Automatic generation of release notes (#35977)

Similar to GitHub, release notes can now be generated automatically.
The generator is server-side and gathers the merged PRs and contributors
and returns the corresponding Markdown text.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/release/notes.go

@@ -0,0 +1,188 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package release
+
+import (
+	"cmp"
+	"context"
+	"fmt"
+	"slices"
+	"strings"
+
+	issues_model "code.gitea.io/gitea/models/issues"
+	repo_model "code.gitea.io/gitea/models/repo"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/container"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/util"
+)
+
+// GenerateReleaseNotesOptions describes how to build release notes content.
+type GenerateReleaseNotesOptions struct {
+	TagName     string
+	TagTarget   string
+	PreviousTag string
+}
+
+// GenerateReleaseNotes builds the markdown snippet for release notes.
+func GenerateReleaseNotes(ctx context.Context, repo *repo_model.Repository, gitRepo *git.Repository, opts GenerateReleaseNotesOptions) (string, error) {
+	headCommit, err := resolveHeadCommit(gitRepo, opts.TagName, opts.TagTarget)
+	if err != nil {
+		return "", err
+	}
+
+	if opts.PreviousTag == "" {
+		// no previous tag, usually due to there is no tag in the repo, use the same content as GitHub
+		content := fmt.Sprintf("**Full Changelog**: %s/commits/tag/%s\n", repo.HTMLURL(ctx), util.PathEscapeSegments(opts.TagName))
+		return content, nil
+	}
+
+	baseCommit, err := gitRepo.GetCommit(opts.PreviousTag)
+	if err != nil {
+		return "", util.ErrorWrapTranslatable(util.ErrNotExist, "repo.release.generate_notes_tag_not_found", opts.TagName)
+	}
+
+	commits, err := gitRepo.CommitsBetweenIDs(headCommit.ID.String(), baseCommit.ID.String())
+	if err != nil {
+		return "", fmt.Errorf("CommitsBetweenIDs: %w", err)
+	}
+
+	prs, err := collectPullRequestsFromCommits(ctx, repo.ID, commits)
+	if err != nil {
+		return "", err
+	}
+
+	contributors, newContributors, err := collectContributors(ctx, repo.ID, prs)
+	if err != nil {
+		return "", err
+	}
+
+	content := buildReleaseNotesContent(ctx, repo, opts.TagName, opts.PreviousTag, prs, contributors, newContributors)
+	return content, nil
+}
+
+func resolveHeadCommit(gitRepo *git.Repository, tagName, tagTarget string) (*git.Commit, error) {
+	ref := tagName
+	if !gitRepo.IsTagExist(tagName) {
+		ref = tagTarget
+	}
+
+	commit, err := gitRepo.GetCommit(ref)
+	if err != nil {
+		return nil, util.ErrorWrapTranslatable(util.ErrNotExist, "repo.release.generate_notes_target_not_found", ref)
+	}
+	return commit, nil
+}
+
+func collectPullRequestsFromCommits(ctx context.Context, repoID int64, commits []*git.Commit) ([]*issues_model.PullRequest, error) {
+	prs := make([]*issues_model.PullRequest, 0, len(commits))
+
+	for _, commit := range commits {
+		pr, err := issues_model.GetPullRequestByMergedCommit(ctx, repoID, commit.ID.String())
+		if err != nil {
+			if issues_model.IsErrPullRequestNotExist(err) {
+				continue
+			}
+			return nil, fmt.Errorf("GetPullRequestByMergedCommit: %w", err)
+		}
+
+		if err = pr.LoadIssue(ctx); err != nil {
+			return nil, fmt.Errorf("LoadIssue: %w", err)
+		}
+		if err = pr.Issue.LoadAttributes(ctx); err != nil {
+			return nil, fmt.Errorf("LoadIssueAttributes: %w", err)
+		}
+
+		prs = append(prs, pr)
+	}
+
+	slices.SortFunc(prs, func(a, b *issues_model.PullRequest) int {
+		if cmpRes := cmp.Compare(b.MergedUnix, a.MergedUnix); cmpRes != 0 {
+			return cmpRes
+		}
+		return cmp.Compare(b.Issue.Index, a.Issue.Index)
+	})
+
+	return prs, nil
+}
+
+func buildReleaseNotesContent(ctx context.Context, repo *repo_model.Repository, tagName, baseRef string, prs []*issues_model.PullRequest, contributors []*user_model.User, newContributors []*issues_model.PullRequest) string {
+	var builder strings.Builder
+	builder.WriteString("## What's Changed\n")
+
+	for _, pr := range prs {
+		prURL := pr.Issue.HTMLURL(ctx)
+		builder.WriteString(fmt.Sprintf("* %s in [#%d](%s)\n", pr.Issue.Title, pr.Issue.Index, prURL))
+	}
+
+	builder.WriteString("\n")
+
+	if len(contributors) > 0 {
+		builder.WriteString("## Contributors\n")
+		for _, contributor := range contributors {
+			builder.WriteString(fmt.Sprintf("* @%s\n", contributor.Name))
+		}
+		builder.WriteString("\n")
+	}
+
+	if len(newContributors) > 0 {
+		builder.WriteString("## New Contributors\n")
+		for _, contributor := range newContributors {
+			prURL := contributor.Issue.HTMLURL(ctx)
+			builder.WriteString(fmt.Sprintf("* @%s made their first contribution in [#%d](%s)\n", contributor.Issue.Poster.Name, contributor.Issue.Index, prURL))
+		}
+		builder.WriteString("\n")
+	}
+
+	builder.WriteString("**Full Changelog**: ")
+	compareURL := fmt.Sprintf("%s/compare/%s...%s", repo.HTMLURL(ctx), util.PathEscapeSegments(baseRef), util.PathEscapeSegments(tagName))
+	builder.WriteString(fmt.Sprintf("[%s...%s](%s)", baseRef, tagName, compareURL))
+	builder.WriteByte('\n')
+	return builder.String()
+}
+
+func collectContributors(ctx context.Context, repoID int64, prs []*issues_model.PullRequest) ([]*user_model.User, []*issues_model.PullRequest, error) {
+	contributors := make([]*user_model.User, 0, len(prs))
+	newContributors := make([]*issues_model.PullRequest, 0, len(prs))
+	seenContributors := container.Set[int64]{}
+	seenNew := container.Set[int64]{}
+
+	for _, pr := range prs {
+		poster := pr.Issue.Poster
+		posterID := poster.ID
+
+		if posterID == 0 {
+			// Migrated PRs may not have a linked local user (PosterID == 0). Skip them for now.
+			continue
+		}
+
+		if !seenContributors.Contains(posterID) {
+			contributors = append(contributors, poster)
+			seenContributors.Add(posterID)
+		}
+
+		if seenNew.Contains(posterID) {
+			continue
+		}
+
+		isFirst, err := isFirstContribution(ctx, repoID, posterID, pr)
+		if err != nil {
+			return nil, nil, err
+		}
+		if isFirst {
+			seenNew.Add(posterID)
+			newContributors = append(newContributors, pr)
+		}
+	}
+
+	return contributors, newContributors, nil
+}
+
+func isFirstContribution(ctx context.Context, repoID, posterID int64, pr *issues_model.PullRequest) (bool, error) {
+	hasMergedBefore, err := issues_model.HasMergedPullRequestInRepoBefore(ctx, repoID, posterID, pr.MergedUnix, pr.ID)
+	if err != nil {
+		return false, fmt.Errorf("check merged PRs for contributor: %w", err)
+	}
+	return !hasMergedBefore, nil
+}