microsoft · sheetalkamat · Mar 3, 2023
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -905,7 +905,7 @@ import {
     removeExtension,
     removePrefix,
     replaceElement,
-    resolutionExtensionIsTSOrJson,
+    resolutionExtensionIsTSOrJsonOrArbitrary,
     ResolutionMode,
     ResolvedModuleFull,
     ResolvedType,
@@ -4874,7 +4874,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             }
 
             if (sourceFile.symbol) {
-                if (resolvedModule.isExternalLibraryImport && !resolutionExtensionIsTSOrJson(resolvedModule.extension)) {
+                if (resolvedModule.isExternalLibraryImport && !resolutionExtensionIsTSOrJsonOrArbitrary(resolvedModule.extension, compilerOptions)) {
                     errorOnImplicitAnyModule(/*isError*/ false, errorNode, currentSourceFile, mode, resolvedModule, moduleReference);
                 }
                 if (moduleResolutionKind === ModuleResolutionKind.Node16 || moduleResolutionKind === ModuleResolutionKind.NodeNext) {
@@ -4957,7 +4957,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
 
         // May be an untyped module. If so, ignore resolutionDiagnostic.
-        if (resolvedModule && !resolutionExtensionIsTSOrJson(resolvedModule.extension) && resolutionDiagnostic === undefined || resolutionDiagnostic === Diagnostics.Could_not_find_a_declaration_file_for_module_0_1_implicitly_has_an_any_type) {
+        if (resolvedModule && !resolutionExtensionIsTSOrJsonOrArbitrary(resolvedModule.extension, compilerOptions) && resolutionDiagnostic === undefined || resolutionDiagnostic === Diagnostics.Could_not_find_a_declaration_file_for_module_0_1_implicitly_has_an_any_type) {
             if (isForAugmentation) {
                 const diag = Diagnostics.Invalid_module_name_in_augmentation_Module_0_resolves_to_an_untyped_module_at_1_which_cannot_be_augmented;
                 error(errorNode, diag, moduleReference, resolvedModule!.resolvedFileName);

diff --git a/src/compiler/moduleNameResolver.ts b/src/compiler/moduleNameResolver.ts
@@ -35,6 +35,7 @@ import {
     forEach,
     forEachAncestorDirectory,
     formatMessage,
+    getAllowArbitraryExtensions,
     getBaseFileName,
     GetCanonicalFileName,
     getCommonSourceDirectory,
@@ -98,6 +99,8 @@ import {
     startsWith,
     stringContains,
     supportedDeclarationExtensions,
+    supportedJSExtensionsFlat,
+    supportedTSExtensionsFlat,
     supportedTSImplementationExtensions,
     toPath,
     tryExtractTSExtension,
@@ -179,7 +182,9 @@ const enum Extensions {
     TypeScript  = 1 << 0, // '.ts', '.tsx', '.mts', '.cts'
     JavaScript  = 1 << 1, // '.js', '.jsx', '.mjs', '.cjs'
     Declaration = 1 << 2, // '.d.ts', etc.
-    Json        = 1 << 3, // '.json'
+    Json = 1 << 3, // '.json'
+
+    Arbitrary = 1 << 4,
 
     ImplementationFiles = TypeScript | JavaScript,
 }
@@ -190,6 +195,7 @@ function formatExtensions(extensions: Extensions) {
     if (extensions & Extensions.JavaScript) result.push("JavaScript");
     if (extensions & Extensions.Declaration) result.push("Declaration");
     if (extensions & Extensions.Json) result.push("JSON");
+    if (extensions & Extensions.Arbitrary) result.push("Arbitrary");
     return result.join(", ");
 }
 
@@ -1636,6 +1642,9 @@ function nodeNextModuleNameResolverWorker(features: NodeResolutionFeatures, modu
     if (getResolveJsonModule(compilerOptions)) {
         extensions |= Extensions.Json;
     }
+    if (getAllowArbitraryExtensions(compilerOptions)) {
+        extensions |= Extensions.Arbitrary;
+    }
     return nodeModuleNameResolverWorker(features | esmMode, moduleName, containingDirectory, compilerOptions, host, cache, extensions, /*isConfigLookup*/ false, redirectedReference);
 }
 
