/b/fs.d.ts' does not exist.",
-                    "File '/a/fs.ts' does not exist.",
-                    "File '/a/fs.tsx' does not exist.",
-                    "File '/a/fs.d.ts' does not exist.",
-                    "File '/fs.ts' does not exist.",
-                    "File '/fs.tsx' does not exist.",
-                    "File '/fs.d.ts' does not exist.",
-                    "File '/a/b/node_modules/@types/fs/package.json' does not exist.",
-                    "File '/a/b/node_modules/@types/fs.d.ts' does not exist.",
-                    "File '/a/b/node_modules/@types/fs/index.d.ts' does not exist.",
-                    "File '/a/node_modules/@types/fs/package.json' does not exist.",
-                    "File '/a/node_modules/@types/fs.d.ts' does not exist.",
-                    "File '/a/node_modules/@types/fs/index.d.ts' does not exist.",
-                    "File '/node_modules/@types/fs/package.json' does not exist.",
-                    "File '/node_modules/@types/fs.d.ts' does not exist.",
-                    "File '/node_modules/@types/fs/index.d.ts' does not exist.",
-                    "File '/a/b/fs.js' does not exist.",
-                    "File '/a/b/fs.jsx' does not exist.",
-                    "File '/a/fs.js' does not exist.",
-                    "File '/a/fs.jsx' does not exist.",
-                    "File '/fs.js' does not exist.",
-                    "File '/fs.jsx' does not exist.",
-                    "======== Module name 'fs' was not resolved. ========",
-                ], "should look for 'fs' again since node.d.ts was changed");
+            traces.push(["should look for 'fs' again since node.d.ts was changed", program3]);
+            baselineTrace("can reuse ambient module declarations from non-modified files", traces);
         });
 
         it("can reuse module resolutions from non-modified files", () => {
@@ -617,38 +534,12 @@ namespace ts {
                         "(new BB).x; (new BB).y;")
                 },
             ];
-
+            const traces: Traces = [];
             const options: CompilerOptions = { target: ScriptTarget.ES2015, traceResolution: true, moduleResolution: ModuleResolutionKind.Classic };
             const program1 = newProgram(files, files.map(f => f.name), options);
             let expectedErrors = 0;
             {
-                assert.deepEqual(program1.host.getTrace(),
-                    [
-                        "======== Resolving type reference directive 'typerefs1', containing file 'f1.ts', root directory 'node_modules/@types'. ========",
-                        "Resolving with primary search path 'node_modules/@types'.",
-                        "File 'node_modules/@types/typerefs1/package.json' does not exist.",
-                        "File 'node_modules/@types/typerefs1/index.d.ts' exist - use it as a name resolution result.",
-                        "======== Type reference directive 'typerefs1' was successfully resolved to 'node_modules/@types/typerefs1/index.d.ts', primary: true. ========",
-                        "======== Resolving module './b1' from 'f1.ts'. ========",
-                        "Explicitly specified module resolution kind: 'Classic'.",
-                        "File 'b1.ts' exist - use it as a name resolution result.",
-                        "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
-                        "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
-                        "Resolving with primary search path 'node_modules/@types'.",
-                        "File 'node_modules/@types/typerefs2/package.json' does not exist.",
-                        "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
-                        "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
-                        "======== Resolving module './b2' from 'f2.ts'. ========",
-                        "Explicitly specified module resolution kind: 'Classic'.",
-                        "File 'b2.ts' exist - use it as a name resolution result.",
-                        "======== Module name './b2' was successfully resolved to 'b2.ts'. ========",
-                        "======== Resolving module './f1' from 'f2.ts'. ========",
-                        "Explicitly specified module resolution kind: 'Classic'.",
-                        "File 'f1.ts' exist - use it as a name resolution result.",
-                        "======== Module name './f1' was successfully resolved to 'f1.ts'. ========"
-                    ],
-                    "program1: execute module resolution normally.");
-
+                traces.push(["program1: execute module resolution normally.", program1]);
                 const program1Diagnostics = program1.getSemanticDiagnostics(program1.getSourceFile("f2.ts"));
                 assert.lengthOf(program1Diagnostics, expectedErrors, `initial program should be well-formed`);
             }
@@ -661,25 +552,7 @@ namespace ts {
             {
                 const program2Diagnostics = program2.getSemanticDiagnostics(program2.getSourceFile("f2.ts"));
                 assert.lengthOf(program2Diagnostics, expectedErrors, `removing no-default-lib shouldn't affect any types used.`);
-
-                assert.deepEqual(program2.host.getTrace(), [
-                    "======== Resolving type reference directive 'typerefs1', containing file 'f1.ts', root directory 'node_modules/@types'. ========",
-                    "Resolving with primary search path 'node_modules/@types'.",
-                    "File 'node_modules/@types/typerefs1/package.json' does not exist.",
-                    "File 'node_modules/@types/typerefs1/index.d.ts' exist - use it as a name resolution result.",
-                    "======== Type reference directive 'typerefs1' was successfully resolved to 'node_modules/@types/typerefs1/index.d.ts', primary: true. ========",
-                    "======== Resolving module './b1' from 'f1.ts'. ========",
-                    "Explicitly specified module resolution kind: 'Classic'.",
-                    "File 'b1.ts' exist - use it as a name resolution result.",
-                    "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
-                    "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
-                    "Resolving with primary search path 'node_modules/@types'.",
-                    "File 'node_modules/@types/typerefs2/package.json' does not exist.",
-                    "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
-                    "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
-                    "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
-                    "Reusing resolution of module './f1' to file 'f2.ts' from old program."
-                ], "program2: reuse module resolutions in f2 since it is unchanged");
+                traces.push(["program2: reuse module resolutions in f2 since it is unchanged", program2]);
             }
 
             const program3 = updateProgram(program2, program2.getRootFileNames(), options, f => {
@@ -690,20 +563,7 @@ namespace ts {
             {
                 const program3Diagnostics = program3.getSemanticDiagnostics(program3.getSourceFile("f2.ts"));
                 assert.lengthOf(program3Diagnostics, expectedErrors, `typerefs2 was unused, so diagnostics should be unaffected.`);
-
-                assert.deepEqual(program3.host.getTrace(), [
-                    "======== Resolving module './b1' from 'f1.ts'. ========",
-                    "Explicitly specified module resolution kind: 'Classic'.",
-                    "File 'b1.ts' exist - use it as a name resolution result.",
-                    "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
-                    "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
-                    "Resolving with primary search path 'node_modules/@types'.",
-                    "File 'node_modules/@types/typerefs2/package.json' does not exist.",
-                    "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
-                    "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
-                    "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
-                    "Reusing resolution of module './f1' to file 'f2.ts' from old program."
-                ], "program3: reuse module resolutions in f2 since it is unchanged");
+                traces.push(["program3: reuse module resolutions in f2 since it is unchanged", program3]);
             }
 
 
@@ -715,20 +575,7 @@ namespace ts {
             {
                 const program4Diagnostics = program4.getSemanticDiagnostics(program4.getSourceFile("f2.ts"));
                 assert.lengthOf(program4Diagnostics, expectedErrors, `a1.ts was unused, so diagnostics should be unaffected.`);
-
-                assert.deepEqual(program4.host.getTrace(), [
-                    "======== Resolving module './b1' from 'f1.ts'. ========",
-                    "Explicitly specified module resolution kind: 'Classic'.",
-                    "File 'b1.ts' exist - use it as a name resolution result.",
-                    "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
-                    "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
-                    "Resolving with primary search path 'node_modules/@types'.",
-                    "File 'node_modules/@types/typerefs2/package.json' does not exist.",
-                    "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
-                    "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
-                    "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
-                    "Reusing resolution of module './f1' to file 'f2.ts' from old program."
-                ], "program_4: reuse module resolutions in f2 since it is unchanged");
+                traces.push(["program_4: reuse module resolutions in f2 since it is unchanged", program4]);
             }
 
             const program5 = updateProgram(program4, program4.getRootFileNames(), options, f => {
@@ -739,13 +586,7 @@ namespace ts {
             {
                 const program5Diagnostics = program5.getSemanticDiagnostics(program5.getSourceFile("f2.ts"));
                 assert.lengthOf(program5Diagnostics, ++expectedErrors, `import of BB in f1 fails. BB is of type any. Add one error`);
-
-                assert.deepEqual(program5.host.getTrace(), [
-                    "======== Resolving module './b1' from 'f1.ts'. ========",
-                    "Explicitly specified module resolution kind: 'Classic'.",
-                    "File 'b1.ts' exist - use it as a name resolution result.",
-                    "======== Module name './b1' was successfully resolved to 'b1.ts'. ========"
-                ], "program_5: exports do not affect program structure, so f2's resolutions are silently reused.");
+                traces.push(["program_5: exports do not affect program structure, so f2's resolutions are silently reused.", program5]);
             }
 
