internal/lsp/cache: invalidate metadata for x_tests and test variants

Invalidating metadata for reverse dependencies isn't necessary, except
for in the case of test variants and x_tests.

An example:

The only way to reload the metadata for
"golang.org/x/tools/internal/lsp/cache
[golang.org/x/tools/internal/lsp/source.test]" is by reloading
"golang.org/x/tools/internal/lsp/source" with "[-test -deps]". That
means we have to invalidate the metadata for that
"golang.org/x/tools/internal/lsp/source_test" when we invalidating
"golang.org/x/tools/internal/lsp/cache".

Fixes golang/go#36165

Change-Id: Iff0e03a7a46158fbdafaffa091f90ca434700a97
Reviewed-on: https://go-review.googlesource.com/c/tools/+/215117
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

internal/lsp/cache/snapshot.go

@@ -666,6 +666,22 @@ func (s *snapshot) clone(ctx context.Context, withoutURI span.URI) *snapshot {
 	for id := range directIDs {
 		addRevDeps(id)
 	}
+	// Invalidate metadata for the transitive dependencies,
+	// if they are x_tests and test variants.
+	//
+	// An example:
+	//
+	// The only way to reload the metadata for
+	// golang.org/x/tools/internal/lsp/cache [golang.org/x/tools/internal/lsp/source.test]
+	// is by reloading golang.org/x/tools/internal/lsp/source.
+	// That means we have to invalidate the metadata for
+	// golang.org/x/tools/internal/lsp/source_test when invalidating metadata for
+	// golang.org/x/tools/internal/lsp/cache.
+	for id := range transitiveIDs {
+		if m := s.metadata[id]; m != nil && m.forTest != "" {
+			directIDs[id] = struct{}{}
+		}
+	}
 
 	result := &snapshot{
 		id:                s.id + 1,