From 121b04ee36da2ad1d958e5b0fffc907460673529 Mon Sep 17 00:00:00 2001
From: Vladimir Matveev <vladima@microsoft.com>
Date: Fri, 16 Sep 2016 15:49:20 -0700
Subject: [PATCH] (lshost): run second module resolution pass if first pass
 yielded non-ts file (#10959)

* (lshost): run second module resolution pass if first pass yielded non-ts file

* use length check
---
 .../unittests/tsserverProjectSystem.ts        | 28 +++++++++++++++++++
 src/server/lsHost.ts                          | 16 +++++++++--
 2 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index b455c0d216..cf5208628c 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -1881,4 +1881,32 @@ namespace ts.projectSystem {
             projectService.checkNumberOfProjects({});
         });
     });
+
+    describe("prefer typings to js", () => {
+        it("during second resolution pass", () => {
+            const typingsCacheLocation = "/a/typings";
+            const f1 = {
+                path: "/a/b/app.js",
+                content: "var x = require('bar')"
+            };
+            const barjs = {
+                path: "/a/b/node_modules/bar/index.js",
+                content: "export let x = 1"
+            };
+            const barTypings = {
+                path: `${typingsCacheLocation}/node_modules/@types/bar/index.d.ts`,
+                content: "export let y: number"
+            };
+            const config = {
+                path: "/a/b/jsconfig.json",
+                content: JSON.stringify({ compilerOptions: { allowJs: true }, exclude: ["node_modules"] })
+            };
+            const host = createServerHost([f1, barjs, barTypings, config]);
+            const projectService = createProjectService(host, { typingsInstaller: new TestTypingsInstaller(typingsCacheLocation, host) });
+
+            projectService.openClientFile(f1.path);
+            projectService.checkNumberOfProjects({ configuredProjects: 1 });
+            checkProjectActualFiles(projectService.configuredProjects[0], [f1.path, barTypings.path]);
+        });
+    });
 }
\ No newline at end of file
diff --git a/src/server/lsHost.ts b/src/server/lsHost.ts
index fd933bace1..f6530953a5 100644
--- a/src/server/lsHost.ts
+++ b/src/server/lsHost.ts
@@ -24,8 +24,15 @@ namespace ts.server {
             this.resolveModuleName = (moduleName, containingFile, compilerOptions, host) => {
                 const primaryResult = resolveModuleName(moduleName, containingFile, compilerOptions, host);
                 if (primaryResult.resolvedModule) {
-                    return primaryResult;
+                    // return result immediately only if it is .ts, .tsx or .d.ts
+                    // otherwise try to load typings from @types
+                    if (fileExtensionIsAny(primaryResult.resolvedModule.resolvedFileName, supportedTypeScriptExtensions)) {
+                        return primaryResult;
+                    }
                 }
+                // create different collection of failed lookup locations for second pass
+                // if it will fail and we've already found something during the first pass - we don't want to pollute its results 
+                const secondaryLookupFailedLookupLocations: string[] = [];
                 const globalCache = this.project.projectService.typingsInstaller.globalTypingsCacheLocation;
                 if (this.project.getTypingOptions().enableAutoDiscovery && globalCache) {
                     const traceEnabled = isTraceEnabled(compilerOptions, host);
@@ -33,11 +40,14 @@ namespace ts.server {
                         trace(host, Diagnostics.Auto_discovery_for_typings_is_enabled_in_project_0_Running_extra_resolution_pass_for_module_1_using_cache_location_2, this.project.getProjectName(), moduleName, globalCache);
                     }
                     const state: ModuleResolutionState = { compilerOptions, host, skipTsx: false, traceEnabled };
-                    const resolvedName = loadModuleFromNodeModules(moduleName, globalCache, primaryResult.failedLookupLocations, state, /*checkOneLevel*/ true);
+                    const resolvedName = loadModuleFromNodeModules(moduleName, globalCache, secondaryLookupFailedLookupLocations, state, /*checkOneLevel*/ true);
                     if (resolvedName) {
-                        return createResolvedModule(resolvedName, /*isExternalLibraryImport*/ true, primaryResult.failedLookupLocations);
+                        return createResolvedModule(resolvedName, /*isExternalLibraryImport*/ true, primaryResult.failedLookupLocations.concat(secondaryLookupFailedLookupLocations));
                     }
                 }
+                if (!primaryResult.resolvedModule && secondaryLookupFailedLookupLocations.length) {
+                    primaryResult.failedLookupLocations = primaryResult.failedLookupLocations.concat(secondaryLookupFailedLookupLocations);
+                }
                 return primaryResult;
             };
         }