WIP

src/compiler/checker.ts

@@ -4665,6 +4665,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             else if (
                 compilerOptions.rewriteRelativeImportExtensions
                 && !(location.flags & NodeFlags.Ambient)
+                && !isDeclarationFileName(moduleReference)
                 && !isLiteralImportTypeNode(location)
                 && !isPartOfTypeOnlyImportOrExportDeclaration(location)
             ) {
@@ -4676,13 +4677,16 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                         getRelativePathFromFile(getNormalizedAbsolutePath(currentSourceFile.fileName, host.getCurrentDirectory()), resolvedModule.resolvedFileName, hostGetCanonicalFileName(host)),
                     );
                 }
-                else if (resolvedModule.resolvedUsingTsExtension && !shouldRewrite && !isDeclarationFileName(moduleReference) && sourceFileMayBeEmitted(sourceFile, host)) {
+                else if (resolvedModule.resolvedUsingTsExtension && !shouldRewrite && sourceFileMayBeEmitted(sourceFile, host)) {
                     error(
                         errorNode,
                         Diagnostics.This_import_uses_a_0_extension_to_resolve_to_an_input_TypeScript_file_but_will_not_be_rewritten_during_emit_because_it_is_not_a_relative_path,
                         getAnyExtensionFromPath(moduleReference),
                     );
                 }
+                else if (resolvedModule.resolvedUsingTsExtension && shouldRewrite && host.isSourceOfProjectReferenceRedirect(resolvedModule.resolvedFileName)) {
+                    // TODO
+                }
             }
 
             if (sourceFile.symbol) {

tests/cases/fourslash/server/rewriteRelativeImportExtensionsProjectReferences1.ts

@@ -0,0 +1,49 @@
+/// <reference path="../fourslash.ts" />
+
+// @Filename: packages/common/tsconfig.json
+//// {
+////     "compilerOptions": {
+////         "composite": true,
+////         "rootDir": "src",
+////         "outDir": "dist",
+////         "module": "nodenext",
+////     }
+//// }
+
+// @Filename: packages/common/package.json
+//// {
+////     "name": "common",
+////     "version": "1.0.0",
+////     "type": "module",
+////     "exports": {
+////         ".": {
+////             "source": "./src/index.ts",
+////             "default": "./dist/index.js"
+////         }
+////     }
+//// }
+
+// @Filename: packages/common/src/index.ts
+//// export {};
+
+// @Filename: packages/main/tsconfig.json
+//// {
+////     "compilerOptions": {
+////         "module": "nodenext",
+////         "rewriteRelativeImportExtensions": true,
+////         "rootDir": "src",
+////         "outDir": "dist",
+////     },
+////     "references": [
+////         { "path": "../common" }
+////     ]
+//// }
+
+// @Filename: packages/main/package.json
+//// { "type": "module" }
+
+// @Filename: packages/main/src/index.ts
+//// import {} from "../../common/src/index.ts";
+
+goTo.file("/tests/cases/fourslash/server/packages/main/src/index.ts");
+verify.baselineSyntacticAndSemanticDiagnostics();