internal/lsp/cache: clarify an error message about mismatching casing

Fixes golang/go#47509

Change-Id: I7a72470b7281277ece301cda4486aed83baaa08d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/339352
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

internal/lsp/cache/os_darwin.go

@@ -52,7 +52,7 @@ func darwinCheckPathCase(path string) error {
 			break
 		}
 		if g != w {
-			return fmt.Errorf("case mismatch in path %q: component %q should be %q", path, g, w)
+			return fmt.Errorf("case mismatch in path %q: component %q is listed by macOS as %q", path, g, w)
 		}
 	}
 	return nil

internal/lsp/cache/os_windows.go

@@ -48,7 +48,7 @@ func windowsCheckPathCase(path string) error {
 	}
 	for got, want := path, longstr; !isRoot(got) && !isRoot(want); got, want = filepath.Dir(got), filepath.Dir(want) {
 		if g, w := filepath.Base(got), filepath.Base(want); g != w {
-			return fmt.Errorf("case mismatch in path %q: component %q should be %q", path, g, w)
+			return fmt.Errorf("case mismatch in path %q: component %q is listed by Windows as %q", path, g, w)
 		}
 	}
 	return nil

internal/lsp/cache/view.go

@@ -727,7 +727,7 @@ func (v *View) updateWorkspaceLocked(ctx context.Context) error {
 
 func (s *Session) getWorkspaceInformation(ctx context.Context, folder span.URI, options *source.Options) (*workspaceInformation, error) {
 	if err := checkPathCase(folder.Filename()); err != nil {
-		return nil, errors.Errorf("invalid workspace configuration: %w", err)
+		return nil, errors.Errorf("invalid workspace folder path: %w; check that the casing of the configured workspace folder path agrees with the casing reported by the operating system", err)
 	}
 	var err error
 	inv := gocommand.Invocation{