Perform only emit on js file if no decl file change

src/compiler/diagnosticMessages.json

@@ -3992,14 +3992,26 @@
         "category": "Message",
         "code": 6371
     },
-    "Project '{0}' is out of date because output to prepend from its dependency '{1}' has changed": {
+    "Project '{0}' is out of date because output javascript and source map (if specified) of its dependency '{1}' has changed": {
         "category": "Message",
         "code": 6372
     },
-    "Updating output of project '{0}'...": {
+    "Updating output javascript and javascript source map (if specified) of project '{0}'...": {
         "category": "Message",
         "code": 6373
     },
+    "A non-dry build would update timestamps for output of project '{0}'": {
+        "category": "Message",
+        "code": 6374
+    },
+    "A non-dry build would update output javascript and javascript source map (if specified) of project '{0}'": {
+        "category": "Message",
+        "code": 6375
+    },
+    "Cannot update output javascript and javascript source map (if specified) of project '{0}' because there was error reading file '{1}'": {
+        "category": "Message",
+        "code": 6376
+    },
 
     "The expected type comes from property '{0}' which is declared here on type '{1}'": {
         "category": "Message",

src/compiler/emitter.ts

@@ -21,8 +21,9 @@ namespace ts {
         const sourceFiles = isArray(sourceFilesOrTargetSourceFile) ? sourceFilesOrTargetSourceFile : getSourceFilesToEmit(host, sourceFilesOrTargetSourceFile);
         const options = host.getCompilerOptions();
         if (options.outFile || options.out) {
-            if (sourceFiles.length) {
-                const bundle = createBundle(sourceFiles, host.getPrependNodes());
+            const prepends = host.getPrependNodes();
+            if (sourceFiles.length || prepends.length) {
+                const bundle = createBundle(sourceFiles, prepends);
                 const result = action(getOutputPathsFor(bundle, host, emitOnlyDtsFiles), bundle);
                 if (result) {
                     return result;
@@ -104,7 +105,7 @@ namespace ts {
 
     /*@internal*/
     // targetSourceFile is when users only want one file in entire project to be emitted. This is used in compileOnSave feature
-    export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile: SourceFile, emitOnlyDtsFiles?: boolean, transformers?: TransformerFactory<Bundle | SourceFile>[], declarationTransformers?: TransformerFactory<Bundle | SourceFile>[]): EmitResult {
+    export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile: SourceFile | undefined, emitOnlyDtsFiles?: boolean, transformers?: TransformerFactory<Bundle | SourceFile>[], declarationTransformers?: TransformerFactory<Bundle | SourceFile>[]): EmitResult {
         const compilerOptions = host.getCompilerOptions();
         const sourceMapDataList: SourceMapEmitResult[] | undefined = (compilerOptions.sourceMap || compilerOptions.inlineSourceMap || getAreDeclarationMapsEnabled(compilerOptions)) ? [] : undefined;
         const emittedFilesList: string[] | undefined = compilerOptions.listEmittedFiles ? [] : undefined;
@@ -136,7 +137,7 @@ namespace ts {
             emitDeclarationFileOrBundle(sourceFileOrBundle, declarationFilePath, declarationMapPath, buildInfo && { sections: buildInfo.dts, sources: buildInfo.sources });
             // Write bundled offset information if applicable
             if (!emitOnlyDtsFiles && !emitSkipped && buildInfoPath) {
-                writeFile(host, emitterDiagnostics, buildInfoPath, JSON.stringify(buildInfo, undefined, 2), /*writeByteOrderMark*/ false);
+                writeFile(host, emitterDiagnostics, buildInfoPath, getBuildInfoText(buildInfo!), /*writeByteOrderMark*/ false);
             }
 
             if (!emitSkipped && emittedFilesList) {
@@ -409,6 +410,131 @@ namespace ts {
         }
     }
 
