build: add a script to detect component ID collisions

[crisbeto]

As of v16, the framework uses the metadata of a component to generate an ID. If two components have identical metadata, they may end up with the same ID which will log a warning. These changes add a script to detect such cases automatically.

Relates to #27163.

[andrewseguin]

Why does Angular throw an error here? Isn't our use case valid - we are making a new version of a component.

[crisbeto]

tl;dr is that Angular has always had a unique ID for each component. Pre-v16 the ID was based on a counter so components were guaranteed to have a unique ID. When hydration was introduced, the counter approach didn't work anymore since different components might be executed on the server and the client so the ID algorithm was switched to use the metadata instead.

The unique ID is used in DI and when keeping track of stylesheets.

[andrewseguin]

Could the ID generation take into account it's filepath or something unique beyond just metadata? It'd be helpful to know they intend to prevent this case otherwise

[crisbeto]

It can't because:

1. JIT compilation doesn't know about the file system.
2. This happens in the runtime, not at compilation.

[andrewseguin]

Oof...well that's a bummer.

When should we run this script? Seems like it's a proactive thing that we ought to run when we change metadata?

EDIT: Or include it in a CI test?

[crisbeto]

There are a few failures that I want to address first before I add it to the CI.

[devversion]

Two quick thoughts:

• Should some of this check be performed in the compiler CLI itself? seems like something other libraries would need too.
• Could we just have a runtime test that imports all components and asserts that nothing breaks?

[crisbeto]

Things don't necessarily break at the moment, they just log a warning and I wanted to automate catching the warnings instead of having users report it to us.

As for having it in the compiler: I think it's trickier to do it there, because compilations might be spread across different build units running in parallel and things would only conflict once they're on the same page.

[devversion]

I thought we could potentially intercept logging and see if there is a matching error/or something, without having to replicate some of the serialization logic. At the same time though- adding all components is likely not super nice either

[crisbeto]

Yeah I feel like having it run as a part of the CI against the source code is the simplest without having to maintain even more code.

[devversion]

Yes, and likely we are overly sensitive here, but it guarantees we are not conflicting.

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