--emitDeclarationsOnly flag to enable declarations only output (#20735)

* Add emitOnlyDeclarations flag

* Fix name

* verifyOptions checking logic

* Passing tests

* doJsEmitBaseline

* Tests !!!

Author: nojvek

src/compiler/commandLineParser.ts

@@ -186,6 +186,12 @@ namespace ts {
             category: Diagnostics.Basic_Options,
             description: Diagnostics.Generates_corresponding_d_ts_file,
         },
+        {
+            name: "emitDeclarationsOnly",
+            type: "boolean",
+            category: Diagnostics.Advanced_Options,
+            description: Diagnostics.Only_emit_d_ts_declaration_files,
+        },
         {
             name: "sourceMap",
             type: "boolean",

src/compiler/diagnosticMessages.json

@@ -2807,6 +2807,10 @@
         "category": "Message",
         "code": 6013
     },
+    "Only emit '.d.ts' declaration files.": {
+        "category": "Message",
+        "code": 6014
+    },
     "Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'.": {
         "category": "Message",
         "code": 6015

src/compiler/emitter.ts

@@ -135,7 +135,7 @@ namespace ts {
 
         function emitSourceFileOrBundle({ jsFilePath, sourceMapFilePath, declarationFilePath }: EmitFileNames, sourceFileOrBundle: SourceFile | Bundle) {
             // Make sure not to write js file and source map file if any of them cannot be written
-            if (!host.isEmitBlocked(jsFilePath) && !compilerOptions.noEmit) {
+            if (!host.isEmitBlocked(jsFilePath) && !compilerOptions.noEmit && !compilerOptions.emitDeclarationsOnly) {
                 if (!emitOnlyDtsFiles) {
                     printSourceFileOrBundle(jsFilePath, sourceMapFilePath, sourceFileOrBundle);
                 }

src/compiler/program.ts

@@ -2201,6 +2201,16 @@ namespace ts {
                 programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Option_0_cannot_be_specified_without_specifying_option_1, "checkJs", "allowJs"));
             }
 
+            if (options.emitDeclarationsOnly) {
+                if (!options.declaration) {
+                    createDiagnosticForOptionName(Diagnostics.Option_0_cannot_be_specified_without_specifying_option_1, "emitDeclarationsOnly", "declarations");
+                }
+
+                if (options.noEmit) {
+                    createDiagnosticForOptionName(Diagnostics.Option_0_cannot_be_specified_with_option_1, "emitDeclarationsOnly", "noEmit");
+                }
+            }
+
             if (options.emitDecoratorMetadata &&
                 !options.experimentalDecorators) {
                 createDiagnosticForOptionName(Diagnostics.Option_0_cannot_be_specified_without_specifying_option_1, "emitDecoratorMetadata", "experimentalDecorators");
@@ -2223,7 +2233,9 @@ namespace ts {
                 const emitHost = getEmitHost();
                 const emitFilesSeen = createMap<true>();
                 forEachEmittedFile(emitHost, (emitFileNames) => {
-                    verifyEmitFilePath(emitFileNames.jsFilePath, emitFilesSeen);
+                    if (!options.emitDeclarationsOnly) {
+                        verifyEmitFilePath(emitFileNames.jsFilePath, emitFilesSeen);
+                    }
                     verifyEmitFilePath(emitFileNames.declarationFilePath, emitFilesSeen);
                 });
             }

src/compiler/types.ts

@@ -3967,6 +3967,7 @@ namespace ts {
         /** configFile is set as non enumerable property so as to avoid checking of json source files */
         /* @internal */ readonly configFile?: JsonSourceFile;
         declaration?: boolean;
+        emitDeclarationsOnly?: boolean;
         declarationDir?: string;
         /* @internal */ diagnostics?: boolean;
         /* @internal */ extendedDiagnostics?: boolean;