             const program6 = updateProgram(program5, program5.getRootFileNames(), options, f => {
@@ -756,20 +597,7 @@ namespace ts {
             {
                 const program6Diagnostics = program6.getSemanticDiagnostics(program6.getSourceFile("f2.ts"));
                 assert.lengthOf(program6Diagnostics, expectedErrors, `import of BB in f1 fails.`);
-
-                assert.deepEqual(program6.host.getTrace(), [
-                    "======== Resolving module './b1' from 'f1.ts'. ========",
-                    "Explicitly specified module resolution kind: 'Classic'.",
-                    "File 'b1.ts' exist - use it as a name resolution result.",
-                    "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
-                    "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
-                    "Resolving with primary search path 'node_modules/@types'.",
-                    "File 'node_modules/@types/typerefs2/package.json' does not exist.",
-                    "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
-                    "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
-                    "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
-                    "Reusing resolution of module './f1' to file 'f2.ts' from old program."
-                ], "program_6: reuse module resolutions in f2 since it is unchanged");
+                traces.push(["program_6: reuse module resolutions in f2 since it is unchanged", program6]);
             }
 
             const program7 = updateProgram(program6, program6.getRootFileNames(), options, f => {
@@ -780,17 +608,9 @@ namespace ts {
             {
                 const program7Diagnostics = program7.getSemanticDiagnostics(program7.getSourceFile("f2.ts"));
                 assert.lengthOf(program7Diagnostics, expectedErrors, `removing import is noop with respect to program, so no change in diagnostics.`);
-
-                assert.deepEqual(program7.host.getTrace(), [
-                    "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
-                    "Resolving with primary search path 'node_modules/@types'.",
-                    "File 'node_modules/@types/typerefs2/package.json' does not exist.",
-                    "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
-                    "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
-                    "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
-                    "Reusing resolution of module './f1' to file 'f2.ts' from old program."
-                ], "program_7 should reuse module resolutions in f2 since it is unchanged");
+                traces.push(["program_7 should reuse module resolutions in f2 since it is unchanged", program7]);
             }
+            baselineTrace("can reuse module resolutions from non-modified files", traces);
         });
 
         describe("redirects", () => {

src/testRunner/unittests/tscWatch/programUpdates.ts

@@ -812,29 +812,37 @@ declare const eval: any`
             ]
         });
 
-        verifyTscWatch({
-            scenario,
-            subScenario: "types should load from config file path if config exists",
-            commandLineArgs: ["-w", "-p", configFilePath],
-            sys: () => {
-                const f1 = {
-                    path: "/a/b/app.ts",
-                    content: "let x = 1"
-                };
-                const config = {
-                    path: configFilePath,
-                    content: JSON.stringify({ compilerOptions: { types: ["node"], typeRoots: [] } })
-                };
-                const node = {
-                    path: "/a/b/node_modules/@types/node/index.d.ts",
-                    content: "declare var process: any"
-                };
-                const cwd = {
-                    path: "/a/c"
-                };
-                return createWatchedSystem([f1, config, node, cwd, libFile], { currentDirectory: cwd.path });
-            },
-            changes: emptyArray
+        describe("types from config file", () => {
+            function verifyTypesLoad(includeTypeRoots: boolean) {
+                verifyTscWatch({
+                    scenario,
+                    subScenario: includeTypeRoots ?
+                        "types should not load from config file path if config exists but does not specifies typeRoots" :
+                        "types should load from config file path if config exists",
+                    commandLineArgs: ["-w", "-p", configFilePath],
+                    sys: () => {
+                        const f1 = {
+                            path: "/a/b/app.ts",
+                            content: "let x = 1"
+                        };
+                        const config = {
+                            path: configFilePath,
+                            content: JSON.stringify({ compilerOptions: { types: ["node"], typeRoots: includeTypeRoots ? [] : undefined } })
+                        };
+                        const node = {
+                            path: "/a/b/node_modules/@types/node/index.d.ts",
+                            content: "declare var process: any"
+                        };
+                        const cwd = {
+                            path: "/a/c"
+                        };
+                        return createWatchedSystem([f1, config, node, cwd, libFile], { currentDirectory: cwd.path });
+                    },
+                    changes: emptyArray
+                });
+            }
+            verifyTypesLoad(/*includeTypeRoots*/ false);
+            verifyTypesLoad(/*includeTypeRoots*/ true);
         });
 
         verifyTscWatch({

src/testRunner/unittests/tsserver/cachingFileSystemInformation.ts

@@ -391,7 +391,7 @@ namespace ts.projectSystem {
                 const { configFileName } = projectService.openClientFile(file1.path);
                 assert.equal(configFileName, tsconfigFile.path as server.NormalizedPath, `should find config`);
                 checkNumberOfConfiguredProjects(projectService, 1);
-                const watchingRecursiveDirectories = [`${canonicalFrontendDir}/src`, `${canonicalFrontendDir}/types`, `${canonicalFrontendDir}/node_modules`].concat(getNodeModuleDirectories(getDirectoryPath(canonicalFrontendDir)));
+                const watchingRecursiveDirectories = [`${canonicalFrontendDir}/src`, `${canonicalFrontendDir}/types`, `${canonicalFrontendDir}/node_modules`];
 
                 const project = projectService.configuredProjects.get(canonicalConfigPath)!;
                 verifyProjectAndWatchedDirectories();

src/testRunner/unittests/tsserver/resolutionCache.ts

@@ -418,27 +418,37 @@ namespace ts.projectSystem {
             projectService.checkNumberOfProjects({ configuredProjects: 1 });
         });
 
-        it("types should load from config file path if config exists", () => {
-            const f1 = {
-                path: "/a/b/app.ts",
-                content: "let x = 1"
-            };
-            const config = {
-                path: "/a/b/tsconfig.json",
-                content: JSON.stringify({ compilerOptions: { types: ["node"], typeRoots: [] } })
-            };
-            const node = {
-                path: "/a/b/node_modules/@types/node/index.d.ts",
-                content: "declare var process: any"
-            };
-            const cwd = {
-                path: "/a/c"
-            };
-            const host = createServerHost([f1, config, node, cwd], { currentDirectory: cwd.path });
-            const projectService = createProjectService(host);
-            projectService.openClientFile(f1.path);
-            projectService.checkNumberOfProjects({ configuredProjects: 1 });
-            checkProjectActualFiles(configuredProjectAt(projectService, 0), [f1.path, node.path, config.path]);
+        describe("types from config file", () => {
+            function verifyTypesLoad(includeTypeRoots: boolean) {
+                const f1 = {
+                    path: "/a/b/app.ts",
+                    content: "let x = 1"
+                };
+                const config = {
+                    path: "/a/b/tsconfig.json",
+                    content: JSON.stringify({ compilerOptions: { types: ["node"], typeRoots: includeTypeRoots ? [] : undefined } })
+                };
+                const node = {
+                    path: "/a/b/node_modules/@types/node/index.d.ts",
+                    content: "declare var process: any"
+                };
+                const cwd = {
+                    path: "/a/c"
+                };
+                const host = createServerHost([f1, config, node, cwd], { currentDirectory: cwd.path });
+                const projectService = createProjectService(host);
+                projectService.openClientFile(f1.path);
+                projectService.checkNumberOfProjects({ configuredProjects: 1 });
+                checkProjectActualFiles(configuredProjectAt(projectService, 0), [f1.path, config.path, ...(includeTypeRoots ? [] : [node.path])]);
+            }
+
+            it("types should load from config file path if config exists", () => {
+                verifyTypesLoad(/*includeTypeRoots*/ false);
+            });
+
+            it("types should not load from config file path if config exists but does not specifies typeRoots", () => {
+                verifyTypesLoad(/*includeTypeRoots*/ true);
+            });
         });
     });
 

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -3722,7 +3722,6 @@ declare namespace ts {
         noEmitHelpers?: boolean;
     }
     export interface GetEffectiveTypeRootsHost {
-        directoryExists?(directoryName: string): boolean;
         getCurrentDirectory?(): string;
     }
     export interface TextSpan {
@@ -5334,6 +5333,7 @@ declare namespace ts {
         readFile?(path: string, encoding?: string): string | undefined;
         realpath?(path: string): string;
         fileExists?(path: string): boolean;
+        directoryExists?(directoryName: string): boolean;
         getTypeRootsVersion?(): number;
         resolveModuleNames?(moduleNames: string[], containingFile: string, reusedNames: string[] | undefined, redirectedReference: ResolvedProjectReference | undefined, options: CompilerOptions): (ResolvedModule | undefined)[];
         getResolvedModuleWithFailedLookupLocationsFromCache?(modulename: string, containingFile: string): ResolvedModuleWithFailedLookupLocations | undefined;
@@ -9304,7 +9304,6 @@ declare namespace ts.server {
         setTypeAcquisition(newTypeAcquisition: TypeAcquisition): void;
         getTypeAcquisition(): TypeAcquisition;
         close(): void;
-        getEffectiveTypeRoots(): string[];
     }
     /**
      * Project whose configuration is handled externally, such as in a '.csproj'.

