Adopt cmp.Diff for showing unmatched arguments

go.mod

@@ -3,6 +3,7 @@ module go.uber.org/mock
 go 1.20
 
 require (
+	github.com/google/go-cmp v0.6.0
 	golang.org/x/mod v0.15.0
 	golang.org/x/tools v0.18.0
 )

go.sum

@@ -1,3 +1,7 @@
+github.com/google/go-cmp v0.5.8 h1:e6P7q2lk1O+qJJb4BtCQXlK8vWEO8V1ZeuEdJNOqZyg=
+github.com/google/go-cmp v0.5.8/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/yuin/goldmark v1.4.13 h1:fVcFKWvrslecOb/tg+Cc05dkeYx540o0FuFt3nUVDoE=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/mod v0.15.0 h1:SernR4v+D55NyBH2QiEQrlBAnj1ECL6AGrA5+dPaMY8=

gomock/call.go

@@ -19,6 +19,8 @@ import (
 	"reflect"
 	"strconv"
 	"strings"
+
+	"github.com/google/go-cmp/cmp"
 )
 
 // Call represents an expected call to a mock.
@@ -42,11 +44,13 @@ type Call struct {
 	// can set the return values by returning a non-nil slice. Actions run in the
 	// order they are created.
 	actions []func([]any) []any
+
+	cmpOpts cmp.Options // comparison options
 }
 
 // newCall creates a *Call. It requires the method type in order to support
 // unexported methods.
-func newCall(t TestHelper, receiver any, method string, methodType reflect.Type, args ...any) *Call {
+func newCall(t TestHelper, receiver any, method string, methodType reflect.Type, cmpOpts cmp.Options, args ...any) *Call {
 	t.Helper()
 
 	// TODO: check arity, types.
@@ -76,7 +80,8 @@ func newCall(t TestHelper, receiver any, method string, methodType reflect.Type,
 		return rets
 	}}
 	return &Call{t: t, receiver: receiver, method: method, methodType: methodType,
-		args: mArgs, origin: origin, minCalls: 1, maxCalls: 1, actions: actions}
+		args: mArgs, origin: origin, minCalls: 1, maxCalls: 1, actions: actions,
+		cmpOpts: cmpOpts}
 }
 
 // AnyTimes allows the expectation to be called 0 or more times
@@ -317,6 +322,30 @@ func (c *Call) String() string {
 	return fmt.Sprintf("%T.%v(%s) %s", c.receiver, c.method, arguments, c.origin)
 }
 
+func (c *Call) matchError(m Matcher, arg any) error {
+	if g, ok := m.(GotFormatter); ok {
+		return fmt.Errorf(
+			"\nGot: %v\nWant: %v",
+			g.Got(arg), m,
+		)
+	}
+	if d, ok := m.(Differ); ok {
+		diff := d.Diff(arg, c.cmpOpts...)
+		// Recover if the diff is empty, implying the match failed on ignored fields.
+		if diff == "" {
+			return nil
+		}
+		return fmt.Errorf(
+			"\nDiff (-want +got): %s",
+			diff,
+		)
+	}
+	return fmt.Errorf(
+		"\nGot: %v\nWant: %v",
+		formatGottenArg(m, arg), m,
+	)
+}
+
 // Tests if the given call matches the expected call.
 // If yes, returns nil. If no, returns error with message explaining why it does not match.
 func (c *Call) matches(args []any) error {
@@ -327,11 +356,9 @@ func (c *Call) matches(args []any) error {
 		}
 
 		for i, m := range c.args {
-			if !m.Matches(args[i]) {
-				return fmt.Errorf(
-					"expected call at %s doesn't match the argument at index %d.\nGot: %v\nWant: %v",
-					c.origin, i, formatGottenArg(m, args[i]), m,
-				)
+			arg := args[i]
+			if !m.Matches(arg) {
+				return fmt.Errorf("expected call at %s doesn't match the argument at index %d: %w", c.origin, i, c.matchError(m, arg))
 			}
 		}
 	} else {
@@ -349,11 +376,12 @@ func (c *Call) matches(args []any) error {
 		}
 
 		for i, m := range c.args {
+			arg := args[i]
 			if i < c.methodType.NumIn()-1 {
 				// 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), formatGottenArg(m, args[i]), m)
+				if !m.Matches(arg) {
+					return fmt.Errorf("expected call at %s doesn't match the argument at index %d: %w",
+						c.origin, i, c.matchError(m, args[i]))
 				}
 				continue
 			}

gomock/callset_test.go

@@ -30,7 +30,7 @@ func TestCallSetAdd(t *testing.T) {
 
 	numCalls := 10
 	for i := 0; i < numCalls; i++ {
-		cs.Add(newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func)))
+		cs.Add(newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func), nil))
 	}
 
 	call, err := cs.FindMatch(receiver, method, []any{})
@@ -47,13 +47,13 @@ func TestCallSetAdd_WhenOverridable_ClearsPreviousExpectedAndExhausted(t *testin
 	var receiver any = "TestReceiver"
 	cs := newOverridableCallSet()
 
-	cs.Add(newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func)))
+	cs.Add(newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func), nil))
 	numExpectedCalls := len(cs.expected[callSetKey{receiver, method}])
 	if numExpectedCalls != 1 {
 		t.Fatalf("Expected 1 expected call in callset, got %d", numExpectedCalls)
 	}
 
-	cs.Add(newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func)))
+	cs.Add(newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func), nil))
 	newNumExpectedCalls := len(cs.expected[callSetKey{receiver, method}])
 	if newNumExpectedCalls != 1 {
 		t.Fatalf("Expected 1 expected call in callset, got %d", newNumExpectedCalls)
@@ -100,7 +100,7 @@ func TestCallSetFindMatch(t *testing.T) {
 		method := "TestMethod"
 		args := []any{}
 
