Implement rewriteRelativeImportExtensions feature

Co-authored-by: andrewbranch <3277153+andrewbranch@users.noreply.github.com>

Author: Copilot

internal/checker/checker.go

@@ -14498,6 +14498,34 @@ func (c *Checker) resolveExternalModule(location *ast.Node, moduleReference stri
 					)
 				}
 			}
+		} else if c.compilerOptions.RewriteRelativeImportExtensions.IsTrue() &&
+			location.Flags&ast.NodeFlagsAmbient == 0 &&
+			!tspath.IsDeclarationFileName(moduleReference) &&
+			!ast.IsLiteralImportTypeNode(location) &&
+			!ast.IsPartOfTypeOnlyImportOrExportDeclaration(location) {
+			shouldRewrite := c.shouldRewriteModuleSpecifier(moduleReference)
+			if !resolvedModule.ResolvedUsingTsExtension && shouldRewrite {
+				relativeToSourceFile := tspath.GetRelativePathFromDirectory(
+					tspath.GetDirectoryPath(tspath.GetNormalizedAbsolutePath(importingSourceFile.FileName(), c.program.GetCurrentDirectory())),
+					resolvedModule.ResolvedFileName,
+					tspath.ComparePathsOptions{
+						UseCaseSensitiveFileNames: c.program.UseCaseSensitiveFileNames(),
+						CurrentDirectory:          c.program.GetCurrentDirectory(),
+					},
+				)
+				c.error(
+					errorNode,
+					diagnostics.This_relative_import_path_is_unsafe_to_rewrite_because_it_looks_like_a_file_name_but_actually_resolves_to_0,
+					relativeToSourceFile,
+				)
+			} else if resolvedModule.ResolvedUsingTsExtension && !shouldRewrite && c.sourceFileMayBeEmitted(sourceFile) {
+				c.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,
+					tspath.GetAnyExtensionFromPath(moduleReference, nil, false),
+				)
+			}
+			// TODO: Add project reference check when GetResolvedProjectReferenceToRedirect is implemented
 		}
 
 		if sourceFile.Symbol != nil {
@@ -30379,3 +30407,26 @@ func (c *Checker) GetEmitResolver(file *ast.SourceFile, skipDiagnostics bool) *e
 func (c *Checker) GetAliasedSymbol(symbol *ast.Symbol) *ast.Symbol {
 	return c.resolveAlias(symbol)
 }
+
+func (c *Checker) sourceFileMayBeEmitted(sourceFile *ast.SourceFile) bool {
+	options := c.compilerOptions
+	if options.NoEmit.IsTrue() || options.EmitDeclarationOnly.IsTrue() {
+		return false
+	}
+	// Check if this source file is a declaration file
+	if tspath.IsDeclarationFileName(sourceFile.FileName()) {
+		return false
+	}
+	// Check if this is a JS file and allowJs is disabled
+	if tspath.HasJSFileExtension(sourceFile.FileName()) && !options.AllowJs.IsTrue() {
+		return false
+	}
+	return true
+}
+
+func (c *Checker) shouldRewriteModuleSpecifier(specifier string) bool {
+	return c.compilerOptions.RewriteRelativeImportExtensions.IsTrue() && 
+		tspath.PathIsRelative(specifier) && 
+		!tspath.IsDeclarationFileName(specifier) && 
+		tspath.HasTSFileExtension(specifier)
+}

internal/transformers/utilities.go

@@ -336,7 +336,7 @@ func tryRenameExternalModule(factory *printer.NodeFactory, moduleName *ast.Liter
 }
 
 func rewriteModuleSpecifier(emitContext *printer.EmitContext, node *ast.Expression, compilerOptions *core.CompilerOptions) *ast.Expression {
-	if node == nil || !ast.IsStringLiteral(node) || !shouldRewriteModuleSpecifier(node.Text(), compilerOptions) {
+	if node == nil || !ast.IsStringLiteral(node) || !ShouldRewriteModuleSpecifier(node.Text(), compilerOptions) {
 		return node
 	}
 	updatedText := tspath.ChangeExtension(node.Text(), outputpaths.GetOutputExtension(node.Text(), compilerOptions.Jsx))
@@ -350,7 +350,7 @@ func rewriteModuleSpecifier(emitContext *printer.EmitContext, node *ast.Expressi
 	return node
 }
 
-func shouldRewriteModuleSpecifier(specifier string, compilerOptions *core.CompilerOptions) bool {
+func ShouldRewriteModuleSpecifier(specifier string, compilerOptions *core.CompilerOptions) bool {
 	return compilerOptions.RewriteRelativeImportExtensions.IsTrue() && tspath.PathIsRelative(specifier) && !tspath.IsDeclarationFileName(specifier) && tspath.HasTSFileExtension(specifier)
 }
 

internal/tsoptions/declscompiler.go

@@ -810,8 +810,8 @@ var commonOptionsWithBuild = []*CommandLineOption{
 		AffectsSemanticDiagnostics: true,
 		AffectsBuildInfo:           true,
 		Category:                   diagnostics.Modules,
-		// description: diagnostics.Rewrite_ts_tsx_mts_and_cts_file_extensions_in_relative_import_paths_to_their_JavaScript_equivalent_in_output_files,
-		DefaultValueDescription: false,
+		Description:                diagnostics.Rewrite_ts_tsx_mts_and_cts_file_extensions_in_relative_import_paths_to_their_JavaScript_equivalent_in_output_files,
+		DefaultValueDescription:    false,
 	},
 	{
 		Name:                    "resolvePackageJsonExports",