6153: Improve prime_caches and display its progress r=matklad a=jonas-schievink
It now computes the `CrateDefMap` of all crates, which is generally a reasonable approximation for "IDE features ready". There is still some delay after this finishes, I suspect mostly due to impl collection, which takes a while, but this should be an improvement already.
For more accurate progress reports, this topologically sorts all crates before starting this operation. ~~Because that is also the ordering in which parallelization makes sense (which was previously attempted in https://github.com/rust-analyzer/rust-analyzer/pull/3529), I decided to throw that into the mix as well. It still doesn't provide *that* much of a performance boost, but it does scale beyond the current single-core architecture, and adding it was very easy.~~
~~Unfortunately, as written, this will not tell the user which crate is actually causing slowdowns, since the displayed crate is the last one that was *started*, not the one we are currently *blocked* on, but that seems fairly difficult to implement unless I'm missing something.~~
(I have removed rayon for now since it does not work correctly with cancellation.)
Co-authored-by: Jonas Schievink <jonas.schievink@ferrous-systems.com>
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