Add a new compiler option moduleSuffixes to expand the node module resolver's search algorithm (#48189)

* Add moduleSuffixes compiler option and related tests. Update baselines for compiler options tests.

* Add a flag to the command-line parser which allows "list" params to preserve "falsy" values such as empty strings. Falsy values are normally stripped out.

* Add tests. Rework resolver logic to only run module-suffix code when needed.

* PR feedback

* Add test

* Remove unnecessary conditional.

src/compiler/commandLineParser.ts

@@ -884,6 +884,18 @@ namespace ts {
             description: Diagnostics.Allow_accessing_UMD_globals_from_modules,
             defaultValueDescription: false,
         },
+        {
+            name: "moduleSuffixes",
+            type: "list",
+            element: {
+                name: "suffix",
+                type: "string",
+            },
+            listPreserveFalsyValues: true,
+            affectsModuleResolution: true,
+            category: Diagnostics.Modules,
+            description: Diagnostics.List_of_file_name_suffixes_to_search_when_resolving_a_module,
+        },
 
         // Source Maps
         {
@@ -3192,7 +3204,7 @@ namespace ts {
         if (option.type === "list") {
             const listOption = option;
             if (listOption.element.isFilePath || !isString(listOption.element.type)) {
-                return filter(map(value, v => normalizeOptionValue(listOption.element, basePath, v)), v => !!v) as CompilerOptionsValue;
+                return filter(map(value, v => normalizeOptionValue(listOption.element, basePath, v)), v => listOption.listPreserveFalsyValues ? true : !!v) as CompilerOptionsValue;
             }
             return value;
         }
@@ -3233,7 +3245,7 @@ namespace ts {
     }
 
     function convertJsonOptionOfListType(option: CommandLineOptionOfListType, values: readonly any[], basePath: string, errors: Push<Diagnostic>): any[] {
-        return filter(map(values, v => convertJsonOption(option.element, v, basePath, errors)), v => !!v);
+        return filter(map(values, v => convertJsonOption(option.element, v, basePath, errors)), v => option.listPreserveFalsyValues ? true : !!v);
     }
 
     /**

src/compiler/diagnosticMessages.json

@@ -5878,6 +5878,10 @@
         "category": "Message",
         "code": 6930
     },
+    "List of file name suffixes to search when resolving a module." : {
+      "category": "Error",
+      "code": 6931
+    },
 
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",

src/compiler/moduleNameResolver.ts

@@ -1576,6 +1576,16 @@ namespace ts {
 
     /** Return the file if it exists. */
     function tryFile(fileName: string, onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
+        if (!state.compilerOptions.moduleSuffixes?.length) {
+            return tryFileLookup(fileName, onlyRecordFailures, state);
+        }
+
+        const ext = tryGetExtensionFromPath(fileName) ?? "";
+        const fileNameNoExtension = ext ? removeExtension(fileName, ext) : fileName;
+        return forEach(state.compilerOptions.moduleSuffixes, suffix => tryFileLookup(fileNameNoExtension + suffix + ext, onlyRecordFailures, state));
+    }
+
+    function tryFileLookup(fileName: string, onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
         if (!onlyRecordFailures) {
             if (state.host.fileExists(fileName)) {
                 if (state.traceEnabled) {

src/compiler/types.ts

@@ -6149,6 +6149,7 @@ namespace ts {
         maxNodeModuleJsDepth?: number;
         module?: ModuleKind;
         moduleResolution?: ModuleResolutionKind;
+        moduleSuffixes?: string[];
         moduleDetection?: ModuleDetectionKind;
         newLine?: NewLineKind;
         noEmit?: boolean;
@@ -6453,6 +6454,7 @@ namespace ts {
     export interface CommandLineOptionOfListType extends CommandLineOptionBase {
         type: "list";
         element: CommandLineOptionOfCustomType | CommandLineOptionOfStringType | CommandLineOptionOfNumberType | CommandLineOptionOfBooleanType | TsConfigOnlyOption;
+        listPreserveFalsyValues?: boolean;
     }
 
     /* @internal */

src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts

@@ -420,6 +420,70 @@ namespace ts {
             );
         });
 
+        it("Convert empty string option of moduleSuffixes to compiler-options ", () => {
+            assertCompilerOptions(
+                {
+                    compilerOptions: {
+                        moduleSuffixes: [".ios", ""]
+                    }
+                }, "tsconfig.json",
+                {
+                    compilerOptions: {
+                        moduleSuffixes: [".ios", ""]
+                    },
+                    errors: []
+                }
+            );
+        });
+
+        it("Convert empty string option of moduleSuffixes to compiler-options ", () => {
+            assertCompilerOptions(
+                {
+                    compilerOptions: {
+                        moduleSuffixes: [""]
+                    }
+                }, "tsconfig.json",
+                {
+                    compilerOptions: {
+                        moduleSuffixes: [""]
+                    },
+                    errors: []
+                }
+            );
+        });
+
+        it("Convert trailing-whitespace string option of moduleSuffixes to compiler-options ", () => {
+            assertCompilerOptions(
+                {
+                    compilerOptions: {
+                        moduleSuffixes: ["   "]
+                    }
+                }, "tsconfig.json",
+                {
+                    compilerOptions: {
+                        moduleSuffixes: ["   "]
+                    },
+                    errors: []
+                }
+            );
+        });
+
+        it("Convert empty option of moduleSuffixes to compiler-options ", () => {
+            assertCompilerOptions(
+                {
+                    compilerOptions: {
+                        moduleSuffixes: []
+                    }
+                }, "tsconfig.json",
+                {
+                    compilerOptions: {
+                        moduleSuffixes: []
+                    },
+                    errors: []
+                }
+            );
+        });
+
         it("Convert incorrectly format tsconfig.json to compiler-options ", () => {
             assertCompilerOptions(
                 {

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2977,6 +2977,7 @@ declare namespace ts {
         maxNodeModuleJsDepth?: number;
         module?: ModuleKind;
         moduleResolution?: ModuleResolutionKind;
+        moduleSuffixes?: string[];
         moduleDetection?: ModuleDetectionKind;
         newLine?: NewLineKind;
         noEmit?: boolean;

tests/baselines/reference/api/typescript.d.ts

@@ -2977,6 +2977,7 @@ declare namespace ts {
         maxNodeModuleJsDepth?: number;
         module?: ModuleKind;
         moduleResolution?: ModuleResolutionKind;
+        moduleSuffixes?: string[];
         moduleDetection?: ModuleDetectionKind;
         newLine?: NewLineKind;
         noEmit?: boolean;

tests/baselines/reference/moduleResolutionWithSuffixes_empty.js

@@ -0,0 +1,17 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_empty.ts] ////
+
+//// [index.ts]
+import { base } from "./foo";
+//// [foo.ts]
+export function base() {}
+
+
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;
+//// [index.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_empty.symbols

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : Symbol(base, Decl(index.ts, 0, 8))
+
+=== /foo.ts ===
+export function base() {}
+>base : Symbol(base, Decl(foo.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_empty.trace.json

@@ -0,0 +1,7 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo.ts' exist - use it as a name resolution result.",
+    "======== Module name './foo' was successfully resolved to '/foo.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_empty.types

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : () => void
+
+=== /foo.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_notSpecified.js

