internal/lsp: fix concurrent map write in file invalidation

The invalidateContent function does not acquire a snapshot's mutex to
avoid blocking other work (even though it probably should since it's
only called after a context is canceled). A case was added to iterate
through files when a file is created, and it did not respect the fact
that the snapshot's mutex was not locked, resulting in a concurrent map
read and write. This change makes sure that the access of the snapshot's
files map is guarded by a mutex.

As a follow-up, we should just acquire snapshot.mu in invalidateContent.

Updates golang/go#36006

Change-Id: Idd904ae582055ce786062df50875ac7f0896fd1c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/210199
Run-TryBot: Rebecca Stambler <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
(cherry picked from commit db903f3)
Reviewed-on: https://go-review.googlesource.com/c/tools/+/210203

Author: stamblerre

internal/lsp/cache/snapshot.go

@@ -231,6 +231,17 @@ func (s *snapshot) getIDs(uri span.URI) []packageID {
 	return s.ids[uri]
 }
 
+func (s *snapshot) getFileURIs() []span.URI {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	var uris []span.URI
+	for uri := range s.files {
+		uris = append(uris, uri)
+	}
+	return uris
+}
+
 func (s *snapshot) getFile(uri span.URI) source.FileHandle {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -348,7 +359,7 @@ func (v *view) invalidateContent(ctx context.Context, f source.File, kind source
 		// of all of the files in the same directory as this one.
 		// TODO(rstambler): Speed this up by mapping directories to filenames.
 		if dirStat, err := os.Stat(dir(f.URI().Filename())); err == nil {
-			for uri := range v.snapshot.files {
+			for _, uri := range v.snapshot.getFileURIs() {
 				if fdirStat, err := os.Stat(dir(uri.Filename())); err == nil {
 					if os.SameFile(dirStat, fdirStat) {
 						for _, id := range v.snapshot.ids[uri] {