Add support to report errors in js files

src/compiler/commandLineParser.ts

@@ -481,6 +481,12 @@ namespace ts {
                 name: "plugin",
                 type: "object"
             }
+        },
+        {
+            name: "checkJsFiles",
+            type: "boolean",
+            experimental: true,
+            description: Diagnostics.Report_errors_in_js_files
         }
     ];
 

src/compiler/diagnosticMessages.json

@@ -3362,5 +3362,9 @@
     "Octal literals are not allowed in enums members initializer. Use the syntax '{0}'.": {
         "category": "Error",
         "code": 8018
+    },
+    "Report errors in .js files.": {
+        "category": "Message",
+        "code": 8019
     }
 }

src/compiler/parser.ts

@@ -5817,6 +5817,7 @@ namespace ts {
             const typeReferenceDirectives: FileReference[] = [];
             const amdDependencies: { path: string; name: string }[] = [];
             let amdModuleName: string;
+            let hasCheckDirective = false;
 
             // Keep scanning all the leading trivia in the file until we get to something that
             // isn't trivia.  Any single line comment will be analyzed to see if it is a
@@ -5878,13 +5879,17 @@ namespace ts {
                             amdDependencies.push(amdDependency);
                         }
                     }
+
+                    const checkDirectiveRegEx = /^\/\/\s*@check\s*/gim;
+                    hasCheckDirective = hasCheckDirective || !!checkDirectiveRegEx.exec(comment);
                 }
             }
 
             sourceFile.referencedFiles = referencedFiles;
             sourceFile.typeReferenceDirectives = typeReferenceDirectives;
             sourceFile.amdDependencies = amdDependencies;
             sourceFile.moduleName = amdModuleName;
+            sourceFile.hasCheckDirective = hasCheckDirective;
         }
 
         function setExternalModuleIndicator(sourceFile: SourceFile) {

src/compiler/program.ts

@@ -907,7 +907,8 @@ namespace ts {
                 // For JavaScript files, we don't want to report semantic errors.
                 // Instead, we'll report errors for using TypeScript-only constructs from within a
                 // JavaScript file when we get syntactic diagnostics for the file.
-                const checkDiagnostics = isSourceFileJavaScript(sourceFile) ? [] : typeChecker.getDiagnostics(sourceFile, cancellationToken);
+                const includeCheckDiagnostics = options.checkJsFiles || sourceFile.hasCheckDirective || !isSourceFileJavaScript(sourceFile);
+                const checkDiagnostics = includeCheckDiagnostics ? typeChecker.getDiagnostics(sourceFile, cancellationToken) : [];
                 const fileProcessingDiagnosticsInFile = fileProcessingDiagnostics.getDiagnostics(sourceFile.fileName);
                 const programDiagnosticsInFile = programDiagnostics.getDiagnostics(sourceFile.fileName);
 

src/compiler/types.ts

@@ -2272,6 +2272,7 @@
         /* @internal */ moduleAugmentations: LiteralExpression[];
         /* @internal */ patternAmbientModules?: PatternAmbientModule[];
         /* @internal */ ambientModuleNames: string[];
+        /* @internal */ hasCheckDirective: boolean;
     }
 
     export interface Bundle extends Node {
@@ -3312,6 +3313,7 @@
         alwaysStrict?: boolean;  // Always combine with strict property
         baseUrl?: string;
         charset?: string;
+        checkJsFiles?: boolean;
         /* @internal */ configFilePath?: string;
         declaration?: boolean;
         declarationDir?: string;

src/services/services.ts

@@ -473,6 +473,7 @@ namespace ts {
         public moduleAugmentations: LiteralExpression[];
         private namedDeclarations: Map<Declaration[]>;
         public ambientModuleNames: string[];
+        public hasCheckDirective: boolean;
 
         constructor(kind: SyntaxKind, pos: number, end: number) {
             super(kind, pos, end);

tests/baselines/reference/checkJsFiles.errors.txt

@@ -0,0 +1,13 @@
+error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
+  Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+tests/cases/compiler/a.js(3,1): error TS2322: Type '0' is not assignable to type 'string'.
+
+
+!!! error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
+!!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+==== tests/cases/compiler/a.js (1 errors) ====
+
+    var x = "string";
+    x = 0;
+    ~
+!!! error TS2322: Type '0' is not assignable to type 'string'.

tests/baselines/reference/checkJsFiles2.errors.txt

@@ -0,0 +1,14 @@
+error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
+  Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+tests/cases/compiler/a.js(4,1): error TS2322: Type '0' is not assignable to type 'string'.
+
+
+!!! error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
+!!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+==== tests/cases/compiler/a.js (1 errors) ====
+
+    // @check
+    var x = "string";
+    x = 0;
+    ~
+!!! error TS2322: Type '0' is not assignable to type 'string'.

tests/baselines/reference/checkJsFiles3.errors.txt

@@ -0,0 +1,14 @@
+error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
+  Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+tests/cases/compiler/a.js(4,1): error TS2322: Type '0' is not assignable to type 'string'.
+
+
+!!! error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
+!!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+==== tests/cases/compiler/a.js (1 errors) ====
+
+    // @check
+    var x = "string";
+    x = 0;
+    ~
+!!! error TS2322: Type '0' is not assignable to type 'string'.

tests/cases/compiler/checkJsFiles.ts

@@ -0,0 +1,6 @@
+// @allowJs: true
+// @checkJsFiles: true
+
+// @fileName: a.js
+var x = "string";
+x = 0;

tests/cases/compiler/checkJsFiles2.ts

@@ -0,0 +1,7 @@
+// @allowJs: true
+// @checkJsFiles: false
+
+// @fileName: a.js
+// @check
+var x = "string";
+x = 0;

tests/cases/compiler/checkJsFiles3.ts

@@ -0,0 +1,6 @@
+// @allowJs: true
+
+// @fileName: a.js
+// @check
+var x = "string";
+x = 0;