Don't allow .ts to appear in an import

src/compiler/program.ts

@@ -668,24 +668,37 @@ namespace ts {
      * @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 resolvedByAddingOrKeepingExtension = loadModuleFromFileWorker(candidate, extensions, failedLookupLocation, onlyRecordFailures, state);
-        if (resolvedByAddingOrKeepingExtension) {
-            return resolvedByAddingOrKeepingExtension;
+    function loadModuleFromFile(candidate: string, extensions: string[], failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
+        // If the candidate already has an extension load that or quit.
+        if (hasTypeScriptFileExtension(candidate)) {
+            // Don't allow `.ts` to appear at the end
+            if (!fileExtensionIs(candidate, ".d.ts")) {
+                return undefined;
+            }
+            return tryFile(candidate, failedLookupLocation, onlyRecordFailures, state);
         }
-        // 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"
+
+        // Next, try adding an extension.
+        // We don't allow an import of "foo.ts" to be matched by "foo.ts.ts", but we do allow "foo.js" to be matched by "foo.js.ts".
+        const resolvedByAddingExtension = tryAddingExtensions(candidate, extensions, failedLookupLocation, onlyRecordFailures, state);
+        if (resolvedByAddingExtension) {
+            return resolvedByAddingExtension;
+        }
+
+        // If that didn't work, 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);
+            return tryAddingExtensions(extensionless, extensions, failedLookupLocation, onlyRecordFailures, state);
         }
     }
 
-    function loadModuleFromFileWorker(candidate: string, extensions: string[], failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string {
+    /** Try to return an existing file that adds one of the `extensions` to `candidate`. */
+    function tryAddingExtensions(candidate: string, extensions: string[], failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
         if (!onlyRecordFailures) {
             // check if containing folder exists - if it doesn't then just record failures for all supported extensions without disk probing
             const directory = getDirectoryPath(candidate);
@@ -693,26 +706,24 @@ namespace ts {
                 onlyRecordFailures = !directoryProbablyExists(directory, state.host);
             }
         }
-        return forEach(extensions, tryLoad);
+        return forEach(extensions, ext =>
+            !(state.skipTsx && isJsxOrTsxExtension(ext)) && tryFile(candidate + ext, failedLookupLocation, onlyRecordFailures, state));
+    }
 
-        function tryLoad(ext: string): string {
-            if (state.skipTsx && isJsxOrTsxExtension(ext)) {
-                return undefined;
+    /** Return the file if it exists. */
+    function tryFile(fileName: string, failedLookupLocation: string[], onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
+        if (!onlyRecordFailures && state.host.fileExists(fileName)) {
+            if (state.traceEnabled) {
+                trace(state.host, Diagnostics.File_0_exist_use_it_as_a_name_resolution_result, fileName);
             }
-            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);
-                }
-                return fileName;
-            }
-            else {
-                if (state.traceEnabled) {
-                    trace(state.host, Diagnostics.File_0_does_not_exist, fileName);
-                }
-                failedLookupLocation.push(fileName);
-                return undefined;
+            return fileName;
+        }
+        else {
+            if (state.traceEnabled) {
+                trace(state.host, Diagnostics.File_0_does_not_exist, fileName);
             }
+            failedLookupLocation.push(fileName);
+            return undefined;
         }
     }
 

src/harness/unittests/moduleResolution.ts

@@ -465,8 +465,8 @@ export = C;
                 "/a/B/c/moduleB.ts": `import a = require("./moduleC")`,
                 "/a/B/c/moduleC.ts": "export var x",
                 "/a/B/c/moduleD.ts": `
-import a = require("./moduleA.ts");
-import b = require("./moduleB.ts");
+import a = require("./moduleA");
+import b = require("./moduleB");
                 `
             };
             test(files, { module: ts.ModuleKind.CommonJS, forceConsistentCasingInFileNames: true },  "/a/B/c", /*useCaseSensitiveFileNames*/ false, ["moduleD.ts"], [1149]);
@@ -477,8 +477,8 @@ import b = require("./moduleB.ts");
                 "/a/B/c/moduleB.ts": `import a = require("./moduleC")`,
                 "/a/B/c/moduleC.ts": "export var x",
                 "/a/B/c/moduleD.ts": `
-import a = require("./moduleA.ts");
-import b = require("./moduleB.ts");
+import a = require("./moduleA");
+import b = require("./moduleB");
                 `
             };
             test(files, { module: ts.ModuleKind.CommonJS, forceConsistentCasingInFileNames: true },  "/a/B/c", /*useCaseSensitiveFileNames*/ false, ["moduleD.ts"], []);

tests/baselines/reference/missingFunctionImplementation2.errors.txt

@@ -4,7 +4,7 @@ tests/cases/compiler/missingFunctionImplementation2_b.ts(1,17): error TS2391: Fu
 
 ==== tests/cases/compiler/missingFunctionImplementation2_a.ts (1 errors) ====
     export {};
-    declare module "./missingFunctionImplementation2_b.ts" {
+    declare module "./missingFunctionImplementation2_b" {
       export function f(a, b): void;
                       ~
 !!! error TS2384: Overload signatures must all be ambient or non-ambient.