+    function getBuildInfoText(buildInfo: BuildInfo) {
+        return JSON.stringify(buildInfo, undefined, 2);
+    }
+
+    const notImplementedResolver: EmitResolver = {
+        hasGlobalName: notImplemented,
+        getReferencedExportContainer: notImplemented,
+        getReferencedImportDeclaration: notImplemented,
+        getReferencedDeclarationWithCollidingName: notImplemented,
+        isDeclarationWithCollidingName: notImplemented,
+        isValueAliasDeclaration: notImplemented,
+        isReferencedAliasDeclaration: notImplemented,
+        isTopLevelValueImportEqualsWithEntityName: notImplemented,
+        getNodeCheckFlags: notImplemented,
+        isDeclarationVisible: notImplemented,
+        isLateBound: (_node): _node is LateBoundDeclaration => false,
+        collectLinkedAliases: notImplemented,
+        isImplementationOfOverload: notImplemented,
+        isRequiredInitializedParameter: notImplemented,
+        isOptionalUninitializedParameterProperty: notImplemented,
+        isExpandoFunctionDeclaration: notImplemented,
+        getPropertiesOfContainerFunction: notImplemented,
+        createTypeOfDeclaration: notImplemented,
+        createReturnTypeOfSignatureDeclaration: notImplemented,
+        createTypeOfExpression: notImplemented,
+        createLiteralConstValue: notImplemented,
+        isSymbolAccessible: notImplemented,
+        isEntityNameVisible: notImplemented,
+        // Returns the constant value this property access resolves to: notImplemented, or 'undefined' for a non-constant
+        getConstantValue: notImplemented,
+        getReferencedValueDeclaration: notImplemented,
+        getTypeReferenceSerializationKind: notImplemented,
+        isOptionalParameter: notImplemented,
+        moduleExportsSomeValue: notImplemented,
+        isArgumentsLocalBinding: notImplemented,
+        getExternalModuleFileFromDeclaration: notImplemented,
+        getTypeReferenceDirectivesForEntityName: notImplemented,
+        getTypeReferenceDirectivesForSymbol: notImplemented,
+        isLiteralConstDeclaration: notImplemented,
+        getJsxFactoryEntity: notImplemented,
+        getAllAccessorDeclarations: notImplemented,
+        getSymbolOfExternalModuleSpecifier: notImplemented,
+        isBindingCapturedByNode: notImplemented,
+    };
+
+    /*@internal*/
+    /** File that isnt present resulting in error or output files */
+    export type EmitUsingBuildInfoResult = string | ReadonlyArray<OutputFile>;
+
+    /*@internal*/
+    export interface EmitUsingBuildInfoHost extends ModuleResolutionHost {
+        getCurrentDirectory(): string;
+        getCanonicalFileName(fileName: string): string;
+        useCaseSensitiveFileNames(): boolean;
+        getNewLine(): string;
+    }
+
+    /*@internal*/
+    export function emitUsingBuildInfo(config: ParsedCommandLine, host: EmitUsingBuildInfoHost, getCommandLine: (ref: ProjectReference) => ParsedCommandLine | undefined): EmitUsingBuildInfoResult {
+        const { buildInfoPath, jsFilePath, sourceMapFilePath } = getOutputPathsForBundle(config.options, /*forceDtsPaths*/ false, config.projectReferences);
+        const buildInfoText = host.readFile(Debug.assertDefined(buildInfoPath));
+        if (!buildInfoText) return buildInfoPath!;
+        const jsFileText = host.readFile(Debug.assertDefined(jsFilePath));
+        if (!jsFileText) return jsFilePath!;
+        const sourceMapText = sourceMapFilePath && host.readFile(sourceMapFilePath);
+        // error if no source map or for now if inline sourcemap
+        if ((sourceMapFilePath && !sourceMapText) || config.options.inlineSourceMap) return sourceMapFilePath || "inline sourcemap decoding";
+
+        const buildInfo = JSON.parse(buildInfoText) as BuildInfo;
+        const ownPrependInput = createInputFiles(
+            jsFileText,
+            /*declarationText*/ undefined!,
+            sourceMapFilePath,
+            sourceMapText,
+            /*declarationMapPath*/ undefined!,
+            /*declarationMaptext*/ undefined!,
+            jsFilePath,
+            /*declarationPath*/ undefined,
+            buildInfoPath,
+            buildInfo,
+            /*onlyOwnText*/ true
+        );
+        const optionsWithoutDeclaration = clone(config.options);
+        optionsWithoutDeclaration.declaration = false;
+        optionsWithoutDeclaration.composite = false;
+        const outputFiles: OutputFile[] = [];
+        const emitHost: EmitHost = {
+            getPrependNodes: () => createPrependNodes(config.projectReferences, getCommandLine, f => host.readFile(f)). concat(ownPrependInput),
+            getProjectReferences: () => config.projectReferences,
+            getCanonicalFileName: host.getCanonicalFileName,
+            getCommonSourceDirectory: () => buildInfo.commonSourceDirectory,
+            getCompilerOptions: () => optionsWithoutDeclaration,
+            getCurrentDirectory: () => host.getCurrentDirectory(),
+            getNewLine: () => host.getNewLine(),
+            getSourceFile: notImplemented,
+            getSourceFileByPath: notImplemented,
+            getSourceFiles: () => emptyArray,
+            getLibFileFromReference: notImplemented,
+            isSourceFileFromExternalLibrary: notImplemented,
+            writeFile: (name, text, writeByteOrderMark) => {
+                if (name === buildInfoPath) {
+                    // Add dts and sources build info since we are not touching that file
+                    const newBuildInfo = JSON.parse(text) as BuildInfo;
+                    newBuildInfo.dts = buildInfo.dts;
+                    newBuildInfo.sources = buildInfo.sources;
+                    text = getBuildInfoText(newBuildInfo);
+                }
+                outputFiles.push({ name, text, writeByteOrderMark });
+            },
+            isEmitBlocked: returnFalse,
+            readFile: f => host.readFile(f),
+            fileExists: f => host.fileExists(f),
+            ...(host.directoryExists ? { directoryExists: f => host.directoryExists!(f) } : {}),
+            useCaseSensitiveFileNames: () => host.useCaseSensitiveFileNames(),
+        };
+        emitFiles(
+            notImplementedResolver,
+            emitHost,
+            /*targetSourceFile*/ undefined,
+            /*emitOnlyDtsFiles*/ false,
+            getTransformers(optionsWithoutDeclaration)
+        );
+        return outputFiles;
+    }
+
     const enum PipelinePhase {
         Notification,
         Substitution,
@@ -562,14 +688,17 @@ namespace ts {
                 writeLine();
                 const pos = getTextPosWithWriteLine();
                 print(EmitHint.Unspecified, prepend, /*sourceFile*/ undefined);
-                if (bundleFileInfo) bundleFileInfo.sections.push({ pos, end: writer.getTextPos(), kind: BundleFileSectionKind.Prepend, data: (prepend as UnparsedSource).fileName });
+                if (bundleFileInfo) {
+                    if (prepend.oldFileOfCurrentEmit) bundleFileInfo.sections.push({ pos, end: writer.getTextPos(), kind: BundleFileSectionKind.Text });
+                    else bundleFileInfo.sections.push({ pos, end: writer.getTextPos(), kind: BundleFileSectionKind.Prepend, data: (prepend as UnparsedSource).fileName });
+                }
             }
 
