Avoid watching non-existing directories and fix null-exception (#11601)

* Avoid watching non-existing directories and fix null-exception

* Add test

* Move the fix to sys to cover tsc -w also

src/compiler/sys.ts

@@ -476,6 +476,10 @@ namespace ts {
                     // Node 4.0 `fs.watch` function supports the "recursive" option on both OSX and Windows
                     // (ref: https://github.com/nodejs/node/pull/2649 and https://github.com/Microsoft/TypeScript/issues/4643)
                     let options: any;
+                    if (!directoryExists(directoryName)) {
+                        return;
+                    }
+
                     if (isNode4OrLater() && (process.platform === "win32" || process.platform === "darwin")) {
                         options = { persistent: true, recursive: !!recursive };
                     }

src/harness/unittests/tsserverProjectSystem.ts

@@ -2387,4 +2387,33 @@ namespace ts.projectSystem {
             assert.isTrue(errorResult.length === 0);
         });
     });
+
+    describe("non-existing directories listed in config file input array", () => {
+        it("should be tolerated without crashing the server", () => {
+            const configFile = {
+                path: "/a/b/tsconfig.json",
+                content: `{
+                    "compilerOptions": {},
+                    "include": ["app/*", "test/**/*", "something"]
+                }`
+            };
+            const file1 = {
+                path: "/a/b/file1.ts",
+                content: "let t = 10;"
+            };
+
+            const host = createServerHost([file1, configFile]);
+            const projectService = createProjectService(host);
+            projectService.openClientFile(file1.path);
+            host.runQueuedTimeoutCallbacks();
+            checkNumberOfConfiguredProjects(projectService, 1);
+            checkNumberOfInferredProjects(projectService, 1);
+
+            const configuredProject = projectService.configuredProjects[0];
+            assert.isTrue(configuredProject.getFileNames().length == 0);
+
+            const inferredProject = projectService.inferredProjects[0];
+            assert.isTrue(inferredProject.containsFile(<server.NormalizedPath>file1.path));
+        });
+    });
 }

src/server/editorServices.ts

@@ -710,7 +710,7 @@ namespace ts.server {
             Debug.assert(!!parsedCommandLine.fileNames);
 
             if (parsedCommandLine.fileNames.length === 0) {
-                errors.push(createCompilerDiagnostic(Diagnostics.The_config_file_0_found_doesn_t_contain_any_source_files, configFilename));
+                (errors || (errors = [])).push(createCompilerDiagnostic(Diagnostics.The_config_file_0_found_doesn_t_contain_any_source_files, configFilename));
                 return { success: false, configFileErrors: errors };
             }