@@ -0,0 +1,17 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_notSpecified.ts] ////
+
+//// [index.ts]
+import { base } from "./foo";
+//// [foo.ts]
+export function base() {}
+
+
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;
+//// [index.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_notSpecified.symbols

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : Symbol(base, Decl(index.ts, 0, 8))
+
+=== /foo.ts ===
+export function base() {}
+>base : Symbol(base, Decl(foo.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_notSpecified.trace.json

@@ -0,0 +1,7 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo.ts' exist - use it as a name resolution result.",
+    "======== Module name './foo' was successfully resolved to '/foo.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_notSpecified.types

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : () => void
+
+=== /foo.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_one.js

@@ -0,0 +1,25 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_one.ts] ////
+
+//// [index.ts]
+import { ios } from "./foo";
+//// [foo.ios.ts]
+export function ios() {}
+//// [foo.ts]
+export function base() {}
+
+
+//// [foo.ios.js]
+"use strict";
+exports.__esModule = true;
+exports.ios = void 0;
+function ios() { }
+exports.ios = ios;
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;

tests/baselines/reference/moduleResolutionWithSuffixes_one.symbols

@@ -0,0 +1,12 @@
+=== /index.ts ===
+import { ios } from "./foo";
+>ios : Symbol(ios, Decl(index.ts, 0, 8))
+
+=== /foo.ios.ts ===
+export function ios() {}
+>ios : Symbol(ios, Decl(foo.ios.ts, 0, 0))
+
+=== /foo.ts ===
+export function base() {}
+>base : Symbol(base, Decl(foo.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_one.trace.json

@@ -0,0 +1,7 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo.ios.ts' exist - use it as a name resolution result.",
+    "======== Module name './foo' was successfully resolved to '/foo.ios.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_one.types

@@ -0,0 +1,12 @@
+=== /index.ts ===
+import { ios } from "./foo";
+>ios : () => void
+
+=== /foo.ios.ts ===
+export function ios() {}
+>ios : () => void
+
+=== /foo.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_oneBlank.js

@@ -0,0 +1,17 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_oneBlank.ts] ////
+
+//// [index.ts]
+import { base } from "./foo";
+//// [foo.ts]
+export function base() {}
+
+
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;
+//// [index.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_oneBlank.symbols

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : Symbol(base, Decl(index.ts, 0, 8))
+
+=== /foo.ts ===
+export function base() {}
+>base : Symbol(base, Decl(foo.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_oneBlank.trace.json

@@ -0,0 +1,7 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo.ts' exist - use it as a name resolution result.",
+    "======== Module name './foo' was successfully resolved to '/foo.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_oneBlank.types

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : () => void
+
+=== /foo.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_oneNotFound.errors.txt