             const pos = getTextPosWithWriteLine();
             for (const sourceFile of bundle.sourceFiles) {
                 print(EmitHint.SourceFile, sourceFile, sourceFile);
             }
-            if (bundleFileInfo) {
+            if (bundleFileInfo && bundle.sourceFiles.length) {
                 bundleFileInfo.sections.push({ pos, end: writer.getTextPos(), kind: BundleFileSectionKind.Text });
                 // Store prologues
                 const prologues = getPrologueDirectivesFromBundledSourceFiles(bundle);

src/compiler/factory.ts

@@ -2666,6 +2666,7 @@ namespace ts {
         let texts: UnparsedSourceText[] | undefined;
         if (!isString(textOrInputFiles)) {
             Debug.assert(mapPathOrType === "js" || mapPathOrType === "dts");
+            node.oldFileOfCurrentEmit = textOrInputFiles.oldFileOfCurrentEmit;
             node.fileName = (mapPathOrType === "js" ? textOrInputFiles.javascriptPath : textOrInputFiles.declarationPath) || "";
             node.sourceMapPath = mapPathOrType === "js" ? textOrInputFiles.javascriptMapPath : textOrInputFiles.declarationMapPath;
             Object.defineProperties(node, {
@@ -2676,6 +2677,7 @@ namespace ts {
             if (textOrInputFiles.buildInfo) {
                 const sections = mapPathOrType === "js" ? textOrInputFiles.buildInfo.js : textOrInputFiles.buildInfo.dts;
                 for (const section of sections) {
+                    if (textOrInputFiles.oldFileOfCurrentEmit && section.kind !== BundleFileSectionKind.Text) continue;
                     switch (section.kind) {
                         case BundleFileSectionKind.Prologue:
                             (prologues || (prologues = [])).push(createUnparsedNode(section, node) as UnparsedPrologue);
@@ -2766,7 +2768,12 @@ namespace ts {
         javascriptMapPath: string | undefined,
         javascriptMapText: string | undefined,
         declarationMapPath: string | undefined,
-        declarationMapText: string | undefined
+        declarationMapText: string | undefined,
+        javascriptPath: string | undefined,
+        declarationPath: string | undefined,
+        buildInfoPath?: string | undefined,
+        buildInfo?: BuildInfo,
+        oldFileOfCurrentEmit?: boolean
     ): InputFiles;
     export function createInputFiles(
         javascriptTextOrReadFileText: string | ((path: string) => string | undefined),
@@ -2774,17 +2781,14 @@ namespace ts {
         javascriptMapPath?: string,
         javascriptMapTextOrDeclarationPath?: string,
         declarationMapPath?: string,
-        declarationMapTextOrBuildInfoPath?: string
+        declarationMapTextOrBuildInfoPath?: string,
+        javascriptPath?: string | undefined,
+        declarationPath?: string | undefined,
+        buildInfoPath?: string | undefined,
+        buildInfo?: BuildInfo,
+        oldFileOfCurrentEmit?: boolean
     ): InputFiles {
         const node = <InputFiles>createNode(SyntaxKind.InputFiles);
-        let buildInfo: BuildInfo | false;
-        const getBuildInfo = (getText: () => string | undefined) => {
-            if (buildInfo === undefined) {
-                const result = getText();
-                buildInfo = result !== undefined ? JSON.parse(result) as BuildInfo : false;
-            }
-            return buildInfo || undefined;
-        };
         if (!isString(javascriptTextOrReadFileText)) {
             const cache = createMap<string | false>();
             const textGetter = (path: string | undefined) => {
@@ -2800,6 +2804,14 @@ namespace ts {
                 const result = textGetter(path);
                 return result !== undefined ? result : `/* Input file ${path} was missing */\r\n`;
             };
+            let buildInfo: BuildInfo | false;
+            const getBuildInfo = (getText: () => string | undefined) => {
+                if (buildInfo === undefined) {
+                    const result = getText();
+                    buildInfo = result !== undefined ? JSON.parse(result) as BuildInfo : false;
+                }
+                return buildInfo || undefined;
+            };
             node.javascriptPath = declarationTextOrJavascriptPath;
             node.javascriptMapPath = javascriptMapPath;
             node.declarationPath = Debug.assertDefined(javascriptMapTextOrDeclarationPath);
@@ -2820,6 +2832,11 @@ namespace ts {
             node.declarationText = declarationTextOrJavascriptPath;
             node.declarationMapPath = declarationMapPath;
             node.declarationMapText = declarationMapTextOrBuildInfoPath;
+            node.javascriptPath = javascriptPath;
+            node.declarationPath = declarationPath,
+            node.buildInfoPath = buildInfoPath;
+            node.buildInfo = buildInfo;
+            node.oldFileOfCurrentEmit = oldFileOfCurrentEmit;
         }
         return node;
     }