tests/baselines/reference/missingFunctionImplementation2.js

@@ -2,7 +2,7 @@
 
 //// [missingFunctionImplementation2_a.ts]
 export {};
-declare module "./missingFunctionImplementation2_b.ts" {
+declare module "./missingFunctionImplementation2_b" {
   export function f(a, b): void;
 }
 

tests/baselines/reference/moduleResolutionNoTs.errors.txt

@@ -0,0 +1,11 @@
+tests/cases/compiler/user.ts(1,15): error TS2307: Cannot find module './m.ts'.
+
+
+==== tests/cases/compiler/m.ts (0 errors) ====
+    export default 0;
+    
+==== tests/cases/compiler/user.ts (1 errors) ====
+    import x from "./m.ts";
+                  ~~~~~~~~
+!!! error TS2307: Cannot find module './m.ts'.
+    

tests/baselines/reference/moduleResolutionNoTs.js

@@ -0,0 +1,15 @@
+//// [tests/cases/compiler/moduleResolutionNoTs.ts] ////
+
+//// [m.ts]
+export default 0;
+
+//// [user.ts]
+import x from "./m.ts";
+
+
+//// [m.js]
+"use strict";
+exports.__esModule = true;
+exports["default"] = 0;
+//// [user.js]
+"use strict";

tests/baselines/reference/moduleResolutionWithExtensions.js

@@ -8,10 +8,6 @@ export default 0;
 //// [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';
@@ -36,9 +32,6 @@ 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";

tests/baselines/reference/moduleResolutionWithExtensions.symbols

@@ -7,11 +7,6 @@ No type information for this code.=== /src/b.ts ===
 import a from './a';
 >a : Symbol(a, Decl(b.ts, 0, 6))
 
-// Matching extension
-=== /src/c.ts ===
-import a from './a.ts';
->a : Symbol(a, Decl(c.ts, 0, 6))
-
 // '.js' extension: stripped and replaced with '.ts'
 === /src/d.ts ===
 import a from './a.js';

tests/baselines/reference/moduleResolutionWithExtensions.trace.json

@@ -5,12 +5,6 @@
     "File '/src/a.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/src/a.ts', result '/src/a.ts'",
     "======== 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 '/src/a.ts'.",
-    "File '/src/a.ts' exist - use it as a name resolution result.",
-    "Resolving real path for '/src/a.ts', result '/src/a.ts'",
-    "======== 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 '/src/a.js'.",

tests/baselines/reference/moduleResolutionWithExtensions.types

@@ -7,11 +7,6 @@ No type information for this code.=== /src/b.ts ===
 import a from './a';
 >a : number
 
-// Matching extension
-=== /src/c.ts ===
-import a from './a.ts';
->a : number
-
 // '.js' extension: stripped and replaced with '.ts'
 === /src/d.ts ===
 import a from './a.js';

tests/baselines/reference/staticInstanceResolution5.errors.txt

@@ -4,7 +4,7 @@ tests/cases/compiler/staticInstanceResolution5_1.ts(6,16): error TS2304: Cannot
 
 
 ==== tests/cases/compiler/staticInstanceResolution5_1.ts (3 errors) ====
-    import WinJS = require('staticInstanceResolution5_0.ts');
+    import WinJS = require('staticInstanceResolution5_0');
     
     // these 3 should be errors
     var x = (w1: WinJS) => { };

tests/baselines/reference/staticInstanceResolution5.js

@@ -8,7 +8,7 @@ export class Promise {
 }
 
 //// [staticInstanceResolution5_1.ts]
-import WinJS = require('staticInstanceResolution5_0.ts');
+import WinJS = require('staticInstanceResolution5_0');
 
 // these 3 should be errors
 var x = (w1: WinJS) => { };

tests/cases/compiler/missingFunctionImplementation2.ts

@@ -1,6 +1,6 @@
 // @Filename: missingFunctionImplementation2_a.ts
 export {};
-declare module "./missingFunctionImplementation2_b.ts" {
+declare module "./missingFunctionImplementation2_b" {
   export function f(a, b): void;
 }
 

tests/cases/compiler/moduleResolutionNoTs.ts

@@ -0,0 +1,5 @@
+// @filename: m.ts
+export default 0;
+
+// @filename: user.ts
+import x from "./m.ts";

tests/cases/compiler/staticInstanceResolution5.ts

@@ -7,7 +7,7 @@ export class Promise {
 }
 
 // @Filename: staticInstanceResolution5_1.ts
-import WinJS = require('staticInstanceResolution5_0.ts');
+import WinJS = require('staticInstanceResolution5_0');
 
 // these 3 should be errors
 var x = (w1: WinJS) => { };

tests/cases/conformance/externalModules/moduleResolutionWithExtensions.ts

@@ -7,10 +7,6 @@ export default 0;
 // @Filename: /src/b.ts
 import a from './a';
 
-// Matching extension
-// @Filename: /src/c.ts
-import a from './a.ts';
-
 // '.js' extension: stripped and replaced with '.ts'
 // @Filename: /src/d.ts
 import a from './a.js';