tests/baselines/reference/api/typescript.d.ts

@@ -3722,7 +3722,6 @@ declare namespace ts {
         noEmitHelpers?: boolean;
     }
     export interface GetEffectiveTypeRootsHost {
-        directoryExists?(directoryName: string): boolean;
         getCurrentDirectory?(): string;
     }
     export interface TextSpan {
@@ -5334,6 +5333,7 @@ declare namespace ts {
         readFile?(path: string, encoding?: string): string | undefined;
         realpath?(path: string): string;
         fileExists?(path: string): boolean;
+        directoryExists?(directoryName: string): boolean;
         getTypeRootsVersion?(): number;
         resolveModuleNames?(moduleNames: string[], containingFile: string, reusedNames: string[] | undefined, redirectedReference: ResolvedProjectReference | undefined, options: CompilerOptions): (ResolvedModule | undefined)[];
         getResolvedModuleWithFailedLookupLocationsFromCache?(modulename: string, containingFile: string): ResolvedModuleWithFailedLookupLocations | undefined;

tests/baselines/reference/library-reference-1.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'jquery', containing file '/src/consumer.ts', root directory 'types'. ========",
     "Resolving with primary search path 'types'.",
+    "Loading module as file / folder, candidate module location 'types/jquery', target file type 'DtsOnly'.",
+    "File 'types/jquery.d.ts' does not exist.",
     "File 'types/jquery/package.json' does not exist.",
     "File 'types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for 'types/jquery/index.d.ts', result '/src/types/jquery/index.d.ts'.",
     "======== Type reference directive 'jquery' was successfully resolved to '/src/types/jquery/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'jquery', containing file '/src/__inferred type names__.ts', root directory 'types'. ========",
     "Resolving with primary search path 'types'.",
+    "Loading module as file / folder, candidate module location 'types/jquery', target file type 'DtsOnly'.",
+    "File 'types/jquery.d.ts' does not exist.",
     "File 'types/jquery/package.json' does not exist.",
     "File 'types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for 'types/jquery/index.d.ts', result '/src/types/jquery/index.d.ts'.",

tests/baselines/reference/library-reference-10.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'jquery', containing file '/foo/consumer.ts', root directory './types'. ========",
     "Resolving with primary search path './types'.",
+    "Loading module as file / folder, candidate module location './types/jquery', target file type 'DtsOnly'.",
+    "File './types/jquery.d.ts' does not exist.",
     "Found 'package.json' at './types/jquery/package.json'.",
     "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'jquery.d.ts' that references 'types/jquery/jquery.d.ts'.",
@@ -9,6 +11,8 @@
     "======== Type reference directive 'jquery' was successfully resolved to '/foo/types/jquery/jquery.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'jquery', containing file '/foo/__inferred type names__.ts', root directory './types'. ========",
     "Resolving with primary search path './types'.",
+    "Loading module as file / folder, candidate module location './types/jquery', target file type 'DtsOnly'.",
+    "File './types/jquery.d.ts' does not exist.",
     "Found 'package.json' at './types/jquery/package.json'.",
     "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'jquery.d.ts' that references 'types/jquery/jquery.d.ts'.",

tests/baselines/reference/library-reference-13.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'jquery', containing file '/a/__inferred type names__.ts', root directory '/a/types'. ========",
     "Resolving with primary search path '/a/types'.",
+    "Loading module as file / folder, candidate module location '/a/types/jquery', target file type 'DtsOnly'.",
+    "File '/a/types/jquery.d.ts' does not exist.",
     "File '/a/types/jquery/package.json' does not exist.",
     "File '/a/types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/a/types/jquery/index.d.ts', result '/a/types/jquery/index.d.ts'.",

tests/baselines/reference/library-reference-14.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'jquery', containing file '/a/__inferred type names__.ts', root directory '/a/types'. ========",
     "Resolving with primary search path '/a/types'.",
+    "Loading module as file / folder, candidate module location '/a/types/jquery', target file type 'DtsOnly'.",
+    "File '/a/types/jquery.d.ts' does not exist.",
     "File '/a/types/jquery/package.json' does not exist.",
     "File '/a/types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/a/types/jquery/index.d.ts', result '/a/types/jquery/index.d.ts'.",

tests/baselines/reference/library-reference-15.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'jquery', containing file '/a/__inferred type names__.ts', root directory 'types'. ========",
     "Resolving with primary search path 'types'.",
+    "Loading module as file / folder, candidate module location 'types/jquery', target file type 'DtsOnly'.",
+    "File 'types/jquery.d.ts' does not exist.",
     "File 'types/jquery/package.json' does not exist.",
     "File 'types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for 'types/jquery/index.d.ts', result '/a/types/jquery/index.d.ts'.",

tests/baselines/reference/library-reference-2.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'jquery', containing file '/consumer.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/jquery', target file type 'DtsOnly'.",
+    "File '/types/jquery.d.ts' does not exist.",
     "Found 'package.json' at '/types/jquery/package.json'.",
     "'package.json' does not have a 'typesVersions' field.",
     "'package.json' does not have a 'typings' field.",
@@ -10,6 +12,8 @@
     "======== Type reference directive 'jquery' was successfully resolved to '/types/jquery/jquery.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'jquery', containing file '/test/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/jquery', target file type 'DtsOnly'.",
+    "File '/types/jquery.d.ts' does not exist.",
     "Found 'package.json' at '/types/jquery/package.json'.",
     "'package.json' does not have a 'typesVersions' field.",
     "'package.json' does not have a 'typings' field.",

tests/baselines/reference/library-reference-4.trace.json

@@ -1,6 +1,9 @@
 [
     "======== Resolving type reference directive 'foo', containing file '/src/root.ts', root directory '/src'. ========",
     "Resolving with primary search path '/src'.",
+    "Loading module as file / folder, candidate module location '/src/foo', target file type 'DtsOnly'.",
+    "File '/src/foo.d.ts' does not exist.",
+    "Directory '/src/foo' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/src'.",
     "Directory '/src/node_modules' does not exist, skipping all lookups in it.",
     "File '/node_modules/foo/package.json' does not exist.",
@@ -10,6 +13,9 @@
     "======== Type reference directive 'foo' was successfully resolved to '/node_modules/foo/index.d.ts', primary: false. ========",
     "======== Resolving type reference directive 'bar', containing file '/src/root.ts', root directory '/src'. ========",
     "Resolving with primary search path '/src'.",
+    "Loading module as file / folder, candidate module location '/src/bar', target file type 'DtsOnly'.",
+    "File '/src/bar.d.ts' does not exist.",
+    "Directory '/src/bar' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/src'.",
     "Directory '/src/node_modules' does not exist, skipping all lookups in it.",
     "File '/node_modules/bar/package.json' does not exist.",
@@ -19,6 +25,9 @@
     "======== Type reference directive 'bar' was successfully resolved to '/node_modules/bar/index.d.ts', primary: false. ========",
     "======== Resolving type reference directive 'alpha', containing file '/node_modules/foo/index.d.ts', root directory '/src'. ========",
     "Resolving with primary search path '/src'.",
+    "Loading module as file / folder, candidate module location '/src/alpha', target file type 'DtsOnly'.",
+    "File '/src/alpha.d.ts' does not exist.",
+    "Directory '/src/alpha' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/node_modules/foo'.",
     "File '/node_modules/foo/node_modules/alpha/package.json' does not exist.",
     "File '/node_modules/foo/node_modules/alpha.d.ts' does not exist.",
@@ -27,6 +36,9 @@
     "======== Type reference directive 'alpha' was successfully resolved to '/node_modules/foo/node_modules/alpha/index.d.ts', primary: false. ========",
     "======== Resolving type reference directive 'alpha', containing file '/node_modules/bar/index.d.ts', root directory '/src'. ========",
     "Resolving with primary search path '/src'.",
+    "Loading module as file / folder, candidate module location '/src/alpha', target file type 'DtsOnly'.",
+    "File '/src/alpha.d.ts' does not exist.",
+    "Directory '/src/alpha' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/node_modules/bar'.",
     "File '/node_modules/bar/node_modules/alpha/package.json' does not exist.",
     "File '/node_modules/bar/node_modules/alpha.d.ts' does not exist.",

tests/baselines/reference/library-reference-5.trace.json

@@ -1,6 +1,7 @@
 [
     "======== Resolving type reference directive 'foo', containing file '/src/root.ts', root directory 'types'. ========",
     "Resolving with primary search path 'types'.",
+    "Loading module as file / folder, candidate module location 'types/foo', target file type 'DtsOnly'.",
     "Directory 'types' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/src'.",
     "Directory '/src/node_modules' does not exist, skipping all lookups in it.",
@@ -11,6 +12,7 @@
     "======== Type reference directive 'foo' was successfully resolved to '/node_modules/foo/index.d.ts', primary: false. ========",
     "======== Resolving type reference directive 'bar', containing file '/src/root.ts', root directory 'types'. ========",
     "Resolving with primary search path 'types'.",
+    "Loading module as file / folder, candidate module location 'types/bar', target file type 'DtsOnly'.",
     "Directory 'types' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/src'.",
     "Directory '/src/node_modules' does not exist, skipping all lookups in it.",
@@ -21,6 +23,7 @@
     "======== Type reference directive 'bar' was successfully resolved to '/node_modules/bar/index.d.ts', primary: false. ========",
     "======== Resolving type reference directive 'alpha', containing file '/node_modules/foo/index.d.ts', root directory 'types'. ========",
     "Resolving with primary search path 'types'.",
+    "Loading module as file / folder, candidate module location 'types/alpha', target file type 'DtsOnly'.",
     "Directory 'types' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/node_modules/foo'.",
     "File '/node_modules/foo/node_modules/alpha/package.json' does not exist.",
@@ -30,6 +33,7 @@
     "======== Type reference directive 'alpha' was successfully resolved to '/node_modules/foo/node_modules/alpha/index.d.ts', primary: false. ========",
     "======== Resolving type reference directive 'alpha', containing file '/node_modules/bar/index.d.ts', root directory 'types'. ========",
     "Resolving with primary search path 'types'.",
+    "Loading module as file / folder, candidate module location 'types/alpha', target file type 'DtsOnly'.",
     "Directory 'types' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/node_modules/bar'.",
     "File '/node_modules/bar/node_modules/alpha/package.json' does not exist.",