src/compiler/program.ts

@@ -1443,30 +1443,16 @@ namespace ts {
             return projectReferences;
         }
 
-        function getPrependNodes(): InputFiles[] {
-            if (!projectReferences) {
-                return emptyArray;
-            }
-
-            const nodes: InputFiles[] = [];
-            for (let i = 0; i < projectReferences.length; i++) {
-                const ref = projectReferences[i];
-                const resolvedRefOpts = resolvedProjectReferences![i]!.commandLine;
-                if (ref.prepend && resolvedRefOpts && resolvedRefOpts.options) {
-                    const out = resolvedRefOpts.options.outFile || resolvedRefOpts.options.out;
-                    // Upstream project didn't have outFile set -- skip (error will have been issued earlier)
-                    if (!out) continue;
-
-                    const { jsFilePath, sourceMapFilePath, declarationFilePath, declarationMapPath, buildInfoPath } = getOutputPathsForBundle(resolvedRefOpts.options, /*forceDtsPaths*/ true, resolvedRefOpts.projectReferences);
-                    const node = createInputFiles(fileName => {
-                        const path = toPath(fileName);
-                        const sourceFile = getSourceFileByPath(path);
-                        return sourceFile ? sourceFile.text : filesByName.has(path) ? undefined : host.readFile(path);
-                    }, jsFilePath! , sourceMapFilePath, declarationFilePath! , declarationMapPath, buildInfoPath);
-                    nodes.push(node);
+        function getPrependNodes() {
+            return createPrependNodes(
+                projectReferences,
+                (_ref, index) => resolvedProjectReferences![index]!.commandLine,
+                fileName => {
+                    const path = toPath(fileName);
+                    const sourceFile = getSourceFileByPath(path);
+                    return sourceFile ? sourceFile.text : filesByName.has(path) ? undefined : host.readFile(path);
                 }
-            }
-            return nodes;
+            );
         }
 
         function isSourceFileFromExternalLibrary(file: SourceFile): boolean {
@@ -1563,7 +1549,7 @@ namespace ts {
             const emitResult = emitFiles(
                 emitResolver,
                 getEmitHost(writeFileCallback),
-                sourceFile!, // TODO: GH#18217
+                sourceFile,
                 emitOnlyDtsFiles,
                 transformers,
                 customTransformers && customTransformers.afterDeclarations
@@ -3141,6 +3127,25 @@ namespace ts {
         fileExists(fileName: string): boolean;
     }
 
