Bug Report

Affected Package

@angular/compiler-cli/linker

Is this a regression?

No.

Description

When using the sourceMapping linker option and Babel generates AST nodes that reference the external template files, babel will not emit any sourcemap.

Minimal Reproduction

• git clone https://github.com/alan-agius4/LibExportTest2
• npm i
• ng build my-lib
• ng s

Exception or Error

Sourcemaps for the library are not emitted.

Your Environment

Angular Version:

Angular CLI: 12.1.1
Node: 14.17.1
Package Manager: npm 6.14.13
OS: darwin x64

Angular: 12.1.1
... animations, cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1201.1
@angular-devkit/build-angular   12.1.1
@angular-devkit/core            12.1.1
@angular-devkit/schematics      12.1.1
@schematics/angular             12.1.1
ng-packagr                      12.1.0
rxjs                            6.6.7
typescript                      4.3.5

Anything else relevant?
CLI issue angular/angular-cli#21271

It also appears that when this option is enabled the sourcemap is read directly from disk instead of using the sourcemap that is already in memory and accessible via the Babel API.

Couple of things I noticed while debugging this.

• The sourcemap happens to load because of the current fallback logic

  angular/packages/compiler-cli/src/ngtsc/sourcemaps/src/source_file_loader.ts

  Lines 175 to 182 in a92a89b

  	const impliedMapPath = this.fs.resolve(sourcePath + '.map');
  	if (this.fs.exists(impliedMapPath)) {
  	return {
  	map: this.readRawSourceMap(impliedMapPath),
  	mapPath: impliedMapPath,
  	origin: ContentOrigin.FileSystem,
  	};
  	}

  . This is because Webpack will remove //# sourceMappingURL from the source code when the a sourcemap is loaded.
• This also potential highlights a problem if the file/sourcemap is processed prior to the linker plugin, in which cases the sourcemap on disk would be out of sync. Therefore, IMHO the sourcemap provided via Babel API should be used instead of using what's on disk.
• In case one uses inline sourcemaps this logic will break, because there wouldn't be any sourcemapping information that the linker can read.