tests/baselines/reference/library-reference-6.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'alpha', containing file '/src/foo.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/alpha', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/alpha.d.ts' does not exist.",
     "File '/node_modules/@types/alpha/package.json' does not exist.",
     "File '/node_modules/@types/alpha/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/alpha/index.d.ts', result '/node_modules/@types/alpha/index.d.ts'.",
     "======== Type reference directive 'alpha' was successfully resolved to '/node_modules/@types/alpha/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'alpha', containing file '/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/alpha', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/alpha.d.ts' does not exist.",
     "File '/node_modules/@types/alpha/package.json' does not exist.",
     "File '/node_modules/@types/alpha/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/alpha/index.d.ts', result '/node_modules/@types/alpha/index.d.ts'.",

tests/baselines/reference/library-reference-8.trace.json

@@ -1,36 +1,48 @@
 [
     "======== Resolving type reference directive 'alpha', containing file '/test/foo.ts', root directory '/test/types'. ========",
     "Resolving with primary search path '/test/types'.",
+    "Loading module as file / folder, candidate module location '/test/types/alpha', target file type 'DtsOnly'.",
+    "File '/test/types/alpha.d.ts' does not exist.",
     "File '/test/types/alpha/package.json' does not exist.",
     "File '/test/types/alpha/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/test/types/alpha/index.d.ts', result '/test/types/alpha/index.d.ts'.",
     "======== Type reference directive 'alpha' was successfully resolved to '/test/types/alpha/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'beta', containing file '/test/foo.ts', root directory '/test/types'. ========",
     "Resolving with primary search path '/test/types'.",
+    "Loading module as file / folder, candidate module location '/test/types/beta', target file type 'DtsOnly'.",
+    "File '/test/types/beta.d.ts' does not exist.",
     "File '/test/types/beta/package.json' does not exist.",
     "File '/test/types/beta/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/test/types/beta/index.d.ts', result '/test/types/beta/index.d.ts'.",
     "======== Type reference directive 'beta' was successfully resolved to '/test/types/beta/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'beta', containing file '/test/types/alpha/index.d.ts', root directory '/test/types'. ========",
     "Resolving with primary search path '/test/types'.",
+    "Loading module as file / folder, candidate module location '/test/types/beta', target file type 'DtsOnly'.",
+    "File '/test/types/beta.d.ts' does not exist.",
     "File '/test/types/beta/package.json' does not exist.",
     "File '/test/types/beta/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/test/types/beta/index.d.ts', result '/test/types/beta/index.d.ts'.",
     "======== Type reference directive 'beta' was successfully resolved to '/test/types/beta/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'alpha', containing file '/test/types/beta/index.d.ts', root directory '/test/types'. ========",
     "Resolving with primary search path '/test/types'.",
+    "Loading module as file / folder, candidate module location '/test/types/alpha', target file type 'DtsOnly'.",
+    "File '/test/types/alpha.d.ts' does not exist.",
     "File '/test/types/alpha/package.json' does not exist.",
     "File '/test/types/alpha/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/test/types/alpha/index.d.ts', result '/test/types/alpha/index.d.ts'.",
     "======== Type reference directive 'alpha' was successfully resolved to '/test/types/alpha/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'alpha', containing file '/test/__inferred type names__.ts', root directory '/test/types'. ========",
     "Resolving with primary search path '/test/types'.",
+    "Loading module as file / folder, candidate module location '/test/types/alpha', target file type 'DtsOnly'.",
+    "File '/test/types/alpha.d.ts' does not exist.",
     "File '/test/types/alpha/package.json' does not exist.",
     "File '/test/types/alpha/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/test/types/alpha/index.d.ts', result '/test/types/alpha/index.d.ts'.",
     "======== Type reference directive 'alpha' was successfully resolved to '/test/types/alpha/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'beta', containing file '/test/__inferred type names__.ts', root directory '/test/types'. ========",
     "Resolving with primary search path '/test/types'.",
+    "Loading module as file / folder, candidate module location '/test/types/beta', target file type 'DtsOnly'.",
+    "File '/test/types/beta.d.ts' does not exist.",
     "File '/test/types/beta/package.json' does not exist.",
     "File '/test/types/beta/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/test/types/beta/index.d.ts', result '/test/types/beta/index.d.ts'.",

tests/baselines/reference/library-reference-scoped-packages.trace.json

@@ -1,6 +1,7 @@
 [
     "======== Resolving type reference directive '@beep/boop', containing file '/a.ts', root directory 'types'. ========",
     "Resolving with primary search path 'types'.",
+    "Loading module as file / folder, candidate module location 'types/@beep/boop', target file type 'DtsOnly'.",
     "Directory 'types/@beep' does not exist, skipping all lookups in it.",
     "Looking up in 'node_modules' folder, initial location '/'.",
     "Scoped package detected, looking in 'beep__boop'",

