Confusing error when preserveSymlinks is missing.

[axos88]

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

router

Is this a regression?

No

Description

Repro:

1. git clone a primeng library
2. npm run build:lib
3. cd myproject
4. npm i ../../primeng/dist
5. import MenubarModule
6. ng build

Observe: modules cannot be resolved

7. Try workaround by adding:

    "paths": {
      "primeng/*": ["../node_modules/primeng/*/public_api"]
    },

8. ng build succeeds
9. Open application, observe NG0203

main.ts:27 ERROR Error: NG0203: inject() must be called from an injection context such as a constructor, a factory function, a field initializer, or a function used with `runInInjectionContext`. Find more at https://angular.io/errors/NG0203

10. spend days debugging the issue
11. solved by adding preserveSymlinks: true.

Please provide a link to a minimal reproduction of the bug

No response

Please provide the exception or error you saw

main.ts:27 ERROR Error: NG0203: inject() must be called from an injection context such as a constructor, a factory function, a field initializer, or a function used with `runInInjectionContext`. Find more at https://angular.io/errors/NG0203

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

Angular CLI: 17.3.6
Node: 20.12.2
Package Manager: npm 10.5.0
OS: linux x64

Angular: 
... 

Package                      Version
------------------------------------------------------
@angular-devkit/architect    0.1703.6 (cli-only)
@angular-devkit/core         17.3.6 (cli-only)
@angular-devkit/schematics   17.3.6 (cli-only)
@schematics/angular          17.3.6 (cli-only)

Anything else?

preserveSymlinks is not well documented (even after the solution I have no idea what it actually preserves), and the error message anything but points to the missing configuration. A more helpful error message would be great!

[JoostK]

Improving this failure mode is being tracked in angular/angular-cli#26774.

Without preserveSymlinks, the real path of a symlink is being used instead of retaining the original path. For example, consider the following structure:

/lib/node_modules/@angular/core/...
/lib/package.json
/app/node_modules/@angular/core/...
/app/lib -> /lib
/app/package.json

Then, a path like /app/lib/entrypoint.ts either remains as is (preserveSymlinks=true) , or is replaced with /lib/entrypoint.ts (preserveSymlinks=false). This then affects module resolution, as it either finds /app/node_modules or /lib/node_modules. in the latter case introducing a secondary copy of @angular/core. That results in a runtime that gets confused, as the two runtimes are not aware of each other and don't have access to the proper state.

Closing as tracked in angular/angular-cli#26774

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