interp: don't panic for undefined types

interp/cfg.go

@@ -203,7 +203,10 @@ func (interp *Interpreter) cfg(root *node) ([]*node, error) {
 				} else if n.anc.typ != nil {
 					n.typ = n.anc.typ.val
 				}
-				// FIXME n.typ can be nil.
+				if n.typ == nil {
+					err = n.cfgErrorf("undefined type")
+					return false
+				}
 				n.typ.untyped = true
 			}
 			// Propagate type to children, to handle implicit types

interp/interp_eval_test.go

@@ -368,6 +368,32 @@ func TestEvalChan(t *testing.T) {
 	})
 }
 
+func TestEvalMissingSymbol(t *testing.T) {
+	defer func() {
+		r := recover()
+		if r != nil {
+			t.Errorf("unexpected panic: %v", r)
+		}
+	}()
+
+	type S2 struct{}
+	type S1 struct {
+		F S2
+	}
+	i := interp.New(interp.Options{})
+	i.Use(interp.Exports{"p": map[string]reflect.Value{
+		"S1": reflect.Zero(reflect.TypeOf(&S1{})),
+	}})
+	_, err := i.Eval(`import "p"`)
+	if err != nil {
+		t.Fatalf("failed to import package: %v", err)
+	}
+	_, err = i.Eval(`p.S1{F: p.S2{}}`)
+	if err == nil {
+		t.Error("unexpected nil error for expression with undefined type")
+	}
+}
+
 func runTests(t *testing.T, i *interp.Interpreter, tests []testCase) {
 	for _, test := range tests {
 		t.Run(test.desc, func(t *testing.T) {