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// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package cache
import (
// An overlayFS is a source.FileSource that keeps track of overlays on top of a
// delegate FileSource.
type overlayFS struct {
delegate source.FileSource
mu sync.Mutex
overlays map[span.URI]*Overlay
func newOverlayFS(delegate source.FileSource) *overlayFS {
return &overlayFS{
delegate: delegate,
overlays: make(map[span.URI]*Overlay),
// Overlays returns a new unordered array of overlays.
func (fs *overlayFS) Overlays() []*Overlay {
overlays := make([]*Overlay, 0, len(fs.overlays))
for _, overlay := range fs.overlays {
overlays = append(overlays, overlay)
return overlays
func (fs *overlayFS) ReadFile(ctx context.Context, uri span.URI) (source.FileHandle, error) {
overlay, ok := fs.overlays[uri]
if ok {
return overlay, nil
return fs.delegate.ReadFile(ctx, uri)
// An Overlay is a file open in the editor. It may have unsaved edits.
// It implements the source.FileHandle interface.
type Overlay struct {
uri span.URI
content []byte
hash source.Hash
version int32
kind source.FileKind
// saved is true if a file matches the state on disk,
// and therefore does not need to be part of the overlay sent to go/packages.
saved bool
func (o *Overlay) URI() span.URI { return o.uri }
func (o *Overlay) FileIdentity() source.FileIdentity {
return source.FileIdentity{
URI: o.uri,
Hash: o.hash,
func (o *Overlay) Content() ([]byte, error) { return o.content, nil }
func (o *Overlay) Version() int32 { return o.version }
func (o *Overlay) Saved() bool { return o.saved }
func (o *Overlay) Kind() source.FileKind { return o.kind }