From fa16a99514e53e97cb2ea95269ba71964c604d03 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Tue, 31 May 2016 09:26:21 -0700
Subject: [PATCH 1/8] Allow an import of "foo.js" to be matched by a file
 "foo.ts"

---
 src/compiler/core.ts                          |  9 +++-
 src/compiler/program.ts                       | 27 ++++++++---
 src/harness/harness.ts                        | 14 +++---
 tests/baselines/reference/moduleResolution.js | 45 +++++++++++++++++++
 .../reference/moduleResolution.symbols        | 36 +++++++++++++++
 .../reference/moduleResolution.types          | 36 +++++++++++++++
 .../nameWithFileExtension.errors.txt          | 12 -----
 .../reference/nameWithFileExtension.js        |  3 ++
 .../reference/nameWithFileExtension.symbols   | 14 ++++++
 .../reference/nameWithFileExtension.types     | 17 +++++++
 .../amd/cantFindTheModule.errors.txt          |  6 +--
 .../node/cantFindTheModule.errors.txt         |  6 +--
 tests/cases/compiler/moduleResolution.ts      | 26 +++++++++++
 tests/cases/projects/NoModule/decl.ts         |  2 +-
 14 files changed, 220 insertions(+), 33 deletions(-)
 create mode 100644 tests/baselines/reference/moduleResolution.js
 create mode 100644 tests/baselines/reference/moduleResolution.symbols
 create mode 100644 tests/baselines/reference/moduleResolution.types
 delete mode 100644 tests/baselines/reference/nameWithFileExtension.errors.txt
 create mode 100644 tests/baselines/reference/nameWithFileExtension.symbols
 create mode 100644 tests/baselines/reference/nameWithFileExtension.types
 create mode 100644 tests/cases/compiler/moduleResolution.ts

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 79b6249539dbc..ba81ee7d103d4 100644
--- a/src/compiler/core.ts
+++ b/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;
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index bab554927e726..f9a583da0cc8b 100644
--- a/src/compiler/program.ts
+++ b/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 +627,29 @@ namespace ts {
                 onlyRecordFailures = !directoryProbablyExists(directory, state.host);
             }
         }
-        return forEach(extensions, tryLoad);
 
-        function tryLoad(ext: string): string {
-            if (ext === ".tsx" && state.skipTsx) {
-                return undefined;
+        if (state.skipTsx)
+            extensions = filter(extensions, ext => ext !== "tsx");
+
+        // 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 =>
+           tryLoad(fileExtensionIs(candidate, ext) ? candidate : candidate + ext));
+        if (keepOrAddExtension) {
+            return keepOrAddExtension;
+        }
+
+        // Then try stripping a ".js" or ".jsx" extension and replacing it with a different one, e.g. "./foo.js" can be matched by "./foo.ts" or "./foo.d.ts"
+        return forEach(supportedJavascriptExtensions, jsExt => {
+            const extensionless = tryRemoveExtension(candidate, jsExt);
+            if (extensionless !== undefined) {
+                return forEach(supportedTypeScriptExtensions, ext => {
+                    if (ext !== jsExt)
+                        return tryLoad(extensionless + ext);
+                });
             }
-            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);
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index d6959c2a54fdd..56d66e753969b 100644
--- a/src/harness/harness.ts
+++ b/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) => []
             };
diff --git a/tests/baselines/reference/moduleResolution.js b/tests/baselines/reference/moduleResolution.js
new file mode 100644
index 0000000000000..be81b926062d6
--- /dev/null
+++ b/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";
diff --git a/tests/baselines/reference/moduleResolution.symbols b/tests/baselines/reference/moduleResolution.symbols
new file mode 100644
index 0000000000000..2a51d416a4af6
--- /dev/null
+++ b/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))
+
diff --git a/tests/baselines/reference/moduleResolution.types b/tests/baselines/reference/moduleResolution.types
new file mode 100644
index 0000000000000..2e1b0f560bc21
--- /dev/null
+++ b/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
+
diff --git a/tests/baselines/reference/nameWithFileExtension.errors.txt b/tests/baselines/reference/nameWithFileExtension.errors.txt
deleted file mode 100644
index 2aa341271cddb..0000000000000
--- a/tests/baselines/reference/nameWithFileExtension.errors.txt
+++ /dev/null
@@ -1,12 +0,0 @@
-tests/cases/conformance/externalModules/foo_1.ts(1,22): error TS2307: Cannot find module './foo_0.js'.
