fix(lsp): never scan the filesystem root for an opened document's siblings

changes/unreleased/lsp-no-root-sibling-scan.fixed.md

@@ -0,0 +1 @@
+- The language server no longer scans the filesystem root for sibling files when a document at the root is opened outside every workspace folder; the walk could take minutes.

internal/frontend/lsp/files.go

@@ -232,16 +232,20 @@ func (s *Server) DidChangeWorkspaceFolders(ctx context.Context, params *protocol
 
 // maxOpenedDirs bounds the directories the scan for an opened document's
 // siblings visits: the document's directory was not chosen as a workspace, and
-// may be a home directory or the filesystem root.
+// may be a home directory.
 const maxOpenedDirs = 2000
 
 // indexOpenedDirectory indexes the directory of a document opened outside every
-// folder, so sibling imports resolve; it is rescanned once all its documents close.
+// folder, so sibling imports resolve; it is rescanned once all its documents
+// close. The filesystem root is never indexed: walking it can take minutes.
 func (s *Server) indexOpenedDirectory(name string) {
 	if !filepath.IsAbs(name) {
 		return
 	}
 	dir := filepath.Dir(name)
+	if dir == filepath.VolumeName(name)+string(filepath.Separator) {
+		return
+	}
 	s.mu.Lock()
 	if underAnyFolder(name, s.folders) || s.openDirs[dir] {
 		s.mu.Unlock()

internal/frontend/lsp/files_test.go

@@ -709,6 +709,30 @@ func TestOpeningFileOutsideFoldersIndexesItsDirectory(t *testing.T) {
 	}
 }
 
+// A document at the filesystem root indexes no siblings: scanning it would
+// walk the whole filesystem.
+func TestOpeningFileAtFilesystemRootIndexesNothing(t *testing.T) {
+	s := NewServer(model.NewWorkspace())
+	fc := &fakeClient{}
+	s.client = fc
+	ctx := context.Background()
+	if _, err := s.Initialize(ctx, &protocol.InitializeParams{}); err != nil {
+		t.Fatalf("Initialize err = %v", err)
+	}
+	if err := s.Initialized(ctx, &protocol.InitializedParams{}); err != nil {
+		t.Fatalf("Initialized err = %v", err)
+	}
+
+	name := filepath.Join(string(filepath.Separator), "m.sysml")
+	openFile(t, s, name, "package M {\n    part def A;\n}\n")
+	if len(s.openDirs) != 0 {
+		t.Errorf("openDirs = %v, want none", s.openDirs)
+	}
+	if msgs := diagnosticsFor(fc, name); len(msgs) != 0 {
+		t.Fatalf("diagnostics for %s = %v, want none", name, msgs)
+	}
+}
+
 // The directory scan an open document triggers never overwrites another open
 // buffer, whose text the editor owns.
 func TestOpeningFileOutsideFoldersKeepsOpenBuffers(t *testing.T) {