@@ -0,0 +1,21 @@
+/index.ts(1,21): error TS2307: Cannot find module './foo' or its corresponding type declarations.
+
+
+==== /tsconfig.json (0 errors) ====
+    // moduleSuffixes has one entry but there isn't a matching file. Module resolution should fail.
+    
+    {
+    	"compilerOptions": {
+    		"moduleResolution": "node",
+    		"traceResolution": true,
+    		"moduleSuffixes": [".ios"]
+    	}
+    }
+    
+==== /index.ts (1 errors) ====
+    import { ios } from "./foo";
+                        ~~~~~~~
+!!! error TS2307: Cannot find module './foo' or its corresponding type declarations.
+==== /foo.ts (0 errors) ====
+    export function base() {}
+    

tests/baselines/reference/moduleResolutionWithSuffixes_oneNotFound.js

@@ -0,0 +1,17 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_oneNotFound.ts] ////
+
+//// [index.ts]
+import { ios } from "./foo";
+//// [foo.ts]
+export function base() {}
+
+
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;

tests/baselines/reference/moduleResolutionWithSuffixes_oneNotFound.symbols

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { ios } from "./foo";
+>ios : Symbol(ios, Decl(index.ts, 0, 8))
+
+=== /foo.ts ===
+export function base() {}
+>base : Symbol(base, Decl(foo.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_oneNotFound.trace.json

@@ -0,0 +1,14 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo.ios.ts' does not exist.",
+    "File '/foo.ios.tsx' does not exist.",
+    "File '/foo.ios.d.ts' does not exist.",
+    "Directory '/foo' does not exist, skipping all lookups in it.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'JavaScript'.",
+    "File '/foo.ios.js' does not exist.",
+    "File '/foo.ios.jsx' does not exist.",
+    "Directory '/foo' does not exist, skipping all lookups in it.",
+    "======== Module name './foo' was not resolved. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_oneNotFound.types

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { ios } from "./foo";
+>ios : any
+
+=== /foo.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_dirModuleWithIndex.js

@@ -0,0 +1,24 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_one_dirModuleWithIndex.ts] ////
+
+//// [index.ts]
+import { ios } from "./foo";
+//// [index.ios.ts]
+export function ios() {}
+//// [index.ts]
+export function base() {}
+
+//// [index.ios.js]
+"use strict";
+exports.__esModule = true;
+exports.ios = void 0;
+function ios() { }
+exports.ios = ios;
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;

tests/baselines/reference/moduleResolutionWithSuffixes_one_dirModuleWithIndex.symbols

@@ -0,0 +1,12 @@
+=== /index.ts ===
+import { ios } from "./foo";
+>ios : Symbol(ios, Decl(index.ts, 0, 8))
+
+=== /foo/index.ios.ts ===
+export function ios() {}
+>ios : Symbol(ios, Decl(index.ios.ts, 0, 0))
+
+=== /foo/index.ts ===
+export function base() {}
+>base : Symbol(base, Decl(index.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_dirModuleWithIndex.trace.json

@@ -0,0 +1,11 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo.ios.ts' does not exist.",
+    "File '/foo.ios.tsx' does not exist.",
+    "File '/foo.ios.d.ts' does not exist.",
+    "File '/foo/package.json' does not exist.",
+    "File '/foo/index.ios.ts' exist - use it as a name resolution result.",
+    "======== Module name './foo' was successfully resolved to '/foo/index.ios.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_one_dirModuleWithIndex.types

@@ -0,0 +1,12 @@
+=== /index.ts ===
+import { ios } from "./foo";
+>ios : () => void
+
+=== /foo/index.ios.ts ===
+export function ios() {}
+>ios : () => void
+
+=== /foo/index.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModule.js

@@ -0,0 +1,34 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_one_externalModule.ts] ////
+
+//// [index.ios.js]
+"use strict";
+exports.__esModule = true;
+function ios() {}
+exports.ios = ios;
+//// [index.ios.d.ts]
+export declare function ios(): void;
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+function base() {}
+exports.base = base;
+//// [index.d.ts]
+export declare function base(): void;
+
+//// [index.ts]
+import { ios } from "some-library";
+
+
+//// [/bin/node_modules/some-library/index.ios.js]
+"use strict";
+exports.__esModule = true;
+function ios() { }
+exports.ios = ios;
+//// [/bin/node_modules/some-library/index.js]
+"use strict";
+exports.__esModule = true;
+function base() { }
+exports.base = base;
+//// [/bin/index.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModule.symbols

@@ -0,0 +1,44 @@
+=== /node_modules/some-library/index.ios.js ===
+"use strict";
+exports.__esModule = true;
+>exports.__esModule : Symbol(__esModule, Decl(index.ios.js, 0, 13))
+>exports : Symbol(__esModule, Decl(index.ios.js, 0, 13))
+>__esModule : Symbol(__esModule, Decl(index.ios.js, 0, 13))
+
+function ios() {}
+>ios : Symbol(ios, Decl(index.ios.js, 1, 26))
+
+exports.ios = ios;
+>exports.ios : Symbol(ios, Decl(index.ios.js, 2, 17))
+>exports : Symbol(ios, Decl(index.ios.js, 2, 17))
+>ios : Symbol(ios, Decl(index.ios.js, 2, 17))
+>ios : Symbol(ios, Decl(index.ios.js, 1, 26))
+
+=== /node_modules/some-library/index.ios.d.ts ===
+export declare function ios(): void;
+>ios : Symbol(ios, Decl(index.ios.d.ts, 0, 0))
+
+=== /node_modules/some-library/index.js ===
+"use strict";
+exports.__esModule = true;
+>exports.__esModule : Symbol(__esModule, Decl(index.js, 0, 13))
+>exports : Symbol(__esModule, Decl(index.js, 0, 13))
+>__esModule : Symbol(__esModule, Decl(index.js, 0, 13))
+
+function base() {}
+>base : Symbol(base, Decl(index.js, 1, 26))
+
+exports.base = base;
+>exports.base : Symbol(base, Decl(index.js, 2, 18))
+>exports : Symbol(base, Decl(index.js, 2, 18))
+>base : Symbol(base, Decl(index.js, 2, 18))
+>base : Symbol(base, Decl(index.js, 1, 26))
+
+=== /node_modules/some-library/index.d.ts ===
+export declare function base(): void;
+>base : Symbol(base, Decl(index.d.ts, 0, 0))
+
+=== /index.ts ===
+import { ios } from "some-library";
+>ios : Symbol(ios, Decl(index.ts, 0, 8))
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModule.trace.json

@@ -0,0 +1,14 @@
+[
+    "======== Resolving module 'some-library' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module 'some-library' from 'node_modules' folder, target file type 'TypeScript'.",
+    "File '/node_modules/some-library/package.json' does not exist.",
+    "File '/node_modules/some-library.ios.ts' does not exist.",
+    "File '/node_modules/some-library.ios.tsx' does not exist.",
+    "File '/node_modules/some-library.ios.d.ts' does not exist.",
+    "File '/node_modules/some-library/index.ios.ts' does not exist.",
+    "File '/node_modules/some-library/index.ios.tsx' does not exist.",
+    "File '/node_modules/some-library/index.ios.d.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/node_modules/some-library/index.ios.d.ts', result '/node_modules/some-library/index.ios.d.ts'.",
+    "======== Module name 'some-library' was successfully resolved to '/node_modules/some-library/index.ios.d.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModule.types

@@ -0,0 +1,54 @@
+=== /node_modules/some-library/index.ios.js ===
+"use strict";
+>"use strict" : "use strict"
+
+exports.__esModule = true;
+>exports.__esModule = true : true
+>exports.__esModule : true
+>exports : typeof import("/node_modules/some-library/index.ios")
+>__esModule : true
+>true : true
+
+function ios() {}
+>ios : () => void
+
+exports.ios = ios;
+>exports.ios = ios : () => void
+>exports.ios : () => void
+>exports : typeof import("/node_modules/some-library/index.ios")
+>ios : () => void
+>ios : () => void
+
+=== /node_modules/some-library/index.ios.d.ts ===
+export declare function ios(): void;
+>ios : () => void
+
+=== /node_modules/some-library/index.js ===
+"use strict";
+>"use strict" : "use strict"
+
+exports.__esModule = true;
+>exports.__esModule = true : true
+>exports.__esModule : true
+>exports : typeof import("/node_modules/some-library/index")
+>__esModule : true
+>true : true
+
+function base() {}
+>base : () => void
+
+exports.base = base;
+>exports.base = base : () => void
+>exports.base : () => void
+>exports : typeof import("/node_modules/some-library/index")
+>base : () => void
+>base : () => void
+
+=== /node_modules/some-library/index.d.ts ===
+export declare function base(): void;
+>base : () => void
+
+=== /index.ts ===
+import { ios } from "some-library";
+>ios : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModulePath.js

@@ -0,0 +1,34 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_one_externalModulePath.ts] ////
+
+//// [foo.ios.js]
+"use strict";
+exports.__esModule = true;
+function iosfoo() {}
+exports.iosfoo = iosfoo;
+//// [foo.ios.d.ts]
+export declare function iosfoo(): void;
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+function basefoo() {}
+exports.basefoo = basefoo;
