internal/lsp/cache: use snapshot ID and view folder in ModTidyHandle key

Just to be safe, the snapshot ID and view's folder should be enough to
uniquely identify the ModTidyHandle.

Change-Id: Ie3a0dc64bf16bcc8e4eb75af107481c07de81967
Reviewed-on: https://go-review.googlesource.com/c/tools/+/217657
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

internal/lsp/cache/mod_tidy.go

@@ -29,7 +29,8 @@ const ModTidyError = "go mod tidy"
 const SyntaxError = "syntax"
 
 type parseModKey struct {
-	snapshot source.Snapshot
+	view       string
+	snapshotID uint64
 	cfg        string
 }
 
@@ -96,7 +97,8 @@ func (s *snapshot) ModTidyHandle(ctx context.Context, realfh source.FileHandle)
 	folder := s.View().Folder().Filename()
 
 	key := parseModKey{
-		snapshot: s,
+		view:       folder,
+		snapshotID: s.ID(),
 		cfg:        hashConfig(cfg),
 	}
 	h := s.view.session.cache.store.Bind(key, func(ctx context.Context) interface{} {