fix: Deduplicate crate graph

[LHolten]

See the discussion in #18804

[LHolten]

Maybe the deduplication test should be brought back too?

[Veykril]

Yes they should

[LHolten]

Brought back the tests

[LHolten]

@Veykril What do you think of just making the CrateGraph::extend method sort the dependencies automatically?
That way it is hard to misuse the CrateGraph api and thus the tests in the rust-analyzer/tests/crate_graph are not really needed, so we can then remove those.

[Veykril]

Yes that should be fine. I just realized these tests will be gone soon enough anyways as we are currently doing a big rewrite that includes splitting the crate graph up into smaller parts.

[LHolten]

Done

[filipwiech]

@rustbot ready

Drive-by question: back when the crate deduplication was originally introduced, I think it promised potential memory usage improvements in r-a. Is it still the case, or has the design changed since then? Sorry for a layman's inquiry. 🙂

[Veykril]

That is the case (for multi cargo workspace projects)

[filipwiech]

That is the case

Nice, thanks! 👍

(for multi cargo workspace projects)

Ah, yes, now I remember, thank you. 🙂