feat: Add avatar stacks (#37594)

Parse `Co-authored-by:` trailers from commit messages and surface
contributors as an avatar stack across the commit page, commits list, PR
commits tab, latest-commit row, blame, graph, and dashboard feed.

- Up to 10 visible 20px avatars, GitHub-style overlap (6px first stride,
4px between subsequent), `+N` chip for the rest.
- Label: 1 → name; 2 → `<a> and <b>`; 3+ → `<N> people` opens a Tippy
popup with all participants.
- Names and avatars link to the repo's commits-by-author search; fall
back to profile or `mailto:`.
- Trailer parsing uses `net/mail.ParseAddress`, scans only the trailing
paragraph, filters out the commit's own author/committer.
- Drops the non-standard `Co-committed-by:` emission on squash merge and
web edits.

Devtest: `/devtest/coauthor-avatars`.

Fixes #25521

----
<img width="353" height="277" alt="image"
src="https://github.com/user-attachments/assets/72092ceb-97ca-4b09-9557-0b72d3c5458e"
/>

<img width="533" height="328"
src="https://github.com/user-attachments/assets/11d0c8f8-8b3f-4f2e-9993-879f1c06bcc5"
/>

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

models/asymkey/gpg_key_commit_verification.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"hash"
 
+	"gitea.dev/models/gituser"
 	repo_model "gitea.dev/models/repo"
 	user_model "gitea.dev/models/user"
 	"gitea.dev/modules/log"
@@ -32,8 +33,8 @@ type CommitVerification struct {
 
 // SignCommit represents a commit with validation of signature.
 type SignCommit struct {
-	Verification *CommitVerification
-	*user_model.UserCommit
+	Verification        *CommitVerification
+	*gituser.UserCommit // TODO: need to use a explicit field name, avoid anonymous field
 }
 
 const (

models/gituser/avatar_stack.go

@@ -0,0 +1,44 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package gituser
+
+import (
+	"context"
+
+	"gitea.dev/models/user"
+	"gitea.dev/modules/git"
+	"gitea.dev/modules/log"
+)
+
+// AvatarStackData is the view-model for the AvatarStack render helpers. Participants[0] is
+// the primary participant (commit author), painted on top; the rest follow.
+type AvatarStackData struct {
+	Participants      []*CommitParticipant
+	SearchByEmailLink string
+}
+
+func BuildAvatarStackData(ctx context.Context, allParticipants []*git.CommitIdentity, emailUserMap *user.EmailUserMap) *AvatarStackData {
+	if emailUserMap == nil {
+		emails := make([]string, len(allParticipants))
+		for i, sig := range allParticipants {
+			emails[i] = sig.Email
+		}
+		var err error
+		emailUserMap, err = user.GetUsersByEmails(ctx, emails)
+		if err != nil {
+			log.Error("GetUsersByEmails failed: %v", err)
+		}
+	}
+	ret := &AvatarStackData{
+		Participants: make([]*CommitParticipant, 0, len(allParticipants)),
+	}
+	for _, p := range allParticipants {
+		var giteaUser *user.User
+		if emailUserMap != nil {
+			giteaUser = emailUserMap.GetByEmail(p.Email)
+		}
+		ret.Participants = append(ret.Participants, &CommitParticipant{GiteaUser: giteaUser, GitIdentity: p})
+	}
+	return ret
+}