@@ -1658,6 +1667,9 @@ export function bundlerModuleNameResolver(moduleName: string, containingFile: st
     if (getResolveJsonModule(compilerOptions)) {
         extensions |= Extensions.Json;
     }
+    if (getAllowArbitraryExtensions(compilerOptions)) {
+        extensions |= Extensions.Arbitrary;
+    }
     return nodeModuleNameResolverWorker(getNodeResolutionFeatures(compilerOptions), moduleName, containingDirectory, compilerOptions, host, cache, extensions, /*isConfigLookup*/ false, redirectedReference);
 }
 
@@ -1671,11 +1683,17 @@ export function nodeModuleNameResolver(moduleName: string, containingFile: strin
     else if (compilerOptions.noDtsResolution) {
         extensions = Extensions.ImplementationFiles;
         if (getResolveJsonModule(compilerOptions)) extensions |= Extensions.Json;
+        if (getAllowArbitraryExtensions(compilerOptions)) {
+            extensions |= Extensions.Arbitrary;
+        }
     }
     else {
         extensions = getResolveJsonModule(compilerOptions)
             ? Extensions.TypeScript | Extensions.JavaScript | Extensions.Declaration | Extensions.Json
             : Extensions.TypeScript | Extensions.JavaScript | Extensions.Declaration;
+        if (getAllowArbitraryExtensions(compilerOptions)) {
+            extensions |= Extensions.Arbitrary;
+        }
     }
     return nodeModuleNameResolverWorker(NodeResolutionFeatures.None, moduleName, getDirectoryPath(containingFile), compilerOptions, host, cache, extensions, !!isConfigLookup, redirectedReference);
 }
@@ -1712,6 +1730,8 @@ function nodeModuleNameResolverWorker(features: NodeResolutionFeatures, moduleNa
         trace(host, Diagnostics.Resolving_in_0_mode_with_conditions_1, features & NodeResolutionFeatures.EsmMode ? "ESM" : "CJS", conditions.map(c => `'${c}'`).join(", "));
     }
 
+    const originalExtensions = extensions;
+    extensions = extensions & ~Extensions.Arbitrary;
     let result;
     if (getEmitModuleResolutionKind(compilerOptions) === ModuleResolutionKind.Node10) {
         const priorityExtensions = extensions & (Extensions.TypeScript | Extensions.Declaration);
@@ -1725,6 +1745,11 @@ function nodeModuleNameResolverWorker(features: NodeResolutionFeatures, moduleNa
         result = tryResolve(extensions, state);
     }
 
+    if (originalExtensions !== extensions) {
+        // try arbitary extension
+        result ??= tryResolve(Extensions.Arbitrary, state);
+    }
+
     // For non-relative names that resolved to JS but no types in modes that look up an "import" condition in package.json "exports",
     // try again with "exports" disabled to try to detect if this is likely a configuration error in a dependency's package.json.
     let legacyResult;
@@ -2016,6 +2041,7 @@ function tryAddingExtensions(candidate: string, extensions: Extensions, original
                 || undefined;
         default:
             return extensions & Extensions.Declaration && !isDeclarationFileName(candidate + originalExtension) && tryExtension(`.d${originalExtension}.ts`)
+                || !!originalExtension && extensions & Extensions.Arbitrary && !some(supportedTSExtensionsFlat, ext => endsWith(originalExtension, ext)) && !some(supportedJSExtensionsFlat, ext => endsWith(originalExtension, ext)) && tryExtension(originalExtension)
                 || undefined;
 
