Add static interface implementation check

Add an additional line of code per interface to the generated mock file,
which allows the go compiler to statically check if the mock implements
the mocked interface.

example/mockpersonstore_test.go

@@ -13,6 +13,10 @@ var (
 	lockPersonStoreMockGet    sync.RWMutex
 )
 
+// Ensure, that PersonStoreMock does implement PersonStore.
+// If this is not the case, regenerate this file with moq.
+var _ PersonStore = &PersonStoreMock{}
+
 // PersonStoreMock is a mock implementation of PersonStore.
 //
 //     func TestSomethingThatUsesPersonStore(t *testing.T) {

generate/generated.go

@@ -13,6 +13,10 @@ var (
 	lockMyInterfaceMockTwo   sync.RWMutex
 )
 
+// Ensure, that MyInterfaceMock does implement MyInterface.
+// If this is not the case, regenerate this file with moq.
+var _ MyInterface = &MyInterfaceMock{}
+
 // MyInterfaceMock is a mock implementation of MyInterface.
 //
 //     func TestSomethingThatUsesMyInterface(t *testing.T) {

main.go

@@ -2,12 +2,12 @@ package main
 
 import (
 	"bytes"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
-	"errors"
 
 	"github.com/matryer/moq/pkg/moq"
 )

pkg/moq/moq.go

@@ -171,6 +171,10 @@ func (m *Mocker) Mock(w io.Writer, name ...string) error {
 		doc.Imports = append(doc.Imports, stripVendorPath(pkgToImport))
 	}
 
+	if tpkg.Name() != m.pkgName {
+		doc.SourcePackagePrefix = tpkg.Name() + "."
+	}
+
 	var buf bytes.Buffer
 	err = m.tmpl.Execute(&buf, doc)
 	if err != nil {
@@ -249,9 +253,10 @@ func pkgInfoFromPath(src string) (*loader.PackageInfo, error) {
 }
 
 type doc struct {
-	PackageName string
-	Objects     []obj
-	Imports     []string
+	PackageName         string
+	SourcePackagePrefix string
+	Objects             []obj
+	Imports             []string
 }
 
 type obj struct {

pkg/moq/moq_test.go

@@ -42,6 +42,40 @@ func TestMoq(t *testing.T) {
 	}
 }
 
+func TestMoqWithStaticCheck(t *testing.T) {
+	m, err := New("testpackages/example", "")
+	if err != nil {
+		t.Fatalf("moq.New: %s", err)
+	}
+	var buf bytes.Buffer
+	err = m.Mock(&buf, "PersonStore")
+	if err != nil {
+		t.Errorf("m.Mock: %s", err)
+	}
+	s := buf.String()
+	// assertions of things that should be mentioned
+	var strs = []string{
+		"package example",
+		"var _ PersonStore = &PersonStoreMock{}",
+		"type PersonStoreMock struct",
+		"CreateFunc func(ctx context.Context, person *Person, confirm bool) error",
+		"GetFunc func(ctx context.Context, id string) (*Person, error)",
+		"func (mock *PersonStoreMock) Create(ctx context.Context, person *Person, confirm bool) error",
+		"func (mock *PersonStoreMock) Get(ctx context.Context, id string) (*Person, error)",
+		"panic(\"PersonStoreMock.CreateFunc: method is nil but PersonStore.Create was just called\")",
+		"panic(\"PersonStoreMock.GetFunc: method is nil but PersonStore.Get was just called\")",
+		"lockPersonStoreMockGet.Lock()",
+		"mock.calls.Get = append(mock.calls.Get, callInfo)",
+		"lockPersonStoreMockGet.Unlock()",
+		"// ID is the id argument value",
+	}
+	for _, str := range strs {
+		if !strings.Contains(s, str) {
+			t.Errorf("expected but missing: \"%s\"", str)
+		}
+	}
+}
+
 func TestMoqExplicitPackage(t *testing.T) {
 	m, err := New("testpackages/example", "different")
 	if err != nil {
@@ -69,6 +103,34 @@ func TestMoqExplicitPackage(t *testing.T) {
 	}
 }
 
+func TestMoqExplicitPackageWithStaticCheck(t *testing.T) {
+	m, err := New("testpackages/example", "different")
+	if err != nil {
+		t.Fatalf("moq.New: %s", err)
+	}
+	var buf bytes.Buffer
+	err = m.Mock(&buf, "PersonStore")
+	if err != nil {
+		t.Errorf("m.Mock: %s", err)
+	}
+	s := buf.String()
+	// assertions of things that should be mentioned
+	var strs = []string{
+		"package different",
+		"var _ example.PersonStore = &PersonStoreMock{}",
+		"type PersonStoreMock struct",
+		"CreateFunc func(ctx context.Context, person *example.Person, confirm bool) error",
+		"GetFunc func(ctx context.Context, id string) (*example.Person, error)",
+		"func (mock *PersonStoreMock) Create(ctx context.Context, person *example.Person, confirm bool) error",
+		"func (mock *PersonStoreMock) Get(ctx context.Context, id string) (*example.Person, error)",
+	}
+	for _, str := range strs {
+		if !strings.Contains(s, str) {
+			t.Errorf("expected but missing: \"%s\"", str)
+		}
+	}
+}
+
 // TestVeradicArguments tests to ensure variadic work as
 // expected.
 // see https://github.com/matryer/moq/issues/5

pkg/moq/template.go

@@ -8,6 +8,7 @@ var moqTemplate = `// Code generated by moq; DO NOT EDIT.
 // github.com/matryer/moq
 
 package {{.PackageName}}
+{{- $sourcePackagePrefix := .SourcePackagePrefix}}
 
 import (
 {{- range .Imports }}
@@ -22,6 +23,10 @@ var (
 {{- end }}
 )
 
+// Ensure, that {{.InterfaceName}}Mock does implement {{.InterfaceName}}.
+// If this is not the case, regenerate this file with moq.
+var _ {{$sourcePackagePrefix}}{{.InterfaceName}} = &{{.InterfaceName}}Mock{}
+
 // {{.InterfaceName}}Mock is a mock implementation of {{.InterfaceName}}.
 //
 //     func TestSomethingThatUses{{.InterfaceName}}(t *testing.T) {

pkg/moq/testpackages/dotimport/service_moq_test.go

@@ -12,6 +12,10 @@ var (
 	lockServiceMockUser sync.RWMutex
 )
 
+// Ensure, that ServiceMock does implement Service.
+// If this is not the case, regenerate this file with moq.
+var _ dotimport.Service = &ServiceMock{}
+
 // ServiceMock is a mock implementation of Service.
 //
 //     func TestSomethingThatUsesService(t *testing.T) {

pkg/moq/testpackages/gogenvendoring/user/user_moq_test.go

@@ -12,6 +12,10 @@ var (
 	lockServiceMockDoSomething sync.RWMutex
 )
 
+// Ensure, that ServiceMock does implement Service.
+// If this is not the case, regenerate this file with moq.
+var _ Service = &ServiceMock{}
+
 // ServiceMock is a mock implementation of Service.
 //
 //     func TestSomethingThatUsesService(t *testing.T) {

pkg/vendor/github.com/matryer/somerepo/yep.go

@@ -1,3 +1,4 @@
 package somerepo
 
+// SomeType is some type
 type SomeType string