Generated code for nested inline attributes doesn't compile

[markbrockhoff]

Hi, I'm trying to build my first Goa Api and ran into an issue when defining a nested attribute inside a type.

The type I'm defining in my design looks like this:

var Project = Type("Project", func() {
	Attribute("id", String, func() {
		Example("123456789")
	})
	Attribute("title", String, func() {
		Example("Test Project")
	})
	Attribute("createdAt", String, func() {
		Format(FormatDateTime)
		Example("2024-01-02T13:59:43+01")
	})
	Attribute("projectDetails", func() {
		Attribute("status", String)
	})
	Required("id", "title", "createdAt")
})

After generating the code using goa gen I get the following function inside ./gen/http/projects/server/encode_decode.go:

// marshalProjectsProjectToProjectResponse builds a value of type
// *ProjectResponse from a value of type *projects.Project.
func marshalProjectsProjectToProjectResponse(v *projects.Project) *ProjectResponse {
	res := &ProjectResponse{
		ID:        v.ID,
		Title:     v.Title,
		CreatedAt: v.CreatedAt,
	}
	if v.ProjectDetails != nil {
		res.ProjectDetails = &struct {
			Status *string
		}{
			Status: v.ProjectDetails.Status,
		}
	}

	return res
}

Problem is that the assignment of the inline struct to res.ProjectDetails fails during compilation with the following error message:
cannot use &struct{Status *string}{…} (value of type *struct{Status *string}) as *struct{Status *string "form:\"status,omitempty\" json:\"status,omitempty\" xml:\"status,omitempty\""} value in assignment

I'm able to fix the issue by editing the function like this:

// marshalProjectsProjectToProjectResponse builds a value of type
// *ProjectResponse from a value of type *projects.Project.
func marshalProjectsProjectToProjectResponse(v *projects.Project) *ProjectResponse {
	res := &ProjectResponse{
		ID:        v.ID,
		Title:     v.Title,
		CreatedAt: v.CreatedAt,
	}
	if v.ProjectDetails != nil {
		res.ProjectDetails = &struct {
			Status *string "form:\"status,omitempty\" json:\"status,omitempty\" xml:\"status,omitempty\""
		}{
			Status: v.ProjectDetails.Status,
		}
	}

	return res
}

Is this a bug inside goa or do I need to do something differently inside my design? I'm pretty new to Goa so any help would be appreciated. :)

Btw.: I'm using Goa v3.14.1 and go v1.21.5

[raphael]

This looks like a bug, are you able to provide a minimal but complete Goa design that reproduces the issue?

[markbrockhoff]

Thanks for the quick response.

Sure, here you go:

package design

import (
	. "goa.design/goa/v3/dsl"
)

var _ = API("goaBugRepro", func() {
	Title("Goa Bug Repro")
	Description("Minimal example to reproduce a bug found inside goa")
})

var _ = Service("bugService", func() {
	Method("createBug", func() {
		// Generation works if the result is just one Bug and not an array of Bugs.
		Result(ArrayOf(Bug))

		HTTP(func() {
			GET("/bug")
		})
	})
})

var Bug = Type("Bug", func() {
	Attribute("id", Int)
	Attribute("nested", func() {
		Attribute("nestedString", String)
		Attribute("nestedNumber", Int)
	})
})

While creating the repro I noticed that the bug only appears once I return an array of bugs as result of the method createBug. When just one Bug is returned, everything's fine.