feat(@angular/cli): build only the projects of a certain type

[nweldev]

Goal feature

Permit to run some architect commands only on projects with a specific projectType.

For example, this will only build the libraries :

ng build --project-type=library

angular/devkit#739 would be needed for filtering project names.

Purpose

Applications and libraries doesn't share the same use-cases : where applications are built (thanks to the build-angular build architect) in order to be served through HTTP, libraries, on the other hand, are bundled by ng-packagr in order to be published to a npm repository. Therefore, deployment / publication processes diverged between the two, so is the CI.

This PR is also a first example of angular/devkit#739 use.

[filipesilva]

Heya @noelmace I talked a bit about this problem in angular/devkit#730 (comment), and at the end of my comment I mention this PR and why I think it is not the right approach to this problem at the moment. Let me know what you think.

[nweldev]

@filipesilva Thanks for this feedback. We continued to speak (a lot) about this in #730, and I think I see now how we could proceed. Please, see if you can add some feedbacks on angular/devkit#730 (comment).

On the other hand, I still think this option could be relevant for a more restricted use case : we have some set on libraries as a whole, like @angular/*. So, we have to build all of them at the same time, but without building our apps. For that, we can only add some dumb script that just run ng build --project liba && ng build --project libb && .... (see angular/devkit#730 (comment) or https://github.com/noelmace/ng-admin/blob/master/scripts/publish.ts#L25 for some more sofisticated approach).

For my use case especially, we could also add a --scope option which would permit to just run build targets for projects of a given npm scope / projects/ sub-folder. If you think this would be a good feature to add, I could make a PR quickly, but this would require angular/devkit#739. Could you take a look at it please ? Thanks.

[filipesilva]

Heya I brought this up with the team and we don't want to do it via filtering through project type. We feel it is a fairly limited way of doing this.

The need for this sort of thing is still there in the cases you mentioned. I have made #11002 to track this. There's other parties with similar needs and we hope to converge on a design that satisfies them.

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