For editing experience, use source instead of .d.ts files from project references

src/compiler/program.ts

@@ -813,6 +813,8 @@ namespace ts {
         let resolvedProjectReferences: ReadonlyArray<ResolvedProjectReference | undefined> | undefined;
         let projectReferenceRedirects: Map<ResolvedProjectReference | false> | undefined;
         let mapFromFileToProjectReferenceRedirects: Map<Path> | undefined;
+        let mapFromToProjectReferenceRedirectSource: Map<SourceOfProjectReferenceRedirect> | undefined;
+        const useSourceOfReference = host.useSourceInsteadOfReferenceRedirect && host.useSourceInsteadOfReferenceRedirect();
 
         const shouldCreateNewSourceFile = shouldProgramCreateNewSourceFiles(oldProgram, options);
         const structuralIsReused = tryReuseStructureFromOldProgram();
@@ -824,17 +826,29 @@ namespace ts {
                 if (!resolvedProjectReferences) {
                     resolvedProjectReferences = projectReferences.map(parseProjectReferenceConfigFile);
                 }
+                if (host.setGetSourceOfProjectReferenceRedirect) {
+                    host.setGetSourceOfProjectReferenceRedirect(getSourceOfProjectReferenceRedirect);
+                }
                 if (rootNames.length) {
                     for (const parsedRef of resolvedProjectReferences) {
                         if (!parsedRef) continue;
                         const out = parsedRef.commandLine.options.outFile || parsedRef.commandLine.options.out;
-                        if (out) {
-                            processSourceFile(changeExtension(out, ".d.ts"), /*isDefaultLib*/ false, /*ignoreNoDefaultLib*/ false, /*packageId*/ undefined);
+                        if (useSourceOfReference) {
+                            if (out || getEmitModuleKind(parsedRef.commandLine.options) === ModuleKind.None) {
+                                for (const fileName of parsedRef.commandLine.fileNames) {
+                                    processSourceFile(fileName, /*isDefaultLib*/ false, /*ignoreNoDefaultLib*/ false, /*packageId*/ undefined);
+                                }
+                            }
                         }
-                        else if (getEmitModuleKind(parsedRef.commandLine.options) === ModuleKind.None) {
-                            for (const fileName of parsedRef.commandLine.fileNames) {
-                                if (!fileExtensionIs(fileName, Extension.Dts) && hasTSFileExtension(fileName)) {
-                                    processSourceFile(getOutputDeclarationFileName(fileName, parsedRef.commandLine, !host.useCaseSensitiveFileNames()), /*isDefaultLib*/ false, /*ignoreNoDefaultLib*/ false, /*packageId*/ undefined);
+                        else {
+                            if (out) {
+                                processSourceFile(changeExtension(out, ".d.ts"), /*isDefaultLib*/ false, /*ignoreNoDefaultLib*/ false, /*packageId*/ undefined);
+                            }
+                            else if (getEmitModuleKind(parsedRef.commandLine.options) === ModuleKind.None) {
+                                for (const fileName of parsedRef.commandLine.fileNames) {
+                                    if (!fileExtensionIs(fileName, Extension.Dts) && hasTSFileExtension(fileName)) {
+                                        processSourceFile(getOutputDeclarationFileName(fileName, parsedRef.commandLine, !host.useCaseSensitiveFileNames()), /*isDefaultLib*/ false, /*ignoreNoDefaultLib*/ false, /*packageId*/ undefined);
+                                    }
                                 }
                             }
                         }
@@ -1212,6 +1226,9 @@ namespace ts {
             }
             if (projectReferences) {
                 resolvedProjectReferences = projectReferences.map(parseProjectReferenceConfigFile);
+                if (host.setGetSourceOfProjectReferenceRedirect) {
+                    host.setGetSourceOfProjectReferenceRedirect(getSourceOfProjectReferenceRedirect);
+                }
             }
 
             // check if program source files has changed in the way that can affect structure of the program
@@ -2220,6 +2237,14 @@ namespace ts {
 
         // Get source file from normalized fileName
         function findSourceFile(fileName: string, path: Path, isDefaultLib: boolean, ignoreNoDefaultLib: boolean, refFile: SourceFile, refPos: number, refEnd: number, packageId: PackageId | undefined): SourceFile | undefined {
+            if (useSourceOfReference) {
+                const source = getSourceOfProjectReferenceRedirect(fileName);
+                if (source) {
+                    return isString(source) ?
+                        findSourceFile(source, toPath(source), isDefaultLib, ignoreNoDefaultLib, refFile, refPos, refEnd, packageId) :
+                        undefined;
+                }
+            }
             const originalFileName = fileName;
             if (filesByName.has(path)) {
                 const file = filesByName.get(path);
@@ -2267,7 +2292,7 @@ namespace ts {
             }
 
             let redirectedPath: Path | undefined;
-            if (refFile) {
+            if (refFile && !useSourceOfReference) {
                 const redirectProject = getProjectReferenceRedirectProject(fileName);
                 if (redirectProject) {
                     if (redirectProject.commandLine.options.outFile || redirectProject.commandLine.options.out) {
@@ -2286,15 +2311,20 @@ namespace ts {
             }
 