+//// [foo.d.ts]
+export declare function basefoo(): void;
+
+//// [index.ts]
+import { iosfoo } from "some-library/foo";
+
+
+//// [/bin/node_modules/some-library/foo.ios.js]
+"use strict";
+exports.__esModule = true;
+function iosfoo() { }
+exports.iosfoo = iosfoo;
+//// [/bin/node_modules/some-library/foo.js]
+"use strict";
+exports.__esModule = true;
+function basefoo() { }
+exports.basefoo = basefoo;
+//// [/bin/index.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModulePath.symbols

@@ -0,0 +1,44 @@
+=== /node_modules/some-library/foo.ios.js ===
+"use strict";
+exports.__esModule = true;
+>exports.__esModule : Symbol(__esModule, Decl(foo.ios.js, 0, 13))
+>exports : Symbol(__esModule, Decl(foo.ios.js, 0, 13))
+>__esModule : Symbol(__esModule, Decl(foo.ios.js, 0, 13))
+
+function iosfoo() {}
+>iosfoo : Symbol(iosfoo, Decl(foo.ios.js, 1, 26))
+
+exports.iosfoo = iosfoo;
+>exports.iosfoo : Symbol(iosfoo, Decl(foo.ios.js, 2, 20))
+>exports : Symbol(iosfoo, Decl(foo.ios.js, 2, 20))
+>iosfoo : Symbol(iosfoo, Decl(foo.ios.js, 2, 20))
+>iosfoo : Symbol(iosfoo, Decl(foo.ios.js, 1, 26))
+
+=== /node_modules/some-library/foo.ios.d.ts ===
+export declare function iosfoo(): void;
+>iosfoo : Symbol(iosfoo, Decl(foo.ios.d.ts, 0, 0))
+
+=== /node_modules/some-library/foo.js ===
+"use strict";
+exports.__esModule = true;
+>exports.__esModule : Symbol(__esModule, Decl(foo.js, 0, 13))
+>exports : Symbol(__esModule, Decl(foo.js, 0, 13))
+>__esModule : Symbol(__esModule, Decl(foo.js, 0, 13))
+
+function basefoo() {}
+>basefoo : Symbol(basefoo, Decl(foo.js, 1, 26))
+
+exports.basefoo = basefoo;
+>exports.basefoo : Symbol(basefoo, Decl(foo.js, 2, 21))
+>exports : Symbol(basefoo, Decl(foo.js, 2, 21))
+>basefoo : Symbol(basefoo, Decl(foo.js, 2, 21))
+>basefoo : Symbol(basefoo, Decl(foo.js, 1, 26))
+
+=== /node_modules/some-library/foo.d.ts ===
+export declare function basefoo(): void;
+>basefoo : Symbol(basefoo, Decl(foo.d.ts, 0, 0))
+
+=== /index.ts ===
+import { iosfoo } from "some-library/foo";
+>iosfoo : Symbol(iosfoo, Decl(index.ts, 0, 8))
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModulePath.trace.json

@@ -0,0 +1,11 @@
+[
+    "======== Resolving module 'some-library/foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module 'some-library/foo' from 'node_modules' folder, target file type 'TypeScript'.",
+    "File '/node_modules/some-library/package.json' does not exist.",
+    "File '/node_modules/some-library/foo.ios.ts' does not exist.",
+    "File '/node_modules/some-library/foo.ios.tsx' does not exist.",
+    "File '/node_modules/some-library/foo.ios.d.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/node_modules/some-library/foo.ios.d.ts', result '/node_modules/some-library/foo.ios.d.ts'.",
+    "======== Module name 'some-library/foo' was successfully resolved to '/node_modules/some-library/foo.ios.d.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModulePath.types

@@ -0,0 +1,54 @@
+=== /node_modules/some-library/foo.ios.js ===
+"use strict";
+>"use strict" : "use strict"
+
+exports.__esModule = true;
+>exports.__esModule = true : true
+>exports.__esModule : true
+>exports : typeof import("/node_modules/some-library/foo.ios")
+>__esModule : true
+>true : true
+
+function iosfoo() {}
+>iosfoo : () => void
+
+exports.iosfoo = iosfoo;
+>exports.iosfoo = iosfoo : () => void
+>exports.iosfoo : () => void
+>exports : typeof import("/node_modules/some-library/foo.ios")
+>iosfoo : () => void
+>iosfoo : () => void
+
+=== /node_modules/some-library/foo.ios.d.ts ===
+export declare function iosfoo(): void;
+>iosfoo : () => void
+
+=== /node_modules/some-library/foo.js ===
+"use strict";
+>"use strict" : "use strict"
+
+exports.__esModule = true;
+>exports.__esModule = true : true
+>exports.__esModule : true
+>exports : typeof import("/node_modules/some-library/foo")
+>__esModule : true
+>true : true
+
+function basefoo() {}
+>basefoo : () => void
+
+exports.basefoo = basefoo;
+>exports.basefoo = basefoo : () => void
+>exports.basefoo : () => void
+>exports : typeof import("/node_modules/some-library/foo")
+>basefoo : () => void
+>basefoo : () => void
+
+=== /node_modules/some-library/foo.d.ts ===
+export declare function basefoo(): void;
+>basefoo : () => void
+
+=== /index.ts ===
+import { iosfoo } from "some-library/foo";
+>iosfoo : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModule_withPaths.js

@@ -0,0 +1,36 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_one_externalModule_withPaths.ts] ////
+
+//// [index.ios.js]
+"use strict";
+exports.__esModule = true;
+function ios() {}
+exports.ios = ios;
+//// [index.ios.d.ts]
+export declare function ios(): void;
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+function base() {}
+exports.base = base;
+//// [index.d.ts]
+export declare function base(): void;
+
+//// [test.ts]
+import { ios } from "some-library";
+import { ios as ios2 } from "some-library/index";
+import { ios as ios3 } from "some-library/index.js";
+
+
+//// [/bin/node_modules/some-library/lib/index.ios.js]
+"use strict";
+exports.__esModule = true;
+function ios() { }
+exports.ios = ios;
+//// [/bin/node_modules/some-library/lib/index.js]
+"use strict";
+exports.__esModule = true;
+function base() { }
+exports.base = base;
+//// [/bin/test.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModule_withPaths.symbols

@@ -0,0 +1,52 @@
+=== /node_modules/some-library/lib/index.ios.js ===
+"use strict";
+exports.__esModule = true;
+>exports.__esModule : Symbol(__esModule, Decl(index.ios.js, 0, 13))
+>exports : Symbol(__esModule, Decl(index.ios.js, 0, 13))
+>__esModule : Symbol(__esModule, Decl(index.ios.js, 0, 13))
+
+function ios() {}
+>ios : Symbol(ios, Decl(index.ios.js, 1, 26))
+
+exports.ios = ios;
+>exports.ios : Symbol(ios, Decl(index.ios.js, 2, 17))
+>exports : Symbol(ios, Decl(index.ios.js, 2, 17))
+>ios : Symbol(ios, Decl(index.ios.js, 2, 17))
+>ios : Symbol(ios, Decl(index.ios.js, 1, 26))
+
+=== /node_modules/some-library/lib/index.ios.d.ts ===
+export declare function ios(): void;
+>ios : Symbol(ios, Decl(index.ios.d.ts, 0, 0))
+
+=== /node_modules/some-library/lib/index.js ===
+"use strict";
+exports.__esModule = true;
+>exports.__esModule : Symbol(__esModule, Decl(index.js, 0, 13))
+>exports : Symbol(__esModule, Decl(index.js, 0, 13))
+>__esModule : Symbol(__esModule, Decl(index.js, 0, 13))
+
+function base() {}
+>base : Symbol(base, Decl(index.js, 1, 26))
+
+exports.base = base;
+>exports.base : Symbol(base, Decl(index.js, 2, 18))
+>exports : Symbol(base, Decl(index.js, 2, 18))
+>base : Symbol(base, Decl(index.js, 2, 18))
+>base : Symbol(base, Decl(index.js, 1, 26))
+
+=== /node_modules/some-library/lib/index.d.ts ===
+export declare function base(): void;
+>base : Symbol(base, Decl(index.d.ts, 0, 0))
+
+=== /test.ts ===
+import { ios } from "some-library";
+>ios : Symbol(ios, Decl(test.ts, 0, 8))
+
+import { ios as ios2 } from "some-library/index";
+>ios : Symbol(ios, Decl(index.ios.d.ts, 0, 0))
+>ios2 : Symbol(ios2, Decl(test.ts, 1, 8))
+
+import { ios as ios3 } from "some-library/index.js";
+>ios : Symbol(ios, Decl(index.ios.d.ts, 0, 0))
+>ios3 : Symbol(ios3, Decl(test.ts, 2, 8))
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModule_withPaths.trace.json

@@ -0,0 +1,45 @@
+[
+    "======== Resolving module 'some-library' from '/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "'baseUrl' option is set to '/', using this value to resolve non-relative module name 'some-library'.",
+    "'paths' option is specified, looking for a pattern to match module name 'some-library'.",
+    "Module name 'some-library', matched pattern 'some-library'.",
+    "Trying substitution 'node_modules/some-library/lib', candidate module location: 'node_modules/some-library/lib'.",
+    "Loading module as file / folder, candidate module location '/node_modules/some-library/lib', target file type 'TypeScript'.",
+    "File '/node_modules/some-library/lib.ios.ts' does not exist.",
+    "File '/node_modules/some-library/lib.ios.tsx' does not exist.",
+    "File '/node_modules/some-library/lib.ios.d.ts' does not exist.",
+    "File '/node_modules/some-library/lib/package.json' does not exist.",
+    "File '/node_modules/some-library/lib/index.ios.ts' does not exist.",
+    "File '/node_modules/some-library/lib/index.ios.tsx' does not exist.",
+    "File '/node_modules/some-library/lib/index.ios.d.ts' exist - use it as a name resolution result.",
+    "======== Module name 'some-library' was successfully resolved to '/node_modules/some-library/lib/index.ios.d.ts'. ========",
+    "======== Resolving module 'some-library/index' from '/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "'baseUrl' option is set to '/', using this value to resolve non-relative module name 'some-library/index'.",
+    "'paths' option is specified, looking for a pattern to match module name 'some-library/index'.",
