Error when mock generating dot import file with different package name

[eyasy1217]

Actual behavior
If your source file contains dot imports and the output package name is different, mockgen's output will be a file that cannot be compiled.

Expected behavior
The output will be a file that can be compiled successfully.

To Reproduce

1. The source file internal.go, which contains a dot import, is as follows:

package internal

//go:generate go run go.uber.org/mock/mockgen -source=internal.go -destination=mocks/internal_gen.go

import (
	. "context"
)

type WithDotImports interface {
	ImportDot() Context
}

2. Run go generate ./.... This produces the file mocks/internal_gen.go.

3. In mocks/internal_gen.go, the return type Context of the ImportDot method is incorrectly qualified as internal.Context, even though such qualification is unnecessary.

package mock_internal

import (
	. "context"
	// ...
)

// ...

func (m *MockWithDotImports) ImportDot() internal.Context {
	m.ctrl.T.Helper()
	ret := m.ctrl.Call(m, "ImportDot")
	ret0, _ := ret[0].(internal.Context)
	return ret0
}

Additional Information

• gomock mode (reflect or source): source (I haven't tried withe reflect, issue might also happen)
• gomock version or git ref: v0.4.0
• golang version: 1.21.3

Triage Notes for the Maintainers

Dot import are seldom used.
This bug may not be worth fixing.
So how about adding the following code to after this line.

	if pkg.Name != outputPackageName && len(pkg.DotImports) > 0 {
		log.Fatalf("Different package name specifications including dot imports are not yet supported: %v != %v", pkg.Name, outputPackageName)
	}

Fundamentally, the issue seems to be that parseType method in mockgen/parse.go does not return the correct package name for dot import types.