[dev.go2go] go/go2go: don't drop type arguments in instantiateType

It's not correct to do it here, as we aren't instantiating this
particular type.

Also had a loop check to avoid endless instantiating a recursive type.

Fixes #39688

Change-Id: Ief4c57bb5cea3013501e33ab5bc82a29707af5be
Reviewed-on: https://go-review.googlesource.com/c/go/+/239137
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/go/go2go/instantiate.go

@@ -29,7 +29,7 @@ func newTypeArgs(typeTypes []types.Type) *typeArgs {
 	}
 }
 
-// typeArgsFromTParams builds mappings from a list of type parameters
+// typeArgsFromFields builds mappings from a list of type parameters
 // expressed as ast.Field values.
 func typeArgsFromFields(t *translator, astTypes []ast.Expr, typeTypes []types.Type, tparams []*ast.Field) *typeArgs {
 	ta := newTypeArgs(typeTypes)
@@ -52,7 +52,7 @@ func typeArgsFromFields(t *translator, astTypes []ast.Expr, typeTypes []types.Ty
 	return ta
 }
 
-// typeArgsFromTParams builds mappings from a list of type parameters
+// typeArgsFromExprs builds mappings from a list of type parameters
 // expressed as ast.Expr values.
 func typeArgsFromExprs(t *translator, astTypes []ast.Expr, typeTypes []types.Type, tparams []ast.Expr) *typeArgs {
 	ta := newTypeArgs(typeTypes)

src/go/go2go/rewrite.go

@@ -128,6 +128,9 @@ type translator struct {
 	typeInstantiations map[types.Type][]*typeInstantiation
 	typePackages       map[*types.Package]bool
 
+	// typeDepth tracks recursive type instantiations.
+	typeDepth int
+
 	// err is set if we have seen an error during this translation.
 	// This is used by the rewrite methods.
 	err error

src/go/go2go/types.go

@@ -43,12 +43,19 @@ func (t *translator) setType(e ast.Expr, nt types.Type) {
 
 // instantiateType instantiates typ using ta.
 func (t *translator) instantiateType(ta *typeArgs, typ types.Type) types.Type {
-	var inProgress *typeInstantiation
-	key := typ
-	if named, ok := typ.(*types.Named); ok {
-		key = t.typeWithoutArgs(named)
+	if t.err != nil {
+		return nil
 	}
-	for _, inst := range t.typeInstantiations[key] {
+
+	t.typeDepth++
+	defer func() { t.typeDepth-- }()
+	if t.typeDepth > 25 {
+		t.err = fmt.Errorf("looping while instantiating %v %v", typ, ta.types)
+		return nil
+	}
+
+	var inProgress *typeInstantiation
+	for _, inst := range t.typeInstantiations[typ] {
 		if t.sameTypes(ta.types, inst.types) {
 			if inst.typ == nil {
 				inProgress = inst
@@ -70,7 +77,7 @@ func (t *translator) instantiateType(ta *typeArgs, typ types.Type) types.Type {
 			types: ta.types,
 			typ:   ityp,
 		}
-		t.typeInstantiations[key] = append(t.typeInstantiations[key], typinst)
+		t.typeInstantiations[typ] = append(t.typeInstantiations[typ], typinst)
 	}
 
 	return ityp