go-swagger: Generate spec fails with invalid type error

Problem statement

It seems that during the last few days, there has been a change (probably the one regarding supporting go modules) that has broken functionality of generating spec.

I had a sample code for generating spec here, a few days ago I ran make swagger and swagger.yaml was generated successfully. Now with last version of go-swagger it results in the following error:

which swagger || (GO111MODULE=off go get -u github.com/go-swagger/go-swagger/cmd/swagger)
/Users/parhamalvani/Documents/Go/bin/swagger
GO111MODULE=on go mod vendor  && GO111MODULE=off swagger generate spec -o ./swagger.yaml --scan-models
unsupported type "invalid type"
make: *** [swagger] Error 1

I did some investingation, it seems that if i change

// swagger:route POST /foobar foobar-tag idOfFoobarEndpoint
// Foobar does some amazing stuff.
// responses:
//   200: foobarResponse

// This text will appear as description of your response body.
// swagger:response foobarResponse
type foobarResponseWrapper struct {
	// in:body
	Body api.FooBarResponse
}

// swagger:parameters idOfFoobarEndpoint
type foobarParamsWrapper struct {
	// This text will appear as description of your request body.
	// in:body
	Body api.FooBarRequest
}

to the following, everything works.

// swagger:route POST /foobar foobar-tag idOfFoobarEndpoint
// Foobar does some amazing stuff.
// responses:
//   200: foobarResponse

// This text will appear as description of your response body.
// swagger:response foobarResponse
type foobarResponseWrapper struct {
	// in:body
	Body struct { A int `json:"int"` }
}

// swagger:parameters idOfFoobarEndpoint
type foobarParamsWrapper struct {
	// This text will appear as description of your request body.
	// in:body
	Body struct { A int `json:"int"` }
}

Therefore I assume, the problem is it does not scan types inside other packages. (i.e. Because api.FoobarRequest is defined outside of docs package, the code scanner fails to find its

This also happens to me in a real world project causing us to not be able to generate spec.

Environment

swagger version: dev go version: 1.12.5 OS: MacOS High Sierra