tests/baselines/reference/moduleResolutionAsTypeReferenceDirective.errors.txt

@@ -0,0 +1,15 @@
+/a.ts(1,20): error TS2307: Cannot find module 'phaser' or its corresponding type declarations.
+
+
+==== /a.ts (1 errors) ====
+    import { a2 } from "phaser";
+                       ~~~~~~~~
+!!! error TS2307: Cannot find module 'phaser' or its corresponding type declarations.
+    
+==== /typings/phaser/types/phaser.d.ts (0 errors) ====
+    export const a2: number;
+    
+==== /typings/phaser/package.json (0 errors) ====
+    { "name": "phaser", "version": "1.2.3", "types": "types/phaser.d.ts" }
+    
+    

tests/baselines/reference/moduleResolutionAsTypeReferenceDirective.js

@@ -0,0 +1,16 @@
+//// [tests/cases/compiler/moduleResolutionAsTypeReferenceDirective.ts] ////
+
+//// [phaser.d.ts]
+export const a2: number;
+
+//// [package.json]
+{ "name": "phaser", "version": "1.2.3", "types": "types/phaser.d.ts" }
+
+
+//// [a.ts]
+import { a2 } from "phaser";
+
+
+//// [a.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionAsTypeReferenceDirective.symbols

@@ -0,0 +1,8 @@
+=== /a.ts ===
+import { a2 } from "phaser";
+>a2 : Symbol(a2, Decl(a.ts, 0, 8))
+
+=== /typings/phaser/types/phaser.d.ts ===
+export const a2: number;
+>a2 : Symbol(a2, Decl(phaser.d.ts, 0, 12))
+

tests/baselines/reference/moduleResolutionAsTypeReferenceDirective.trace.json

@@ -0,0 +1,20 @@
+[
+    "======== Resolving module 'phaser' from '/a.ts'. ========",
+    "Module resolution kind is not specified, using 'NodeJs'.",
+    "Loading module 'phaser' from 'node_modules' folder, target file type 'TypeScript'.",
+    "Directory '/node_modules' does not exist, skipping all lookups in it.",
+    "Loading module 'phaser' from 'node_modules' folder, target file type 'JavaScript'.",
+    "Directory '/node_modules' does not exist, skipping all lookups in it.",
+    "======== Module name 'phaser' was not resolved. ========",
+    "======== Resolving type reference directive 'phaser', containing file '/__inferred type names__.ts', root directory '/typings'. ========",
+    "Resolving with primary search path '/typings'.",
+    "Loading module as file / folder, candidate module location '/typings/phaser', target file type 'DtsOnly'.",
+    "File '/typings/phaser.d.ts' does not exist.",
+    "Found 'package.json' at '/typings/phaser/package.json'.",
+    "'package.json' does not have a 'typesVersions' field.",
+    "'package.json' does not have a 'typings' field.",
+    "'package.json' has 'types' field 'types/phaser.d.ts' that references '/typings/phaser/types/phaser.d.ts'.",
+    "File '/typings/phaser/types/phaser.d.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/typings/phaser/types/phaser.d.ts', result '/typings/phaser/types/phaser.d.ts'.",
+    "======== Type reference directive 'phaser' was successfully resolved to '/typings/phaser/types/phaser.d.ts' with Package ID 'phaser/types/phaser.d.ts@1.2.3', primary: true. ========"
+]

tests/baselines/reference/moduleResolutionAsTypeReferenceDirective.types

@@ -0,0 +1,8 @@
+=== /a.ts ===
+import { a2 } from "phaser";
+>a2 : any
+
+=== /typings/phaser/types/phaser.d.ts ===
+export const a2: number;
+>a2 : number
+

tests/baselines/reference/moduleResolutionAsTypeReferenceDirectiveAmbient.js

@@ -0,0 +1,18 @@
+//// [tests/cases/compiler/moduleResolutionAsTypeReferenceDirectiveAmbient.ts] ////
+
+//// [phaser.d.ts]
+declare module "phaser" {
+    export const a2: number;
+}
+
+//// [package.json]
+{ "name": "phaser", "version": "1.2.3", "types": "types/phaser.d.ts" }
+
+
+//// [a.ts]
+import { a2 } from "phaser";
+
+
+//// [a.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionAsTypeReferenceDirectiveAmbient.symbols

@@ -0,0 +1,12 @@
+=== /a.ts ===
+import { a2 } from "phaser";
+>a2 : Symbol(a2, Decl(a.ts, 0, 8))
+
+=== /typings/phaser/types/phaser.d.ts ===
+declare module "phaser" {
+>"phaser" : Symbol("phaser", Decl(phaser.d.ts, 0, 0))
+
+    export const a2: number;
+>a2 : Symbol(a2, Decl(phaser.d.ts, 1, 16))
+}
+

tests/baselines/reference/moduleResolutionAsTypeReferenceDirectiveAmbient.trace.json

@@ -0,0 +1,20 @@
+[
+    "======== Resolving module 'phaser' from '/a.ts'. ========",
+    "Module resolution kind is not specified, using 'NodeJs'.",
+    "Loading module 'phaser' from 'node_modules' folder, target file type 'TypeScript'.",
+    "Directory '/node_modules' does not exist, skipping all lookups in it.",
+    "Loading module 'phaser' from 'node_modules' folder, target file type 'JavaScript'.",
+    "Directory '/node_modules' does not exist, skipping all lookups in it.",
+    "======== Module name 'phaser' was not resolved. ========",
+    "======== Resolving type reference directive 'phaser', containing file '/__inferred type names__.ts', root directory '/typings'. ========",
+    "Resolving with primary search path '/typings'.",
+    "Loading module as file / folder, candidate module location '/typings/phaser', target file type 'DtsOnly'.",
+    "File '/typings/phaser.d.ts' does not exist.",
+    "Found 'package.json' at '/typings/phaser/package.json'.",
+    "'package.json' does not have a 'typesVersions' field.",
+    "'package.json' does not have a 'typings' field.",
+    "'package.json' has 'types' field 'types/phaser.d.ts' that references '/typings/phaser/types/phaser.d.ts'.",
+    "File '/typings/phaser/types/phaser.d.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/typings/phaser/types/phaser.d.ts', result '/typings/phaser/types/phaser.d.ts'.",
+    "======== Type reference directive 'phaser' was successfully resolved to '/typings/phaser/types/phaser.d.ts' with Package ID 'phaser/types/phaser.d.ts@1.2.3', primary: true. ========"
+]

tests/baselines/reference/moduleResolutionAsTypeReferenceDirectiveAmbient.types

@@ -0,0 +1,12 @@
+=== /a.ts ===
+import { a2 } from "phaser";
+>a2 : number
+
+=== /typings/phaser/types/phaser.d.ts ===
+declare module "phaser" {
+>"phaser" : typeof import("phaser")
+
+    export const a2: number;
+>a2 : number
+}
+

tests/baselines/reference/reuseProgramStructure/can-reuse-ambient-module-declarations-from-non-modified-files.trace.json

@@ -0,0 +1,63 @@
+{
+    "should look for 'fs'.": [
+        "======== Resolving module 'fs' from '/a/b/app.ts'. ========",
+        "Module resolution kind is not specified, using 'Classic'.",
+        "File '/a/b/fs.ts' does not exist.",
+        "File '/a/b/fs.tsx' does not exist.",
+        "File '/a/b/fs.d.ts' does not exist.",
+        "File '/a/fs.ts' does not exist.",
+        "File '/a/fs.tsx' does not exist.",
+        "File '/a/fs.d.ts' does not exist.",
+        "File '/fs.ts' does not exist.",
+        "File '/fs.tsx' does not exist.",
+        "File '/fs.d.ts' does not exist.",
+        "File '/a/b/node_modules/@types/fs/package.json' does not exist.",
+        "File '/a/b/node_modules/@types/fs.d.ts' does not exist.",
+        "File '/a/b/node_modules/@types/fs/index.d.ts' does not exist.",
+        "File '/a/node_modules/@types/fs/package.json' does not exist.",
+        "File '/a/node_modules/@types/fs.d.ts' does not exist.",
+        "File '/a/node_modules/@types/fs/index.d.ts' does not exist.",
+        "File '/node_modules/@types/fs/package.json' does not exist.",
+        "File '/node_modules/@types/fs.d.ts' does not exist.",
+        "File '/node_modules/@types/fs/index.d.ts' does not exist.",
+        "File '/a/b/fs.js' does not exist.",
+        "File '/a/b/fs.jsx' does not exist.",
+        "File '/a/fs.js' does not exist.",
+        "File '/a/fs.jsx' does not exist.",
+        "File '/fs.js' does not exist.",
+        "File '/fs.jsx' does not exist.",
+        "======== Module name 'fs' was not resolved. ========"
+    ],
+    "should reuse 'fs' since node.d.ts was not changed": [
+        "Module 'fs' was resolved as ambient module declared in '/a/b/node.d.ts' since this file was not modified."
+    ],
+    "should look for 'fs' again since node.d.ts was changed": [
+        "======== Resolving module 'fs' from '/a/b/app.ts'. ========",
+        "Module resolution kind is not specified, using 'Classic'.",
+        "File '/a/b/fs.ts' does not exist.",
+        "File '/a/b/fs.tsx' does not exist.",
+        "File '/a/b/fs.d.ts' does not exist.",
+        "File '/a/fs.ts' does not exist.",
+        "File '/a/fs.tsx' does not exist.",
+        "File '/a/fs.d.ts' does not exist.",
+        "File '/fs.ts' does not exist.",
+        "File '/fs.tsx' does not exist.",
+        "File '/fs.d.ts' does not exist.",
+        "File '/a/b/node_modules/@types/fs/package.json' does not exist.",
+        "File '/a/b/node_modules/@types/fs.d.ts' does not exist.",
+        "File '/a/b/node_modules/@types/fs/index.d.ts' does not exist.",
+        "File '/a/node_modules/@types/fs/package.json' does not exist.",
+        "File '/a/node_modules/@types/fs.d.ts' does not exist.",
+        "File '/a/node_modules/@types/fs/index.d.ts' does not exist.",
+        "File '/node_modules/@types/fs/package.json' does not exist.",
+        "File '/node_modules/@types/fs.d.ts' does not exist.",
+        "File '/node_modules/@types/fs/index.d.ts' does not exist.",
+        "File '/a/b/fs.js' does not exist.",
+        "File '/a/b/fs.jsx' does not exist.",
+        "File '/a/fs.js' does not exist.",
+        "File '/a/fs.jsx' does not exist.",
+        "File '/fs.js' does not exist.",
+        "File '/fs.jsx' does not exist.",
+        "======== Module name 'fs' was not resolved. ========"
+    ]
+}

tests/baselines/reference/reuseProgramStructure/can-reuse-module-resolutions-from-non-modified-files.trace.json

@@ -0,0 +1,114 @@
+{
+    "program1: execute module resolution normally.": [
+        "======== Resolving type reference directive 'typerefs1', containing file 'f1.ts', root directory 'node_modules/@types'. ========",
+        "Resolving with primary search path 'node_modules/@types'.",
+        "Loading module as file / folder, candidate module location 'node_modules/@types/typerefs1', target file type 'DtsOnly'.",
+        "File 'node_modules/@types/typerefs1.d.ts' does not exist.",
+        "File 'node_modules/@types/typerefs1/package.json' does not exist.",
+        "File 'node_modules/@types/typerefs1/index.d.ts' exist - use it as a name resolution result.",
+        "======== Type reference directive 'typerefs1' was successfully resolved to 'node_modules/@types/typerefs1/index.d.ts', primary: true. ========",
