1 files changed, 37 insertions, 2 deletions
diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
index be05d06fd0..d6a2eb4eb3 100644
--- a/src/cmd/compile/internal/types2/api_test.go
+++ b/src/cmd/compile/internal/types2/api_test.go
@@ -1871,8 +1871,10 @@ func TestInstantiate(t *testing.T) {
 
 	// instantiation should succeed (no endless recursion)
 	// even with a nil *Checker
-	var check *Checker
-	res := check.Instantiate(nopos, T, []Type{Typ[Int]}, nil, false)
+	res, err := Instantiate(nil, T, []Type{Typ[Int]}, false)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	// instantiated type should point to itself
 	if p := res.Underlying().(*Pointer).Elem(); p != res {
@@ -1880,6 +1882,39 @@ func TestInstantiate(t *testing.T) {
 	}
 }
 
+func TestInstantiateErrors(t *testing.T) {
+	tests := []struct {
+		src    string // by convention, T must be the type being instantiated
+		targs  []Type
+		wantAt int // -1 indicates no error
+	}{
+		{"type T[P interface{~string}] int", []Type{Typ[Int]}, 0},
+		{"type T[P1 interface{int}, P2 interface{~string}] int", []Type{Typ[Int], Typ[Int]}, 1},
+		{"type T[P1 any, P2 interface{~[]P1}] int", []Type{Typ[Int], NewSlice(Typ[String])}, 1},
+		{"type T[P1 interface{~[]P2}, P2 any] int", []Type{NewSlice(Typ[String]), Typ[Int]}, 0},
+	}
+
+	for _, test := range tests {
+		src := genericPkg + "p; " + test.src
+		pkg, err := pkgFor(".", src, nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		T := pkg.Scope().Lookup("T").Type().(*Named)
+
+		_, err = Instantiate(nil, T, test.targs, true)
+		if err == nil {
+			t.Fatalf("Instantiate(%v, %v) returned nil error, want non-nil", T, test.targs)
+		}
+
+		gotAt := err.(ArgumentError).Index()
+		if gotAt != test.wantAt {
+			t.Errorf("Instantate(%v, %v): error at index %d, want index %d", T, test.targs, gotAt, test.wantAt)
+		}
+	}
+}
+
 func TestInstanceIdentity(t *testing.T) {
 	imports := make(testImporter)
 	conf := Config{Importer: imports}