refactor(@ngtools/webpack): simplify changed file handling

Author: clydin

packages/ngtools/webpack/src/angular_compiler_plugin.ts

@@ -850,7 +850,7 @@ export class AngularCompilerPlugin {
 
     // If nothing we care about changed and it isn't the first run, don't do anything.
     if (changedFiles.length === 0 && !this._firstRun) {
-      return Promise.resolve();
+      return;
     }
 
     // Make a new program and load the Angular structure.
@@ -876,24 +876,9 @@ export class AngularCompilerPlugin {
       }
     }
 
-    // Emit and report errors.
-
-    // We now have the final list of changed TS files.
-    // Go through each changed file and add transforms as needed.
-    const sourceFiles = this._getChangedTsFiles()
-      .map((fileName) => (this._getTsProgram() as ts.Program).getSourceFile(fileName))
-      // At this point we shouldn't need to filter out undefined files, because any ts file
-      // that changed should be emitted.
-      // But due to hostReplacementPaths there can be files (the environment files)
-      // that changed but aren't part of the compilation, specially on `ng test`.
-      // So we ignore missing source files files here.
-      // hostReplacementPaths needs to be fixed anyway to take care of the following issue.
-      // https://github.com/angular/angular-cli/issues/7305#issuecomment-332150230
-      .filter((x) => !!x) as ts.SourceFile[];
-
     // Emit files.
     time('AngularCompilerPlugin._update._emit');
-    const { emitResult, diagnostics } = this._emit(sourceFiles);
+    const { emitResult, diagnostics } = this._emit(changedFiles);
     timeEnd('AngularCompilerPlugin._update._emit');
 
     // Report diagnostics.
@@ -1036,7 +1021,7 @@ export class AngularCompilerPlugin {
   // This code mostly comes from `performCompilation` in `@angular/compiler-cli`.
   // It skips the program creation because we need to use `loadNgStructureAsync()`,
   // and uses CustomTransformers.
-  private _emit(sourceFiles: ts.SourceFile[]) {
+  private _emit(changedFiles: string[]) {
     time('AngularCompilerPlugin._emit');
     const program = this._program;
     const allDiagnostics: Array<ts.Diagnostic | Diagnostic> = [];
@@ -1059,7 +1044,7 @@ export class AngularCompilerPlugin {
         }
 
         if (!hasErrors(allDiagnostics)) {
-          if (this._firstRun || sourceFiles.length > 20) {
+          if (this._firstRun) {
             emitResult = tsProgram.emit(
               undefined,
               undefined,
@@ -1069,15 +1054,19 @@ export class AngularCompilerPlugin {
             );
             allDiagnostics.push(...emitResult.diagnostics);
           } else {
-            sourceFiles.forEach((sf) => {
-              const timeLabel = `AngularCompilerPlugin._emit.ts+${sf.fileName}+.emit`;
-              time(timeLabel);
-              emitResult = tsProgram.emit(sf, undefined, undefined, undefined,
-                { before: this._transformers },
-              );
-              allDiagnostics.push(...emitResult.diagnostics);
-              timeEnd(timeLabel);
-            });
+            for (const file of changedFiles) {
+              const sourceFile = tsProgram.getSourceFile(file);
+
+              if (sourceFile) {
+                const timeLabel = `AngularCompilerPlugin._emit.ts+${sourceFile.fileName}+.emit`;
+                time(timeLabel);
+                emitResult = tsProgram.emit(sourceFile, undefined, undefined, undefined,
+                  { before: this._transformers },
+                );
+                allDiagnostics.push(...emitResult.diagnostics);
+                timeEnd(timeLabel);
+              }
+            }
           }
         }
       } else {