[dev.go2go] go/go2go: avoid crashing on predeclared error type

It has no package, so we need to check for Pkg() == nil.

Fixes #39878

Change-Id: I14a47c5098f97ce42dfa8cc875819f244a2b0201
Reviewed-on: https://go-review.googlesource.com/c/go/+/240013
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: ianlancetaylor

src/go/go2go/rewrite.go

@@ -1031,7 +1031,7 @@ func (t *translator) instantiationTypes(call *ast.CallExpr) (argList []ast.Expr,
 	// Instantiating with a locally defined type won't work.
 	// Check that here.
 	for i, typ := range typeList {
-		if named, ok := typ.(*types.Named); ok {
+		if named, ok := typ.(*types.Named); ok && named.Obj().Pkg() != nil {
 			if scope := named.Obj().Parent(); scope != nil && scope != named.Obj().Pkg().Scope() {
 				var pos token.Pos
 				if haveInferred {

src/go/go2go/types.go

@@ -299,7 +299,9 @@ func (t *translator) addTypePackages(typ types.Type) {
 		t.addTypePackages(typ.Elem())
 	case *types.Named:
 		// This is the point of this whole method.
-		t.typePackages[typ.Obj().Pkg()] = true
+		if typ.Obj().Pkg() != nil {
+			t.typePackages[typ.Obj().Pkg()] = true
+		}
 	case *types.TypeParam:
 	default:
 		panic(fmt.Sprintf("unimplemented Type %T", typ))

test/gen/g038.go2

@@ -0,0 +1,15 @@
+// compile
+
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func F(type T comparable)(a T) bool {
+	return a == a
+}
+
+func G() {
+	F(error(nil))
+}