Allow an import of "foo.js" to be matched by a file "foo.ts"

src/compiler/core.ts

@@ -849,13 +849,18 @@ namespace ts {
     const extensionsToRemove = [".d.ts", ".ts", ".js", ".tsx", ".jsx"];
     export function removeFileExtension(path: string): string {
         for (const ext of extensionsToRemove) {
-            if (fileExtensionIs(path, ext)) {
-                return path.substr(0, path.length - ext.length);
+            const extensionless = tryRemoveExtension(path, ext);
+            if (extensionless !== undefined) {
+                return extensionless;
             }
         }
         return path;
     }
 
+    export function tryRemoveExtension(path: string, extension: string): string {
+        return fileExtensionIs(path, extension) ? path.substring(0, path.length - extension.length) : undefined;
+    }
+
     export interface ObjectAllocator {
         getNodeConstructor(): new (kind: SyntaxKind, pos?: number, end?: number) => Node;
         getSourceFileConstructor(): new (kind: SyntaxKind, pos?: number, end?: number) => SourceFile;

src/compiler/program.ts

@@ -615,6 +615,7 @@ namespace ts {
     }
 
     /**
+     * @param extensions - Either supportedTypeScriptExtensions or if --allowJs, allSupportedExtensions
      * @param {boolean} onlyRecordFailures - if true then function won't try to actually load files but instead record all attempts as failures. This flag is necessary
      * in cases when we know upfront that all load attempts will fail (because containing folder does not exists) however we still need to record all failed lookup locations.
      */
@@ -626,13 +627,30 @@ namespace ts {
                 onlyRecordFailures = !directoryProbablyExists(directory, state.host);
             }
         }
-        return forEach(extensions, tryLoad);
 
-        function tryLoad(ext: string): string {
-            if (ext === ".tsx" && state.skipTsx) {
-                return undefined;
+        // First try to keep/add an extension: importing "./foo.ts" can be matched by a file "./foo.ts", and "./foo" by "./foo.d.ts"
+        const keepOrAddExtension = forEach(extensions, ext => {
+            if (state.skipTsx && (ext === ".jsx" || ext === ".tsx")) {
+                return;
+            }
+            return tryLoad(fileExtensionIs(candidate, ext) ? candidate : candidate + ext);
+        });
+        if (keepOrAddExtension) {
+            return keepOrAddExtension;
+        }
+
+        // Then try stripping a ".js" or ".jsx" extension and replacing it with a TypeScript one, e.g. "./foo.js" can be matched by "./foo.ts" or "./foo.d.ts"
+        return forEach(supportedJavascriptExtensions, jsExt => {
+            if (state.skipTsx && jsExt === ".jsx") {
+                return;
+            }
+            const extensionless = tryRemoveExtension(candidate, jsExt);
+            if (extensionless !== undefined) {
+                return forEach(supportedTypeScriptExtensions, tsExt => tryLoad(extensionless + tsExt));
             }
-            const fileName = fileExtensionIs(candidate, ext) ? candidate : candidate + ext;
+        });
+
+        function tryLoad(fileName: string): string {
             if (!onlyRecordFailures && state.host.fileExists(fileName)) {
                 if (state.traceEnabled) {
                     trace(state.host, Diagnostics.File_0_exist_use_it_as_a_name_resolution_result, fileName);

src/harness/harness.ts

@@ -1,7 +1,7 @@
 
 //
 // Copyright (c) Microsoft Corporation.  All rights reserved.
-// 
+//
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
@@ -350,7 +350,7 @@ namespace Utils {
         assert.equal(node1.end, node2.end, "node1.end !== node2.end");
         assert.equal(node1.kind, node2.kind, "node1.kind !== node2.kind");
 
-        // call this on both nodes to ensure all propagated flags have been set (and thus can be 
+        // call this on both nodes to ensure all propagated flags have been set (and thus can be
         // compared).
         assert.equal(ts.containsParseError(node1), ts.containsParseError(node2));
         assert.equal(node1.flags, node2.flags, "node1.flags !== node2.flags");
@@ -751,7 +751,7 @@ namespace Harness {
         (emittedFile: string, emittedLine: number, emittedColumn: number, sourceFile: string, sourceLine: number, sourceColumn: number, sourceName: string): void;
     }
 
-    // Settings 
+    // Settings
     export let userSpecifiedRoot = "";
     export let lightMode = false;
 
@@ -790,7 +790,7 @@ namespace Harness {
             fileName: string,
             sourceText: string,
             languageVersion: ts.ScriptTarget) {
-            // We'll only assert invariants outside of light mode. 
+            // We'll only assert invariants outside of light mode.
             const shouldAssertInvariants = !Harness.lightMode;
 
             // Only set the parent nodes if we're asserting invariants.  We don't need them otherwise.
@@ -935,7 +935,7 @@ namespace Harness {
             libFiles?: string;
         }
 
