Angular 19 Build unable to use sourcemaps for locally mapped library

[TheKrisSodroski]

Which @angular/* package(s) are the source of the bug?

compiler

Is this a regression?

Yes

Description

When watching a locally mapped library, once the library is rebuilt, sourcemaps for the library are lost completely.

Please provide a link to a minimal reproduction of the bug

https://github.com/TheKrisSodroski/Angular19LibraryWatchBug

Please provide the exception or error you saw

Dev Tools is unable to show the true source of the newly generated code.

Please provide the environment you discovered this bug in (run ng version)

_                      _                 ____ _     ___
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/


Angular CLI: 19.1.7
Node: 20.17.0
Package Manager: npm 10.8.2
OS: win32 x64

Angular: 19.1.6
... animations, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1901.7
@angular-devkit/build-angular   19.1.7
@angular-devkit/core            19.1.7
@angular-devkit/schematics      19.1.7
@angular/cli                    19.1.7
@schematics/angular             19.1.7
rxjs                            7.8.1
typescript                      5.7.3
zone.js                         0.15.0

Anything else?

Github reproduction repo contains a readme with additional information:

https://github.com/TheKrisSodroski/Angular19LibraryWatchBug

[roma2341]

Weird issue, angular builds sourcemaps for some components and doesn't build for other components inside my project

[ChristianGalla]

Possible related / duplicate of: #28426

[TheKrisSodroski]

@ChristianGalla looks tangentially related.

My sample has no configuration overrides; both the library and application were built without any customization to the cli generated code.

[alan-agius4]

This is the same root cause as #28426

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