-
-
-==== tests/cases/conformance/externalModules/foo_1.ts (1 errors) ====
-    import foo = require('./foo_0.js');
-                         ~~~~~~~~~~~~
-!!! error TS2307: Cannot find module './foo_0.js'.
-    var x = foo.foo + 42;
-    
-==== tests/cases/conformance/externalModules/foo_0.ts (0 errors) ====
-    export var foo = 42;
-    
\ No newline at end of file
diff --git a/tests/baselines/reference/nameWithFileExtension.js b/tests/baselines/reference/nameWithFileExtension.js
index 2d487ede24572..8a7506c2d4298 100644
--- a/tests/baselines/reference/nameWithFileExtension.js
+++ b/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');
diff --git a/tests/baselines/reference/nameWithFileExtension.symbols b/tests/baselines/reference/nameWithFileExtension.symbols
new file mode 100644
index 0000000000000..61e6a768ea6aa
--- /dev/null
+++ b/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))
+
diff --git a/tests/baselines/reference/nameWithFileExtension.types b/tests/baselines/reference/nameWithFileExtension.types
new file mode 100644
index 0000000000000..a0fca3d456219
--- /dev/null
+++ b/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
+
diff --git a/tests/baselines/reference/project/cantFindTheModule/amd/cantFindTheModule.errors.txt b/tests/baselines/reference/project/cantFindTheModule/amd/cantFindTheModule.errors.txt
index 7c071fdc208c2..e9f8842d5cbb5 100644
--- a/tests/baselines/reference/project/cantFindTheModule/amd/cantFindTheModule.errors.txt
+++ b/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'.
diff --git a/tests/baselines/reference/project/cantFindTheModule/node/cantFindTheModule.errors.txt b/tests/baselines/reference/project/cantFindTheModule/node/cantFindTheModule.errors.txt
index 7c071fdc208c2..e9f8842d5cbb5 100644
--- a/tests/baselines/reference/project/cantFindTheModule/node/cantFindTheModule.errors.txt
+++ b/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'.
diff --git a/tests/cases/compiler/moduleResolution.ts b/tests/cases/compiler/moduleResolution.ts
new file mode 100644
index 0000000000000..c21614577c0e5
--- /dev/null
+++ b/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"
diff --git a/tests/cases/projects/NoModule/decl.ts b/tests/cases/projects/NoModule/decl.ts
index a8a29852ac267..064f777c5512e 100644
--- a/tests/cases/projects/NoModule/decl.ts
+++ b/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");
 

From a0546a9310aa18a097fa8edb5276dc0c16fedfc2 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Tue, 31 May 2016 10:39:29 -0700
Subject: [PATCH 2/8] Improve loadModuleFromFile code

---
 src/compiler/program.ts | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index f9a583da0cc8b..720b99d89008c 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -628,24 +628,25 @@ namespace ts {
             }
         }
 
-        if (state.skipTsx)
-            extensions = filter(extensions, ext => ext !== "tsx");
-
         // 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 =>
-           tryLoad(fileExtensionIs(candidate, ext) ? candidate : candidate + ext));
+        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 different one, e.g. "./foo.js" can be matched by "./foo.ts" or "./foo.d.ts"
+        // 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, ext => {
-                    if (ext !== jsExt)
-                        return tryLoad(extensionless + ext);
-                });
+                return forEach(supportedTypeScriptExtensions, tsExt => tryLoad(extensionless + tsExt));
             }
         });
 

From f4d6b67cb0973ed3366190e10f61c0cf3a4e4229 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Tue, 31 May 2016 11:39:11 -0700
Subject: [PATCH 3/8] Respond to PR comments

---
 src/compiler/core.ts                          |  7 ++++
 src/compiler/diagnosticMessages.json          |  4 +++
 src/compiler/program.ts                       | 34 +++++++++----------
 .../reference/moduleResolution.trace.json     | 32 +++++++++++++++++
 tests/cases/compiler/moduleResolution.ts      |  1 +
 5 files changed, 61 insertions(+), 17 deletions(-)
 create mode 100644 tests/baselines/reference/moduleResolution.trace.json

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index ba81ee7d103d4..932acdc632438 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -861,6 +861,13 @@ namespace ts {
         return fileExtensionIs(path, extension) ? path.substring(0, path.length - extension.length) : undefined;
     }
 
+    export function getFileExtension(path: string): string {
+        const dot = path.lastIndexOf(".");
+        if (dot !== -1) {
+            return path.substring(dot);
+        }
+    }
+
     export interface ObjectAllocator {
         getNodeConstructor(): new (kind: SyntaxKind, pos?: number, end?: number) => Node;
         getSourceFileConstructor(): new (kind: SyntaxKind, pos?: number, end?: number) => SourceFile;
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index af8dd8ceb6971..373e5fc3388c1 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -2768,6 +2768,10 @@
         "category": "Error",
         "code": 6131
     },
+    "File name '{0}' has a '{1}' extension - stripping it": {
+        "category": "Message",
+        "code": 6132
+    },
 
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 720b99d89008c..c7b2cd66cafe2 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -615,11 +615,26 @@ 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.
