commit ae05609bd034f8eb7ded41b73e6af55c77b0d983
author Robert Findley <rfindley@google.com> Sun Feb 19 21:14:18 2023 -0500
committer Robert Findley <rfindley@google.com> Fri Mar 03 22:59:25 2023 +0000
tree 07def0961e75a01f10f11f17f3fcd583c2f7dfaa
parent de54582dcdd822706d853f5f7353b05aea448cc9

internal/lsp/cache: add an LRU parse cache

As work proceeds on incremental type-checking, two observations have
emerged from benchmarking:
- Using a global FileSet is impossible, as IImportShallow allocates a
  large number of new token.Files (in early experiments 75%+ of in-use memory
  was consumed by the FileSet!)
- Several benchmarks regressed with incremental type-checking due to
  re-parsing package files following a change. Ideally after a single file
  changes we would be able to re-typecheck packages containing that file
  after only re-parsing the single file that changed.

These observations are in tension: because type-checking requires that
parsed ast.Files live in the same token.FileSet as the type-checked
package, we cannot naively save the results of parsing and still use a
package-scoped FileSet.

This CL seeks to address both observations, by introducing a new
mechanism for caching parsed files (a parseCache) that parses files in a
standalone FileSet offset to avoid collision with other parsed files.
This cache exposes a batch API to parse multiple files and return a
FileSet describing all of them.

Benchmarking indicates that this partially mitigates performance
regressions without sacrificing the memory improvement we by avoiding a
global cache of parsed files.

In this CL the parse cache is not yet integrated with type-checking, but
replaces certain call-sites where we previously tried to avoid parsing
through the cache.

For golang/go#57987

Change-Id: I840cf003db835a40721f086abcc7bf00486b8108
Reviewed-on: https://go-review.googlesource.com/c/tools/+/469858
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>