+    "Module name 'some-library/index', matched pattern 'some-library/*'.",
+    "Trying substitution 'node_modules/some-library/lib/*', candidate module location: 'node_modules/some-library/lib/index'.",
+    "Loading module as file / folder, candidate module location '/node_modules/some-library/lib/index', target file type 'TypeScript'.",
+    "File '/node_modules/some-library/lib/index.ios.ts' does not exist.",
+    "File '/node_modules/some-library/lib/index.ios.tsx' does not exist.",
+    "File '/node_modules/some-library/lib/index.ios.d.ts' exist - use it as a name resolution result.",
+    "File '/node_modules/some-library/package.json' does not exist.",
+    "======== Module name 'some-library/index' was successfully resolved to '/node_modules/some-library/lib/index.ios.d.ts'. ========",
+    "======== Resolving module 'some-library/index.js' from '/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "'baseUrl' option is set to '/', using this value to resolve non-relative module name 'some-library/index.js'.",
+    "'paths' option is specified, looking for a pattern to match module name 'some-library/index.js'.",
+    "Module name 'some-library/index.js', matched pattern 'some-library/*'.",
+    "Trying substitution 'node_modules/some-library/lib/*', candidate module location: 'node_modules/some-library/lib/index.js'.",
+    "Loading module as file / folder, candidate module location '/node_modules/some-library/lib/index.js', target file type 'TypeScript'.",
+    "File '/node_modules/some-library/lib/index.js.ios.ts' does not exist.",
+    "File '/node_modules/some-library/lib/index.js.ios.tsx' does not exist.",
+    "File '/node_modules/some-library/lib/index.js.ios.d.ts' does not exist.",
+    "File name '/node_modules/some-library/lib/index.js' has a '.js' extension - stripping it.",
+    "File '/node_modules/some-library/lib/index.ios.ts' does not exist.",
+    "File '/node_modules/some-library/lib/index.ios.tsx' does not exist.",
+    "File '/node_modules/some-library/lib/index.ios.d.ts' exist - use it as a name resolution result.",
+    "File '/node_modules/some-library/package.json' does not exist according to earlier cached lookups.",
+    "======== Module name 'some-library/index.js' was successfully resolved to '/node_modules/some-library/lib/index.ios.d.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalModule_withPaths.types

@@ -0,0 +1,62 @@
+=== /node_modules/some-library/lib/index.ios.js ===
+"use strict";
+>"use strict" : "use strict"
+
+exports.__esModule = true;
+>exports.__esModule = true : true
+>exports.__esModule : true
+>exports : typeof import("/node_modules/some-library/lib/index.ios")
+>__esModule : true
+>true : true
+
+function ios() {}
+>ios : () => void
+
+exports.ios = ios;
+>exports.ios = ios : () => void
+>exports.ios : () => void
+>exports : typeof import("/node_modules/some-library/lib/index.ios")
+>ios : () => void
+>ios : () => void
+
+=== /node_modules/some-library/lib/index.ios.d.ts ===
+export declare function ios(): void;
+>ios : () => void
+
+=== /node_modules/some-library/lib/index.js ===
+"use strict";
+>"use strict" : "use strict"
+
+exports.__esModule = true;
+>exports.__esModule = true : true
+>exports.__esModule : true
+>exports : typeof import("/node_modules/some-library/lib/index")
+>__esModule : true
+>true : true
+
+function base() {}
+>base : () => void
+
+exports.base = base;
+>exports.base = base : () => void
+>exports.base : () => void
+>exports : typeof import("/node_modules/some-library/lib/index")
+>base : () => void
+>base : () => void
+
+=== /node_modules/some-library/lib/index.d.ts ===
+export declare function base(): void;
+>base : () => void
+
+=== /test.ts ===
+import { ios } from "some-library";
+>ios : () => void
+
+import { ios as ios2 } from "some-library/index";
+>ios : () => void
+>ios2 : () => void
+
+import { ios as ios3 } from "some-library/index.js";
+>ios : () => void
+>ios3 : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalTSModule.js

@@ -0,0 +1,25 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_one_externalTSModule.ts] ////
+
+//// [index.ios.ts]
+export function ios() {}
+//// [index.ts]
+export function base() {}
+//// [test.ts]
+import { ios } from "some-library";
+
+
+//// [/bin/node_modules/some-library/index.ios.js]
+"use strict";
+exports.__esModule = true;
+exports.ios = void 0;
+function ios() { }
+exports.ios = ios;
+//// [/bin/node_modules/some-library/index.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;
+//// [/bin/test.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalTSModule.symbols

@@ -0,0 +1,12 @@
+=== /node_modules/some-library/index.ios.ts ===
+export function ios() {}
+>ios : Symbol(ios, Decl(index.ios.ts, 0, 0))
+
+=== /node_modules/some-library/index.ts ===
+export function base() {}
+>base : Symbol(base, Decl(index.ts, 0, 0))
+
+=== /test.ts ===
+import { ios } from "some-library";
+>ios : Symbol(ios, Decl(test.ts, 0, 8))
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalTSModule.trace.json

@@ -0,0 +1,12 @@
+[
+    "======== Resolving module 'some-library' from '/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module 'some-library' from 'node_modules' folder, target file type 'TypeScript'.",
+    "File '/node_modules/some-library/package.json' does not exist.",
+    "File '/node_modules/some-library.ios.ts' does not exist.",
+    "File '/node_modules/some-library.ios.tsx' does not exist.",
+    "File '/node_modules/some-library.ios.d.ts' does not exist.",
+    "File '/node_modules/some-library/index.ios.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/node_modules/some-library/index.ios.ts', result '/node_modules/some-library/index.ios.ts'.",
+    "======== Module name 'some-library' was successfully resolved to '/node_modules/some-library/index.ios.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_one_externalTSModule.types

@@ -0,0 +1,12 @@
+=== /node_modules/some-library/index.ios.ts ===
+export function ios() {}
+>ios : () => void
+
+=== /node_modules/some-library/index.ts ===
+export function base() {}
+>base : () => void
+
+=== /test.ts ===
+import { ios } from "some-library";
+>ios : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_jsModule.js

@@ -0,0 +1,29 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_one_jsModule.ts] ////
+
+//// [index.ts]
+import { ios } from "./foo.js";
+//// [foo.ios.js]
+"use strict";
+exports.__esModule = true;
+function ios() {}
+exports.ios = ios;
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+function base() {}
+exports.base = base;
+
+
+//// [/bin/foo.ios.js]
+"use strict";
+exports.__esModule = true;
+function ios() { }
+exports.ios = ios;
+//// [/bin/index.js]
+"use strict";
+exports.__esModule = true;
+//// [/bin/foo.js]
+"use strict";
+exports.__esModule = true;
+function base() { }
+exports.base = base;

tests/baselines/reference/moduleResolutionWithSuffixes_one_jsModule.symbols

@@ -0,0 +1,36 @@
+=== /index.ts ===
+import { ios } from "./foo.js";
+>ios : Symbol(ios, Decl(index.ts, 0, 8))
+
+=== /foo.ios.js ===
+"use strict";
+exports.__esModule = true;
+>exports.__esModule : Symbol(__esModule, Decl(foo.ios.js, 0, 13))
+>exports : Symbol(__esModule, Decl(foo.ios.js, 0, 13))
+>__esModule : Symbol(__esModule, Decl(foo.ios.js, 0, 13))
+
+function ios() {}
+>ios : Symbol(ios, Decl(foo.ios.js, 1, 26))
+
+exports.ios = ios;
+>exports.ios : Symbol(ios, Decl(foo.ios.js, 2, 17))
+>exports : Symbol(ios, Decl(foo.ios.js, 2, 17))
+>ios : Symbol(ios, Decl(foo.ios.js, 2, 17))
+>ios : Symbol(ios, Decl(foo.ios.js, 1, 26))
+
+=== /foo.js ===
+"use strict";
+exports.__esModule = true;
+>exports.__esModule : Symbol(__esModule, Decl(foo.js, 0, 13))
+>exports : Symbol(__esModule, Decl(foo.js, 0, 13))
+>__esModule : Symbol(__esModule, Decl(foo.js, 0, 13))
+
+function base() {}
+>base : Symbol(base, Decl(foo.js, 1, 26))
+
+exports.base = base;
+>exports.base : Symbol(base, Decl(foo.js, 2, 18))
+>exports : Symbol(base, Decl(foo.js, 2, 18))
+>base : Symbol(base, Decl(foo.js, 2, 18))
+>base : Symbol(base, Decl(foo.js, 1, 26))
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_jsModule.trace.json

@@ -0,0 +1,19 @@
+[
+    "======== Resolving module './foo.js' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo.js', target file type 'TypeScript'.",
+    "File '/foo.js.ios.ts' does not exist.",
+    "File '/foo.js.ios.tsx' does not exist.",
+    "File '/foo.js.ios.d.ts' does not exist.",
+    "File name '/foo.js' has a '.js' extension - stripping it.",
+    "File '/foo.ios.ts' does not exist.",
+    "File '/foo.ios.tsx' does not exist.",
+    "File '/foo.ios.d.ts' does not exist.",
+    "Directory '/foo.js' does not exist, skipping all lookups in it.",
+    "Loading module as file / folder, candidate module location '/foo.js', target file type 'JavaScript'.",
+    "File '/foo.js.ios.js' does not exist.",