      */
     function loadModuleFromFile(candidate: string, extensions: string[], failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string {
+        // 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 = loadModuleFromFileWorker(candidate, extensions, failedLookupLocation, onlyRecordFailures, state);
+        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"
+        if (hasJavaScriptFileExtension(candidate)) {
+            const extensionless = removeFileExtension(candidate);
+            if (state.traceEnabled) {
+                const extension = candidate.substring(extensionless.length);
+                trace(state.host, Diagnostics.File_name_0_has_a_1_extension_stripping_it, candidate, extension);
+            }
+            return loadModuleFromFileWorker(extensionless, extensions, failedLookupLocation, onlyRecordFailures, state);
+        }
+    }
+    function loadModuleFromFileWorker(candidate: string, extensions: string[], failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string {
         if (!onlyRecordFailures) {
             // check if containig folder exists - if it doesn't then just record failures for all supported extensions without disk probing
             const directory = getDirectoryPath(candidate);
@@ -628,27 +643,12 @@ namespace ts {
             }
         }
 
-        // 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 => {
+        return 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));
-            }
-        });
 
         function tryLoad(fileName: string): string {
             if (!onlyRecordFailures && state.host.fileExists(fileName)) {
diff --git a/tests/baselines/reference/moduleResolution.trace.json b/tests/baselines/reference/moduleResolution.trace.json
new file mode 100644
index 0000000000000..f51251810a71d
--- /dev/null
+++ b/tests/baselines/reference/moduleResolution.trace.json
@@ -0,0 +1,32 @@
+[
+    "======== Resolving module './a' from 'C:/Users/anhans/TypeScript/tests/cases/compiler/b.ts'. ========",
+    "Module resolution kind is not specified, using 'NodeJs'.",
+    "Loading module as file / folder, candidate module location 'C:/Users/anhans/TypeScript/tests/cases/compiler/a'.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
+    "======== Module name './a' was successfully resolved to 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts'. ========",
+    "======== Resolving module './a.ts' from 'C:/Users/anhans/TypeScript/tests/cases/compiler/c.ts'. ========",
+    "Module resolution kind is not specified, using 'NodeJs'.",
+    "Loading module as file / folder, candidate module location 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts'.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
+    "======== Module name './a.ts' was successfully resolved to 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts'. ========",
+    "======== Resolving module './a.js' from 'C:/Users/anhans/TypeScript/tests/cases/compiler/d.ts'. ========",
+    "Module resolution kind is not specified, using 'NodeJs'.",
+    "Loading module as file / folder, candidate module location 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js'.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js.ts' does not exist.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js.tsx' does not exist.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js.d.ts' does not exist.",
+    "File name 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js' has a '.js' extension - stripping it",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
+    "======== Module name './a.js' was successfully resolved to 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts'. ========",
+    "======== Resolving module './jquery.js' from 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery_user_1.ts'. ========",
+    "Module resolution kind is not specified, using 'NodeJs'.",
+    "Loading module as file / folder, candidate module location 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js'.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js.ts' does not exist.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js.tsx' does not exist.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js.d.ts' does not exist.",
+    "File name 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js' has a '.js' extension - stripping it",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.ts' does not exist.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.tsx' does not exist.",
+    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.d.ts' exist - use it as a name resolution result.",