+    /* @internal */
+    export function createPrependNodes(projectReferences: ReadonlyArray<ProjectReference> | undefined, getCommandLine: (ref: ProjectReference, index: number) => ParsedCommandLine | undefined, readFile: (path: string) => string | undefined) {
+        if (!projectReferences) return emptyArray;
+        let nodes: InputFiles[] | undefined;
+        for (let i = 0; i < projectReferences.length; i++) {
+            const ref = projectReferences[i];
+            const resolvedRefOpts = getCommandLine(ref, i);
+            if (ref.prepend && resolvedRefOpts && resolvedRefOpts.options) {
+                const out = resolvedRefOpts.options.outFile || resolvedRefOpts.options.out;
+                // Upstream project didn't have outFile set -- skip (error will have been issued earlier)
+                if (!out) continue;
+
+                const { jsFilePath, sourceMapFilePath, declarationFilePath, declarationMapPath, buildInfoPath } = getOutputPathsForBundle(resolvedRefOpts.options, /*forceDtsPaths*/ true, resolvedRefOpts.projectReferences);
+                const node = createInputFiles(readFile, jsFilePath!, sourceMapFilePath, declarationFilePath!, declarationMapPath, buildInfoPath);
+                (nodes || (nodes = [])).push(node);
+            }
+        }
+        return nodes || emptyArray;
+    }
     /**
      * Returns the target config filename of a project reference.
      * Note: The file might not exist.

src/compiler/tsbuild.ts

@@ -1007,13 +1007,9 @@ namespace ts {
                 return;
             }
 
-            //if (status.type === UpToDateStatusType.OutOfDateWithPrepend) {
-            //    // Fake that files have been built by manipulating prepend and existing output
-            //    //updateOutputTimestamps(proj);
-            //    return;
-            //}
-
-            const buildResult = buildSingleProject(resolved);
+            const buildResult = status.type === UpToDateStatusType.OutOfDateWithPrepend ?
+                updateBundle(resolved) : // Fake that files have been built by manipulating prepend and existing output
+                buildSingleProject(resolved); // Actual build
             if (buildResult & BuildResultFlags.AnyErrors) return;
 
             const { referencingProjectsMap, buildQueue } = getGlobalDependencyGraph();
@@ -1109,8 +1105,7 @@ namespace ts {
 
             if (options.verbose) reportStatus(Diagnostics.Building_project_0, proj);
 
-            let resultFlags = BuildResultFlags.None;
-            resultFlags |= BuildResultFlags.DeclarationOutputUnchanged;
+            let resultFlags = BuildResultFlags.DeclarationOutputUnchanged;
 
             const configFile = parseConfigFile(proj);
             if (!configFile) {
@@ -1136,7 +1131,6 @@ namespace ts {
                 configFile.errors,
                 configFile.projectReferences
             );
-            projectCompilerOptions = baseCompilerOptions;
 
             // Don't emit anything in the presence of syntactic errors or options diagnostics
             const syntaxDiagnostics = [
@@ -1208,6 +1202,7 @@ namespace ts {
             diagnostics.removeKey(proj);
             projectStatus.setValue(proj, status);
             afterProgramCreate(proj, program);
+            projectCompilerOptions = baseCompilerOptions;
             return resultFlags;
 
             function buildErrors(diagnostics: ReadonlyArray<Diagnostic>, errorFlags: BuildResultFlags, errorType: string) {
@@ -1215,6 +1210,7 @@ namespace ts {
                 reportAndStoreErrors(proj, diagnostics);
                 projectStatus.setValue(proj, { type: UpToDateStatusType.Unbuildable, reason: `${errorType} errors` });
                 afterProgramCreate(proj, program);
+                projectCompilerOptions = baseCompilerOptions;
                 return resultFlags;
             }
         }
@@ -1229,9 +1225,60 @@ namespace ts {
             }
         }
 