     }
@@ -2355,6 +2381,7 @@ function extensionIsOk(extensions: Extensions, extension: string): boolean {
         || extensions & Extensions.TypeScript && (extension === Extension.Ts || extension === Extension.Tsx || extension === Extension.Mts || extension === Extension.Cts)
         || extensions & Extensions.Declaration && (extension === Extension.Dts || extension === Extension.Dmts || extension === Extension.Dcts)
         || extensions & Extensions.Json && extension === Extension.Json
+        || extensions & Extensions.Arbitrary && !!extension
         || false;
 }
 

diff --git a/src/compiler/program.ts b/src/compiler/program.ts
@@ -152,6 +152,7 @@ import {
     getTsConfigObjectLiteralExpression,
     getTsConfigPropArray,
     getTsConfigPropArrayElementValue,
+    hasArbitraryExtension,
     HasChangedAutomaticTypeDirectiveNames,
     hasChangesInResolutions,
     hasExtension,
@@ -266,7 +267,7 @@ import {
     removeFileExtension,
     removePrefix,
     removeSuffix,
-    resolutionExtensionIsTSOrJson,
+    resolutionExtensionIsTSOrJsonOrArbitrary,
     ResolutionMode,
     resolveConfigFileProjectName,
     ResolvedConfigFileName,
@@ -1484,6 +1485,8 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
 
     const host = createProgramOptions.host || createCompilerHost(options);
     const configParsingHost = parseConfigHostFromCompilerHostLike(host);
+    const createArbitrarySourceFile: CompilerHost["getSourceFile"] = host.getDeclarationFileForArbitraryExtension?.bind(host) ||
+        ((fileName, languageVersionOrOptions) => createSourceFile(fileName + ".d.ts", "export {}", languageVersionOrOptions, /*setParentNodes*/ true));
 
     let skipDefaultLib = options.noLib;
     const getDefaultLibraryFileName = memoize(() => host.getDefaultLibFileName(options));
@@ -3373,7 +3376,7 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
     function processSourceFile(fileName: string, isDefaultLib: boolean, ignoreNoDefaultLib: boolean, packageId: PackageId | undefined, reason: FileIncludeReason): void {
         getSourceFileFromReferenceWorker(
             fileName,
-            fileName => findSourceFile(fileName, isDefaultLib, ignoreNoDefaultLib, reason, packageId), // TODO: GH#18217
+            fileName => findSourceFile(fileName, isDefaultLib, ignoreNoDefaultLib, reason, packageId, /*isArbitraryExtensionFile*/ false), // TODO: GH#18217
             (diagnostic, ...args) => addFilePreprocessingFileExplainingDiagnostic(/*file*/ undefined, reason, diagnostic, args),
             reason
         );
@@ -3406,13 +3409,13 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
     }
 
     // Get source file from normalized fileName
-    function findSourceFile(fileName: string, isDefaultLib: boolean, ignoreNoDefaultLib: boolean, reason: FileIncludeReason, packageId: PackageId | undefined): SourceFile | undefined {
+    function findSourceFile(fileName: string, isDefaultLib: boolean, ignoreNoDefaultLib: boolean, reason: FileIncludeReason, packageId: PackageId | undefined, isArbitraryExtensionFile: boolean): SourceFile | undefined {
         tracing?.push(tracing.Phase.Program, "findSourceFile", {
             fileName,
             isDefaultLib: isDefaultLib || undefined,
             fileIncludeKind: (FileIncludeKind as any)[reason.kind],
         });
-        const result = findSourceFileWorker(fileName, isDefaultLib, ignoreNoDefaultLib, reason, packageId);
+        const result = findSourceFileWorker(fileName, isDefaultLib, ignoreNoDefaultLib, reason, packageId, isArbitraryExtensionFile);
         tracing?.pop();
         return result;
     }
@@ -3429,9 +3432,9 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
             { languageVersion, impliedNodeFormat: result, setExternalModuleIndicator };
     }
 
