Fix: wrong print msg when comparing initialized and uninitialized slice

gomock/call.go

@@ -463,7 +463,7 @@ func (c *Call) addAction(action func([]any) []any) {
 }
 
 func formatGottenArg(m Matcher, arg any) string {
-	got := fmt.Sprintf("%v (%T)", arg, arg)
+	got := fmt.Sprintf("%#v (%T)", arg, arg)
 	if gs, ok := m.(GotFormatter); ok {
 		got = gs.Got(arg)
 	}

gomock/controller_test.go

@@ -152,6 +152,7 @@ func (s *Subject) VariadicMethod(arg int, vararg ...string) {}
 type TestStruct struct {
 	Number  int
 	Message string
+	Slice   []int
 }
 
 func (s *Subject) ActOnTestStructMethod(arg TestStruct, arg1 int) int {
@@ -282,20 +283,26 @@ func TestUnexpectedArgValue_FirstArg(t *testing.T) {
 	defer reporter.recoverUnexpectedFatal()
 	subject := new(Subject)
 
-	expectedArg0 := TestStruct{Number: 123, Message: "hello %s"}
+	expectedArg0 := TestStruct{Number: 123, Message: "hello %s", Slice: []int{1, 2}}
 	ctrl.RecordCall(subject, "ActOnTestStructMethod", expectedArg0, 15)
 
 	reporter.assertFatal(func() {
 		// the method argument (of TestStruct type) has 1 unexpected value (for the Message field)
-		ctrl.Call(subject, "ActOnTestStructMethod", TestStruct{Number: 123, Message: "no message"}, 15)
+		ctrl.Call(subject, "ActOnTestStructMethod", TestStruct{Number: 123, Message: "no message", Slice: []int{1, 2}}, 15)
 	}, "Unexpected call to", "doesn't match the argument at index 0",
-		"Got: {123 no message} (gomock_test.TestStruct)\nWant: is equal to {123 hello %s} (gomock_test.TestStruct)")
+		"Got: gomock_test.TestStruct{Number:123, Message:\"no message\", Slice:[]int{1, 2}} (gomock_test.TestStruct)\nWant: is equal to gomock_test.TestStruct{Number:123, Message:\"hello %s\", Slice:[]int{1, 2}} (gomock_test.TestStruct)")
 
 	reporter.assertFatal(func() {
-		// the method argument (of TestStruct type) has 2 unexpected values (for both fields)
-		ctrl.Call(subject, "ActOnTestStructMethod", TestStruct{Number: 11, Message: "no message"}, 15)
+		// the method argument (of TestStruct type) has 3 unexpected values (for all fields)
+		ctrl.Call(subject, "ActOnTestStructMethod", TestStruct{Number: 11, Message: "no message", Slice: []int{}}, 15)
 	}, "Unexpected call to", "doesn't match the argument at index 0",
-		"Got: {11 no message} (gomock_test.TestStruct)\nWant: is equal to {123 hello %s} (gomock_test.TestStruct)")
+		"Got: gomock_test.TestStruct{Number:11, Message:\"no message\", Slice:[]int{}} (gomock_test.TestStruct)\nWant: is equal to gomock_test.TestStruct{Number:123, Message:\"hello %s\", Slice:[]int{1, 2}} (gomock_test.TestStruct)")
+
+	reporter.assertFatal(func() {
+		// the method argument (of TestStruct type) has 1 unexpected values (for slice field)
+		ctrl.Call(subject, "ActOnTestStructMethod", TestStruct{Number: 123, Message: "hello %s", Slice: nil}, 15)
+	}, "Unexpected call to", "doesn't match the argument at index 0",
+		"Got: gomock_test.TestStruct{Number:123, Message:\"hello %s\", Slice:[]int(nil)} (gomock_test.TestStruct)\nWant: is equal to gomock_test.TestStruct{Number:123, Message:\"hello %s\", Slice:[]int{1, 2}} (gomock_test.TestStruct)")
 
 	reporter.assertFatal(func() {
 		// The expected call wasn't made.
@@ -821,7 +828,7 @@ func TestVariadicArgumentsGotFormatterTooManyArgsFailure(t *testing.T) {
 	rep.assertFatal(func() {
 		ctrl.Call(s, "VariadicMethod", 0, "2", "3")
 	}, "expected call to", "doesn't match the argument at index 1",
-		"Got: test{[2 3]}\nWant: is equal to 1")
+		"Got: test{[2 3]}\nWant: is equal to \"1\" (string)")
 	ctrl.Call(s, "VariadicMethod", 0, "1")
 	ctrl.Finish()
 }

gomock/matchers.go

@@ -132,7 +132,7 @@ func (e eqMatcher) Matches(x any) bool {
 }
 
 func (e eqMatcher) String() string {
-	return fmt.Sprintf("is equal to %v (%T)", e.x, e.x)
+	return fmt.Sprintf("is equal to %#v (%T)", e.x, e.x)
 }
 
 type nilMatcher struct{}