+        function updateBundle(proj: ResolvedConfigFileName): BuildResultFlags {
+            if (options.dry) {
+                reportStatus(Diagnostics.A_non_dry_build_would_update_output_javascript_and_javascript_source_map_if_specified_of_project_0, proj);
+                return BuildResultFlags.Success;
+            }
+
+            if (options.verbose) reportStatus(Diagnostics.Updating_output_javascript_and_javascript_source_map_if_specified_of_project_0, proj);
+
+            // Update js, and source map
+            const config = Debug.assertDefined(parseConfigFile(proj));
+            projectCompilerOptions = config.options;
+            const outputFiles = emitUsingBuildInfo(
+                config,
+                compilerHost,
+                ref => parseConfigFile(resolveProjectName(ref.path)));
+            if (isString(outputFiles)) {
+                reportStatus(Diagnostics.Cannot_update_output_javascript_and_javascript_source_map_if_specified_of_project_0_because_there_was_error_reading_file_1, proj, relName(outputFiles));
+                return buildSingleProject(proj);
+            }
+
+            // Actual Emit
+            Debug.assert(!!outputFiles.length);
+            const emitterDiagnostics = createDiagnosticCollection();
+            const emittedOutputs = createFileMap<true>(toPath as ToPath);
+            outputFiles.forEach(({ name, text, writeByteOrderMark }) => {
+                emittedOutputs.setValue(name, true);
+                writeFile(compilerHost, emitterDiagnostics, name, text, writeByteOrderMark);
+            });
+            const emitDiagnostics = emitterDiagnostics.getDiagnostics();
+            if (emitDiagnostics.length) {
+                reportAndStoreErrors(proj, emitDiagnostics);
+                projectStatus.setValue(proj, { type: UpToDateStatusType.Unbuildable, reason: "Emit errors" });
+                projectCompilerOptions = baseCompilerOptions;
+                return BuildResultFlags.DeclarationOutputUnchanged | BuildResultFlags.EmitErrors;
+            }
+
+            // Update timestamps for dts
+            const newestDeclarationFileContentChangedTime = updateOutputTimestampsWorker(config, minimumDate, Diagnostics.Updating_unchanged_output_timestamps_of_project_0, emittedOutputs);
+
+            const status: UpToDateStatus = {
+                type: UpToDateStatusType.UpToDate,
+                newestDeclarationFileContentChangedTime,
+                oldestOutputFileName: outputFiles[0].name
+            };
+
+            diagnostics.removeKey(proj);
+            projectStatus.setValue(proj, status);
+            projectCompilerOptions = baseCompilerOptions;
+            return BuildResultFlags.DeclarationOutputUnchanged;
+        }
+
         function updateOutputTimestamps(proj: ParsedCommandLine) {
             if (options.dry) {
-                return reportStatus(Diagnostics.A_non_dry_build_would_build_project_0, proj.options.configFilePath!);
+                return reportStatus(Diagnostics.A_non_dry_build_would_update_timestamps_for_output_of_project_0, proj.options.configFilePath!);
             }
             const priorNewestUpdateTime = updateOutputTimestampsWorker(proj, minimumDate, Diagnostics.Updating_output_timestamps_of_project_0);
             projectStatus.setValue(proj.options.configFilePath as ResolvedConfigFilePath, { type: UpToDateStatusType.UpToDate, newestDeclarationFileContentChangedTime: priorNewestUpdateTime } as UpToDateStatus);
@@ -1354,13 +1401,6 @@ namespace ts {
                     continue;
                 }
 
-                //if (status.type === UpToDateStatusType.OutOfDateWithPrepend && !options.force) {
-                //    reportAndStoreErrors(next, errors);
-                //    // Fake that files have been built by manipulating prepend and existing output
-                //    // updateOutputTimestamps(proj);
-                //    continue;
-                //}
-
                 if (status.type === UpToDateStatusType.UpstreamBlocked) {
                     reportAndStoreErrors(next, errors);
                     if (options.verbose) reportStatus(Diagnostics.Skipping_build_of_project_0_because_its_dependency_1_has_errors, projName, status.upstreamProjectName);
@@ -1373,7 +1413,9 @@ namespace ts {
                     continue;
                 }
 
-                const buildResult = buildSingleProject(next);
+                const buildResult = status.type === UpToDateStatusType.OutOfDateWithPrepend && !options.force ?
+                    updateBundle(next) : // Fake that files have been built by manipulating prepend and existing output
+                    buildSingleProject(next); // Actual build
                 anyFailed = anyFailed || !!(buildResult & BuildResultFlags.AnyErrors);
             }
             reportErrorSummary();
@@ -1484,7 +1526,7 @@ namespace ts {
                 // Don't report anything for "up to date because it was already built" -- too verbose
                 break;
             case UpToDateStatusType.OutOfDateWithPrepend:
-                return formatMessage(Diagnostics.Project_0_is_out_of_date_because_output_to_prepend_from_its_dependency_1_has_changed,
+                return formatMessage(Diagnostics.Project_0_is_out_of_date_because_output_javascript_and_source_map_if_specified_of_its_dependency_1_has_changed,
                     relName(configFileName),
                     relName(status.newerProjectName));
             case UpToDateStatusType.UpToDateWithUpstreamTypes:

src/compiler/types.ts

@@ -2775,8 +2775,9 @@ namespace ts {
         declarationText: string;
         declarationMapPath?: string;
         declarationMapText?: string;
-        buildInfoPath?: string;
+        /*@internal*/ buildInfoPath?: string;
         /*@internal*/ buildInfo?: BuildInfo;
+        /*@internal*/ oldFileOfCurrentEmit?: boolean;
     }
 