-        // Additional options not already in ts.optionDeclarations 
+        // Additional options not already in ts.optionDeclarations
         const harnessOptionDeclarations: ts.CommandLineOption[] = [
             { name: "allowNonTsExtensions", type: "boolean" },
             { name: "useCaseSensitiveFileNames", type: "boolean" },
@@ -1187,7 +1187,7 @@ namespace Harness {
                 errLines.forEach(e => outputLines.push(e));
 
                 // do not count errors from lib.d.ts here, they are computed separately as numLibraryDiagnostics
-                // if lib.d.ts is explicitly included in input files and there are some errors in it (i.e. because of duplicate identifiers) 
+                // if lib.d.ts is explicitly included in input files and there are some errors in it (i.e. because of duplicate identifiers)
                 // then they will be added twice thus triggering 'total errors' assertion with condition
                 // 'totalErrorsReportedInNonLibraryFiles + numLibraryDiagnostics + numTest262HarnessDiagnostics, diagnostics.length
 
@@ -1497,7 +1497,7 @@ namespace Harness {
             };
             testUnitData.push(newTestFile2);
 
-            // unit tests always list files explicitly 
+            // unit tests always list files explicitly
             const parseConfigHost: ts.ParseConfigHost = {
                 readDirectory: (name) => []
             };

tests/baselines/reference/moduleResolution.js

@@ -0,0 +1,45 @@
+//// [tests/cases/compiler/moduleResolution.ts] ////
+
+//// [a.ts]
+export default 0;
+
+// No extension: '.ts' added
+//// [b.ts]
+import a from './a';
+
+// Matching extension
+//// [c.ts]
+import a from './a.ts';
+
+// '.js' extension: stripped and replaced with '.ts'
+//// [d.ts]
+import a from './a.js';
+
+//// [jquery.d.ts]
+declare var x: number;
+export default x;
+
+// No extension: '.d.ts' added
+//// [jquery_user_1.ts]
+import j from "./jquery";
+
+// '.js' extension: stripped and replaced with '.d.ts'
+//// [jquery_user_1.ts]
+import j from "./jquery.js"
+
+
+//// [a.js]
+"use strict";
+exports.__esModule = true;
+exports["default"] = 0;
+// No extension: '.ts' added 
+//// [b.js]
+"use strict";
+// Matching extension 
+//// [c.js]
+"use strict";
+// '.js' extension: stripped and replaced with '.ts' 
+//// [d.js]
+"use strict";
+//// [jquery_user_1.js]
+"use strict";

tests/baselines/reference/moduleResolution.symbols

@@ -0,0 +1,36 @@
+=== tests/cases/compiler/a.ts ===
+export default 0;
+No type information for this code.
+No type information for this code.// No extension: '.ts' added
+No type information for this code.=== tests/cases/compiler/b.ts ===
+import a from './a';
+>a : Symbol(a, Decl(b.ts, 0, 6))
+
+// Matching extension
+=== tests/cases/compiler/c.ts ===
+import a from './a.ts';
+>a : Symbol(a, Decl(c.ts, 0, 6))
+
+// '.js' extension: stripped and replaced with '.ts'
+=== tests/cases/compiler/d.ts ===
+import a from './a.js';
+>a : Symbol(a, Decl(d.ts, 0, 6))
+
+=== tests/cases/compiler/jquery.d.ts ===
+declare var x: number;
+>x : Symbol(x, Decl(jquery.d.ts, 0, 11))
+
+export default x;
+>x : Symbol(x, Decl(jquery.d.ts, 0, 11))
+
+// No extension: '.d.ts' added
+=== tests/cases/compiler/jquery_user_1.ts ===
+import j from "./jquery";
+>j : Symbol(j, Decl(jquery_user_1.ts, 0, 6))
+
+// '.js' extension: stripped and replaced with '.d.ts'
+=== tests/cases/compiler/jquery_user_1.ts ===
+import j from "./jquery.js"
+>j : Symbol(j, Decl(jquery_user_1.ts, 0, 6))
+>j : Symbol(j, Decl(jquery_user_1.ts, 0, 6))
+

tests/baselines/reference/moduleResolution.types

@@ -0,0 +1,36 @@
+=== tests/cases/compiler/a.ts ===
+export default 0;
+No type information for this code.
+No type information for this code.// No extension: '.ts' added
+No type information for this code.=== tests/cases/compiler/b.ts ===
+import a from './a';
+>a : number
+
+// Matching extension
+=== tests/cases/compiler/c.ts ===
+import a from './a.ts';
+>a : number
+
+// '.js' extension: stripped and replaced with '.ts'
+=== tests/cases/compiler/d.ts ===
+import a from './a.js';
+>a : number
+
+=== tests/cases/compiler/jquery.d.ts ===
+declare var x: number;
+>x : number
+
+export default x;
+>x : number
+
+// No extension: '.d.ts' added
+=== tests/cases/compiler/jquery_user_1.ts ===
+import j from "./jquery";
+>j : number
+
+// '.js' extension: stripped and replaced with '.d.ts'
+=== tests/cases/compiler/jquery_user_1.ts ===
+import j from "./jquery.js"
+>j : number
+>j : number
+

tests/baselines/reference/nameWithFileExtension.js

@@ -8,6 +8,9 @@ import foo = require('./foo_0.js');
 var x = foo.foo + 42;
 
