Add hook for adding transforms into the declaration emit pipeline after the main one (microsoft#23946)

* Add hook for adding transforms into the declaration emit pipeline after the main one

* Fix lint

Author: weswigham

src/compiler/emitter.ts

@@ -95,7 +95,7 @@ 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<SourceFile | Bundle>[]): EmitResult {
+    export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile: SourceFile, emitOnlyDtsFiles?: boolean, transformers?: TransformerFactory<Bundle | SourceFile>[], declarationTransformers?: TransformerFactory<Bundle | SourceFile>[]): EmitResult {
         const compilerOptions = host.getCompilerOptions();
         const sourceMapDataList: SourceMapData[] = (compilerOptions.sourceMap || compilerOptions.inlineSourceMap || getAreDeclarationMapsEnabled(compilerOptions)) ? [] : undefined;
         const emittedFilesList: string[] = compilerOptions.listEmittedFiles ? [] : undefined;
@@ -192,7 +192,7 @@ namespace ts {
             // Setup and perform the transformation to retrieve declarations from the input files
             const nonJsFiles = filter(sourceFiles, isSourceFileNotJavaScript);
             const inputListOrBundle = (compilerOptions.outFile || compilerOptions.out) ? [createBundle(nonJsFiles, !isSourceFile(sourceFileOrBundle) ? sourceFileOrBundle.prepends : undefined)] : nonJsFiles;
-            const declarationTransform = transformNodes(resolver, host, compilerOptions, inputListOrBundle, [transformDeclarations], /*allowDtsFiles*/ false);
+            const declarationTransform = transformNodes(resolver, host, compilerOptions, inputListOrBundle, concatenate([transformDeclarations], declarationTransformers), /*allowDtsFiles*/ false);
             if (length(declarationTransform.diagnostics)) {
                 for (const diagnostic of declarationTransform.diagnostics) {
                     emitterDiagnostics.add(diagnostic);

src/compiler/program.ts

@@ -1296,7 +1296,9 @@ namespace ts {
                 getEmitHost(writeFileCallback),
                 sourceFile,
                 emitOnlyDtsFiles,
-                transformers);
+                transformers,
+                customTransformers && customTransformers.afterDeclarations
+            );
 
             performance.mark("afterEmit");
             performance.measure("Emit", "beforeEmit", "afterEmit");

src/compiler/types.ts

@@ -2788,10 +2788,12 @@ namespace ts {
     }
 
     export interface CustomTransformers {
-        /** Custom transformers to evaluate before built-in transformations. */
+        /** Custom transformers to evaluate before built-in .js transformations. */
         before?: TransformerFactory<SourceFile>[];
-        /** Custom transformers to evaluate after built-in transformations. */
+        /** Custom transformers to evaluate after built-in .js transformations. */
         after?: TransformerFactory<SourceFile>[];
+        /** Custom transformers to evaluate after built-in .d.ts transformations. */
+        afterDeclarations?: TransformerFactory<Bundle | SourceFile>[];
     }
 
     export interface SourceMapSpan {

src/harness/unittests/transform.ts

@@ -250,6 +250,26 @@ namespace ts {
                 }
             }
         });
+
+        testBaseline("transformDeclarationFile", () => {
+            return baselineDeclarationTransform(`var oldName = undefined;`, {
+                transformers: {
+                    afterDeclarations: [replaceIdentifiersNamedOldNameWithNewName]
+                },
+                compilerOptions: {
+                    newLine: NewLineKind.CarriageReturnLineFeed,
+                    declaration: true
+                }
+            });
+        });
+
+        function baselineDeclarationTransform(text: string, opts: TranspileOptions) {
+            const fs = vfs.createFromFileSystem(Harness.IO, /*caseSensitive*/ true, { documents: [new documents.TextDocument("/.src/index.ts", text)] });
+            const host = new fakes.CompilerHost(fs, opts.compilerOptions);
+            const program = createProgram(["/.src/index.ts"], opts.compilerOptions, host);
+            program.emit(program.getSourceFiles()[1], (p, s, bom) => host.writeFile(p, s, bom), /*cancellationToken*/ undefined, /*onlyDts*/ true, opts.transformers);
+            return fs.readFileSync("/.src/index.d.ts").toString();
+        }
     });
 }
 

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -1735,10 +1735,12 @@ declare namespace ts {
         sourceFile: SourceFile;
     }
     interface CustomTransformers {
-        /** Custom transformers to evaluate before built-in transformations. */
+        /** Custom transformers to evaluate before built-in .js transformations. */
         before?: TransformerFactory<SourceFile>[];
-        /** Custom transformers to evaluate after built-in transformations. */
+        /** Custom transformers to evaluate after built-in .js transformations. */
         after?: TransformerFactory<SourceFile>[];
+        /** Custom transformers to evaluate after built-in .d.ts transformations. */
+        afterDeclarations?: TransformerFactory<Bundle | SourceFile>[];
     }
     interface SourceMapSpan {
         /** Line number in the .js file. */

tests/baselines/reference/api/typescript.d.ts

@@ -1735,10 +1735,12 @@ declare namespace ts {
         sourceFile: SourceFile;
     }
     interface CustomTransformers {
-        /** Custom transformers to evaluate before built-in transformations. */
+        /** Custom transformers to evaluate before built-in .js transformations. */
         before?: TransformerFactory<SourceFile>[];
-        /** Custom transformers to evaluate after built-in transformations. */
+        /** Custom transformers to evaluate after built-in .js transformations. */
         after?: TransformerFactory<SourceFile>[];
+        /** Custom transformers to evaluate after built-in .d.ts transformations. */
+        afterDeclarations?: TransformerFactory<Bundle | SourceFile>[];
     }
     interface SourceMapSpan {
         /** Line number in the .js file. */

tests/baselines/reference/transformApi/transformsCorrectly.transformDeclarationFile.js

@@ -0,0 +1 @@
+declare var newName: any;