gopls: minor cleanup of standalone package support

Remove an unused err value, and update tests to exercise multiple
standaloneTags.

Change-Id: I88daace99111cba6f8bc74fad8aa0db844cb2654
Reviewed-on: https://go-review.googlesource.com/c/tools/+/442776
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Findley <rfindley@google.com>

gopls/internal/lsp/cache/standalone_go116_test.go

@@ -30,6 +30,12 @@ func TestIsStandaloneFile(t *testing.T) {
 			[]string{"ignore"},
 			true,
 		},
+		{
+			"multiple tags",
+			"//go:build ignore\n\npackage main\n",
+			[]string{"exclude", "ignore"},
+			true,
+		},
 		{
 			"invalid tag",
 			"// +build ignore\n\npackage main\n",

gopls/internal/lsp/diagnostics.go

@@ -534,7 +534,7 @@ func (s *Server) checkForOrphanedFile(ctx context.Context, snapshot source.Snaps
 	if snapshot.IsBuiltin(ctx, fh.URI()) {
 		return nil
 	}
-	pkgs, err := snapshot.PackagesForFile(ctx, fh.URI(), source.TypecheckWorkspace, false)
+	pkgs, _ := snapshot.PackagesForFile(ctx, fh.URI(), source.TypecheckWorkspace, false)
 	if len(pkgs) > 0 {
 		return nil
 	}

gopls/internal/regtest/workspace/standalone_test.go

@@ -214,7 +214,7 @@ func main() {}
 
 	WithOptions(
 		Settings{
-			"standaloneTags": []string{"standalone"},
+			"standaloneTags": []string{"standalone", "script"},
 		},
 	).Run(t, files, func(t *testing.T, env *Env) {
 		env.OpenFile("ignore.go")