internal/lsp: check file content on disk when opening

As per discussion on golang/go#32810, to avoid the `go list` storm caused by many
files being opened, we check if the file content opened is equivalent to
the content on disk. If so, we mark this file as "on disk" so that we
don't send it as an overlay to go/packages.

Updates golang/go#32810

Change-Id: I0a520cf91bbe933c9afb76d0842f5556ac4e5b28
Reviewed-on: https://go-review.googlesource.com/c/tools/+/184257
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>

internal/lsp/cache/session.go

@@ -44,9 +44,9 @@ type overlay struct {
 	hash    string
 	kind    source.FileKind
 
-	// onDisk is true if a file has been saved on disk,
+	// sameContentOnDisk is true if a file has been saved on disk,
 	// and therefore does not need to be part of the overlay sent to go/packages.
-	onDisk bool
+	sameContentOnDisk bool
 }
 
 func (s *session) Shutdown(ctx context.Context) {
@@ -182,14 +182,17 @@ func (s *session) Logger() xlog.Logger {
 	return s.log
 }
 
-func (s *session) DidOpen(ctx context.Context, uri span.URI) {
+func (s *session) DidOpen(ctx context.Context, uri span.URI, text []byte) {
+	// Mark the file as open.
 	s.openFiles.Store(uri, true)
 
+	// Read the file on disk and compare it to the text provided.
+	// If it is the same as on disk, we can avoid sending it as an overlay to go/packages.
+	s.openOverlay(ctx, uri, text)
+
 	// Mark the file as just opened so that we know to re-run packages.Load on it.
 	// We do this because we may not be aware of all of the packages the file belongs to.
-
 	// A file may be in multiple views.
-	// For each view, get the file and mark it as just opened.
 	for _, view := range s.views {
 		if strings.HasPrefix(string(uri), string(view.Folder())) {
 			f, err := view.GetFile(ctx, uri)
@@ -215,7 +218,7 @@ func (s *session) DidSave(uri span.URI) {
 	defer s.overlayMu.Unlock()
 
 	if overlay, ok := s.overlays[uri]; ok {
-		overlay.onDisk = true
+		overlay.sameContentOnDisk = true
 	}
 }
 
@@ -255,6 +258,30 @@ func (s *session) SetOverlay(uri span.URI, data []byte) {
 	}
 }
 
+// openOverlay adds the file content to the overlay.
+// It also checks if the provided content is equivalent to the file's content on disk.
+func (s *session) openOverlay(ctx context.Context, uri span.URI, data []byte) {
+	s.overlayMu.Lock()
+	defer func() {
+		s.overlayMu.Unlock()
+		s.filesWatchMap.Notify(uri)
+	}()
+	s.overlays[uri] = &overlay{
+		session: s,
+		uri:     uri,
+		data:    data,
+		hash:    hashContents(data),
+	}
+	_, hash, err := s.cache.GetFile(uri).Read(ctx)
+	if err != nil {
+		s.log.Errorf(ctx, "failed to read %s: %v", uri, err)
+		return
+	}
+	if hash == s.overlays[uri].hash {
+		s.overlays[uri].sameContentOnDisk = true
+	}
+}
+
 func (s *session) readOverlay(uri span.URI) *overlay {
 	s.overlayMu.Lock()
 	defer s.overlayMu.Unlock()
@@ -272,7 +299,7 @@ func (s *session) buildOverlay() map[string][]byte {
 
 	overlays := make(map[string][]byte)
 	for uri, overlay := range s.overlays {
-		if overlay.onDisk {
+		if overlay.sameContentOnDisk {
 			continue
 		}
 		overlays[uri.Filename()] = overlay.data

internal/lsp/source/view.go

@@ -154,7 +154,7 @@ type Session interface {
 	FileSystem
 
 	// DidOpen is invoked each time a file is opened in the editor.
-	DidOpen(ctx context.Context, uri span.URI)
+	DidOpen(ctx context.Context, uri span.URI, text []byte)
 
 	// DidSave is invoked each time an open file is saved in the editor.
 	DidSave(uri span.URI)

internal/lsp/text_synchronization.go

@@ -17,8 +17,18 @@ import (
 
 func (s *Server) didOpen(ctx context.Context, params *protocol.DidOpenTextDocumentParams) error {
 	uri := span.NewURI(params.TextDocument.URI)
-	s.session.DidOpen(ctx, uri)
+	text := []byte(params.TextDocument.Text)
-	return s.cacheAndDiagnose(ctx, uri, []byte(params.TextDocument.Text))
+
+	// Open the file.
+	s.session.DidOpen(ctx, uri, text)
+
+	// Run diagnostics on the newly-changed file.
+	view := s.session.ViewOf(uri)
+	go func() {
+		ctx := view.BackgroundContext()
+		s.Diagnostics(ctx, view, uri)
+	}()
+	return nil
 }
 
 func (s *Server) didChange(ctx context.Context, params *protocol.DidChangeTextDocumentParams) error {
@@ -46,16 +56,12 @@ func (s *Server) didChange(ctx context.Context, params *protocol.DidChangeTextDo
 			}
 		}
 	}
-
 	// Cache the new file content and send fresh diagnostics.
-	return s.cacheAndDiagnose(ctx, uri, []byte(text))
-}
-
-func (s *Server) cacheAndDiagnose(ctx context.Context, uri span.URI, content []byte) error {
 	view := s.session.ViewOf(uri)
-	if err := view.SetContent(ctx, uri, content); err != nil {
+	if err := view.SetContent(ctx, uri, []byte(text)); err != nil {
 		return err
 	}
+	// Run diagnostics on the newly-changed file.
 	go func() {
 		ctx := view.BackgroundContext()
 		s.Diagnostics(ctx, view, uri)