+    "File '/foo.js.ios.jsx' does not exist.",
+    "File name '/foo.js' has a '.js' extension - stripping it.",
+    "File '/foo.ios.js' exist - use it as a name resolution result.",
+    "======== Module name './foo.js' was successfully resolved to '/foo.ios.js'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_one_jsModule.types

@@ -0,0 +1,46 @@
+=== /index.ts ===
+import { ios } from "./foo.js";
+>ios : () => void
+
+=== /foo.ios.js ===
+"use strict";
+>"use strict" : "use strict"
+
+exports.__esModule = true;
+>exports.__esModule = true : true
+>exports.__esModule : true
+>exports : typeof import("/foo.ios")
+>__esModule : true
+>true : true
+
+function ios() {}
+>ios : () => void
+
+exports.ios = ios;
+>exports.ios = ios : () => void
+>exports.ios : () => void
+>exports : typeof import("/foo.ios")
+>ios : () => void
+>ios : () => void
+
+=== /foo.js ===
+"use strict";
+>"use strict" : "use strict"
+
+exports.__esModule = true;
+>exports.__esModule = true : true
+>exports.__esModule : true
+>exports : typeof import("/foo")
+>__esModule : true
+>true : true
+
+function base() {}
+>base : () => void
+
+exports.base = base;
+>exports.base = base : () => void
+>exports.base : () => void
+>exports : typeof import("/foo")
+>base : () => void
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_one_jsonModule.js

@@ -0,0 +1,27 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_one_jsonModule.ts] ////
+
+//// [index.ts]
+import foo from "./foo.json";
+console.log(foo.ios);
+//// [foo.ios.json]
+{
+	"ios": "platform ios"
+}
+//// [foo.json]
+{
+	"base": "platform base"
+}
+
+
+//// [/bin/foo.ios.json]
+{
+    "ios": "platform ios"
+}
+//// [/bin/index.js]
+"use strict";
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+exports.__esModule = true;
+var foo_json_1 = __importDefault(require("./foo.json"));
+console.log(foo_json_1["default"].ios);

tests/baselines/reference/moduleResolutionWithSuffixes_one_jsonModule.symbols

@@ -0,0 +1,17 @@
+=== /index.ts ===
+import foo from "./foo.json";
+>foo : Symbol(foo, Decl(index.ts, 0, 6))
+
+console.log(foo.ios);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>foo.ios : Symbol("ios", Decl(foo.ios.json, 0, 1))
+>foo : Symbol(foo, Decl(index.ts, 0, 6))
+>ios : Symbol("ios", Decl(foo.ios.json, 0, 1))
+
+=== /foo.ios.json ===
+{
+	"ios": "platform ios"
+>"ios" : Symbol("ios", Decl(foo.ios.json, 0, 1))
+}

tests/baselines/reference/moduleResolutionWithSuffixes_one_jsonModule.trace.json

@@ -0,0 +1,17 @@
+[
+    "======== Resolving module './foo.json' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo.json', target file type 'TypeScript'.",
+    "File '/foo.json.ios.ts' does not exist.",
+    "File '/foo.json.ios.tsx' does not exist.",
+    "File '/foo.json.ios.d.ts' does not exist.",
+    "File name '/foo.json' has a '.json' extension - stripping it.",
+    "File '/foo.json.ios.d.ts' does not exist.",
+    "Directory '/foo.json' does not exist, skipping all lookups in it.",
+    "Loading module as file / folder, candidate module location '/foo.json', target file type 'JavaScript'.",
+    "File '/foo.json.ios.js' does not exist.",
+    "File '/foo.json.ios.jsx' does not exist.",
+    "File name '/foo.json' has a '.json' extension - stripping it.",
+    "File '/foo.ios.json' exist - use it as a name resolution result.",
+    "======== Module name './foo.json' was successfully resolved to '/foo.ios.json'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_one_jsonModule.types

@@ -0,0 +1,21 @@
+=== /index.ts ===
+import foo from "./foo.json";
+>foo : { ios: string; }
+
+console.log(foo.ios);
+>console.log(foo.ios) : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>foo.ios : string
+>foo : { ios: string; }
+>ios : string
+
+=== /foo.ios.json ===
+{
+>{	"ios": "platform ios"} : { ios: string; }
+
+	"ios": "platform ios"
+>"ios" : string
+>"platform ios" : "platform ios"
+}

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank1.js

@@ -0,0 +1,33 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_threeLastIsBlank1.ts] ////
+
+//// [index.ts]
+import { ios } from "./foo";
+//// [foo-ios.ts]
+export function ios() {}
+//// [foo__native.ts]
+export function native() {}
+//// [foo.ts]
+export function base() {}
+
+
+//// [foo-ios.js]
+"use strict";
+exports.__esModule = true;
+exports.ios = void 0;
+function ios() { }
+exports.ios = ios;
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+//// [foo__native.js]
+"use strict";
+exports.__esModule = true;
+exports.native = void 0;
+function native() { }
+exports.native = native;
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank1.symbols

@@ -0,0 +1,16 @@
+=== /index.ts ===
+import { ios } from "./foo";
+>ios : Symbol(ios, Decl(index.ts, 0, 8))
+
+=== /foo-ios.ts ===
+export function ios() {}
+>ios : Symbol(ios, Decl(foo-ios.ts, 0, 0))
+
+=== /foo__native.ts ===
+export function native() {}
+>native : Symbol(native, Decl(foo__native.ts, 0, 0))
+
+=== /foo.ts ===
+export function base() {}
+>base : Symbol(base, Decl(foo.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank1.trace.json

@@ -0,0 +1,7 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo-ios.ts' exist - use it as a name resolution result.",
+    "======== Module name './foo' was successfully resolved to '/foo-ios.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank1.types

@@ -0,0 +1,16 @@
+=== /index.ts ===
+import { ios } from "./foo";
+>ios : () => void
+
+=== /foo-ios.ts ===
+export function ios() {}
+>ios : () => void
+
+=== /foo__native.ts ===
+export function native() {}
+>native : () => void
+
+=== /foo.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank2.js

@@ -0,0 +1,25 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_threeLastIsBlank2.ts] ////
+
+//// [index.ts]
+import { native } from "./foo";
+//// [foo__native.ts]
+export function native() {}
+//// [foo.ts]
+export function base() {}
+
+
+//// [foo__native.js]
+"use strict";
+exports.__esModule = true;
+exports.native = void 0;
+function native() { }
+exports.native = native;
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank2.symbols

@@ -0,0 +1,12 @@
+=== /index.ts ===
+import { native } from "./foo";
+>native : Symbol(native, Decl(index.ts, 0, 8))
+
+=== /foo__native.ts ===
+export function native() {}
+>native : Symbol(native, Decl(foo__native.ts, 0, 0))
+
+=== /foo.ts ===
+export function base() {}
+>base : Symbol(base, Decl(foo.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank2.trace.json

@@ -0,0 +1,8 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo-ios.ts' does not exist.",
+    "File '/foo__native.ts' exist - use it as a name resolution result.",
+    "======== Module name './foo' was successfully resolved to '/foo__native.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank2.types

@@ -0,0 +1,12 @@
+=== /index.ts ===
+import { native } from "./foo";
+>native : () => void
+
+=== /foo__native.ts ===
+export function native() {}
+>native : () => void
+
+=== /foo.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank3.js

@@ -0,0 +1,17 @@
+//// [tests/cases/compiler/moduleResolutionWithSuffixes_threeLastIsBlank3.ts] ////
+
+//// [index.ts]
+import { base } from "./foo";
+//// [foo.ts]
+export function base() {}
+
+
+//// [foo.js]
+"use strict";
+exports.__esModule = true;
+exports.base = void 0;
+function base() { }
+exports.base = base;
+//// [index.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank3.symbols

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : Symbol(base, Decl(index.ts, 0, 8))
+
+=== /foo.ts ===
+export function base() {}
+>base : Symbol(base, Decl(foo.ts, 0, 0))
+

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank3.trace.json

@@ -0,0 +1,9 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo-ios.ts' does not exist.",
+    "File '/foo__native.ts' does not exist.",
+    "File '/foo.ts' exist - use it as a name resolution result.",
+    "======== Module name './foo' was successfully resolved to '/foo.ts'. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank3.types

@@ -0,0 +1,8 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : () => void
+
+=== /foo.ts ===
+export function base() {}
+>base : () => void
+

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank4.errors.txt

@@ -0,0 +1,19 @@
+/index.ts(1,22): error TS2307: Cannot find module './foo' or its corresponding type declarations.
+
+
+==== /tsconfig.json (0 errors) ====
+    // moduleSuffixes has three entries, and the last one is blank. Module resolution should fail.
+    
+    {
+    	"compilerOptions": {
+    		"moduleResolution": "node",
+    		"traceResolution": true,
+    		"moduleSuffixes": ["-ios", "__native", ""]
+    	}
+    }
+    
+==== /index.ts (1 errors) ====
+    import { base } from "./foo";
+                         ~~~~~~~
+!!! error TS2307: Cannot find module './foo' or its corresponding type declarations.
+    