models/gituser/gituser.go

@@ -0,0 +1,64 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package gituser
+
+import (
+	"context"
+	"net/url"
+
+	"gitea.dev/models/user"
+	"gitea.dev/modules/container"
+	"gitea.dev/modules/git"
+)
+
+// CommitParticipant is one participant of a commit (its author or a co-author):
+// a git identity, optionally matched to a Gitea user.
+type CommitParticipant struct {
+	GitIdentity *git.CommitIdentity // git identity (name/email), never nil
+	GiteaUser   *user.User          // matched Gitea user, nil if unmatched
+}
+
+// UserCommit represents a commit with matched of database "author" user.
+type UserCommit struct {
+	GitCommit       *git.Commit
+	AuthorUser      *user.User
+	AvatarStackData *AvatarStackData
+}
+
+func RepoCommitSearchByEmailLink(repoLink string, ref git.RefName) string {
+	if curRefWebLinkPath := ref.RefWebLinkPath(); curRefWebLinkPath != "" {
+		return repoLink + "/commits/" + curRefWebLinkPath + "/search?q=" + url.QueryEscape("author:") + "{email}"
+	}
+	return ""
+}
+
+// GetUserCommitsByGitCommits checks if authors' e-mails of commits are corresponding to users.
+func GetUserCommitsByGitCommits(ctx context.Context, gitCommits []*git.Commit, repoLink string, currentRef git.RefName) ([]*UserCommit, error) {
+	userCommits := make([]*UserCommit, 0, len(gitCommits))
+	emailSet := make(container.Set[string])
+	for _, c := range gitCommits {
+		emailSet.Add(c.Author.Email)
+		emailSet.Add(c.Committer.Email)
+		for _, p := range c.AllParticipantIdentities() {
+			emailSet.Add(p.Email)
+		}
+	}
+
+	emailUserMap, err := user.GetUsersByEmails(ctx, emailSet.Values())
+	if err != nil {
+		return nil, err
+	}
+
+	searchByEmailLink := RepoCommitSearchByEmailLink(repoLink, currentRef)
+	for _, c := range gitCommits {
+		uc := &UserCommit{
+			AuthorUser:      emailUserMap.GetByEmail(c.Author.Email), // FIXME: why GetUserCommitsByGitCommits uses "Author", but ParseCommitsWithSignature uses "Committer"?
+			GitCommit:       c,
+			AvatarStackData: BuildAvatarStackData(ctx, c.AllParticipantIdentities(), emailUserMap),
+		}
+		uc.AvatarStackData.SearchByEmailLink = searchByEmailLink
+		userCommits = append(userCommits, uc)
+	}
+	return userCommits, nil
+}

models/user/user.go

@@ -1148,14 +1148,7 @@ func GetUsersBySource(ctx context.Context, s *auth.Source) ([]*User, error) {
 	return users, err
 }
 
-// UserCommit represents a commit with validation of user.
-type UserCommit struct { //revive:disable-line:exported
-	User *User
-	*git.Commit
-}
-
-// ValidateCommitWithEmail check if author's e-mail of commit is corresponding to a user.
-func ValidateCommitWithEmail(ctx context.Context, c *git.Commit) *User {
+func GetUserByGitAuthor(ctx context.Context, c *git.Commit) *User {
 	if c.Author == nil {
 		return nil
 	}
@@ -1166,33 +1159,6 @@ func ValidateCommitWithEmail(ctx context.Context, c *git.Commit) *User {
 	return u
 }
 
-// ValidateCommitsWithEmails checks if authors' e-mails of commits are corresponding to users.
-func ValidateCommitsWithEmails(ctx context.Context, oldCommits []*git.Commit) ([]*UserCommit, error) {
-	var (
-		newCommits = make([]*UserCommit, 0, len(oldCommits))
-		emailSet   = make(container.Set[string])
-	)
-	for _, c := range oldCommits {
-		if c.Author != nil {
-			emailSet.Add(c.Author.Email)
-		}
-	}
-
-	emailUserMap, err := GetUsersByEmails(ctx, emailSet.Values())
-	if err != nil {
-		return nil, err
-	}
-
-	for _, c := range oldCommits {
-		user := emailUserMap.GetByEmail(c.Author.Email) // FIXME: why ValidateCommitsWithEmails uses "Author", but ParseCommitsWithSignature uses "Committer"?
-		newCommits = append(newCommits, &UserCommit{
-			User:   user,
-			Commit: c,
-		})
-	}
-	return newCommits, nil
-}
-
 type EmailUserMap struct {
 	m map[string]*User
 }
@@ -1203,7 +1169,7 @@ func (eum *EmailUserMap) GetByEmail(email string) *User {
 
 func GetUsersByEmails(ctx context.Context, emails []string) (*EmailUserMap, error) {
 	if len(emails) == 0 {
-		return nil, nil //nolint:nilnil // return nil when there are no emails to look up
+		return &EmailUserMap{}, nil
 	}
 
 	needCheckEmails := make(container.Set[string])