src/harness/harness.ts

@@ -1252,8 +1252,18 @@ namespace Harness {
             options: ts.CompilerOptions,
             // Current directory is needed for rwcRunner to be able to use currentDirectory defined in json file
             currentDirectory: string): DeclarationCompilationContext | undefined {
-            if (options.declaration && result.errors.length === 0 && result.declFilesCode.length !== result.files.length) {
-                throw new Error("There were no errors and declFiles generated did not match number of js files generated");
+
+            if (result.errors.length === 0) {
+                if (options.declaration) {
+                    if (options.emitDeclarationsOnly) {
+                        if (result.files.length > 0 || result.declFilesCode.length === 0) {
+                            throw new Error("Only declaration files should be generated when emitDeclarationsOnly:true");
+                        }
+                    }
+                    else if (result.declFilesCode.length !== result.files.length) {
+                        throw new Error("There were no errors and declFiles generated did not match number of js files generated");
+                    }
+                }
             }
 
             const declInputFiles: TestFile[] = [];
@@ -1654,7 +1664,7 @@ namespace Harness {
         }
 
         export function doJsEmitBaseline(baselinePath: string, header: string, options: ts.CompilerOptions, result: CompilerResult, tsConfigFiles: Harness.Compiler.TestFile[], toBeCompiled: Harness.Compiler.TestFile[], otherFiles: Harness.Compiler.TestFile[], harnessSettings: Harness.TestCaseParser.CompilerSettings) {
-            if (!options.noEmit && result.files.length === 0 && result.errors.length === 0) {
+            if (!options.noEmit && !options.emitDeclarationsOnly && result.files.length === 0 && result.errors.length === 0) {
                 throw new Error("Expected at least one js file to be emitted or at least one error to be created.");
             }
 

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

@@ -2266,6 +2266,7 @@ declare namespace ts {
         charset?: string;
         checkJs?: boolean;
         declaration?: boolean;
+        emitDeclarationsOnly?: boolean;
         declarationDir?: string;
         disableSizeLimit?: boolean;
         downlevelIteration?: boolean;

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

@@ -2266,6 +2266,7 @@ declare namespace ts {
         charset?: string;
         checkJs?: boolean;
         declaration?: boolean;
+        emitDeclarationsOnly?: boolean;
         declarationDir?: string;
         disableSizeLimit?: boolean;
         downlevelIteration?: boolean;

tests/baselines/reference/declFileEmitDeclarationsOnly.js

@@ -0,0 +1,26 @@
+//// [helloworld.ts]
+const Log = {
+  info(msg: string) {}
+}
+
+class HelloWorld {
+  constructor(private name: string) {
+  }
+
+  public hello() {
+    Log.info(`Hello ${this.name}`);
+  }
+}
+
+
+
+
+//// [helloworld.d.ts]
+declare const Log: {
+    info(msg: string): void;
+};
+declare class HelloWorld {
+    private name;
+    constructor(name: string);
+    hello(): void;
+}

tests/baselines/reference/declFileEmitDeclarationsOnly.symbols

@@ -0,0 +1,29 @@
+=== tests/cases/compiler/helloworld.ts ===
+const Log = {
+>Log : Symbol(Log, Decl(helloworld.ts, 0, 5))
+
+  info(msg: string) {}
+>info : Symbol(info, Decl(helloworld.ts, 0, 13))
+>msg : Symbol(msg, Decl(helloworld.ts, 1, 7))
+}
+
+class HelloWorld {
+>HelloWorld : Symbol(HelloWorld, Decl(helloworld.ts, 2, 1))
+
+  constructor(private name: string) {
+>name : Symbol(HelloWorld.name, Decl(helloworld.ts, 5, 14))
+  }
+
+  public hello() {
+>hello : Symbol(HelloWorld.hello, Decl(helloworld.ts, 6, 3))
+
+    Log.info(`Hello ${this.name}`);
+>Log.info : Symbol(info, Decl(helloworld.ts, 0, 13))
+>Log : Symbol(Log, Decl(helloworld.ts, 0, 5))
+>info : Symbol(info, Decl(helloworld.ts, 0, 13))
+>this.name : Symbol(HelloWorld.name, Decl(helloworld.ts, 5, 14))
+>this : Symbol(HelloWorld, Decl(helloworld.ts, 2, 1))
+>name : Symbol(HelloWorld.name, Decl(helloworld.ts, 5, 14))
+  }
+}
+