+        "======== Resolving module './b1' from 'f1.ts'. ========",
+        "Explicitly specified module resolution kind: 'Classic'.",
+        "File 'b1.ts' exist - use it as a name resolution result.",
+        "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
+        "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
+        "Resolving with primary search path 'node_modules/@types'.",
+        "Loading module as file / folder, candidate module location 'node_modules/@types/typerefs2', target file type 'DtsOnly'.",
+        "File 'node_modules/@types/typerefs2.d.ts' does not exist.",
+        "File 'node_modules/@types/typerefs2/package.json' does not exist.",
+        "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
+        "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
+        "======== Resolving module './b2' from 'f2.ts'. ========",
+        "Explicitly specified module resolution kind: 'Classic'.",
+        "File 'b2.ts' exist - use it as a name resolution result.",
+        "======== Module name './b2' was successfully resolved to 'b2.ts'. ========",
+        "======== Resolving module './f1' from 'f2.ts'. ========",
+        "Explicitly specified module resolution kind: 'Classic'.",
+        "File 'f1.ts' exist - use it as a name resolution result.",
+        "======== Module name './f1' was successfully resolved to 'f1.ts'. ========"
+    ],
+    "program2: reuse module resolutions in f2 since it is unchanged": [
+        "======== Resolving type reference directive 'typerefs1', containing file 'f1.ts', root directory 'node_modules/@types'. ========",
+        "Resolving with primary search path 'node_modules/@types'.",
+        "Loading module as file / folder, candidate module location 'node_modules/@types/typerefs1', target file type 'DtsOnly'.",
+        "File 'node_modules/@types/typerefs1.d.ts' does not exist.",
+        "File 'node_modules/@types/typerefs1/package.json' does not exist.",
+        "File 'node_modules/@types/typerefs1/index.d.ts' exist - use it as a name resolution result.",
+        "======== Type reference directive 'typerefs1' was successfully resolved to 'node_modules/@types/typerefs1/index.d.ts', primary: true. ========",
+        "======== Resolving module './b1' from 'f1.ts'. ========",
+        "Explicitly specified module resolution kind: 'Classic'.",
+        "File 'b1.ts' exist - use it as a name resolution result.",
+        "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
+        "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
+        "Resolving with primary search path 'node_modules/@types'.",
+        "Loading module as file / folder, candidate module location 'node_modules/@types/typerefs2', target file type 'DtsOnly'.",
+        "File 'node_modules/@types/typerefs2.d.ts' does not exist.",
+        "File 'node_modules/@types/typerefs2/package.json' does not exist.",
+        "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
+        "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
+        "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
+        "Reusing resolution of module './f1' to file 'f2.ts' from old program."
+    ],
+    "program3: reuse module resolutions in f2 since it is unchanged": [
+        "======== Resolving module './b1' from 'f1.ts'. ========",
+        "Explicitly specified module resolution kind: 'Classic'.",
+        "File 'b1.ts' exist - use it as a name resolution result.",
+        "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
+        "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
+        "Resolving with primary search path 'node_modules/@types'.",
+        "Loading module as file / folder, candidate module location 'node_modules/@types/typerefs2', target file type 'DtsOnly'.",
+        "File 'node_modules/@types/typerefs2.d.ts' does not exist.",
+        "File 'node_modules/@types/typerefs2/package.json' does not exist.",
+        "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
+        "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
+        "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
+        "Reusing resolution of module './f1' to file 'f2.ts' from old program."
+    ],
+    "program_4: reuse module resolutions in f2 since it is unchanged": [
+        "======== Resolving module './b1' from 'f1.ts'. ========",
+        "Explicitly specified module resolution kind: 'Classic'.",
+        "File 'b1.ts' exist - use it as a name resolution result.",
+        "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
+        "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
+        "Resolving with primary search path 'node_modules/@types'.",
+        "Loading module as file / folder, candidate module location 'node_modules/@types/typerefs2', target file type 'DtsOnly'.",
+        "File 'node_modules/@types/typerefs2.d.ts' does not exist.",
+        "File 'node_modules/@types/typerefs2/package.json' does not exist.",
+        "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
+        "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
+        "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
+        "Reusing resolution of module './f1' to file 'f2.ts' from old program."
+    ],
+    "program_5: exports do not affect program structure, so f2's resolutions are silently reused.": [
+        "======== Resolving module './b1' from 'f1.ts'. ========",
+        "Explicitly specified module resolution kind: 'Classic'.",
+        "File 'b1.ts' exist - use it as a name resolution result.",
+        "======== Module name './b1' was successfully resolved to 'b1.ts'. ========"
+    ],
+    "program_6: reuse module resolutions in f2 since it is unchanged": [
+        "======== Resolving module './b1' from 'f1.ts'. ========",
+        "Explicitly specified module resolution kind: 'Classic'.",
+        "File 'b1.ts' exist - use it as a name resolution result.",
+        "======== Module name './b1' was successfully resolved to 'b1.ts'. ========",
+        "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
+        "Resolving with primary search path 'node_modules/@types'.",
+        "Loading module as file / folder, candidate module location 'node_modules/@types/typerefs2', target file type 'DtsOnly'.",
+        "File 'node_modules/@types/typerefs2.d.ts' does not exist.",
+        "File 'node_modules/@types/typerefs2/package.json' does not exist.",
+        "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
+        "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
+        "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
+        "Reusing resolution of module './f1' to file 'f2.ts' from old program."
+    ],
+    "program_7 should reuse module resolutions in f2 since it is unchanged": [
+        "======== Resolving type reference directive 'typerefs2', containing file 'f2.ts', root directory 'node_modules/@types'. ========",
+        "Resolving with primary search path 'node_modules/@types'.",
+        "Loading module as file / folder, candidate module location 'node_modules/@types/typerefs2', target file type 'DtsOnly'.",
+        "File 'node_modules/@types/typerefs2.d.ts' does not exist.",
+        "File 'node_modules/@types/typerefs2/package.json' does not exist.",
+        "File 'node_modules/@types/typerefs2/index.d.ts' exist - use it as a name resolution result.",
+        "======== Type reference directive 'typerefs2' was successfully resolved to 'node_modules/@types/typerefs2/index.d.ts', primary: true. ========",
+        "Reusing resolution of module './b2' to file 'f2.ts' from old program.",
+        "Reusing resolution of module './f1' to file 'f2.ts' from old program."
+    ]
+}

tests/baselines/reference/reuseProgramStructure/fetches-imports-after-npm-install.trace.json

@@ -0,0 +1,37 @@
+{
+    "initialProgram: execute module resolution normally.": [
+        "======== Resolving module 'a' from 'file1.ts'. ========",
+        "Explicitly specified module resolution kind: 'NodeJs'.",
+        "Loading module 'a' from 'node_modules' folder, target file type 'TypeScript'.",
+        "File 'node_modules/a/package.json' does not exist.",
+        "File 'node_modules/a.ts' does not exist.",
+        "File 'node_modules/a.tsx' does not exist.",
+        "File 'node_modules/a.d.ts' does not exist.",
+        "File 'node_modules/a/index.ts' does not exist.",
+        "File 'node_modules/a/index.tsx' does not exist.",
+        "File 'node_modules/a/index.d.ts' does not exist.",
+        "File 'node_modules/@types/a/package.json' does not exist.",
+        "File 'node_modules/@types/a.d.ts' does not exist.",
+        "File 'node_modules/@types/a/index.d.ts' does not exist.",
+        "Loading module 'a' from 'node_modules' folder, target file type 'JavaScript'.",
+        "File 'node_modules/a/package.json' does not exist.",
+        "File 'node_modules/a.js' does not exist.",
+        "File 'node_modules/a.jsx' does not exist.",
+        "File 'node_modules/a/index.js' does not exist.",
+        "File 'node_modules/a/index.jsx' does not exist.",
+        "======== Module name 'a' was not resolved. ========"
+    ],
+    "afterNpmInstallProgram: execute module resolution normally.": [
+        "======== Resolving module 'a' from 'file1.ts'. ========",
+        "Explicitly specified module resolution kind: 'NodeJs'.",
+        "Loading module 'a' from 'node_modules' folder, target file type 'TypeScript'.",
+        "File 'node_modules/a/package.json' does not exist.",
+        "File 'node_modules/a.ts' does not exist.",
+        "File 'node_modules/a.tsx' does not exist.",
+        "File 'node_modules/a.d.ts' does not exist.",
+        "File 'node_modules/a/index.ts' does not exist.",
+        "File 'node_modules/a/index.tsx' does not exist.",
+        "File 'node_modules/a/index.d.ts' exist - use it as a name resolution result.",
+        "======== Module name 'a' was successfully resolved to 'node_modules/a/index.d.ts'. ========"
+    ]
+}

tests/baselines/reference/tscWatch/programUpdates/types-should-load-from-config-file-path-if-config-exists.js

@@ -3,7 +3,7 @@ Input::
 let x = 1
 
 //// [/a/b/tsconfig.json]
-{"compilerOptions":{"types":["node"],"typeRoots":[]}}
+{"compilerOptions":{"types":["node"]}}
 
