Versioning of Angular between Angular Applications and Angular Libraries

Description

I’m getting an error when I compile an angular library that uses a different version of Angular than the library it’s including.

Please provide the steps to reproduce the issue

Create an Angular application in which your package.json has

"dependencies": {
    "@angular/forms": "^11",
}

Create an Angular library in which your package.json has

"dependencies": {
     "@angular/forms": "^11.2.12"
}

Then link the application to the library with ng link Compile the application with with ng build.

Please provide the expected behavior vs the actual behavior you encountered

I would prefer to know can an application be versioned newer than a library? Can a library be versioned newer than the application it’s compiled in? Or do all Angular things (applications and libraries) need to have the same version?

It would be nice to have a better warning and documentation on this.

Please provide the exception or error you saw

Error: src/app/components/forms/forms.component.ts:48:54 - error TS2345: Argument of type 'ValidatorFn' is not assignable to parameter of type 'ValidatorFn | ValidatorFn[] | AbstractControlOptions'.
  Type 'import("/root/libs/angular-validators/node_modules/@angular/forms/forms").ValidatorFn' is not assignable to type 'import("/root/demo-app/node_modules/@angular/forms/forms").ValidatorFn'.
    Types of parameters 'control' and 'control' are incompatible.
      Type 'import("/root/demo-app/node_modules/@angular/forms/forms").AbstractControl' is not assignable to type 'import("/root/libs/angular-validators/node_modules/@angular/forms/forms").AbstractControl'.
        Types have separate declarations of a private property '_parent'.

[petebacondarwin]

In terms of compatibility:

I would prefer to know can an application be versioned newer than a library? Can a library be versioned newer than the application it’s compiled in? Or do all Angular things (applications and libraries) need to have the same version?

We try to ensure that Angular applications can use libraries that are versioned up to 2 major versions prior to the version of the application. (But in practice, you can usually go much further back than that - there are a number of libraries that are built with v8, for example, that work fine with v12 applications).

We do not officially support an application using a library that was built with a newer version of Angular than the application. So if your application is built with Angular v11, then all the libraries it depends upon ought to be built with v11 or earlier. This actually also includes minor versions, but not patch versions. (Again, in practice, you may well be able to get away with using a library with a newer version, although v13 has a hard break in this regards since it is not possible to consume v13 libraries with ViewEngine applications).

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