+    "======== Module name './jquery.js' was successfully resolved to 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.d.ts'. ========"
+]
\ No newline at end of file
diff --git a/tests/cases/compiler/moduleResolution.ts b/tests/cases/compiler/moduleResolution.ts
index c21614577c0e5..0af824100a78a 100644
--- a/tests/cases/compiler/moduleResolution.ts
+++ b/tests/cases/compiler/moduleResolution.ts
@@ -1,3 +1,4 @@
+// @traceResolution: true
 // @Filename: a.ts
 export default 0;
 

From d4b88899840edd218ae2638538aebcaf7b13c15c Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Tue, 31 May 2016 12:58:05 -0700
Subject: [PATCH 4/8] Respond to more PR comments

---
 src/compiler/core.ts    | 7 -------
 src/compiler/program.ts | 9 +++++----
 2 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 932acdc632438..ba81ee7d103d4 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -861,13 +861,6 @@ namespace ts {
         return fileExtensionIs(path, extension) ? path.substring(0, path.length - extension.length) : undefined;
     }
 
-    export function getFileExtension(path: string): string {
-        const dot = path.lastIndexOf(".");
-        if (dot !== -1) {
-            return path.substring(dot);
-        }
-    }
-
     export interface ObjectAllocator {
         getNodeConstructor(): new (kind: SyntaxKind, pos?: number, end?: number) => Node;
         getSourceFileConstructor(): new (kind: SyntaxKind, pos?: number, end?: number) => SourceFile;
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index c7b2cd66cafe2..dd3102410ef42 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -620,9 +620,9 @@ namespace ts {
      */
     function loadModuleFromFile(candidate: string, extensions: string[], failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string {
         // 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 = loadModuleFromFileWorker(candidate, extensions, failedLookupLocation, onlyRecordFailures, state);
-        if (keepOrAddExtension) {
-            return keepOrAddExtension;
+        const resolvedByAddingOrKeepingExtension = loadModuleFromFileWorker(candidate, extensions, failedLookupLocation, onlyRecordFailures, state);
+        if (resolvedByAddingOrKeepingExtension) {
+            return resolvedByAddingOrKeepingExtension;
         }
         // 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"
         if (hasJavaScriptFileExtension(candidate)) {
@@ -634,9 +634,10 @@ namespace ts {
             return loadModuleFromFileWorker(extensionless, extensions, failedLookupLocation, onlyRecordFailures, state);
         }
     }
+
     function loadModuleFromFileWorker(candidate: string, extensions: string[], failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string {
         if (!onlyRecordFailures) {
-            // check if containig folder exists - if it doesn't then just record failures for all supported extensions without disk probing
+            // check if containing folder exists - if it doesn't then just record failures for all supported extensions without disk probing
             const directory = getDirectoryPath(candidate);
             if (directory) {
                 onlyRecordFailures = !directoryProbablyExists(directory, state.host);

From 9179f4ca42c81f9ebd6e054abe2ff5bb39a69554 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Wed, 1 Jun 2016 10:43:39 -0700
Subject: [PATCH 5/8] Fix test

---
 tests/baselines/reference/moduleResolution.js |  1 +
 .../reference/moduleResolution.symbols        | 17 +++---
 .../reference/moduleResolution.trace.json     | 52 +++++++++----------
 .../reference/moduleResolution.types          | 17 +++---
 tests/cases/compiler/moduleResolution.ts      | 15 +++---
 5 files changed, 53 insertions(+), 49 deletions(-)

diff --git a/tests/baselines/reference/moduleResolution.js b/tests/baselines/reference/moduleResolution.js
index be81b926062d6..101089b635503 100644
--- a/tests/baselines/reference/moduleResolution.js
+++ b/tests/baselines/reference/moduleResolution.js
@@ -1,6 +1,7 @@
 //// [tests/cases/compiler/moduleResolution.ts] ////
 
 //// [a.ts]
+
 export default 0;
 
 // No extension: '.ts' added
diff --git a/tests/baselines/reference/moduleResolution.symbols b/tests/baselines/reference/moduleResolution.symbols
index 2a51d416a4af6..e9934946a64fd 100644
--- a/tests/baselines/reference/moduleResolution.symbols
+++ b/tests/baselines/reference/moduleResolution.symbols
@@ -1,22 +1,23 @@
-=== tests/cases/compiler/a.ts ===
-export default 0;
+=== /src/a.ts ===