     export interface UnparsedSource extends Node {
@@ -2785,13 +2786,17 @@ namespace ts {
         text: string;
         prologues: ReadonlyArray<UnparsedPrologue>;
         helpers: ReadonlyArray<UnscopedEmitHelpers> | undefined;
+
+        // References and noDefaultLibAre Dts only
         referencedFiles: ReadonlyArray<FileReference>;
         typeReferenceDirectives: ReadonlyArray<string> | undefined;
         libReferenceDirectives: ReadonlyArray<FileReference>;
         hasNoDefaultLib?: boolean;
+
         sourceMapPath?: string;
         sourceMapText?: string;
         texts: ReadonlyArray<UnparsedSourceText>;
+        /*@internal*/ oldFileOfCurrentEmit?: boolean;
         /*@internal*/ parsedSourceMap?: RawSourceMap | false | undefined;
         // Adding this to satisfy services, fix later
         /*@internal*/

src/testRunner/unittests/tsbuild/outFile.ts

@@ -241,38 +241,7 @@ Mismatch Actual: ${JSON.stringify(mapDefined(arrayFrom(actualReadFileMap.entries
 
                 incrementalBuild(
                     "incremental declaration doesnt change",
-                    [
-                        // Configs
-                        sources[project.first][source.config],
-                        sources[project.second][source.config],
-                        sources[project.third][source.config],
-
-                        // Source files
-                        ...sources[project.first][source.ts],
-                        ...sources[project.third][source.ts],
-
-                        // Additional source Files
-                        ...(additionalSourceFiles || emptyArray),
-
-                        // outputs
-                        ...outputFiles[project.first],
-                        ...outputFiles[project.second],
-                        outputFiles[project.third][ext.dts],
-                    ],
-                    fs => appendFileContent(fs, relSources[project.first][source.ts][part.one], "console.log(s);"),
-                    [
-                        getExpectedDiagnosticForProjectsInBuild(relSources[project.first][source.config], relSources[project.second][source.config], relSources[project.third][source.config]),
-                        [Diagnostics.Project_0_is_out_of_date_because_oldest_output_1_is_older_than_newest_input_2, relSources[project.first][source.config], relOutputFiles[project.first][ext.js], relSources[project.first][source.ts][part.one]],
-                        [Diagnostics.Building_project_0, sources[project.first][source.config]],
-                        [Diagnostics.Project_0_is_up_to_date_because_newest_input_1_is_older_than_oldest_output_2, relSources[project.second][source.config], relSources[project.second][source.ts][part.one], relOutputFiles[project.second][ext.js]],
-                        [Diagnostics.Project_0_is_out_of_date_because_output_to_prepend_from_its_dependency_1_has_changed, relSources[project.third][source.config], "src/first"],
-                        [Diagnostics.Building_project_0, sources[project.third][source.config]]
-                    ]
-                );
-
-                if (modifyAgainFs) {
-                    incrementalBuild(
-                        "incremental headers change",
+                    withoutBuildInfo ?
                         [
                             // Configs
                             sources[project.first][source.config],
@@ -290,15 +259,122 @@ Mismatch Actual: ${JSON.stringify(mapDefined(arrayFrom(actualReadFileMap.entries
                             ...outputFiles[project.first],
                             ...outputFiles[project.second],
                             outputFiles[project.third][ext.dts],
+
+                            // To prepend:: checked to see if we can do prepend manipulation
+                            outputFiles[project.third][ext.buildinfo],
+                        ] :
+                        [
+                            // Configs
+                            sources[project.first][source.config],
+                            sources[project.second][source.config],
+                            sources[project.third][source.config],
+
+                            // Source files
+                            ...sources[project.first][source.ts],
+
+                            // Additional source Files
+                            ...(additionalSourceFiles && additionalSourceFiles.length === 3 ? [additionalSourceFiles[project.first]] : emptyArray),
+
+                            // outputs without d.ts since we just update js
+                            outputFiles[project.first][ext.js],
+                            outputFiles[project.first][ext.jsmap],
+                            outputFiles[project.first][ext.dts],
+                            outputFiles[project.first][ext.buildinfo],
+                            outputFiles[project.second][ext.js],
+                            outputFiles[project.second][ext.jsmap],
+                            outputFiles[project.second][ext.buildinfo],
+
+                            // To prepend::
+                            outputFiles[project.third][ext.buildinfo],
+                            outputFiles[project.third][ext.js],
+                            outputFiles[project.third][ext.jsmap]
                         ],
+                    fs => appendFileContent(fs, relSources[project.first][source.ts][part.one], "console.log(s);"),
+                    [
+                        getExpectedDiagnosticForProjectsInBuild(relSources[project.first][source.config], relSources[project.second][source.config], relSources[project.third][source.config]),
+                        [Diagnostics.Project_0_is_out_of_date_because_oldest_output_1_is_older_than_newest_input_2, relSources[project.first][source.config], relOutputFiles[project.first][ext.js], relSources[project.first][source.ts][part.one]],
+                        [Diagnostics.Building_project_0, sources[project.first][source.config]],
+                        [Diagnostics.Project_0_is_up_to_date_because_newest_input_1_is_older_than_oldest_output_2, relSources[project.second][source.config], relSources[project.second][source.ts][part.one], relOutputFiles[project.second][ext.js]],
