gopls: fix a few bugs related to the new modcache imports source

Fix the following bugs related to the new "gopls" imports source and
module cache index:
- Only construct the modcacheState if the imports source is "gopls",
  which is not yet the default. This was causing memory regressions, as
  the modcache table is non-trivial.
- Add missing error handling.
- Don't call modcacheState.stopTimer if the modcacheState is nil, which
  may already have been the case with "importsSource": "off".

For golang/go#71607

Change-Id: I33c90ee4b97c8675b342cb0c045eef183a1ef365
Reviewed-on: https://go-review.googlesource.com/c/tools/+/650397
Reviewed-by: Alan Donovan <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: findleyr

gopls/internal/cache/session.go

@@ -238,7 +238,12 @@ func (s *Session) createView(ctx context.Context, def *viewDefinition) (*View, *
 		viewDefinition:       def,
 		importsState:         newImportsState(backgroundCtx, s.cache.modCache, pe),
 	}
-	if def.folder.Options.ImportsSource != settings.ImportsSourceOff {
+
+	// Keep this in sync with golang.computeImportEdits.
+	//
+	// TODO(rfindley): encapsulate the imports state logic so that the handling
+	// for Options.ImportsSource is in a single location.
+	if def.folder.Options.ImportsSource == settings.ImportsSourceGopls {
 		v.modcacheState = newModcacheState(def.folder.Env.GOMODCACHE)
 	}
 

gopls/internal/cache/view.go

@@ -109,7 +109,10 @@ type View struct {
 	// importsState is for the old imports code
 	importsState *importsState
 
-	// maintain the current module cache index
+	// modcacheState is the replacement for importsState, to be used for
+	// goimports operations when the imports source is "gopls".
+	//
+	// It may be nil, if the imports source is not "gopls".
 	modcacheState *modcacheState
 
 	// pkgIndex is an index of package IDs, for efficient storage of typerefs.
@@ -492,7 +495,9 @@ func (v *View) shutdown() {
 	// Cancel the initial workspace load if it is still running.
 	v.cancelInitialWorkspaceLoad()
 	v.importsState.stopTimer()
-	v.modcacheState.stopTimer()
+	if v.modcacheState != nil {
+		v.modcacheState.stopTimer()
+	}
 
 	v.snapshotMu.Lock()
 	if v.snapshot != nil {

gopls/internal/golang/format.go

@@ -137,7 +137,13 @@ func computeImportEdits(ctx context.Context, pgf *parsego.File, snapshot *cache.
 
 	// Build up basic information about the original file.
 	isource, err := imports.NewProcessEnvSource(options.Env, filename, pgf.File.Name.Name)
+	if err != nil {
+		return nil, nil, err
+	}
 	var source imports.Source
+
+	// Keep this in sync with [cache.Session.createView] (see the TODO there: we
+	// should factor out the handling of the ImportsSource setting).
 	switch snapshot.Options().ImportsSource {
 	case settings.ImportsSourceGopls:
 		source = snapshot.NewGoplsSource(isource)