fix(compiler-cli): don't report emit diagnostics when --noEmitOnError is off (#20063)

packages/compiler-cli/index.ts

@@ -22,3 +22,5 @@ export * from './src/perform_compile';
 // and usages in G3 are changed to `CompilerOptions`.
 export {CompilerOptions as AngularCompilerOptions} from './src/transformers/api';
 export {NgTools_InternalApi_NG_2 as __NGTOOLS_PRIVATE_API_2} from './src/ngtools_api';
+
+export {ngToTsDiagnostic} from './src/transformers/util';

packages/compiler-cli/src/transformers/program.ts

@@ -300,10 +300,16 @@ class AngularCompilerProgram implements Program {
       }
     }
     this.emittedSourceFiles = emittedSourceFiles;
+
+    // Match behavior of tsc: only produce emit diagnostics if it would block
+    // emit. If noEmitOnError is false, the emit will happen in spite of any
+    // errors, so we should not report them.
+    if (this.options.noEmitOnError === true) {
       // translate the diagnostics in the emitResult as well.
       const translatedEmitDiags = translateDiagnostics(this.hostAdapter, emitResult.diagnostics);
       emitResult.diagnostics = translatedEmitDiags.ts.concat(
           this.structuralDiagnostics.concat(translatedEmitDiags.ng).map(ngToTsDiagnostic));
+    }
 
     if (!outSrcMapping.length) {
       // if no files were emitted by TypeScript, also don't emit .json files

packages/compiler-cli/test/transformers/program_spec.ts

@@ -893,6 +893,19 @@ describe('ng program', () => {
             `src/main.html(1,1): error TS100: Property 'nonExistent' does not exist on type 'MyComp'.`);
   });
 
+  it('should not report emit errors with noEmitOnError=false', () => {
+    testSupport.writeFiles({
+      'src/main.ts': `
+        @NgModule()
+      `
+    });
+    const options = testSupport.createCompilerOptions({noEmitOnError: false});
+    const host = ng.createCompilerHost({options});
+    const program1 = ng.createProgram(
+        {rootNames: [path.resolve(testSupport.basePath, 'src/main.ts')], options, host});
+    expect(program1.emit().diagnostics.length).toBe(0);
+  });
+
   describe('errors', () => {
     const fileWithStructuralError = `
       import {NgModule} from '@angular/core';