+                        [Diagnostics.Project_0_is_out_of_date_because_output_javascript_and_source_map_if_specified_of_its_dependency_1_has_changed, relSources[project.third][source.config], "src/first"],
+                        [Diagnostics.Updating_output_javascript_and_javascript_source_map_if_specified_of_project_0, sources[project.third][source.config]],
+                        ...<ReadonlyArray<fakes.ExpectedDiagnostic>>(!withoutBuildInfo ?
+                            [
+                                [Diagnostics.Updating_unchanged_output_timestamps_of_project_0, sources[project.third][source.config]]
+                            ] :
+                            [
+                                [Diagnostics.Cannot_update_output_javascript_and_javascript_source_map_if_specified_of_project_0_because_there_was_error_reading_file_1, sources[project.third][source.config], relOutputFiles[project.third][ext.buildinfo]],
+                                [Diagnostics.Building_project_0, sources[project.third][source.config]]
+                            ])
+                    ]
+                );
+
+                if (modifyAgainFs) {
+                    incrementalBuild(
+                        "incremental headers change",
+                        withoutBuildInfo ?
+                            [
+                                // Configs
+                                sources[project.first][source.config],
+                                sources[project.second][source.config],
+                                sources[project.third][source.config],
+
+                                // Source files
+                                ...sources[project.first][source.ts],
+                                ...sources[project.third][source.ts],
+
+                                // Additional source Files
+                                ...(additionalSourceFiles || emptyArray),
+
+                                // outputs
+                                ...outputFiles[project.first],
+                                ...outputFiles[project.second],
+                                outputFiles[project.third][ext.dts],
+
+                                // To prepend:: checked to see if we can do prepend manipulation
+                                outputFiles[project.third][ext.buildinfo],
+                            ] :
+                            [
+                                // Configs
+                                sources[project.first][source.config],
+                                sources[project.second][source.config],
+                                sources[project.third][source.config],
+
+                                // Source files
+                                ...sources[project.first][source.ts],
+
+                                // Additional source Files
+                                ...(additionalSourceFiles || emptyArray),
+
+                                // outputs without d.ts since we just update js
+                                outputFiles[project.first][ext.js],
+                                outputFiles[project.first][ext.jsmap],
+                                outputFiles[project.first][ext.dts],
+                                outputFiles[project.first][ext.buildinfo],
+                                outputFiles[project.second][ext.js],
+                                outputFiles[project.second][ext.jsmap],
+                                outputFiles[project.second][ext.buildinfo],
+
+                                // To prepend::
+                                outputFiles[project.third][ext.buildinfo],
+                                outputFiles[project.third][ext.js],
+                                outputFiles[project.third][ext.jsmap]
+                            ],
                         fs => modifyAgainFs(fs),
                         [
                             getExpectedDiagnosticForProjectsInBuild(relSources[project.first][source.config], relSources[project.second][source.config], relSources[project.third][source.config]),
                             [Diagnostics.Project_0_is_out_of_date_because_oldest_output_1_is_older_than_newest_input_2, relSources[project.first][source.config], relOutputFiles[project.first][ext.js], relSources[project.first][source.ts][part.one]],
                             [Diagnostics.Building_project_0, sources[project.first][source.config]],
                             [Diagnostics.Project_0_is_up_to_date_because_newest_input_1_is_older_than_oldest_output_2, relSources[project.second][source.config], relSources[project.second][source.ts][part.one], relOutputFiles[project.second][ext.js]],
-                            [Diagnostics.Project_0_is_out_of_date_because_output_to_prepend_from_its_dependency_1_has_changed, relSources[project.third][source.config], "src/first"],
-                            [Diagnostics.Building_project_0, sources[project.third][source.config]]
+                            [Diagnostics.Project_0_is_out_of_date_because_output_javascript_and_source_map_if_specified_of_its_dependency_1_has_changed, relSources[project.third][source.config], "src/first"],
+                            [Diagnostics.Updating_output_javascript_and_javascript_source_map_if_specified_of_project_0, sources[project.third][source.config]],
+                            ...<ReadonlyArray<fakes.ExpectedDiagnostic>>(!withoutBuildInfo ?
+                                [
+                                    [Diagnostics.Updating_unchanged_output_timestamps_of_project_0, sources[project.third][source.config]]
+                                ] :
+                                [
+                                    [Diagnostics.Cannot_update_output_javascript_and_javascript_source_map_if_specified_of_project_0_because_there_was_error_reading_file_1, sources[project.third][source.config], relOutputFiles[project.third][ext.buildinfo]],
+                                    [Diagnostics.Building_project_0, sources[project.third][source.config]]
+                                ])
                         ]
                     );
                 }