Fix two module specifier ending preference detection issues (#53691)

src/compiler/moduleSpecifiers.ts

@@ -147,7 +147,9 @@ function getPreferences(
                 return [ModuleSpecifierEnding.JsExtension];
             }
             if (getEmitModuleResolutionKind(compilerOptions) === ModuleResolutionKind.Classic) {
-                return [ModuleSpecifierEnding.Index, ModuleSpecifierEnding.JsExtension];
+                return preferredEnding === ModuleSpecifierEnding.JsExtension
+                    ? [ModuleSpecifierEnding.JsExtension, ModuleSpecifierEnding.Index]
+                    : [ModuleSpecifierEnding.Index, ModuleSpecifierEnding.JsExtension];
             }
             switch (preferredEnding) {
                 case ModuleSpecifierEnding.JsExtension: return [ModuleSpecifierEnding.JsExtension, ModuleSpecifierEnding.Minimal, ModuleSpecifierEnding.Index];

src/compiler/utilities.ts

@@ -9094,6 +9094,8 @@ const allSupportedExtensionsWithJson: readonly Extension[][] = [...allSupportedE
 export const supportedDeclarationExtensions: readonly Extension[] = [Extension.Dts, Extension.Dcts, Extension.Dmts];
 /** @internal */
 export const supportedTSImplementationExtensions: readonly Extension[] = [Extension.Ts, Extension.Cts, Extension.Mts, Extension.Tsx];
+/** @internal */
+export const extensionsNotSupportingExtensionlessResolution: readonly Extension[] = [Extension.Mts, Extension.Dmts, Extension.Mjs, Extension.Cts, Extension.Dcts, Extension.Cjs];
 
 /** @internal */
 export function getSupportedExtensions(options?: CompilerOptions): readonly Extension[][];
@@ -9156,7 +9158,9 @@ export const enum ModuleSpecifierEnding {
 
 /** @internal */
 export function usesExtensionsOnImports({ imports }: SourceFile, hasExtension: (text: string) => boolean = or(hasJSFileExtension, hasTSFileExtension)): boolean {
-    return firstDefined(imports, ({ text }) => pathIsRelative(text) ? hasExtension(text) : undefined) || false;
+    return firstDefined(imports, ({ text }) => pathIsRelative(text) && !fileExtensionIsOneOf(text, extensionsNotSupportingExtensionlessResolution)
+        ? hasExtension(text)
+        : undefined) || false;
 }
 
 /** @internal */
@@ -9197,6 +9201,10 @@ export function getModuleSpecifierEndingPreference(preference: UserPreferences["
             emptyArray;
         for (const specifier of specifiers) {
             if (pathIsRelative(specifier)) {
+                if (fileExtensionIsOneOf(specifier, extensionsNotSupportingExtensionlessResolution)) {
+                    // These extensions are not optional, so do not indicate a preference.
+                    continue;
+                }
                 if (hasTSFileExtension(specifier)) {
                     return ModuleSpecifierEnding.TsExtension;
                 }

tests/cases/fourslash/importNameCodeFixInferEndingPreference.ts

@@ -0,0 +1,21 @@
+/// <reference path="fourslash.ts" />
+
+// @module: esnext
+// @moduleResolution: bundler
+
+// @Filename: /a.mts
+//// export {};
+
+// @Filename: /b.ts
+//// export {};
+
+// @Filename: /c.ts
+//// export const c = 0;
+
+// @Filename: /main.ts
+//// import {} from "./a.mjs";
+//// import {} from "./b";
+////
+//// c/**/;
+
+verify.importFixModuleSpecifiers("", ["./c"]);

tests/cases/fourslash/importNameCodeFixInferEndingPreference_classic.ts

@@ -0,0 +1,19 @@
+/// <reference path="fourslash.ts" />
+
+// @module: esnext
+// @checkJs: true
+// @allowJs: true
+// @noEmit: true
+
+// @Filename: /a.js
+//// export const a = 0;
+
+// @Filename: /b.js
+//// export const b = 0;
+
+// @Filename: /c.js
+//// import { a } from "./a.js";
+////
+//// b/**/;
+
+verify.importFixModuleSpecifiers("", ["./b.js"]);