Missed return statement in generated code

[maratori]

Bug description

Wire generates broken code. It generates function body without return statement.

To Reproduce

Run wire with following file

// +build wireinject

package storage

import "github.com/google/wire"

type MyInterface interface {
	Method()
}

type MyImplementation struct{}

func (MyImplementation) Method() {}

func XXX(MyImplementation) MyInterface {
	wire.Build(wire.Bind(new(MyInterface), new(MyImplementation)))
	return nil
}

It will generate following file

// Code generated by Wire. DO NOT EDIT.

//go:generate wire
//+build !wireinject

package storage

// Injectors from missed_return.go:

func XXX(myImplementation MyImplementation) MyInterface {

}

// missed_return.go:

type MyInterface interface {
	Method()
}

type MyImplementation struct{}

func (MyImplementation) Method() {}

Expected behavior

Wire should generate following file

//+build !wireinject

package storage

// Injectors from missed_return.go:

func XXX(myImplementation MyImplementation) MyInterface {
	return myImplementation
}

// missed_return.go:

type MyInterface interface {
	Method()
}

type MyImplementation struct{}

func (MyImplementation) Method() {}

Version

github.com/google/wire v0.3.0
go version go1.13 darwin/amd64

[zombiezen]

Thanks for the bug report! Expect a fix in the next week or so.