format variadic arguments with GotFormatter (#434)

Matchers implementing the GotFormatter interface are no longer ignored.
Match failures are formatted correctly. 

Fixes: #432

gomock/call.go

@@ -304,14 +304,9 @@ func (c *Call) matches(args []interface{}) error {
 
 		for i, m := range c.args {
 			if !m.Matches(args[i]) {
-				got := fmt.Sprintf("%v", args[i])
-				if gs, ok := m.(GotFormatter); ok {
-					got = gs.Got(args[i])
-				}
-
 				return fmt.Errorf(
 					"expected call at %s doesn't match the argument at index %d.\nGot: %v\nWant: %v",
-					c.origin, i, got, m,
+					c.origin, i, formatGottenArg(m, args[i]), m,
 				)
 			}
 		}
@@ -334,7 +329,7 @@ func (c *Call) matches(args []interface{}) error {
 				// Non-variadic args
 				if !m.Matches(args[i]) {
 					return fmt.Errorf("expected call at %s doesn't match the argument at index %s.\nGot: %v\nWant: %v",
-						c.origin, strconv.Itoa(i), args[i], m)
+						c.origin, strconv.Itoa(i), formatGottenArg(m, args[i]), m)
 				}
 				continue
 			}
@@ -376,9 +371,9 @@ func (c *Call) matches(args []interface{}) error {
 			// Got Foo(a, b, c, d) want Foo(matcherA, matcherB, matcherC, matcherD, matcherE)
 			// Got Foo(a, b, c, d, e) want Foo(matcherA, matcherB, matcherC, matcherD)
 			// Got Foo(a, b, c) want Foo(matcherA, matcherB)
-			return fmt.Errorf("Expected call at %s doesn't match the argument at index %s.\nGot: %v\nWant: %v",
-				c.origin, strconv.Itoa(i), args[i:], c.args[i])
 
+			return fmt.Errorf("expected call at %s doesn't match the argument at index %s.\nGot: %v\nWant: %v",
+				c.origin, strconv.Itoa(i), formatGottenArg(m, args[i:]), c.args[i])
 		}
 	}
 
@@ -428,3 +423,11 @@ func setSlice(arg interface{}, v reflect.Value) {
 func (c *Call) addAction(action func([]interface{}) []interface{}) {
 	c.actions = append(c.actions, action)
 }
+
+func formatGottenArg(m Matcher, arg interface{}) string {
+	got := fmt.Sprintf("%v", arg)
+	if gs, ok := m.(GotFormatter); ok {
+		got = gs.Got(arg)
+	}
+	return got
+}

gomock/controller_test.go

@@ -749,6 +749,55 @@ func TestVariadicMatchingWithSlice(t *testing.T) {
 	}
 }
 
+func TestVariadicArgumentsGotFormatter(t *testing.T) {
+	rep, ctrl := createFixtures(t)
+	defer rep.recoverUnexpectedFatal()
+
+	s := new(Subject)
+	ctrl.RecordCall(
+		s,
+		"VariadicMethod",
+		gomock.GotFormatterAdapter(
+			gomock.GotFormatterFunc(func(i interface{}) string {
+				return fmt.Sprintf("test{%v}", i)
+			}),
+			gomock.Eq(0),
+		),
+	)
+
+	rep.assertFatal(func() {
+		ctrl.Call(s, "VariadicMethod", 1)
+	}, "expected call to", "doesn't match the argument at index 0",
+		"Got: test{1}\nWant: is equal to 0")
+	ctrl.Call(s, "VariadicMethod", 0)
+	ctrl.Finish()
+}
+
+func TestVariadicArgumentsGotFormatterTooManyArgsFailure(t *testing.T) {
+	rep, ctrl := createFixtures(t)
+	defer rep.recoverUnexpectedFatal()
+
+	s := new(Subject)
+	ctrl.RecordCall(
+		s,
+		"VariadicMethod",
+		0,
+		gomock.GotFormatterAdapter(
+			gomock.GotFormatterFunc(func(i interface{}) string {
+				return fmt.Sprintf("test{%v}", i)
+			}),
+			gomock.Eq("1"),
+		),
+	)
+
+	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")
+	ctrl.Call(s, "VariadicMethod", 0, "1")
+	ctrl.Finish()
+}
+
 func TestNoHelper(t *testing.T) {
 	ctrlNoHelper := gomock.NewController(NewErrorReporter(t))