 //// [/a/b/node_modules/@types/node/index.d.ts]
 declare var process: any
@@ -33,7 +33,7 @@ Output::
 
 
 Program root files: ["/a/b/app.ts"]
-Program options: {"types":["node"],"typeRoots":[],"watch":true,"project":"/a/b/tsconfig.json","configFilePath":"/a/b/tsconfig.json"}
+Program options: {"types":["node"],"watch":true,"project":"/a/b/tsconfig.json","configFilePath":"/a/b/tsconfig.json"}
 Program files::
 /a/lib/lib.d.ts
 /a/b/app.ts

tests/baselines/reference/tscWatch/programUpdates/types-should-not-load-from-config-file-path-if-config-exists-but-does-not-specifies-typeRoots.js

@@ -0,0 +1,65 @@
+Input::
+//// [/a/b/app.ts]
+let x = 1
+
+//// [/a/b/tsconfig.json]
+{"compilerOptions":{"types":["node"],"typeRoots":[]}}
+
+//// [/a/b/node_modules/@types/node/index.d.ts]
+declare var process: any
+
+//// [/a/lib/lib.d.ts]
+/// <reference no-default-lib="true"/>
+interface Boolean {}
+interface Function {}
+interface CallableFunction {}
+interface NewableFunction {}
+interface IArguments {}
+interface Number { toExponential: any; }
+interface Object {}
+interface RegExp {}
+interface String { charAt: any; }
+interface Array<T> { length: number; [n: number]: T; }
+
+
+/a/lib/tsc.js -w -p /a/b/tsconfig.json
+Output::
+>> Screen clear
+[12:00:25 AM] Starting compilation in watch mode...
+
+
+error TS2688: Cannot find type definition file for 'node'.
+
+
+[12:00:28 AM] Found 1 error. Watching for file changes.
+
+
+
+Program root files: ["/a/b/app.ts"]
+Program options: {"types":["node"],"typeRoots":[],"watch":true,"project":"/a/b/tsconfig.json","configFilePath":"/a/b/tsconfig.json"}
+Program files::
+/a/lib/lib.d.ts
+/a/b/app.ts
+
+No cached semantic diagnostics in the builder::
+
+WatchedFiles::
+/a/b/tsconfig.json:
+  {"fileName":"/a/b/tsconfig.json","pollingInterval":250}
+/a/b/app.ts:
+  {"fileName":"/a/b/app.ts","pollingInterval":250}
+/a/lib/lib.d.ts:
+  {"fileName":"/a/lib/lib.d.ts","pollingInterval":250}
+
+FsWatches::
+
+FsWatchesRecursive::
+/a/b:
+  {"directoryName":"/a/b","fallbackPollingInterval":500,"fallbackOptions":{"watchFile":"PriorityPollingInterval"}}
+
+exitCode:: ExitStatus.undefined
+
+//// [/a/b/app.js]
+var x = 1;
+
+

tests/baselines/reference/tscWatch/resolutionCache/works-when-module-resolution-changes-to-ambient-module.js

@@ -114,6 +114,8 @@ WatchedFiles::
 FsWatches::
 
 FsWatchesRecursive::
+/a/b/node_modules:
+  {"directoryName":"/a/b/node_modules","fallbackPollingInterval":500,"fallbackOptions":{"watchFile":"PriorityPollingInterval"}}
 /a/b/node_modules/@types:
   {"directoryName":"/a/b/node_modules/@types","fallbackPollingInterval":500,"fallbackOptions":{"watchFile":"PriorityPollingInterval"}}
 

tests/baselines/reference/typeReferenceDirectiveWithFailedFromTypeRoot.errors.txt

@@ -0,0 +1,19 @@
+error TS2688: Cannot find type definition file for 'phaser'.
+/a.ts(1,1): error TS2304: Cannot find name 'a'.
+
+
+!!! error TS2688: Cannot find type definition file for 'phaser'.
+==== /a.ts (1 errors) ====
+    a;
+    ~
+!!! error TS2304: Cannot find name 'a'.
+    
+==== /typings/dummy.d.ts (0 errors) ====
+    declare const a2: number;
+    
+==== /node_modules/phaser/types/phaser.d.ts (0 errors) ====
+    declare const a: number;
+    
+==== /node_modules/phaser/package.json (0 errors) ====
+    { "name": "phaser", "version": "1.2.3", "types": "types/phaser.d.ts" }
+    

tests/baselines/reference/typeReferenceDirectiveWithFailedFromTypeRoot.js

@@ -0,0 +1,17 @@
+//// [tests/cases/compiler/typeReferenceDirectiveWithFailedFromTypeRoot.ts] ////
+
+//// [dummy.d.ts]
+declare const a2: number;
+
+//// [phaser.d.ts]
+declare const a: number;
+
+//// [package.json]
+{ "name": "phaser", "version": "1.2.3", "types": "types/phaser.d.ts" }
+
+//// [a.ts]
+a;
+
+
+//// [a.js]
+a;

tests/baselines/reference/typeReferenceDirectiveWithFailedFromTypeRoot.symbols

@@ -0,0 +1,4 @@
+=== /a.ts ===
+a;
+No type information for this code.
+No type information for this code.

tests/baselines/reference/typeReferenceDirectiveWithFailedFromTypeRoot.trace.json

@@ -0,0 +1,9 @@
+[
+    "======== Resolving type reference directive 'phaser', containing file '/__inferred type names__.ts', root directory '/typings'. ========",
+    "Resolving with primary search path '/typings'.",
+    "Loading module as file / folder, candidate module location '/typings/phaser', target file type 'DtsOnly'.",
+    "File '/typings/phaser.d.ts' does not exist.",
+    "Directory '/typings/phaser' does not exist, skipping all lookups in it.",
+    "Resolving type reference directive for program with typeRoots, skipping lookup in 'node_modules' folder.",
+    "======== Type reference directive 'phaser' was not resolved. ========"
+]

tests/baselines/reference/typeReferenceDirectiveWithFailedFromTypeRoot.types

@@ -0,0 +1,4 @@
+=== /a.ts ===
+a;
+>a : any
+

tests/baselines/reference/typeReferenceDirectiveWithTypeAsFile.js

@@ -0,0 +1,11 @@
+//// [tests/cases/compiler/typeReferenceDirectiveWithTypeAsFile.ts] ////
+
+//// [phaser.d.ts]
+declare const a: number;
+
+//// [a.ts]
+a;
+
+
+//// [a.js]
+a;

tests/baselines/reference/typeReferenceDirectiveWithTypeAsFile.symbols

@@ -0,0 +1,8 @@
+=== /a.ts ===
+a;
+>a : Symbol(a, Decl(phaser.d.ts, 0, 13))
+
+=== /node_modules/phaser/types/phaser.d.ts ===
+declare const a: number;
+>a : Symbol(a, Decl(phaser.d.ts, 0, 13))
+

tests/baselines/reference/typeReferenceDirectiveWithTypeAsFile.trace.json

@@ -0,0 +1,9 @@
+[
+    "======== Resolving type reference directive 'phaser', containing file '/__inferred type names__.ts', root directory '/node_modules/phaser/types'. ========",
+    "Resolving with primary search path '/node_modules/phaser/types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/phaser/types/phaser', target file type 'DtsOnly'.",
+    "File '/node_modules/phaser/types/phaser.d.ts' exist - use it as a name resolution result.",
+    "File '/node_modules/phaser/package.json' does not exist.",
+    "Resolving real path for '/node_modules/phaser/types/phaser.d.ts', result '/node_modules/phaser/types/phaser.d.ts'.",
+    "======== Type reference directive 'phaser' was successfully resolved to '/node_modules/phaser/types/phaser.d.ts', primary: true. ========"
+]

tests/baselines/reference/typeReferenceDirectiveWithTypeAsFile.types

@@ -0,0 +1,8 @@
+=== /a.ts ===
+a;
+>a : number
+
+=== /node_modules/phaser/types/phaser.d.ts ===
+declare const a: number;
+>a : number
+

tests/baselines/reference/typeReferenceDirectives1.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/app.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
     "======== Type reference directive 'lib' was successfully resolved to '/types/lib/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives10.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/app.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
@@ -14,6 +16,8 @@
     "======== Module name './ref' was successfully resolved to '/ref.d.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives11.trace.json

@@ -6,6 +6,8 @@
     "======== Module name './mod1' was successfully resolved to '/mod1.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives12.trace.json

@@ -11,6 +11,8 @@
     "======== Module name './mod1' was successfully resolved to '/mod1.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/mod1.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
@@ -20,6 +22,8 @@
     "======== Module name './main' was successfully resolved to '/main.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives13.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/app.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
@@ -14,6 +16,8 @@
     "======== Module name './ref' was successfully resolved to '/ref.d.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives2.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives3.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/app.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
     "======== Type reference directive 'lib' was successfully resolved to '/types/lib/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives4.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/app.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
     "======== Type reference directive 'lib' was successfully resolved to '/types/lib/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives5.trace.json

@@ -1,6 +1,8 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/app.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
@@ -14,6 +16,8 @@
     "======== Module name './ref' was successfully resolved to '/ref.d.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives6.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/app.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
     "======== Type reference directive 'lib' was successfully resolved to '/types/lib/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives7.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'lib', containing file '/app.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
     "======== Type reference directive 'lib' was successfully resolved to '/types/lib/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives8.trace.json

@@ -6,6 +6,8 @@
     "======== Module name './mod1' was successfully resolved to '/mod1.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeReferenceDirectives9.trace.json

@@ -11,6 +11,8 @@
     "======== Module name './mod1' was successfully resolved to '/mod1.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/mod1.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",
@@ -20,6 +22,8 @@
     "======== Module name './main' was successfully resolved to '/main.ts'. ========",
     "======== Resolving type reference directive 'lib', containing file '/__inferred type names__.ts', root directory '/types'. ========",
     "Resolving with primary search path '/types'.",
+    "Loading module as file / folder, candidate module location '/types/lib', target file type 'DtsOnly'.",
+    "File '/types/lib.d.ts' does not exist.",
     "File '/types/lib/package.json' does not exist.",
     "File '/types/lib/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/types/lib/index.d.ts', result '/types/lib/index.d.ts'.",

tests/baselines/reference/typeRootsFromMultipleNodeModulesDirectories.trace.json

@@ -58,18 +58,27 @@
     "======== Module name 'abc' was not resolved. ========",
