genqlient/generate/marshal.go.tmpl

{{/* We generate MarshalJSON for much the same reasons as UnmarshalJSON -- see
     unmarshal.go.tmpl for details.  (Note we generate both even if genqlient
     itself needs only UnmarshalJSON, for the benefit of callers who want to,
     for example, put genqlient responses in a cache.)  But our implementation
     for marshaling is quite different.

     Specifically, the treatment of field-visibility with embedded fields must
     differ from both ordinary encoding/json and unmarshaling: we need to
     choose exactly one conflicting field in all cases (whereas Go chooses at
     most one and when unmarshaling we choose them all).  See
     goStructType.FlattenedFields in types.go for more discussion of embedding
     and visibility.

     To accomplish that, we essentially flatten out all the embedded fields
     when marshaling, following those precedence rules.  Then we basically
     follow what we do in unmarshaling, but in reverse order: first we marshal
     the special fields, then we glue everything together with the ordinary
     fields.

     We do one other thing differently, for the benefit of the marshal-helper
     in marshal_helper.go.tmpl.  While when unmarshaling it's easy to unmarshal
     out the __typename field, then unmarshal out everything else, with
     marshaling we can't do the same (at least not without some careful
     JSON-stitching; the considerations are basically the same as those
     discussed in FlattenedFields).  So we write out a helper method
     __premarshalJSON() which basically does all but the final JSON-marshal.
     (Then the real MarshalJSON() just calls that, and then marshals.)
     Thus a marshal-helper for this type, if any, can call __premarshalJSON()
     directly, and embed its result. */}}

type __premarshal{{.GoName}} struct{
    {{range .FlattenedFields -}}
    {{if .NeedsMarshaling -}}
    {{.GoName}} {{repeat .GoType.SliceDepth "[]"}}{{ref "encoding/json.RawMessage"}} `json:"{{.JSONName}}{{if .Omitempty -}},omitempty{{end}}"`
    {{else}}
    {{.GoName}} {{.GoType.Reference}} `json:"{{.JSONName}}{{if .Omitempty -}},omitempty{{end}}"`
    {{end}}
    {{end}}
}

func (v *{{.GoName}}) MarshalJSON() ([]byte, error) {
    premarshaled, err := v.__premarshalJSON()
    if err != nil {
        return nil, err
    }
    return json.Marshal(premarshaled)
}

func (v *{{.GoName}}) __premarshalJSON() (*__premarshal{{.GoName}}, error) {
    var retval __premarshal{{.GoName}}

    {{range $field := .FlattenedFields -}}
    {{if $field.NeedsMarshaling -}}
    {
        {{/* Here dst is the json.RawMessage, and src is the Go type. */}}
        dst := &retval.{{$field.GoName}}
        src := v.{{$field.Selector}}
        {{range $i := intRange $field.GoType.SliceDepth -}}
        *dst = make(
            {{repeat (sub $field.GoType.SliceDepth $i) "[]"}}{{ref "encoding/json.RawMessage"}},
            len(src))
        for i, src := range src {
            dst := &(*dst)[i]
        {{end -}}
        {{/* src now has type <GoType>; dst is json.RawMessage */ -}}
        {{if $field.GoType.IsPointer -}}
        {{/* If you passed a pointer, and it's nil, don't call the
             marshaler.  This matches json.Marshal's behavior. */ -}}
        if src != nil {
        {{end -}}
        var err error
        *dst, err = {{$field.Marshaler $.Generator}}(
            {{/* src is the struct-field (or field-element, etc.).
                 We want to pass a pointer to the type you specified, so if
                 there's a pointer on the field that's exactly what we want,
                 and if not we need to take the address. */ -}}
            {{if not $field.GoType.IsPointer}}&{{end}}src)
        if err != nil {
            return nil, fmt.Errorf(
                "unable to marshal {{$.GoName}}.{{$field.Selector}}: %w", err)
        }
        {{if $field.GoType.IsPointer -}}
        }{{/* end if src != nil */}}
        {{end -}}
        {{range $i := intRange $field.GoType.SliceDepth -}}
        }
        {{end -}}
    }
    {{else -}}
    retval.{{$field.GoName}} = v.{{$field.Selector}}
    {{end -}}
    {{end -}}

    return &retval, nil
}