internal/lsp: do not reinitialize the workspace for didOpen events

Previously, we would treat file opens/closes as workspace
reinitialization events.

Change-Id: Ib8ca490fe7a44768a757311b058093d0bf3888c6
Reviewed-on: https://go-review.googlesource.com/c/tools/+/317450
Trust: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

gopls/internal/regtest/diagnostics/diagnostics_test.go

@@ -1912,3 +1912,27 @@ func foo() int {
 		)
 	})
 }
+
+// This test confirms that the view does not reinitialize when a go.mod file is
+// opened.
+func TestNoReinitialize(t *testing.T) {
+	const files = `
+-- go.mod --
+module mod.com
+
+go 1.12
+-- main.go --
+package main
+
+func main() {}
+`
+	Run(t, files, func(t *testing.T, env *Env) {
+		env.OpenFile("go.mod")
+		env.Await(
+			OnceMet(
+				env.DoneWithOpen(),
+				LogMatching(protocol.Info, `.*query=\[builtin mod.com/...\].*`, 1),
+			),
+		)
+	})
+}

internal/lsp/cache/session.go

@@ -408,6 +408,11 @@ type fileChange struct {
 	content    []byte
 	exists     bool
 	fileHandle source.VersionedFileHandle
+
+	// isUnchanged indicates whether the file action is one that does not
+	// change the actual contents of the file. Opens and closes should not
+	// be treated like other changes, since the file content doesn't change.
+	isUnchanged bool
 }
 
 func (s *Session) DidModifyFiles(ctx context.Context, changes []source.FileModification) (map[source.Snapshot][]span.URI, []func(), error) {
@@ -448,6 +453,8 @@ func (s *Session) DidModifyFiles(ctx context.Context, changes []source.FileModif
 		}
 		affectedViews[c.URI] = changedViews
 
+		isUnchanged := c.Action == source.Open || c.Action == source.Close
+
 		// Apply the changes to all affected views.
 		for _, view := range changedViews {
 			// Make sure that the file is added to the view.
@@ -457,9 +464,10 @@ func (s *Session) DidModifyFiles(ctx context.Context, changes []source.FileModif
 			}
 			if fh, ok := overlays[c.URI]; ok {
 				views[view][c.URI] = &fileChange{
-					content:    fh.text,
-					exists:     true,
-					fileHandle: fh,
+					content:     fh.text,
+					exists:      true,
+					fileHandle:  fh,
+					isUnchanged: isUnchanged,
 				}
 			} else {
 				fsFile, err := s.cache.getFile(ctx, c.URI)
@@ -469,9 +477,10 @@ func (s *Session) DidModifyFiles(ctx context.Context, changes []source.FileModif
 				content, err := fsFile.Read()
 				fh := &closedFile{fsFile}
 				views[view][c.URI] = &fileChange{
-					content:    content,
-					exists:     err == nil,
-					fileHandle: fh,
+					content:     content,
+					exists:      err == nil,
+					fileHandle:  fh,
+					isUnchanged: isUnchanged,
 				}
 			}
 		}

internal/lsp/cache/workspace.go

@@ -277,7 +277,8 @@ func (w *workspace) invalidate(ctx context.Context, changes map[span.URI]*fileCh
 		// If gopls.mod has changed we need to either re-read it if it exists or
 		// walk the filesystem if it has been deleted.
 		gmURI := goplsModURI(w.root)
-		if change, ok := changes[gmURI]; ok {
+		// File opens/closes are just no-ops.
+		if change, ok := changes[gmURI]; ok && !change.isUnchanged {
 			if change.exists {
 				// Only invalidate if the gopls.mod actually parses.
 				// Otherwise, stick with the current gopls.mod.
@@ -326,7 +327,7 @@ 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 change.isUnchanged || !isGoMod(uri) || !source.InDir(result.root.Filename(), uri.Filename()) {
 				continue
 			}
 			changed = true