-    function findSourceFileWorker(fileName: string, isDefaultLib: boolean, ignoreNoDefaultLib: boolean, reason: FileIncludeReason, packageId: PackageId | undefined): SourceFile | undefined {
+    function findSourceFileWorker(fileName: string, isDefaultLib: boolean, ignoreNoDefaultLib: boolean, reason: FileIncludeReason, packageId: PackageId | undefined, isArbitraryExtensionFile: boolean): SourceFile | undefined {
         const path = toPath(fileName);
-        if (useSourceOfProjectReferenceRedirect) {
+        if (useSourceOfProjectReferenceRedirect && !isArbitraryExtensionFile) {
             let source = getSourceOfProjectReferenceRedirect(path);
             // If preserveSymlinks is true, module resolution wont jump the symlink
             // but the resolved real path may be the .d.ts from project reference
@@ -3447,7 +3450,7 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
             }
             if (source) {
                 const file = isString(source) ?
-                    findSourceFile(source, isDefaultLib, ignoreNoDefaultLib, reason, packageId) :
+                    findSourceFile(source, isDefaultLib, ignoreNoDefaultLib, reason, packageId, /*isArbitraryExtensionFile*/ false) :
                     undefined;
                 if (file) addFileToFilesByName(file, path, /*redirectedPath*/ undefined);
                 return file;
@@ -3520,12 +3523,14 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
 
         // We haven't looked for this file, do so now and cache result
         const sourceFileOptions = getCreateSourceFileOptions(fileName, moduleResolutionCache, host, options);
-        const file = host.getSourceFile(
+        debugger;
+        const file = (!isArbitraryExtensionFile ? host.getSourceFile : createArbitrarySourceFile)(
             fileName,
             sourceFileOptions,
             hostErrorMessage => addFilePreprocessingFileExplainingDiagnostic(/*file*/ undefined, reason, Diagnostics.Cannot_read_file_0_Colon_1, [fileName, hostErrorMessage]),
             shouldCreateNewSourceFile || (oldProgram?.getSourceFileByPath(toPath(fileName))?.impliedNodeFormat !== sourceFileOptions.impliedNodeFormat)
         );
+        if (isArbitraryExtensionFile && file) file.isDeclarationFile = true;
 
         if (packageId) {
             const packageIdKey = packageIdToString(packageId);
@@ -3868,9 +3873,10 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
                 }
 
                 const isFromNodeModulesSearch = resolution.isExternalLibraryImport;
-                const isJsFile = !resolutionExtensionIsTSOrJson(resolution.extension);
+                const isJsFile = !resolutionExtensionIsTSOrJsonOrArbitrary(resolution.extension, options);
                 const isJsFileFromNodeModules = isFromNodeModulesSearch && isJsFile;
                 const resolvedFileName = resolution.resolvedFileName;
+                const isArbitraryExtensionFile = hasArbitraryExtension(resolution.extension);
 
                 if (isFromNodeModulesSearch) {
                     currentNodeModulesDepth++;
@@ -3902,6 +3908,7 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
                         /*ignoreNoDefaultLib*/ false,
                         { kind: FileIncludeKind.Import, file: file.path, index, },
                         resolution.packageId,
+                        isArbitraryExtensionFile,
                     );
                 }
 

diff --git a/src/compiler/resolutionCache.ts b/src/compiler/resolutionCache.ts
@@ -57,7 +57,7 @@ import {
     Program,
     removeSuffix,
     removeTrailingDirectorySeparator,
-    resolutionExtensionIsTSOrJson,
+    resolutionExtensionIsTSOrJsonOrArbitrary,
     ResolutionLoader,
     ResolutionMode,
     ResolvedModuleWithFailedLookupLocations,
@@ -684,7 +684,7 @@ export function createResolutionCache(resolutionHost: ResolutionCacheHost, rootD
                 options,
             ),
             getResolutionWithResolvedFileName: getResolvedModule,
-            shouldRetryResolution: resolution => !resolution.resolvedModule || !resolutionExtensionIsTSOrJson(resolution.resolvedModule.extension),
+            shouldRetryResolution: resolution => !resolution.resolvedModule || !resolutionExtensionIsTSOrJsonOrArbitrary(resolution.resolvedModule.extension, options),
             logChanges: logChangesWhenResolvingModule,
         });
     }