+
+No type information for this code.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 ===
+No type information for this code.=== /src/b.ts ===
 import a from './a';
 >a : Symbol(a, Decl(b.ts, 0, 6))
 
 // Matching extension
-=== tests/cases/compiler/c.ts ===
+=== /src/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 ===
+=== /src/d.ts ===
 import a from './a.js';
 >a : Symbol(a, Decl(d.ts, 0, 6))
 
-=== tests/cases/compiler/jquery.d.ts ===
+=== /src/jquery.d.ts ===
 declare var x: number;
 >x : Symbol(x, Decl(jquery.d.ts, 0, 11))
 
@@ -24,12 +25,12 @@ export default x;
 >x : Symbol(x, Decl(jquery.d.ts, 0, 11))
 
 // No extension: '.d.ts' added
-=== tests/cases/compiler/jquery_user_1.ts ===
+=== /src/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 ===
+=== /src/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))
diff --git a/tests/baselines/reference/moduleResolution.trace.json b/tests/baselines/reference/moduleResolution.trace.json
index f51251810a71d..6e6589d7c1f8a 100644
--- a/tests/baselines/reference/moduleResolution.trace.json
+++ b/tests/baselines/reference/moduleResolution.trace.json
@@ -1,32 +1,32 @@
 [
-    "======== Resolving module './a' from 'C:/Users/anhans/TypeScript/tests/cases/compiler/b.ts'. ========",
+    "======== Resolving module './a' from '/src/b.ts'. ========",
     "Module resolution kind is not specified, using 'NodeJs'.",
-    "Loading module as file / folder, candidate module location 'C:/Users/anhans/TypeScript/tests/cases/compiler/a'.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
-    "======== Module name './a' was successfully resolved to 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts'. ========",
-    "======== Resolving module './a.ts' from 'C:/Users/anhans/TypeScript/tests/cases/compiler/c.ts'. ========",
+    "Loading module as file / folder, candidate module location '/src/a'.",
+    "File '/src/a.ts' exist - use it as a name resolution result.",
+    "======== Module name './a' was successfully resolved to '/src/a.ts'. ========",
+    "======== Resolving module './a.ts' from '/src/c.ts'. ========",
     "Module resolution kind is not specified, using 'NodeJs'.",
-    "Loading module as file / folder, candidate module location 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts'.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
-    "======== Module name './a.ts' was successfully resolved to 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts'. ========",
-    "======== Resolving module './a.js' from 'C:/Users/anhans/TypeScript/tests/cases/compiler/d.ts'. ========",
+    "Loading module as file / folder, candidate module location '/src/a.ts'.",
+    "File '/src/a.ts' exist - use it as a name resolution result.",
+    "======== Module name './a.ts' was successfully resolved to '/src/a.ts'. ========",
+    "======== Resolving module './a.js' from '/src/d.ts'. ========",
     "Module resolution kind is not specified, using 'NodeJs'.",
-    "Loading module as file / folder, candidate module location 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js'.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js.ts' does not exist.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js.tsx' does not exist.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js.d.ts' does not exist.",
-    "File name 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.js' has a '.js' extension - stripping it",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
-    "======== Module name './a.js' was successfully resolved to 'C:/Users/anhans/TypeScript/tests/cases/compiler/a.ts'. ========",
-    "======== Resolving module './jquery.js' from 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery_user_1.ts'. ========",
+    "Loading module as file / folder, candidate module location '/src/a.js'.",
+    "File '/src/a.js.ts' does not exist.",
+    "File '/src/a.js.tsx' does not exist.",
+    "File '/src/a.js.d.ts' does not exist.",
+    "File name '/src/a.js' has a '.js' extension - stripping it",
+    "File '/src/a.ts' exist - use it as a name resolution result.",
+    "======== Module name './a.js' was successfully resolved to '/src/a.ts'. ========",
+    "======== Resolving module './jquery.js' from '/src/jquery_user_1.ts'. ========",
     "Module resolution kind is not specified, using 'NodeJs'.",
-    "Loading module as file / folder, candidate module location 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js'.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js.ts' does not exist.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js.tsx' does not exist.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js.d.ts' does not exist.",
