Nicely handle missing user in collaborations (#17049)

* Nicely handle missing user in collaborations

It is possible to have a collaboration in a repository which refers to a no-longer
existing user. This causes the repository transfer to fail with an unusual error.

This PR makes `repo.getCollaborators()` nicely handle the missing user by ghosting
the collaboration but also adds consistency check. It also adds an
Access consistency check.

Fix #17044

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

3 files changed, 23 insertions, 5 deletions

diff --git a/models/access.go b/models/access.go
index 560234aae8..7bbc04bd45 100644
--- a/models/access.go
+++ b/models/access.go
@@ -230,6 +230,9 @@ func (repo *Repository) refreshCollaboratorAccesses(e db.Engine, accessMap map[i
 		return fmt.Errorf("getCollaborations: %v", err)
 	}
 	for _, c := range collaborators {
+		if c.User.IsGhost() {
+			continue
+		}
 		updateUserAccess(accessMap, c.User, c.Collaboration.Mode)
 	}
 	return nil
diff --git a/models/repo_collaboration.go b/models/repo_collaboration.go
index 08360c102d..bc9d0100ef 100644
--- a/models/repo_collaboration.go
+++ b/models/repo_collaboration.go
@@ -9,6 +9,7 @@ import (
 	"fmt"
 
 	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/timeutil"
 
 	"xorm.io/builder"
@@ -88,16 +89,21 @@ func (repo *Repository) getCollaborators(e db.Engine, listOptions db.ListOptions
 		return nil, fmt.Errorf("getCollaborations: %v", err)
 	}
 
-	collaborators := make([]*Collaborator, len(collaborations))
-	for i, c := range collaborations {
+	collaborators := make([]*Collaborator, 0, len(collaborations))
+	for _, c := range collaborations {
 		user, err := getUserByID(e, c.UserID)
 		if err != nil {
-			return nil, err
+			if IsErrUserNotExist(err) {
+				log.Warn("Inconsistent DB: User: %d is listed as collaborator of %-v but does not exist", c.UserID, repo)
+				user = NewGhostUser()
+			} else {
+				return nil, err
+			}
 		}
-		collaborators[i] = &Collaborator{
+		collaborators = append(collaborators, &Collaborator{
 			User:          user,
 			Collaboration: c,
-		}
+		})
 	}
 	return collaborators, nil
 }
diff --git a/models/repo_transfer.go b/models/repo_transfer.go
index fe50c1cc04..082c3d19dc 100644
--- a/models/repo_transfer.go
+++ b/models/repo_transfer.go
@@ -274,6 +274,14 @@ func TransferOwnership(doer *User, newOwnerName string, repo *Repository) (err e
 	// Dummy object.
 	collaboration := &Collaboration{RepoID: repo.ID}
 	for _, c := range collaborators {
+		if c.IsGhost() {
+			collaboration.ID = c.Collaboration.ID
+			if _, err := sess.Delete(collaboration); err != nil {
+				return fmt.Errorf("remove collaborator '%d': %v", c.ID, err)
+			}
+			collaboration.ID = 0
+		}
+
 		if c.ID != newOwner.ID {
 			isMember, err := isOrganizationMember(sess, newOwner.ID, c.ID)
 			if err != nil {
@@ -286,6 +294,7 @@ func TransferOwnership(doer *User, newOwnerName string, repo *Repository) (err e
 		if _, err := sess.Delete(collaboration); err != nil {
 			return fmt.Errorf("remove collaborator '%d': %v", c.ID, err)
 		}
+		collaboration.UserID = 0
 	}
 
 	// Remove old team-repository relations.