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank4.js

@@ -0,0 +1,7 @@
+//// [index.ts]
+import { base } from "./foo";
+
+
+//// [index.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank4.symbols

@@ -0,0 +1,4 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : Symbol(base, Decl(index.ts, 0, 8))
+

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank4.trace.json

@@ -0,0 +1,24 @@
+[
+    "======== Resolving module './foo' from '/index.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'TypeScript'.",
+    "File '/foo-ios.ts' does not exist.",
+    "File '/foo__native.ts' does not exist.",
+    "File '/foo.ts' does not exist.",
+    "File '/foo-ios.tsx' does not exist.",
+    "File '/foo__native.tsx' does not exist.",
+    "File '/foo.tsx' does not exist.",
+    "File '/foo-ios.d.ts' does not exist.",
+    "File '/foo__native.d.ts' does not exist.",
+    "File '/foo.d.ts' does not exist.",
+    "Directory '/foo' does not exist, skipping all lookups in it.",
+    "Loading module as file / folder, candidate module location '/foo', target file type 'JavaScript'.",
+    "File '/foo-ios.js' does not exist.",
+    "File '/foo__native.js' does not exist.",
+    "File '/foo.js' does not exist.",
+    "File '/foo-ios.jsx' does not exist.",
+    "File '/foo__native.jsx' does not exist.",
+    "File '/foo.jsx' does not exist.",
+    "Directory '/foo' does not exist, skipping all lookups in it.",
+    "======== Module name './foo' was not resolved. ========"
+]

tests/baselines/reference/moduleResolutionWithSuffixes_threeLastIsBlank4.types

@@ -0,0 +1,4 @@
+=== /index.ts ===
+import { base } from "./foo";
+>base : any
+

tests/baselines/reference/showConfig/Shows tsconfig for single option/moduleSuffixes/tsconfig.json

@@ -0,0 +1,5 @@
+{
+    "compilerOptions": {
+        "moduleSuffixes": []
+    }
+}

tests/baselines/reference/tsConfig/Default initialized TSConfig/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tsConfig/Initialized TSConfig with advanced options/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tsConfig/Initialized TSConfig with boolean value compiler options/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tsConfig/Initialized TSConfig with enum value compiler options/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tsConfig/Initialized TSConfig with files options/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tsConfig/Initialized TSConfig with incorrect compiler option value/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tsConfig/Initialized TSConfig with incorrect compiler option/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tsConfig/Initialized TSConfig with list compiler options with enum value/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tsConfig/Initialized TSConfig with list compiler options/tsconfig.json

@@ -34,6 +34,7 @@
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     "types": ["jquery","mocha"],                         /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/declarationDir-is-specified.js