-    "File name 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.js' has a '.js' extension - stripping it",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.ts' does not exist.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.tsx' does not exist.",
-    "File 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.d.ts' exist - use it as a name resolution result.",
-    "======== Module name './jquery.js' was successfully resolved to 'C:/Users/anhans/TypeScript/tests/cases/compiler/jquery.d.ts'. ========"
+    "Loading module as file / folder, candidate module location '/src/jquery.js'.",
+    "File '/src/jquery.js.ts' does not exist.",
+    "File '/src/jquery.js.tsx' does not exist.",
+    "File '/src/jquery.js.d.ts' does not exist.",
+    "File name '/src/jquery.js' has a '.js' extension - stripping it",
+    "File '/src/jquery.ts' does not exist.",
+    "File '/src/jquery.tsx' does not exist.",
+    "File '/src/jquery.d.ts' exist - use it as a name resolution result.",
+    "======== Module name './jquery.js' was successfully resolved to '/src/jquery.d.ts'. ========"
 ]
\ No newline at end of file
diff --git a/tests/baselines/reference/moduleResolution.types b/tests/baselines/reference/moduleResolution.types
index 2e1b0f560bc21..fbc0091ee3b95 100644
--- a/tests/baselines/reference/moduleResolution.types
+++ b/tests/baselines/reference/moduleResolution.types
@@ -1,22 +1,23 @@
-=== tests/cases/compiler/a.ts ===
-export default 0;
+=== /src/a.ts ===
+
+No type information for this code.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 ===
+No type information for this code.=== /src/b.ts ===
 import a from './a';
 >a : number
 
 // Matching extension
-=== tests/cases/compiler/c.ts ===
+=== /src/c.ts ===
 import a from './a.ts';
 >a : number
 
 // '.js' extension: stripped and replaced with '.ts'
-=== tests/cases/compiler/d.ts ===
+=== /src/d.ts ===
 import a from './a.js';
 >a : number
 
-=== tests/cases/compiler/jquery.d.ts ===
+=== /src/jquery.d.ts ===
 declare var x: number;
 >x : number
 
@@ -24,12 +25,12 @@ export default x;
 >x : number
 
 // No extension: '.d.ts' added
-=== tests/cases/compiler/jquery_user_1.ts ===
+=== /src/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 ===
+=== /src/jquery_user_1.ts ===
 import j from "./jquery.js"
 >j : number
 >j : number
diff --git a/tests/cases/compiler/moduleResolution.ts b/tests/cases/compiler/moduleResolution.ts
index 0af824100a78a..6ad3565862337 100644
--- a/tests/cases/compiler/moduleResolution.ts
+++ b/tests/cases/compiler/moduleResolution.ts
@@ -1,27 +1,28 @@
 // @traceResolution: true
-// @Filename: a.ts
+
+// @Filename: /src/a.ts
 export default 0;
 
 // No extension: '.ts' added
-// @Filename: b.ts
+// @Filename: /src/b.ts
 import a from './a';
 
 // Matching extension
-// @Filename: c.ts
+// @Filename: /src/c.ts
 import a from './a.ts';
 
 // '.js' extension: stripped and replaced with '.ts'
-// @Filename: d.ts
+// @Filename: /src/d.ts
 import a from './a.js';
 
-// @Filename: jquery.d.ts
+// @Filename: /src/jquery.d.ts
 declare var x: number;
 export default x;
 
 // No extension: '.d.ts' added
-// @Filename: jquery_user_1.ts
+// @Filename: /src/jquery_user_1.ts
 import j from "./jquery";
 
 // '.js' extension: stripped and replaced with '.d.ts'
-// @Filename: jquery_user_1.ts
+// @Filename: /src/jquery_user_1.ts
 import j from "./jquery.js"

From 9575b3c3ca06935ab22e36d9d1dfb04b6c133bc4 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Wed, 1 Jun 2016 11:44:12 -0700
Subject: [PATCH 6/8] Revert to old tryLoad implementation

---
 src/compiler/program.ts | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index dd3102410ef42..0c060807b1fa2 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -643,15 +643,13 @@ namespace ts {
                 onlyRecordFailures = !directoryProbablyExists(directory, state.host);
             }
         }
+        return forEach(extensions, tryLoad);
 
-        return forEach(extensions, ext => {
+        function tryLoad(ext: string): string {
             if (state.skipTsx && (ext === ".jsx" || ext === ".tsx")) {
-                return;
+                return undefined;
             }
-            return tryLoad(fileExtensionIs(candidate, ext) ? candidate : candidate + ext);
-        });
-
-        function tryLoad(fileName: string): string {
+            const fileName = fileExtensionIs(candidate, ext) ? candidate : candidate + ext;
