gopls/internal/cache: remove overzealous bug.Report

defineView's doc comment confidently states that the only
possible failure is a canceled context...  yet the very
first thing it does is return an error if the folder path
is invalid---and it was ever thus since the comment was
added in CL 552315. D'oh!

Downgrading to a non-bug error.

Fixes golang/go#70909

Change-Id: Ic58199786816ad7de9f77d18a7d46795440bdf01
Reviewed-on: https://go-review.googlesource.com/c/tools/+/639435
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: adonovan

gopls/internal/cache/session.go

@@ -348,7 +348,7 @@ func (s *Session) View(id string) (*View, error) {
 // SnapshotOf returns a Snapshot corresponding to the given URI.
 //
 // In the case where the file can be  can be associated with a View by
-// bestViewForURI (based on directory information alone, without package
+// [RelevantViews] (based on directory information alone, without package
 // metadata), SnapshotOf returns the current Snapshot for that View. Otherwise,
 // it awaits loading package metadata and returns a Snapshot for the first View
 // containing a real (=not command-line-arguments) package for the file.
@@ -551,13 +551,12 @@ checkFiles:
 		}
 		def, err = defineView(ctx, fs, folder, fh)
 		if err != nil {
-			// We should never call selectViewDefs with a cancellable context, so
-			// this should never fail.
-			return nil, bug.Errorf("failed to define view for open file: %v", err)
+			// e.g. folder path is invalid?
+			return nil, fmt.Errorf("failed to define view for open file: %v", err)
 		}
 		// It need not strictly be the case that the best view for a file is
 		// distinct from other views, as the logic of getViewDefinition and
-		// bestViewForURI does not align perfectly. This is not necessarily a bug:
+		// [RelevantViews] does not align perfectly. This is not necessarily a bug:
 		// there may be files for which we can't construct a valid view.
 		//
 		// Nevertheless, we should not create redundant views.
@@ -572,7 +571,7 @@ checkFiles:
 	return defs, nil
 }
 
-// The viewDefiner interface allows the bestView algorithm to operate on both
+// The viewDefiner interface allows the [RelevantViews] algorithm to operate on both
 // Views and viewDefinitions.
 type viewDefiner interface{ definition() *viewDefinition }
 

gopls/internal/cache/view.go

@@ -809,9 +809,10 @@ func (s *Session) invalidateViewLocked(ctx context.Context, v *View, changed Sta
 // If forURI is non-empty, this view should be the best view including forURI.
 // Otherwise, it is the default view for the folder.
 //
-// defineView only returns an error in the event of context cancellation.
+// defineView may return an error if the context is cancelled, or the
+// workspace folder path is invalid.
 //
-// Note: keep this function in sync with bestView.
+// Note: keep this function in sync with [RelevantViews].
 //
 // TODO(rfindley): we should be able to remove the error return, as
 // findModules is going away, and all other I/O is memoized.
@@ -838,11 +839,11 @@ func defineView(ctx context.Context, fs file.Source, folder *Folder, forFile fil
 		// add those constraints to the viewDefinition's environment.
 
 		// Content trimming is nontrivial, so do this outside of the loop below.
-		// Keep this in sync with bestView.
+		// Keep this in sync with [RelevantViews].
 		path := forFile.URI().Path()
 		if content, err := forFile.Content(); err == nil {
 			// Note the err == nil condition above: by convention a non-existent file
-			// does not have any constraints. See the related note in bestView: this
+			// does not have any constraints. See the related note in [RelevantViews]: this
 			// choice of behavior shouldn't actually matter. In this case, we should
 			// only call defineView with Overlays, which always have content.
 			content = trimContentForPortMatch(content)