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Rethink our VFS abstraction #18948
Description
The current setup is brittle and tends to break very easily in unexpected ways (#18886 (comment) being an example). The system is also somewhat difficult to follow (the way we partition the VFS into sourceroots is not easily understandable). We should simplify this and clean it up. One idea we've had is to first and foremost move the VFS state into salsa (once we have migrated over to the new one), as currently we have a weird middle ground between the two (some info is outside salsa, some is inside). The other thing is that we need to likely add support for lazily loading file contents (which likely means incurring i/o within salsa queries).
Reacted by stefnotch
Activity
Veykril commentedon Jan 16, 2025
cc @davidbarsky opening this so we can keep track of it (might want to link to this from the perf tracking issue even)
davidbarsky commentedon Jan 16, 2025
Unless I misunderstood what you said, we can lazily load files and file contents in Salsa today. Regardless, my opinion is that we should try to batch IO as much as possible instead of being lazy.
Yeah, I'll update that issue to include this.
davidbarsky commentedon Jan 24, 2025
For posterity, I imagine that the new VFS will end up looking a lot like Dada's or Ruff's new Salsa-powered VFS abstractions.
[-]Re-think our VFS abstraction[/-][+]Rethink our VFS abstraction[/+]tamird commentedon Feb 10, 2025
Is #15836 also related?
davidbarsky commentedon Feb 10, 2025
Yes, probably.
alanz commentedon Mar 4, 2025
A note about source roots from our usage in ELP, which is based on RA.
We recently updated the project model to match internal buck2 targets. These generate a test target per test file, and each can have different config, which we store in
AppData. To know which options to use for a file we need itsAppData, which used to come via the source root. But, now having one source root containing one target does not hold. So we have to jump though hoops to get a mapping from FileId to application information, based on individual FileId, but falling back to source root.See e.g. this commit