perf: optimize converting releases to feed items (#7221)

- `releasesToFeedItems` is called to convert release structs to feed items, which is then used to render RSS or Atom feeds.
- Optimize the loading of attributes for the releases, introduce `ReleaseList` type which uses caching to load repository and publishers. It also no longer loads release attachments and downloads counts as that is not used in feed items.
- Optimize the composing of meta by introducing caching, this operation is especially slow when the owner is an organization.
- Add unit test (ensures new `LoadAttributes` works correctly).
- Add integration test (ensures that feed output is still as expected).

Loading https://codeberg.org/forgejo/forgejo/releases.rss reduced from ~15s to ~1s. (It is currently is deployed on codeberg.org)

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7221
Reviewed-by: Otto <otto@codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

models/repo/release_list.go

@@ -0,0 +1,45 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package repo
+
+import (
+	"context"
+
+	user_model "code.gitea.io/gitea/models/user"
+)
+
+type ReleaseList []*Release
+
+// LoadAttributes loads the repository and publisher for the releases.
+func (r ReleaseList) LoadAttributes(ctx context.Context) error {
+	repoCache := make(map[int64]*Repository)
+	userCache := make(map[int64]*user_model.User)
+
+	for _, release := range r {
+		var err error
+		repo, ok := repoCache[release.RepoID]
+		if !ok {
+			repo, err = GetRepositoryByID(ctx, release.RepoID)
+			if err != nil {
+				return err
+			}
+			repoCache[release.RepoID] = repo
+		}
+		release.Repo = repo
+
+		publisher, ok := userCache[release.PublisherID]
+		if !ok {
+			publisher, err = user_model.GetUserByID(ctx, release.PublisherID)
+			if err != nil {
+				if !user_model.IsErrUserNotExist(err) {
+					return err
+				}
+				publisher = user_model.NewGhostUser()
+			}
+			userCache[release.PublisherID] = publisher
+		}
+		release.Publisher = publisher
+	}
+	return nil
+}

models/repo/release_list_test.go

@@ -0,0 +1,42 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package repo
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/unittest"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestReleaseListLoadAttributes(t *testing.T) {
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	releases := ReleaseList{&Release{
+		RepoID:      1,
+		PublisherID: 1,
+	}, &Release{
+		RepoID:      2,
+		PublisherID: 2,
+	}, &Release{
+		RepoID:      1,
+		PublisherID: 2,
+	}, &Release{
+		RepoID:      2,
+		PublisherID: 1,
+	}}
+
+	require.NoError(t, releases.LoadAttributes(t.Context()))
+
+	assert.EqualValues(t, 1, releases[0].Repo.ID)
+	assert.EqualValues(t, 1, releases[0].Publisher.ID)
+	assert.EqualValues(t, 2, releases[1].Repo.ID)
+	assert.EqualValues(t, 2, releases[1].Publisher.ID)
+	assert.EqualValues(t, 1, releases[2].Repo.ID)
+	assert.EqualValues(t, 2, releases[2].Publisher.ID)
+	assert.EqualValues(t, 2, releases[3].Repo.ID)
+	assert.EqualValues(t, 1, releases[3].Publisher.ID)
+}