 
+//// [foo_0.js]
+"use strict";
+exports.foo = 42;
 //// [foo_1.js]
 "use strict";
 var foo = require('./foo_0.js');

tests/baselines/reference/nameWithFileExtension.symbols

@@ -0,0 +1,14 @@
+=== tests/cases/conformance/externalModules/foo_1.ts ===
+import foo = require('./foo_0.js');
+>foo : Symbol(foo, Decl(foo_1.ts, 0, 0))
+
+var x = foo.foo + 42;
+>x : Symbol(x, Decl(foo_1.ts, 1, 3))
+>foo.foo : Symbol(foo.foo, Decl(foo_0.ts, 0, 10))
+>foo : Symbol(foo, Decl(foo_1.ts, 0, 0))
+>foo : Symbol(foo.foo, Decl(foo_0.ts, 0, 10))
+
+=== tests/cases/conformance/externalModules/foo_0.ts ===
+export var foo = 42;
+>foo : Symbol(foo, Decl(foo_0.ts, 0, 10))
+

tests/baselines/reference/nameWithFileExtension.types

@@ -0,0 +1,17 @@
+=== tests/cases/conformance/externalModules/foo_1.ts ===
+import foo = require('./foo_0.js');
+>foo : typeof foo
+
+var x = foo.foo + 42;
+>x : number
+>foo.foo + 42 : number
+>foo.foo : number
+>foo : typeof foo
+>foo : number
+>42 : number
+
+=== tests/cases/conformance/externalModules/foo_0.ts ===
+export var foo = 42;
+>foo : number
+>42 : number
+

tests/baselines/reference/project/cantFindTheModule/amd/cantFindTheModule.errors.txt

@@ -1,12 +1,12 @@
-decl.ts(1,26): error TS2307: Cannot find module './foo/bar.js'.
+decl.ts(1,26): error TS2307: Cannot find module './foo/bar.tx'.
 decl.ts(2,26): error TS2307: Cannot find module 'baz'.
 decl.ts(3,26): error TS2307: Cannot find module './baz'.
 
 
 ==== decl.ts (3 errors) ====
-    import modErr  = require("./foo/bar.js");
+    import modErr  = require("./foo/bar.tx");
                              ~~~~~~~~~~~~~~
-!!! error TS2307: Cannot find module './foo/bar.js'.
+!!! error TS2307: Cannot find module './foo/bar.tx'.
     import modErr1 = require("baz");
                              ~~~~~
 !!! error TS2307: Cannot find module 'baz'.

tests/baselines/reference/project/cantFindTheModule/node/cantFindTheModule.errors.txt

@@ -1,12 +1,12 @@
-decl.ts(1,26): error TS2307: Cannot find module './foo/bar.js'.
+decl.ts(1,26): error TS2307: Cannot find module './foo/bar.tx'.
 decl.ts(2,26): error TS2307: Cannot find module 'baz'.
 decl.ts(3,26): error TS2307: Cannot find module './baz'.
 
 
 ==== decl.ts (3 errors) ====
-    import modErr  = require("./foo/bar.js");
+    import modErr  = require("./foo/bar.tx");
                              ~~~~~~~~~~~~~~
-!!! error TS2307: Cannot find module './foo/bar.js'.
+!!! error TS2307: Cannot find module './foo/bar.tx'.
     import modErr1 = require("baz");
                              ~~~~~
 !!! error TS2307: Cannot find module 'baz'.

tests/cases/compiler/moduleResolution.ts

@@ -0,0 +1,26 @@
+// @Filename: a.ts
+export default 0;
+
+// No extension: '.ts' added
+// @Filename: b.ts
+import a from './a';
+
+// Matching extension
+// @Filename: c.ts
+import a from './a.ts';
+
+// '.js' extension: stripped and replaced with '.ts'
+// @Filename: d.ts
+import a from './a.js';
+
+// @Filename: jquery.d.ts
+declare var x: number;
+export default x;
+
+// No extension: '.d.ts' added
+// @Filename: jquery_user_1.ts
+import j from "./jquery";
+
+// '.js' extension: stripped and replaced with '.d.ts'
+// @Filename: jquery_user_1.ts
+import j from "./jquery.js"

tests/cases/projects/NoModule/decl.ts

@@ -1,4 +1,4 @@
-import modErr  = require("./foo/bar.js");
+import modErr  = require("./foo/bar.tx");
 import modErr1 = require("baz");
 import modErr2 = require("./baz");