             if (!onlyRecordFailures && state.host.fileExists(fileName)) {
                 if (state.traceEnabled) {
                     trace(state.host, Diagnostics.File_0_exist_use_it_as_a_name_resolution_result, fileName);

From a918730df0919357fbe8accd88a873991ef11fa6 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Mon, 6 Jun 2016 12:17:11 -0700
Subject: [PATCH 7/8] factor out isJsxOrTsxExtension

---
 src/compiler/core.ts    | 4 ++++
 src/compiler/program.ts | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index ba81ee7d103d4..8a2040a83df07 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -861,6 +861,10 @@ namespace ts {
         return fileExtensionIs(path, extension) ? path.substring(0, path.length - extension.length) : undefined;
     }
 
+    export function isJsxOrTsxExtension(ext: string): boolean {
+        return ext === ".jsx" || ext === ".tsx";
+    }
+
     export interface ObjectAllocator {
         getNodeConstructor(): new (kind: SyntaxKind, pos?: number, end?: number) => Node;
         getSourceFileConstructor(): new (kind: SyntaxKind, pos?: number, end?: number) => SourceFile;
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 0c060807b1fa2..5440b1a782b2d 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -646,7 +646,7 @@ namespace ts {
         return forEach(extensions, tryLoad);
 
         function tryLoad(ext: string): string {
-            if (state.skipTsx && (ext === ".jsx" || ext === ".tsx")) {
+            if (state.skipTsx && isJsxOrTsxExtension(ext)) {
                 return undefined;
             }
             const fileName = fileExtensionIs(candidate, ext) ? candidate : candidate + ext;

From 704f9874e058da4bad7bcb003710002c410570fd Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Mon, 6 Jun 2016 12:28:36 -0700
Subject: [PATCH 8/8] Move to a conformance test

---
 .../{moduleResolution.js => moduleResolutionWithExtensions.js}  | 2 +-
 ...esolution.symbols => moduleResolutionWithExtensions.symbols} | 0
 ...ion.trace.json => moduleResolutionWithExtensions.trace.json} | 0
 ...uleResolution.types => moduleResolutionWithExtensions.types} | 0
 .../externalModules/moduleResolutionWithExtensions.ts}          | 0
 5 files changed, 1 insertion(+), 1 deletion(-)
 rename tests/baselines/reference/{moduleResolution.js => moduleResolutionWithExtensions.js} (87%)
 rename tests/baselines/reference/{moduleResolution.symbols => moduleResolutionWithExtensions.symbols} (100%)
 rename tests/baselines/reference/{moduleResolution.trace.json => moduleResolutionWithExtensions.trace.json} (100%)
 rename tests/baselines/reference/{moduleResolution.types => moduleResolutionWithExtensions.types} (100%)
 rename tests/cases/{compiler/moduleResolution.ts => conformance/externalModules/moduleResolutionWithExtensions.ts} (100%)

diff --git a/tests/baselines/reference/moduleResolution.js b/tests/baselines/reference/moduleResolutionWithExtensions.js
similarity index 87%
rename from tests/baselines/reference/moduleResolution.js
rename to tests/baselines/reference/moduleResolutionWithExtensions.js
index 101089b635503..df12a3531bcfa 100644
--- a/tests/baselines/reference/moduleResolution.js
+++ b/tests/baselines/reference/moduleResolutionWithExtensions.js
@@ -1,4 +1,4 @@
-//// [tests/cases/compiler/moduleResolution.ts] ////
+//// [tests/cases/conformance/externalModules/moduleResolutionWithExtensions.ts] ////
 
 //// [a.ts]
 
diff --git a/tests/baselines/reference/moduleResolution.symbols b/tests/baselines/reference/moduleResolutionWithExtensions.symbols
similarity index 100%
rename from tests/baselines/reference/moduleResolution.symbols
rename to tests/baselines/reference/moduleResolutionWithExtensions.symbols
diff --git a/tests/baselines/reference/moduleResolution.trace.json b/tests/baselines/reference/moduleResolutionWithExtensions.trace.json
similarity index 100%
rename from tests/baselines/reference/moduleResolution.trace.json
rename to tests/baselines/reference/moduleResolutionWithExtensions.trace.json
diff --git a/tests/baselines/reference/moduleResolution.types b/tests/baselines/reference/moduleResolutionWithExtensions.types
similarity index 100%
rename from tests/baselines/reference/moduleResolution.types
rename to tests/baselines/reference/moduleResolutionWithExtensions.types
diff --git a/tests/cases/compiler/moduleResolution.ts b/tests/cases/conformance/externalModules/moduleResolutionWithExtensions.ts
similarity index 100%
rename from tests/cases/compiler/moduleResolution.ts
rename to tests/cases/conformance/externalModules/moduleResolutionWithExtensions.ts