feat: support generic interface generation (#175)

Allow the generation of mocks for generics as introduced in golang 1.18

internal/template/template.go

@@ -48,7 +48,22 @@ import (
 {{- if not $.SkipEnsure -}}
 // Ensure, that {{.MockName}} does implement {{$.SrcPkgQualifier}}{{.InterfaceName}}.
 // If this is not the case, regenerate this file with moq.
-var _ {{$.SrcPkgQualifier}}{{.InterfaceName}} = &{{.MockName}}{}
+var _ {{$.SrcPkgQualifier}}{{.InterfaceName -}} 
+	{{- if .TypeParams }}[
+		{{- range $index, $param := .TypeParams}}
+			{{- if $index}}, {{end -}}
+			{{if $param.Constraint}}{{$param.Constraint.String}}{{else}}{{$param.TypeString}}{{end}}
+		{{- end -}}
+		]
+	{{- end }} = &{{.MockName}}
+	 {{- if .TypeParams }}[
+		{{- range $index, $param := .TypeParams}}
+			{{- if $index}}, {{end -}}
+			{{if $param.Constraint}}{{$param.Constraint.String}}{{else}}{{$param.TypeString}}{{end}}
+		{{- end -}}
+		]
+	{{- end -}}
+{}
 {{- end}}
 
 // {{.MockName}} is a mock implementation of {{$.SrcPkgQualifier}}{{.InterfaceName}}.
@@ -68,7 +83,12 @@ var _ {{$.SrcPkgQualifier}}{{.InterfaceName}} = &{{.MockName}}{}
 // 		// and then make assertions.
 //
 // 	}
-type {{.MockName}} struct {
+type {{.MockName}} 
+{{- if .TypeParams -}}
+	[{{- range $index, $param := .TypeParams}}
+			{{- if $index}}, {{end}}{{$param.Name | Exported}} {{$param.TypeString}}
+	{{- end -}}]
+{{- end }} struct {
 {{- range .Methods}}
 	// {{.Name}}Func mocks the {{.Name}} method.
 	{{.Name}}Func func({{.ArgList}}) {{.ReturnArgTypeList}}
@@ -91,7 +111,13 @@ type {{.MockName}} struct {
 }
 {{range .Methods}}
 // {{.Name}} calls {{.Name}}Func.
-func (mock *{{$mock.MockName}}) {{.Name}}({{.ArgList}}) {{.ReturnArgTypeList}} {
+func (mock *{{$mock.MockName}}
+{{- if $mock.TypeParams -}}
+	[{{- range $index, $param := $mock.TypeParams}}
+		{{- if $index}}, {{end}}{{$param.Name | Exported}}
+	{{- end -}}]
+{{- end -}}	
+) {{.Name}}({{.ArgList}}) {{.ReturnArgTypeList}} {
 {{- if not $.StubImpl}}
 	if mock.{{.Name}}Func == nil {
 		panic("{{$mock.MockName}}.{{.Name}}Func: method is nil but {{$mock.InterfaceName}}.{{.Name}} was just called")
@@ -134,7 +160,13 @@ func (mock *{{$mock.MockName}}) {{.Name}}({{.ArgList}}) {{.ReturnArgTypeList}} {
 // {{.Name}}Calls gets all the calls that were made to {{.Name}}.
 // Check the length with:
 //     len(mocked{{$mock.InterfaceName}}.{{.Name}}Calls())
-func (mock *{{$mock.MockName}}) {{.Name}}Calls() []struct {
+func (mock *{{$mock.MockName}}
+{{- if $mock.TypeParams -}}
+	[{{- range $index, $param := $mock.TypeParams}}
+		{{- if $index}}, {{end}}{{$param.Name | Exported}}
+	{{- end -}}]
+{{- end -}}	
+) {{.Name}}Calls() []struct {
 		{{- range .Params}}
 		{{.Name | Exported}} {{.TypeString}}
 		{{- end}}

internal/template/template_data.go

@@ -2,6 +2,7 @@ package template
 
 import (
 	"fmt"
+	"go/types"
 	"strings"
 
 	"github.com/matryer/moq/internal/registry"
@@ -33,6 +34,7 @@ func (d Data) MocksSomeMethod() bool {
 type MockData struct {
 	InterfaceName string
 	MockName      string
+	TypeParams    []TypeParamData
 	Methods       []MethodData
 }
 
@@ -87,6 +89,11 @@ func (m MethodData) ReturnArgNameList() string {
 	return strings.Join(params, ", ")
 }
 
+type TypeParamData struct {
+	ParamData
+	Constraint types.Type
+}
+
 // ParamData is the data which represents a parameter to some method of
 // an interface.
 type ParamData struct {