cannot generate mockfile for generic type

[zhangjianxing]

Actual behavior A clear and concise description of what the bug is.

# gogen.go
package src

//go:generate mockgen -source=gogen.go -destination=gogen_mock.go -package=src_test

type Base[M any] interface {
	Get() M
}

type MyInterface interface {
	Base[int]
}

type IntInterface = Base[int]

type MyInterface2 interface {
	IntInterface
}

Mockgen is able to generate MyInterface successfully, but not able to generate MyInterface2, and returns following bug

2025/07/28 10:05:40 Loading input failed: gogen.go:18:2: unknown embedded interface interview/src.IntInterface
gogen.go:3: running "mockgen": exit status 1

Expected behavior A clear and concise description of what you expected to
happen.

Mockgen should be able to generate MyInterface2 since the interface should be exactally same as MyInterface

To Reproduce Steps to reproduce the behavior

1. run go generage ./...

Additional Information

• gomock mode (reflect or source): source
• gomock version or git ref: v0.5.2
• golang version: 1.24.4

Triage Notes for the Maintainers

[JuanBC9]

Hi, adding (what I think is) a related finding to this issue.

I've found that when using direct embedding of an instantiated generic (e.g., Base[MyStruct]). Mockgen generates syntactically incorrect code by using the fully qualified package path for the type argument, instead of the local type.

Example:

package mypackage

// A generic function type
type Callback[T any] func(item T)

// A generic base interface
type Base[T any] interface {
    OnEvent(callback Callback[T])
}

// A concrete struct
type MyStruct struct {
}

// The interface to be mocked
type MyInterface interface {
    Base[MyStruct]
}

mockgen "-destination" "mypackage/my_interface.go" "-package" "mypackage" -- "github.com/org/repo/mypackage" "MyInterface"

Error: Failed to format generated source code: mypackage/my_interface.go missing ',' in type argument list

Generated Code:

// Uses the fully qualified path, which is a syntax error
func (m *MockMyInterface) OnEvent(arg0 Callback[github.com/org/repo/mypackage.MyStruct]) {
	m.ctrl.T.Helper()
	m.ctrl.Call(m, "OnEvent", arg0)
}

Expected::

// Should use the local type name
func (m *MockMyInterface) OnEvent(arg0 Callback[MyStruct]) {
	m.ctrl.T.Helper()
	m.ctrl.Call(m, "OnEvent", arg0)
}

• golang version: 1.25.2
• gomock version: v0.6.0