api: fix related field API incompatibility in /patches

In Patchwork 3.x, in API versions above 1.1, the related field
of /patches is always an array. It is not present at all in API
version 1.1.

In Patchwork 4.0, the field is null in 1.1, and is an array in later API
versions.

Adding the omitempty tag causes the field to disappear from 1.1, but
then it's either an array or not present if empty in 1.4.

Make the API more compatible with Patchwork 3.x by changing the field
into a pointer to a slice, adding the omitzero tag, and always
explicitly allocating an empty slice (&nil != &[]string{}) for /patches
responses.

Signed-off-by: Franciszek Stachura <fbstachura@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

Author: fstachura

pkg/api/patches.go

@@ -364,6 +364,7 @@ func applyPatchFilters(q *bun.SelectQuery, input *ListPatchesInput) *bun.SelectQ
 }
 
 func patchToListResponse(p *db.Patch, base string) PatchListResponse {
+	related := make([]PatchEmbedded, 0)
 	r := PatchListResponse{
 		ID:        p.ID,
 		URL:       fmt.Sprintf("%s/patches/%d", base, p.ID),
@@ -378,7 +379,7 @@ func patchToListResponse(p *db.Patch, base string) PatchListResponse {
 		Checks:    fmt.Sprintf("%s/patches/%d/checks", base, p.ID),
 		Tags:      p.Tags,
 		Series:    []SeriesEmbedded{},
-		Related:   []PatchEmbedded{},
+		Related:   &related,
 	}
 	if p.Hash != nil {
 		r.Hash = *p.Hash
@@ -405,7 +406,7 @@ func patchToListResponse(p *db.Patch, base string) PatchListResponse {
 		r.Tags = map[string]int{}
 	}
 	for _, ref := range p.Related {
-		r.Related = append(r.Related, PatchEmbedded{
+		related = append(related, PatchEmbedded{
 			ID:   ref.ID,
 			URL:  fmt.Sprintf("%s/patches/%d", base, ref.ID),
 			Name: ref.Name,
@@ -419,9 +420,6 @@ func patchToListResponse(p *db.Patch, base string) PatchListResponse {
 			Mbox: fmt.Sprintf("%s/series/%d/mbox", base, ref.ID),
 		})
 	}
-	if r.Related == nil {
-		r.Related = []PatchEmbedded{}
-	}
 	if r.Series == nil {
 		r.Series = []SeriesEmbedded{}
 	}

pkg/api/types.go

@@ -128,7 +128,7 @@ type PatchListResponse struct {
 	Check          string           `json:"check" enum:"pending,success,warning,fail"`
 	Checks         string           `json:"checks" format:"uri"`
 	Tags           map[string]int   `json:"tags"`
-	Related        []PatchEmbedded  `json:"related" since:"1.2"`
+	Related        *[]PatchEmbedded `json:"related,omitzero" since:"1.2"`
 }
 
 type PatchDetailResponse struct {