     "======== Resolving type reference directive 'grumpy', containing file '/foo/bar/__inferred type names__.ts', root directory '/foo/node_modules/@types,/node_modules/@types'. ========",
     "Resolving with primary search path '/foo/node_modules/@types, /node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/foo/node_modules/@types/grumpy', target file type 'DtsOnly'.",
+    "File '/foo/node_modules/@types/grumpy.d.ts' does not exist.",
     "File '/foo/node_modules/@types/grumpy/package.json' does not exist.",
     "File '/foo/node_modules/@types/grumpy/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/foo/node_modules/@types/grumpy/index.d.ts', result '/foo/node_modules/@types/grumpy/index.d.ts'.",
     "======== Type reference directive 'grumpy' was successfully resolved to '/foo/node_modules/@types/grumpy/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'sneezy', containing file '/foo/bar/__inferred type names__.ts', root directory '/foo/node_modules/@types,/node_modules/@types'. ========",
     "Resolving with primary search path '/foo/node_modules/@types, /node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/foo/node_modules/@types/sneezy', target file type 'DtsOnly'.",
+    "File '/foo/node_modules/@types/sneezy.d.ts' does not exist.",
     "File '/foo/node_modules/@types/sneezy/package.json' does not exist.",
     "File '/foo/node_modules/@types/sneezy/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/foo/node_modules/@types/sneezy/index.d.ts', result '/foo/node_modules/@types/sneezy/index.d.ts'.",
     "======== Type reference directive 'sneezy' was successfully resolved to '/foo/node_modules/@types/sneezy/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'dopey', containing file '/foo/bar/__inferred type names__.ts', root directory '/foo/node_modules/@types,/node_modules/@types'. ========",
     "Resolving with primary search path '/foo/node_modules/@types, /node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/foo/node_modules/@types/dopey', target file type 'DtsOnly'.",
+    "File '/foo/node_modules/@types/dopey.d.ts' does not exist.",
+    "Directory '/foo/node_modules/@types/dopey' does not exist, skipping all lookups in it.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/dopey', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/dopey.d.ts' does not exist.",
     "File '/node_modules/@types/dopey/package.json' does not exist.",
     "File '/node_modules/@types/dopey/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/dopey/index.d.ts', result '/node_modules/@types/dopey/index.d.ts'.",

tests/baselines/reference/typeRootsFromNodeModulesInParentDirectory.trace.json

@@ -14,6 +14,8 @@
     "======== Module name 'xyz' was not resolved. ========",
     "======== Resolving type reference directive 'foo', containing file '/src/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/foo', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/foo.d.ts' does not exist.",
     "File '/node_modules/@types/foo/package.json' does not exist.",
     "File '/node_modules/@types/foo/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/foo/index.d.ts', result '/node_modules/@types/foo/index.d.ts'.",

tests/baselines/reference/typingsLookup1.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'jquery', containing file '/a.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/jquery', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/jquery.d.ts' does not exist.",
     "File '/node_modules/@types/jquery/package.json' does not exist.",
     "File '/node_modules/@types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/jquery/index.d.ts', result '/node_modules/@types/jquery/index.d.ts'.",
     "======== Type reference directive 'jquery' was successfully resolved to '/node_modules/@types/jquery/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'jquery', containing file '/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/jquery', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/jquery.d.ts' does not exist.",
     "File '/node_modules/@types/jquery/package.json' does not exist.",
     "File '/node_modules/@types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/jquery/index.d.ts', result '/node_modules/@types/jquery/index.d.ts'.",

tests/baselines/reference/typingsLookup3.trace.json

@@ -1,12 +1,16 @@
 [
     "======== Resolving type reference directive 'jquery', containing file '/a.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/jquery', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/jquery.d.ts' does not exist.",
     "File '/node_modules/@types/jquery/package.json' does not exist.",
     "File '/node_modules/@types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/jquery/index.d.ts', result '/node_modules/@types/jquery/index.d.ts'.",
     "======== Type reference directive 'jquery' was successfully resolved to '/node_modules/@types/jquery/index.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'jquery', containing file '/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/jquery', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/jquery.d.ts' does not exist.",
     "File '/node_modules/@types/jquery/package.json' does not exist.",
     "File '/node_modules/@types/jquery/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/jquery/index.d.ts', result '/node_modules/@types/jquery/index.d.ts'.",

tests/baselines/reference/typingsLookup4.trace.json

@@ -65,6 +65,8 @@
     "======== Module name 'mquery' was successfully resolved to '/node_modules/@types/mquery/mquery/index.tsx'. ========",
     "======== Resolving type reference directive 'jquery', containing file '/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/jquery', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/jquery.d.ts' does not exist.",
     "Found 'package.json' at '/node_modules/@types/jquery/package.json'.",
     "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'jquery.d.ts' that references '/node_modules/@types/jquery/jquery.d.ts'.",
@@ -73,6 +75,8 @@
     "======== Type reference directive 'jquery' was successfully resolved to '/node_modules/@types/jquery/jquery.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'kquery', containing file '/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/kquery', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/kquery.d.ts' does not exist.",
     "Found 'package.json' at '/node_modules/@types/kquery/package.json'.",
     "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'kquery' that references '/node_modules/@types/kquery/kquery'.",
@@ -85,6 +89,8 @@
     "======== Type reference directive 'kquery' was successfully resolved to '/node_modules/@types/kquery/kquery.d.ts', primary: true. ========",
     "======== Resolving type reference directive 'lquery', containing file '/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/lquery', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/lquery.d.ts' does not exist.",
     "Found 'package.json' at '/node_modules/@types/lquery/package.json'.",
     "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'lquery' that references '/node_modules/@types/lquery/lquery'.",
@@ -95,6 +101,8 @@
     "======== Type reference directive 'lquery' was successfully resolved to '/node_modules/@types/lquery/lquery.ts', primary: true. ========",
     "======== Resolving type reference directive 'mquery', containing file '/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/mquery', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/mquery.d.ts' does not exist.",
     "Found 'package.json' at '/node_modules/@types/mquery/package.json'.",
     "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'mquery' that references '/node_modules/@types/mquery/mquery'.",

tests/baselines/reference/typingsLookupAmd.trace.json

@@ -41,6 +41,8 @@
     "======== Module name 'a' was successfully resolved to '/node_modules/@types/a/index.d.ts'. ========",
     "======== Resolving type reference directive 'a', containing file '/__inferred type names__.ts', root directory '/node_modules/@types'. ========",
     "Resolving with primary search path '/node_modules/@types'.",
+    "Loading module as file / folder, candidate module location '/node_modules/@types/a', target file type 'DtsOnly'.",
+    "File '/node_modules/@types/a.d.ts' does not exist.",
     "File '/node_modules/@types/a/package.json' does not exist.",
     "File '/node_modules/@types/a/index.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/a/index.d.ts', result '/node_modules/@types/a/index.d.ts'.",

tests/cases/compiler/moduleResolutionAsTypeReferenceDirective.ts

@@ -0,0 +1,15 @@
+// @noImplicitReferences: true
+// @typeRoots: /typings
+// @types: phaser
+// @traceResolution: true
+// @currentDirectory: /
+
+// @Filename: /typings/phaser/types/phaser.d.ts
+export const a2: number;
+
+// @Filename: /typings/phaser/package.json
+{ "name": "phaser", "version": "1.2.3", "types": "types/phaser.d.ts" }
+
+
+// @Filename: /a.ts
+import { a2 } from "phaser";

tests/cases/compiler/moduleResolutionAsTypeReferenceDirectiveAmbient.ts

@@ -0,0 +1,17 @@
+// @noImplicitReferences: true
+// @typeRoots: /typings
+// @types: phaser
+// @traceResolution: true
+// @currentDirectory: /
+
+// @Filename: /typings/phaser/types/phaser.d.ts
+declare module "phaser" {
+    export const a2: number;
+}
+
+// @Filename: /typings/phaser/package.json
+{ "name": "phaser", "version": "1.2.3", "types": "types/phaser.d.ts" }
+
+
+// @Filename: /a.ts
+import { a2 } from "phaser";

tests/cases/compiler/typeReferenceDirectiveWithFailedFromTypeRoot.ts

@@ -0,0 +1,17 @@
+// @noImplicitReferences: true
+// @typeRoots: /typings
+// @types: phaser
+// @traceResolution: true
+// @currentDirectory: /
+
+// @Filename: /typings/dummy.d.ts
+declare const a2: number;
+
+// @Filename: /node_modules/phaser/types/phaser.d.ts
+declare const a: number;
+
+// @Filename: /node_modules/phaser/package.json
+{ "name": "phaser", "version": "1.2.3", "types": "types/phaser.d.ts" }
+
+// @Filename: /a.ts
+a;

tests/cases/compiler/typeReferenceDirectiveWithTypeAsFile.ts

@@ -0,0 +1,11 @@
+// @noImplicitReferences: true
+// @typeRoots: /node_modules/phaser/types
+// @types: phaser
+// @traceResolution: true
+// @currentDirectory: /
+
+// @Filename: /node_modules/phaser/types/phaser.d.ts
+declare const a: number;
+
+// @Filename: /a.ts
+a;