From 665220df08a50d925c1f2ffa09b0107913c40e80 Mon Sep 17 00:00:00 2001
From: Damiano Petrungaro <damianopetrungaro@gmail.com>
Date: Wed, 16 Aug 2023 19:16:57 +0200
Subject: [PATCH] feat: add Cond matcher  (#60)

This adds `Cond`, a new `Matcher` that can match using an arbitrary function.
If the function returns true for the parameter to the mock,
then there's a match.
---
 gomock/matchers.go      | 22 ++++++++++++++++++++++
 gomock/matchers_test.go |  4 ++++
 sample/imp4/imp4.go     |  4 +++-
 sample/user_test.go     | 17 +++++++++++++++++
 4 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/gomock/matchers.go b/gomock/matchers.go
index c1edac5..bac4623 100644
--- a/gomock/matchers.go
+++ b/gomock/matchers.go
@@ -97,6 +97,18 @@ func (anyMatcher) String() string {
 	return "is anything"
 }
 
+type condMatcher struct {
+	fn func(x any) bool
+}
+
+func (c condMatcher) Matches(x any) bool {
+	return c.fn(x)
+}
+
+func (condMatcher) String() string {
+	return "adheres to a custom condition"
+}
+
 type eqMatcher struct {
 	x any
 }
@@ -280,6 +292,16 @@ func All(ms ...Matcher) Matcher { return allMatcher{ms} }
 // Any returns a matcher that always matches.
 func Any() Matcher { return anyMatcher{} }
 
+// Cond returns a matcher that matches when the given function returns true
+// after passing it the parameter to the mock function.
+// This is particularly useful in case you want to match over a field of a custom struct, or dynamic logic.
+//
+// Example usage:
+//
+//	Cond(func(x any){return x.(int) == 1}).Matches(1) // returns true
+//	Cond(func(x any){return x.(int) == 2}).Matches(1) // returns false
+func Cond(fn func(x any) bool) Matcher { return condMatcher{fn} }
+
 // Eq returns a matcher that matches on equality.
 //
 // Example usage:
diff --git a/gomock/matchers_test.go b/gomock/matchers_test.go
index 3966075..8de86a2 100644
--- a/gomock/matchers_test.go
+++ b/gomock/matchers_test.go
@@ -27,6 +27,9 @@ import (
 )
 
 type A []string
+type B struct {
+	Name string
+}
 
 func TestMatchers(t *testing.T) {
 	type e any
@@ -50,6 +53,7 @@ func TestMatchers(t *testing.T) {
 			[]e{[]string{"a", "b"}, A{"a", "b"}},
 			[]e{[]string{"a"}, A{"b"}},
 		},
+		{"test Cond", gomock.Cond(func(x any) bool { return x.(B).Name == "Dam" }), []e{B{Name: "Dam"}}, []e{B{Name: "Dave"}}},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
diff --git a/sample/imp4/imp4.go b/sample/imp4/imp4.go
index 30a7076..021d701 100644
--- a/sample/imp4/imp4.go
+++ b/sample/imp4/imp4.go
@@ -1,3 +1,5 @@
 package imp_four
 
-type Imp4 struct{}
+type Imp4 struct {
+	Field string
+}
diff --git a/sample/user_test.go b/sample/user_test.go
index 651e30e..55856e3 100644
--- a/sample/user_test.go
+++ b/sample/user_test.go
@@ -7,6 +7,7 @@ import (
 	"go.uber.org/mock/gomock"
 	user "go.uber.org/mock/sample"
 	"go.uber.org/mock/sample/imp1"
+	imp_four "go.uber.org/mock/sample/imp4"
 )
 
 func TestRemember(t *testing.T) {
@@ -193,3 +194,19 @@ func TestDoAndReturnSignature(t *testing.T) {
 		mockIndex.Slice([]int{0}, []byte("meow"))
 	})
 }
+
+func TestExpectCondForeignFour(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+
+	mockIndex := NewMockIndex(ctrl)
+	mockIndex.EXPECT().ForeignFour(gomock.Cond(func(x any) bool {
+		four, ok := x.(imp_four.Imp4)
+		if !ok {
+			return false
+		}
+		return four.Field == "Cool"
+	}))
+
+	mockIndex.ForeignFour(imp_four.Imp4{Field: "Cool"})
+}