             // We haven't looked for this file, do so now and cache result
-            const file = host.getSourceFile(fileName, options.target!, hostErrorMessage => { // TODO: GH#18217
-                if (refFile !== undefined && refPos !== undefined && refEnd !== undefined) {
-                    fileProcessingDiagnostics.add(createFileDiagnostic(refFile, refPos, refEnd - refPos,
-                        Diagnostics.Cannot_read_file_0_Colon_1, fileName, hostErrorMessage));
-                }
-                else {
-                    fileProcessingDiagnostics.add(createCompilerDiagnostic(Diagnostics.Cannot_read_file_0_Colon_1, fileName, hostErrorMessage));
-                }
-            }, shouldCreateNewSourceFile);
+            const file = host.getSourceFile(
+                fileName,
+                options.target!,
+                hostErrorMessage => { // TODO: GH#18217
+                    if (refFile !== undefined && refPos !== undefined && refEnd !== undefined) {
+                        fileProcessingDiagnostics.add(createFileDiagnostic(refFile, refPos, refEnd - refPos,
+                            Diagnostics.Cannot_read_file_0_Colon_1, fileName, hostErrorMessage));
+                    }
+                    else {
+                        fileProcessingDiagnostics.add(createCompilerDiagnostic(Diagnostics.Cannot_read_file_0_Colon_1, fileName, hostErrorMessage));
+                    }
+                },
+                shouldCreateNewSourceFile
+            );
 
             if (packageId) {
                 const packageIdKey = packageIdToString(packageId);
@@ -2424,6 +2454,30 @@ namespace ts {
             });
         }
 
+        function getSourceOfProjectReferenceRedirect(file: string) {
+            if (!isDeclarationFileName(file)) return undefined;
+            if (mapFromToProjectReferenceRedirectSource === undefined) {
+                mapFromToProjectReferenceRedirectSource = createMap();
+                forEachResolvedProjectReference(resolvedRef => {
+                    if (resolvedRef) {
+                        const out = resolvedRef.commandLine.options.outFile || resolvedRef.commandLine.options.out;
+                        if (out) {
+                            // Dont know which source file it means so return true?
+                            const outputDts = changeExtension(out, Extension.Dts);
+                            mapFromToProjectReferenceRedirectSource!.set(toPath(outputDts), true);
+                        }
+                        else {
+                            forEach(resolvedRef.commandLine.fileNames, fileName => {
+                                const outputDts = getOutputDeclarationFileName(fileName, resolvedRef.commandLine, host.useCaseSensitiveFileNames());
+                                mapFromToProjectReferenceRedirectSource!.set(toPath(outputDts), fileName);
+                            });
+                        }
+                    }
+                });
+            }
+            return mapFromToProjectReferenceRedirectSource.get(toPath(file));
+        }
+
         function forEachProjectReference<T>(
             projectReferences: ReadonlyArray<ProjectReference> | undefined,
             resolvedProjectReferences: ReadonlyArray<ResolvedProjectReference | undefined> | undefined,

src/compiler/types.ts

@@ -5166,11 +5166,20 @@ namespace ts {
         /* @internal */ hasChangedAutomaticTypeDirectiveNames?: boolean;
         createHash?(data: string): string;
         getParsedCommandLine?(fileName: string): ParsedCommandLine | undefined;
+        /* @internal */ setGetSourceOfProjectReferenceRedirect?(getSource: GetSourceOfProjectReferenceRedirect): void;
+        /* @internal */ useSourceInsteadOfReferenceRedirect?(): boolean;
 
         // TODO: later handle this in better way in builder host instead once the api for tsbuild finalizes and doesn't use compilerHost as base
         /*@internal*/createDirectory?(directory: string): void;
     }
 