@@ -55,6 +55,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/when-outDir-and-declarationDir-is-specified.js

@@ -55,6 +55,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/when-outDir-is-specified.js

@@ -55,6 +55,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/with-outFile.js

@@ -55,6 +55,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/without-outDir-or-outFile-is-specified-with-declaration-enabled.js

@@ -55,6 +55,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/without-outDir-or-outFile-is-specified.js

@@ -55,6 +55,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
     // "resolveJsonModule": true,                        /* Enable importing .json files. */
     // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
 

tests/cases/compiler/moduleResolutionWithSuffixes_empty.ts

@@ -0,0 +1,14 @@
+// moduleSuffixes is empty. Normal module resolution should occur.
+
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": []
+	}
+}
+// @filename: /index.ts
+import { base } from "./foo";
+// @filename: /foo.ts
+export function base() {}

tests/cases/compiler/moduleResolutionWithSuffixes_notSpecified.ts

@@ -0,0 +1,12 @@
+// moduleSuffixes is not specified. Normal module resolution should occur.
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"moduleResolution": "node",
+		"traceResolution": true,
+	}
+}
+// @filename: /index.ts
+import { base } from "./foo";
+// @filename: /foo.ts
+export function base() {}

tests/cases/compiler/moduleResolutionWithSuffixes_one.ts

@@ -0,0 +1,17 @@
+// moduleSuffixes has one entry and there's a matching file.
+
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [".ios"]
+	}
+}
+
+// @filename: /index.ts
+import { ios } from "./foo";
+// @filename: /foo.ios.ts
+export function ios() {}
+// @filename: /foo.ts
+export function base() {}

tests/cases/compiler/moduleResolutionWithSuffixes_oneBlank.ts

@@ -0,0 +1,15 @@
+// moduleSuffixes has one blank entry. Normal module resolution should occur.
+
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [""]
+	}
+}
+
+// @filename: /index.ts
+import { base } from "./foo";
+// @filename: /foo.ts
+export function base() {}

tests/cases/compiler/moduleResolutionWithSuffixes_oneNotFound.ts

@@ -0,0 +1,15 @@
+// moduleSuffixes has one entry but there isn't a matching file. Module resolution should fail.
+
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [".ios"]
+	}
+}
+
+// @filename: /index.ts
+import { ios } from "./foo";
+// @filename: /foo.ts
+export function base() {}

tests/cases/compiler/moduleResolutionWithSuffixes_one_dirModuleWithIndex.ts

@@ -0,0 +1,17 @@
+// moduleSuffixes has one entry and there's a matching dir with an index file.
+
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [".ios"]
+	}
+}
+
+// @filename: /index.ts
+import { ios } from "./foo";
+// @filename: /foo/index.ios.ts
+export function ios() {}
+// @filename: /foo/index.ts
+export function base() {}

tests/cases/compiler/moduleResolutionWithSuffixes_one_externalModule.ts

@@ -0,0 +1,31 @@
+// moduleSuffixes has one entry and there's a matching package.
+// @fullEmitPaths: true
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"allowJs": true,
+		"checkJs": false,
+		"outDir": "bin",
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [".ios"]
+	}
+}
+
+// @filename: /node_modules/some-library/index.ios.js
+"use strict";
+exports.__esModule = true;
+function ios() {}
+exports.ios = ios;
+// @filename: /node_modules/some-library/index.ios.d.ts
+export declare function ios(): void;
+// @filename: /node_modules/some-library/index.js
+"use strict";
+exports.__esModule = true;
+function base() {}
+exports.base = base;
+// @filename: /node_modules/some-library/index.d.ts
+export declare function base(): void;
+
+// @filename: /index.ts
+import { ios } from "some-library";

tests/cases/compiler/moduleResolutionWithSuffixes_one_externalModulePath.ts

@@ -0,0 +1,31 @@
+// moduleSuffixes has one entry and there's a matching package with a specific path.
+// @fullEmitPaths: true
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"allowJs": true,
+		"checkJs": false,
+		"outDir": "bin",
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [".ios"]
+	}
+}
+
+// @filename: /node_modules/some-library/foo.ios.js
+"use strict";
+exports.__esModule = true;
+function iosfoo() {}
+exports.iosfoo = iosfoo;
+// @filename: /node_modules/some-library/foo.ios.d.ts
+export declare function iosfoo(): void;
+// @filename: /node_modules/some-library/foo.js
+"use strict";
+exports.__esModule = true;
+function basefoo() {}
+exports.basefoo = basefoo;
+// @filename: /node_modules/some-library/foo.d.ts
+export declare function basefoo(): void;
+
+// @filename: /index.ts
+import { iosfoo } from "some-library/foo";

tests/cases/compiler/moduleResolutionWithSuffixes_one_externalModule_withPaths.ts

@@ -0,0 +1,38 @@
+// moduleSuffixes has one entry and there's a matching package. use the 'paths' option to map the package.
+// @fullEmitPaths: true
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"allowJs": true,
+		"checkJs": false,
+		"outDir": "bin",
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [".ios"],
+		"baseUrl": "/",
+		"paths": {
+			"some-library": ["node_modules/some-library/lib"],
+			"some-library/*": ["node_modules/some-library/lib/*"]
+		}
+	}
+}
+
+// @filename: /node_modules/some-library/lib/index.ios.js
+"use strict";
+exports.__esModule = true;
+function ios() {}
+exports.ios = ios;
+// @filename: /node_modules/some-library/lib/index.ios.d.ts
+export declare function ios(): void;
+// @filename: /node_modules/some-library/lib/index.js
+"use strict";
+exports.__esModule = true;
+function base() {}
+exports.base = base;
+// @filename: /node_modules/some-library/lib/index.d.ts
+export declare function base(): void;
+
+// @filename: /test.ts
+import { ios } from "some-library";
+import { ios as ios2 } from "some-library/index";
+import { ios as ios3 } from "some-library/index.js";

tests/cases/compiler/moduleResolutionWithSuffixes_one_externalTSModule.ts

@@ -0,0 +1,18 @@
+// moduleSuffixes has one entry and there's a matching package with TS files.
+// @fullEmitPaths: true
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"outDir": "bin",
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [".ios"]
+	}
+}
+
+// @filename: /node_modules/some-library/index.ios.ts
+export function ios() {}
+// @filename: /node_modules/some-library/index.ts
+export function base() {}
+// @filename: /test.ts
+import { ios } from "some-library";

tests/cases/compiler/moduleResolutionWithSuffixes_one_jsModule.ts

@@ -0,0 +1,26 @@
+// moduleSuffixes has one entry and there's a matching file. module name explicitly includes JS file extension.
+// @fullEmitPaths: true
+// @filename: /tsconfig.json
+{
+	"compilerOptions": {
+		"allowJs": true,
+		"checkJs": false,
+		"outDir": "bin",
+		"moduleResolution": "node",
+		"traceResolution": true,
+		"moduleSuffixes": [".ios"]
+	}
+}
+
+// @filename: /index.ts
+import { ios } from "./foo.js";
+// @filename: /foo.ios.js
+"use strict";
+exports.__esModule = true;
+function ios() {}
+exports.ios = ios;
+// @filename: /foo.js
+"use strict";
+exports.__esModule = true;
+function base() {}
+exports.base = base;