make rust-analyzer use a dedicated build directory

[tshepang]

inspired by #132794

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[jieyouxu]

I feel like this was discussed #general > ✔ Setup multiple editors for work on standard lib? @ 💬 but I don't remember why we used a top-level build-rust-analyzer/ as opposed to nesting inside of build/... @Zalathar do you happen to remember why? (It's been a while)

[jieyouxu]

Oh I think it just happens to be an option that works.

[Zalathar]

It has unintuitive interactions with x clean and caching, for example. IIRC x clean won’t delete your download cache, but it will delete your nested RA download cache, because it’s just indiscriminately deleting a subdirectory it doesn’t know about.

If people choose to inflict those risks on themselves, fine, but I don’t think a nested RA build directory is a responsible default.

[jieyouxu]

Oh right. I think that's the caveat I was vaguely recalling...

[tshepang]

would it be good to get x clean not delete what it does not recognize

[mati865]

Or even just avoid deleting build/rust-analyzer.

[Zalathar]

would it be good to get x clean not delete what it does not recognize

Bootstrap “owns” the build directory, so I think it's reasonable for x clean to delete anything it doesn't know about, on the assumption that it's junk left over from an earlier version of bootstrap.

Or even just avoid deleting build/rust-analyzer.

IIRC, one of the motivations people commonly cite for using build/rust-analyzer is that they want x clean to also clean their RA build directory. (And it does accomplish that, as a consequence of deleting build/rust-analyzer entirely.)

[Zalathar]

Anyhow, I strongly agree that our default IDE configs really should be using a separate build dir (e.g. build-rust-analyzer).

[tshepang]

I recently found that x clean does not in fact remove build/rust-analyzer

[Mark-Simulacrum]

Could you file a compiler MCP for this? I'd like to see some more eyes on this before we move in this direction.

[lolbinarycat]

This won't actually work reliably due to a bug in rustic: emacs-rustic/rustic#105

[Mark-Simulacrum]

That seems specific to emacs?

r=me on the change itself once MCP is approved.

[lolbinarycat]

Ah, right, this will still improve things for other editors (this PR was linked to me as "changing the default for emacs"), so there's no point blocking it on emacs being fixed.

[tshepang]

the MCP is now accepted and the pr updated to match

[tshepang]

made the move to build-rust-analyzer/ more comprehensive... it did not cover rustfmt and procmacro settings

should be ready now @Mark-Simulacrum