-		c1 := newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func))
+		c1 := newCall(t, receiver, method, reflect.TypeOf(receiverType{}.Func), nil)
 		cs.exhausted = map[callSetKey][]*Call{
 			{receiver: receiver, fname: method}: {c1},
 		}

gomock/controller.go

@@ -20,6 +20,8 @@ import (
 	"reflect"
 	"runtime"
 	"sync"
+
+	"github.com/google/go-cmp/cmp"
 )
 
 // A TestReporter is something that can be used to report test failures.  It
@@ -76,6 +78,7 @@ type Controller struct {
 	mu            sync.Mutex
 	expectedCalls *callSet
 	finished      bool
+	cmpOpts       cmp.Options
 }
 
 // NewController returns a new Controller. It is the preferred way to create a Controller.
@@ -121,6 +124,20 @@ func (o overridableExpectationsOption) apply(ctrl *Controller) {
 	ctrl.expectedCalls = newOverridableCallSet()
 }
 
+type cmpOptions struct {
+	opts []cmp.Option
+}
+
+func (o cmpOptions) apply(ctrl *Controller) {
+	ctrl.cmpOpts = o.opts
+}
+
+// WithCmpOpts is a ControllerOption that configures the options to pass to
+// cmp.Diff.
+func WithCmpOpts(opts ...cmp.Option) cmpOptions {
+	return cmpOptions{opts: opts}
+}
+
 type cancelReporter struct {
 	t      TestHelper
 	cancel func()
@@ -181,7 +198,7 @@ func (ctrl *Controller) RecordCall(receiver any, method string, args ...any) *Ca
 func (ctrl *Controller) RecordCallWithMethodType(receiver any, method string, methodType reflect.Type, args ...any) *Call {
 	ctrl.T.Helper()
 
-	call := newCall(ctrl.T, receiver, method, methodType, args...)
+	call := newCall(ctrl.T, receiver, method, methodType, ctrl.cmpOpts, args...)
 
 	ctrl.mu.Lock()
 	defer ctrl.mu.Unlock()

gomock/controller_test.go

@@ -20,6 +20,8 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/google/go-cmp/cmp/cmpopts"
+
 	"go.uber.org/mock/gomock"
 )
 
@@ -74,8 +76,11 @@ func (e *ErrorReporter) assertFatal(fn func(), expectedErrMsgs ...string) {
 				// check the last actualErrMsg, because the previous messages come from previous errors
 				actualErrMsg := e.log[len(e.log)-1]
 				for _, expectedErrMsg := range expectedErrMsgs {
-					if !strings.Contains(actualErrMsg, expectedErrMsg) {
+					i := strings.Index(actualErrMsg, expectedErrMsg)
+					if i == -1 {
 						e.t.Errorf("Error message:\ngot: %q\nwant to contain: %q\n", actualErrMsg, expectedErrMsg)
+					} else {
+						actualErrMsg = actualErrMsg[i+len(expectedErrMsg):]
 					}
 				}
 			}
@@ -149,8 +154,9 @@ func (s *Subject) VariadicMethod(arg int, vararg ...string) {}
 
 // A type purely for ActOnTestStructMethod
 type TestStruct struct {
-	Number  int
-	Message string
+	Number        int
+	Message       string
+	secretMessage string
 }
 
 func (s *Subject) ActOnTestStructMethod(arg TestStruct, arg1 int) int {
@@ -171,7 +177,9 @@ func createFixtures(t *testing.T) (reporter *ErrorReporter, ctrl *gomock.Control
 	// Controller. We use it to test that the mock considered tests
 	// successful or failed.
 	reporter = NewErrorReporter(t)
-	ctrl = gomock.NewController(reporter)
+	ctrl = gomock.NewController(
+		reporter, gomock.WithCmpOpts(cmpopts.IgnoreUnexported(TestStruct{})),
+	)
 	return
 }
 
@@ -298,13 +306,13 @@ func TestUnexpectedArgValue_FirstArg(t *testing.T) {
 		// 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)
 	}, "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)")
+		"Diff (-want +got):", "gomock_test.TestStruct{", "Number:  123", "-", "Message: \"hello %s\",", "+", "Message: \"no message\",", "}")
 
 	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)
 	}, "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)")
+		"Diff (-want +got):", "gomock_test.TestStruct{", "-", "Number:  123,", "+", "Number:  11,", "-", "Message: \"hello %s\",", "+", "Message: \"no message\",", "}")
 
 	reporter.assertFatal(func() {
 		// The expected call wasn't made.
@@ -323,7 +331,7 @@ func TestUnexpectedArgValue_SecondArg(t *testing.T) {
 	reporter.assertFatal(func() {
 		ctrl.Call(subject, "ActOnTestStructMethod", TestStruct{Number: 123, Message: "hello"}, 3)
 	}, "Unexpected call to", "doesn't match the argument at index 1",
-		"Got: 3 (int)\nWant: is equal to 15 (int)")
+		"Diff (-want +got):", "int(", "-", "15,", "+", "3,", ")")
 
 	reporter.assertFatal(func() {
 		// The expected call wasn't made.
@@ -742,8 +750,8 @@ func TestVariadicNoMatch(t *testing.T) {
 	ctrl.RecordCall(s, "VariadicMethod", 0)
 	rep.assertFatal(func() {
 		ctrl.Call(s, "VariadicMethod", 1)
-	}, "expected call at", "doesn't match the argument at index 0",
-		"Got: 1 (int)\nWant: is equal to 0 (int)")
+	}, "expected call at", "doesn't match the argument at index 0:",
+		"Diff (-want +got):", "int(", "-", "0,", "+", "1,", ")")
 	ctrl.Call(s, "VariadicMethod", 0)
 }