Cache FS in LS #996

jakebailey · 2025-05-30T18:49:14Z

I think this is right; within a Project, cache the FS accesses and clear them out on graph update for safety. Then, things get faster in load time in module resolution and so on.

Not a mega fan of the whole host wrapping but I don't see a better way.

Copilot

Pull Request Overview

This PR introduces a caching layer for file system accesses in ProjectHost to improve module resolution performance and clears the cache whenever the project graph is updated.

Wraps the host’s FS() in a cachedvfs.FS via a new projectHostWithCachedFS
Updates NewProject to use the cached host and clears the cache in updateGraph
Leaves NewInferredProject unchanged (uses uncached host)

Comments suppressed due to low confidence (3)

internal/project/project.go:142

NewInferredProject still uses the original host without wrapping in cachedvfs. This leads to inconsistent caching behavior between inferred and regular projects. Consider wrapping the host here as well, e.g., host = newProjectHostWithCachedFS(host).

func NewInferredProject(compilerOptions *core.CompilerOptions, currentDirectory

internal/project/project.go:169

[nitpick] The type name projectHostWithCachedFS is lengthy and mixed-case. Consider renaming to cachedProjectHost for improved readability.

type projectHostWithCachedFS struct {

internal/project/project.go:174

There's no existing test coverage for the caching wrapper. Add unit tests that verify: 1) FS methods are delegated correctly, and 2) ClearCache() actually resets the cache.

func newProjectHostWithCachedFS(host ProjectHost) *projectHostWithCachedFS {

internal/project/project.go

sheetalkamat · 2025-05-30T19:24:01Z

We did this in Strada too (though we did it before creating program in service) this is known to help perf.

andrewbranch

Thanks, this was on my to-do list.

jakebailey · 2025-05-30T21:03:54Z

Unfortunately this method doesn't really work, the project test system replaces the FS out from under the cache, but the cache FS grabs the FS on creation.

I've been able to change the tests to not do that, but I'm not clearing the cache in places that seemingly we need it. So this will need more work.

jakebailey · 2025-05-30T21:04:20Z

Oh oops, sorry, this was supposed to be a draft when I sent it 😄

jakebailey · 2025-05-31T00:07:24Z

CI fails because the new ATA code runs before updateGraph and therefore reads from the cached FS before it's cleared.

sheetalkamat · 2025-06-03T04:12:56Z

internal/project/project.go

@@ -462,6 +486,7 @@ func (p *Project) updateGraph() bool {

 	start := time.Now()
 	p.Log("Starting updateGraph: Project: " + p.name)
+	p.host.fs.ClearCache()


I think we should keep the cache only for updateGraph duration as otherwise we dont know if its correct or not.

you probably saw this with typings installer tests but in practice this could be watch events as well

I'm not sure where you're telling me to put the call; I don't know where this would go otherwise.

Are you saying to clear the cache at the end of updateGraph?

I can do it that way, but I don't think that would affect ATA, since that code can happen any time concurrently (part of the reason why I am not giving it a cached FS, and plan to decouple it from the Project in a followup to fix the races)

i meant to keep the cache only for duration of update graph " so uncached before and after that call. (eg of how we did this in strada - this ensures the correctness if for some reason we need to check with FS on file existence etc https://github.com/microsoft/TypeScript/blob/main/src/services/services.ts#L1782 where cache lives only for program creation and then goes away

So, defer this call so it runs when updateGraph returns?

start caching at start of updateGraph and end cacheing when returning from it

Updated, PTAL

sheetalkamat · 2025-06-03T21:25:33Z

internal/project/project.go

@@ -460,6 +484,8 @@ func (p *Project) updateGraph() bool {
 		return false
 	}

+	defer p.host.fs.ClearCache()


But this still keeps cache outside of upate graph right. You probably want cache to be present only during updateGraph and use uncached version outside of it, that is it should not cache not consult cache when outside the updateGraph call

I see, you want me to pass a custom host into the Program?

The trouble is that the entire project is "a host", so it's pretty tough to do that, unless I make the cached FS able to be disabled entirely on some sort of toggle, which seems odd...

(This is why I hate every object turning into a host, but here we are...)

Maybe what I should do is create the cache in Program, which is how it's done for the other code (NewCachedFSCompilerHost).

i think if you create cache in program you wont be able to use it for your globs etc for watching.. you would want cache host to be "enabled" only for duration of the update graph. we did this eg in tsbuild in strada where we would cache only when build was in progress

I'll give it a shot.

Well, I did it, but it's not pretty 😄

I think you want to set and unset cacheHost inself ? so that its not checked all over the place?

also i think ata needs to used uncached version all the time? since it could be doing things in background while project is updating

I really do not want to swap the hosts out from under anything. That was done once before in testing and it was a pain because many things call FS(), etc, storing off the value, and so are not updated, which then has to be chased down. Ensuring everything is always static is very simplifying.

I'm less concerned about the extra check just because it's only a single atomic access most of the time.

also i think ata needs to used uncached version all the time? since it could be doing things in background while project is updating

I thought about this, but if both are happening concurrently, there's no harm in both using the same cached info, since updateGraph will clear it on exit anyhow.

jakebailey · 2025-06-03T22:31:27Z

Another ATA test race 😦

Cache FS in LS

976c156

jakebailey requested review from andrewbranch and Copilot May 30, 2025 18:49

Copilot AI reviewed May 30, 2025

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sheetalkamat approved these changes May 30, 2025

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andrewbranch approved these changes May 30, 2025

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jakebailey marked this pull request as draft May 30, 2025 21:03

jakebailey added 3 commits May 30, 2025 14:05

Don't replace FS out from under host

163289c

Fix files map use

a68ac74

Merge branch 'main' into jabaile/lsp-fs-cache

9a62fef

jakebailey mentioned this pull request Jun 2, 2025

[lsp][bug] LSP locks up for ~12s when navigating to files within the same project #813

Open

jakebailey added 5 commits June 2, 2025 13:26

Merge branch 'main' into jabaile/lsp-fs-cache

0cddce2

Hack ATA to not use the cached host

7945901

Merge branch 'main' into jabaile/lsp-fs-cache

cfccc05

fix other impl

2f2be30

Silence lint

71d6154

jakebailey marked this pull request as ready for review June 2, 2025 21:30

jakebailey requested review from andrewbranch and sheetalkamat June 2, 2025 22:15

sheetalkamat reviewed Jun 3, 2025

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jakebailey added 2 commits June 3, 2025 13:24

Merge branch 'main' into jabaile/lsp-fs-cache

2e70fea

Defer it

2eff771

sheetalkamat reviewed Jun 3, 2025

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Only cache during updateGraph

fa6df89

Merge branch 'main' into jabaile/lsp-fs-cache

90a8226

Tests

ffcef9f

jakebailey requested a review from sheetalkamat June 5, 2025 01:01

jakebailey enabled auto-merge June 5, 2025 19:29

gabritto approved these changes Jun 5, 2025

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jakebailey added this pull request to the merge queue Jun 5, 2025

github-merge-queue bot removed this pull request from the merge queue due to failed status checks Jun 5, 2025

jakebailey added this pull request to the merge queue Jun 5, 2025

Merged via the queue into main with commit 9bc5e3f Jun 5, 2025
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jakebailey deleted the jabaile/lsp-fs-cache branch June 5, 2025 20:39

Cache FS in LS #996

Cache FS in LS #996

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jakebailey commented May 30, 2025

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sheetalkamat Jun 3, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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jakebailey commented Jun 3, 2025

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sheetalkamat Jun 3, 2025 •

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