diff --git a/src/compiler/types.ts b/src/compiler/types.ts
@@ -7647,6 +7647,7 @@ export type HasInvalidatedResolutions = (sourceFile: Path) => boolean;
 export type HasChangedAutomaticTypeDirectiveNames = () => boolean;
 
 export interface CompilerHost extends ModuleResolutionHost {
+    getDeclarationFileForArbitraryExtension?(arbitraryExtensionFileName: string, languageVersionOrOptions: ScriptTarget | CreateSourceFileOptions, onError?: (message: string) => void, shouldCreateNewSourceFile?: boolean): SourceFile | undefined;
     getSourceFile(fileName: string, languageVersionOrOptions: ScriptTarget | CreateSourceFileOptions, onError?: (message: string) => void, shouldCreateNewSourceFile?: boolean): SourceFile | undefined;
     getSourceFileByPath?(fileName: string, path: Path, languageVersionOrOptions: ScriptTarget | CreateSourceFileOptions, onError?: (message: string) => void, shouldCreateNewSourceFile?: boolean): SourceFile | undefined;
     getCancellationToken?(): CancellationToken;

diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
@@ -8464,6 +8464,14 @@ export function getResolveJsonModule(compilerOptions: CompilerOptions) {
     return getEmitModuleResolutionKind(compilerOptions) === ModuleResolutionKind.Bundler;
 }
 
+/** @internal */
+export function getAllowArbitraryExtensions(compilerOptions: CompilerOptions) {
+    if (compilerOptions.allowArbitraryExtensions !== undefined) {
+        return compilerOptions.allowArbitraryExtensions;
+    }
+    return getEmitModuleResolutionKind(compilerOptions) === ModuleResolutionKind.Bundler;
+}
+
 /** @internal */
 export function getEmitDeclarations(compilerOptions: CompilerOptions): boolean {
     return !!(compilerOptions.declaration || compilerOptions.composite);
@@ -9298,9 +9306,17 @@ export function extensionIsTS(ext: string): boolean {
     return ext === Extension.Ts || ext === Extension.Tsx || ext === Extension.Dts || ext === Extension.Cts || ext === Extension.Mts || ext === Extension.Dmts || ext === Extension.Dcts || (startsWith(ext, ".d.") && endsWith(ext, ".ts"));
 }
 
+export function hasArbitraryExtension(ext: string) {
+    return !some(supportedTSExtensionsFlat, tsExt => endsWith(ext, tsExt)) &&
+        !some(supportedJSExtensionsFlat, jsExt => endsWith(ext, jsExt)) &&
+        !endsWith(ext, Extension.Json);
+}
+
 /** @internal */
-export function resolutionExtensionIsTSOrJson(ext: string) {
-    return extensionIsTS(ext) || ext === Extension.Json;
+export function resolutionExtensionIsTSOrJsonOrArbitrary(ext: string, options: CompilerOptions) {
+    return extensionIsTS(ext) ||
+        ext === Extension.Json ||
+        getAllowArbitraryExtensions(options) && !some(supportedJSExtensionsFlat, jsExt => endsWith(ext, jsExt));
 }
 
 /**

diff --git a/src/harness/fourslashImpl.ts b/src/harness/fourslashImpl.ts
@@ -644,7 +644,7 @@ export class TestState {
             if (!ts.isAnySupportedFileExtension(fileName)
                 || Harness.getConfigNameFromFileName(fileName)
                 // Can't get a Program in Server tests
-                || this.testType !== FourSlashTestType.Server && !ts.getAllowJSCompilerOption(this.getProgram().getCompilerOptions()) && !ts.resolutionExtensionIsTSOrJson(ts.extensionFromPath(fileName))
+                || this.testType !== FourSlashTestType.Server && !ts.getAllowJSCompilerOption(this.getProgram().getCompilerOptions()) && !ts.resolutionExtensionIsTSOrJsonOrArbitrary(ts.extensionFromPath(fileName))
                 || ts.getBaseFileName(fileName) === "package.json") return;
             const errors = this.getDiagnostics(fileName).filter(e => e.category !== ts.DiagnosticCategory.Suggestion);
             if (errors.length) {