+    /** true if --out otherwise source file name */
+    /*@internal*/
+    export type SourceOfProjectReferenceRedirect = string | true ;
+
+    /*@internal*/
+    export type GetSourceOfProjectReferenceRedirect = (fileName: string) => SourceOfProjectReferenceRedirect | undefined;
+
     /* @internal */
     export const enum TransformFlags {
         None = 0,

src/server/editorServices.ts

@@ -1798,7 +1798,7 @@ namespace ts.server {
                 let scriptInfo: ScriptInfo | NormalizedPath;
                 let path: Path;
                 // Use the project's fileExists so that it can use caching instead of reaching to disk for the query
-                if (!isDynamic && !project.fileExists(newRootFile)) {
+                if (!isDynamic && !project.fileExistsWithCache(newRootFile)) {
                     path = normalizedPathToPath(normalizedPath, this.currentDirectory, this.toCanonicalFileName);
                     const existingValue = projectRootFilesMap.get(path)!;
                     if (isScriptInfo(existingValue)) {
@@ -1831,7 +1831,7 @@ namespace ts.server {
                 projectRootFilesMap.forEach((value, path) => {
                     if (!newRootScriptInfoMap.has(path)) {
                         if (isScriptInfo(value)) {
-                            project.removeFile(value, project.fileExists(path), /*detachFromProject*/ true);
+                            project.removeFile(value, project.fileExistsWithCache(path), /*detachFromProject*/ true);
                         }
                         else {
                             projectRootFilesMap.delete(path);

src/server/project.ts

@@ -381,6 +381,11 @@ namespace ts.server {
         }
 
         fileExists(file: string): boolean {
+            return this.fileExistsWithCache(file);
+        }
+
+        /* @internal */
+        fileExistsWithCache(file: string): boolean {
             // As an optimization, don't hit the disks for files we already know don't exist
             // (because we're watching for their creation).
             const path = this.toPath(file);
@@ -1369,6 +1374,7 @@ namespace ts.server {
         configFileWatcher: FileWatcher | undefined;
         private directoriesWatchedForWildcards: Map<WildcardDirectoryWatcher> | undefined;
         readonly canonicalConfigFilePath: NormalizedPath;
+        private getSourceOfProjectReferenceRedirect: GetSourceOfProjectReferenceRedirect | undefined;
 
         /* @internal */
         pendingReload: ConfigFileProgramReloadLevel | undefined;
@@ -1414,6 +1420,25 @@ namespace ts.server {
             this.canonicalConfigFilePath = asNormalizedPath(projectService.toCanonicalFileName(configFileName));
         }
 
+        /* @internal */
+        setGetSourceOfProjectReferenceRedirect(getSource: GetSourceOfProjectReferenceRedirect) {
+            this.getSourceOfProjectReferenceRedirect = getSource;
+        }
+
+        /* @internal */
+        useSourceInsteadOfReferenceRedirect() {
+            return true;
+        }
+
+        fileExists(file: string): boolean {
+            // Project references go to source file instead of .d.ts file
+            if (this.getSourceOfProjectReferenceRedirect) {
+                const source = this.getSourceOfProjectReferenceRedirect(file);
+                if (source) return isString(source) ? super.fileExists(source) : true;
+            }
+            return super.fileExists(file);
+        }
+
         /**
          * If the project has reload from disk pending, it reloads (and then updates graph as part of that) instead of just updating the graph
          * @returns: true if set of files in the project stays the same and false - otherwise.
@@ -1436,6 +1461,7 @@ namespace ts.server {
                 default:
                     result = super.updateGraph();
             }
+            this.getSourceOfProjectReferenceRedirect = undefined;
             this.projectService.sendProjectLoadingFinishEvent(this);
             this.projectService.sendProjectTelemetry(this);
             return result;

src/services/services.ts

@@ -1245,6 +1245,12 @@ namespace ts {
                     return host.resolveTypeReferenceDirectives!(typeReferenceDirectiveNames, containingFile, redirectedReference);
                 };
             }
+            if (host.setGetSourceOfProjectReferenceRedirect) {
+                compilerHost.setGetSourceOfProjectReferenceRedirect = getSource => host.setGetSourceOfProjectReferenceRedirect!(getSource);
+            }
+            if (host.useSourceInsteadOfReferenceRedirect) {
+                compilerHost.useSourceInsteadOfReferenceRedirect = () => host.useSourceInsteadOfReferenceRedirect!();
+            }
 
             const documentRegistryBucketKey = documentRegistry.getKeyForCompilationSettings(newSettings);
             const options: CreateProgramOptions = {

src/services/types.ts

@@ -236,6 +236,10 @@ namespace ts {
         getDocumentPositionMapper?(generatedFileName: string, sourceFileName?: string): DocumentPositionMapper | undefined;
         /* @internal */
         getSourceFileLike?(fileName: string): SourceFileLike | undefined;
+        /* @internal */
+        setGetSourceOfProjectReferenceRedirect?(getSource: GetSourceOfProjectReferenceRedirect): void;
+        /* @internal */
+        useSourceInsteadOfReferenceRedirect?(): boolean;
     }
 
     /* @internal */