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

compiler-cli, compiler

Is this a regression?

Yes

Description

When using @Input({transform: transformFn}) and the transformation function is exported from another file, the Angular compiler generates incorrect/mashed up types for the @Input. However, if the transformation function is in the same file as the @Input, everything works as expected. This bug only affects string literal types (I think).

To illustrate the issue, here are screenshots of the incorrect and correct types:

Incorrect types:

Correct types:

Please provide a link to a minimal reproduction of the bug

https://codesandbox.io/p/github/uneknown/reproduce-angular-transform-issue/master

Please provide the exception or error you saw

None

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

Angular CLI: 16.2.0
Node: 16.17.0
Package Manager: npm 8.15.0
OS: linux x64

Angular: 16.2.2
... animations, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1602.0
@angular-devkit/build-angular   16.2.0
@angular-devkit/core            16.2.0
@angular-devkit/schematics      16.2.0
@angular/cli                    16.2.0
@schematics/angular             16.2.0
ng-packagr                      16.2.1
rxjs                            7.8.1
typescript                      5.1.6
zone.js                         0.13.1

Anything else?

Steps to Reproduce:

1. Open CodeSandbox using the link provided above.
2. Wait until the sandbox has finished booting up, installed all dependencies, and completed the build.
3. Click on the terminal icon and select "show-output."

At this point, you should be able to view the content of the ...component.d.ts file in the terminal output.