internal/lsp/cache: improve snapshot clone perfomance

The existing implementation uses a lot of URI.Filename() calls,
which are pretty expensive. Moreover, these calls are not necessary,
as long as all the actions could be done with the raw URI string.
This patch removes such calls and uses simple string casts.

Updates golang/go#45686

internal/lsp/cache/snapshot.go

@@ -1279,7 +1279,7 @@ func contains(views []*View, view *View) bool {
 }
 
 func inVendor(uri span.URI) bool {
-	toSlash := filepath.ToSlash(uri.Filename())
+	toSlash := filepath.ToSlash(string(uri))
 	if !strings.Contains(toSlash, "/vendor/") {
 		return false
 	}
@@ -1548,7 +1548,7 @@ func (s *snapshot) clone(ctx, bgCtx context.Context, changes map[span.URI]*fileC
 				// For internal tests, we need _test files, not just the normal
 				// ones. External tests only have _test files, but we can check
 				// them anyway.
-				if m.forTest != "" && !strings.HasSuffix(uri.Filename(), "_test.go") {
+				if m.forTest != "" && !strings.HasSuffix(string(uri), "_test.go") {
 					continue
 				}
 				if _, ok := result.files[uri]; ok {

internal/lsp/cache/workspace.go

@@ -326,7 +326,7 @@ func (w *workspace) invalidate(ctx context.Context, changes map[span.URI]*fileCh
 	// here.
 	if result.moduleSource != goplsModWorkspace {
 		for uri, change := range changes {
-			if !isGoMod(uri) || !source.InDir(result.root.Filename(), uri.Filename()) {
+			if !isGoMod(uri) || !source.InDir(string(result.root), string(uri)) {
 				continue
 			}
 			changed = true
@@ -350,7 +350,7 @@ func (w *workspace) invalidate(ctx context.Context, changes map[span.URI]*fileCh
 			continue
 		}
 		// TODO(rFindley) factor out this URI mangling.
-		dir := filepath.Dir(uri.Filename())
+		dir := filepath.Dir(string(uri))
 		modURI := span.URIFromPath(filepath.Join(dir, "go.mod"))
 		if _, active := result.activeModFiles[modURI]; !active {
 			continue