fix: never set Poster or Assignee to nil

When a user is not found for whatever reason, it must be mapped to the
GhostUser.

Fixes: https://codeberg.org/forgejo/forgejo/issues/4718
(cherry picked from commit e6786db393)

models/issues/comment_list.go

@@ -23,7 +23,7 @@ func (comments CommentList) LoadPosters(ctx context.Context) error {
 	}
 
 	posterIDs := container.FilterSlice(comments, func(c *Comment) (int64, bool) {
-		return c.PosterID, c.Poster == nil && c.PosterID > 0
+		return c.PosterID, c.Poster == nil && user_model.IsValidUserID(c.PosterID)
 	})
 
 	posterMaps, err := getPostersByIDs(ctx, posterIDs)
@@ -33,7 +33,7 @@ func (comments CommentList) LoadPosters(ctx context.Context) error {
 
 	for _, comment := range comments {
 		if comment.Poster == nil {
-			comment.Poster = getPoster(comment.PosterID, posterMaps)
+			comment.PosterID, comment.Poster = user_model.GetUserFromMap(comment.PosterID, posterMaps)
 		}
 	}
 	return nil
@@ -165,7 +165,7 @@ func (comments CommentList) loadOldMilestones(ctx context.Context) error {
 
 func (comments CommentList) getAssigneeIDs() []int64 {
 	return container.FilterSlice(comments, func(comment *Comment) (int64, bool) {
-		return comment.AssigneeID, comment.AssigneeID > 0
+		return comment.AssigneeID, user_model.IsValidUserID(comment.AssigneeID)
 	})
 }
 
@@ -206,11 +206,7 @@ func (comments CommentList) loadAssignees(ctx context.Context) error {
 	}
 
 	for _, comment := range comments {
-		comment.Assignee = assignees[comment.AssigneeID]
-		if comment.Assignee == nil {
-			comment.AssigneeID = user_model.GhostUserID
-			comment.Assignee = user_model.NewGhostUser()
-		}
+		comment.AssigneeID, comment.Assignee = user_model.GetUserFromMap(comment.AssigneeID, assignees)
 	}
 	return nil
 }

models/issues/comment_list_test.go

@@ -0,0 +1,86 @@
+// Copyright 2024 The Forgejo Authors
+// SPDX-License-Identifier: MIT
+
+package issues
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCommentListLoadUser(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	issue := unittest.AssertExistsAndLoadBean(t, &Issue{})
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: issue.RepoID})
+	doer := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: repo.OwnerID})
+
+	for _, testCase := range []struct {
+		poster   int64
+		assignee int64
+		user     *user_model.User
+	}{
+		{
+			poster:   user_model.ActionsUserID,
+			assignee: user_model.ActionsUserID,
+			user:     user_model.NewActionsUser(),
+		},
+		{
+			poster:   user_model.GhostUserID,
+			assignee: user_model.GhostUserID,
+			user:     user_model.NewGhostUser(),
+		},
+		{
+			poster:   doer.ID,
+			assignee: doer.ID,
+			user:     doer,
+		},
+		{
+			poster:   0,
+			assignee: 0,
+			user:     user_model.NewGhostUser(),
+		},
+		{
+			poster:   -200,
+			assignee: -200,
+			user:     user_model.NewGhostUser(),
+		},
+		{
+			poster:   200,
+			assignee: 200,
+			user:     user_model.NewGhostUser(),
+		},
+	} {
+		t.Run(testCase.user.Name, func(t *testing.T) {
+			comment, err := CreateComment(db.DefaultContext, &CreateCommentOptions{
+				Type:    CommentTypeComment,
+				Doer:    testCase.user,
+				Repo:    repo,
+				Issue:   issue,
+				Content: "Hello",
+			})
+			assert.NoError(t, err)
+
+			list := CommentList{comment}
+
+			comment.PosterID = testCase.poster
+			comment.Poster = nil
+			assert.NoError(t, list.LoadPosters(db.DefaultContext))
+			require.NotNil(t, comment.Poster)
+			assert.Equal(t, testCase.user.ID, comment.Poster.ID)
+
+			comment.AssigneeID = testCase.assignee
+			comment.Assignee = nil
+			assert.NoError(t, list.loadAssignees(db.DefaultContext))
+			require.NotNil(t, comment.Assignee)
+			assert.Equal(t, testCase.user.ID, comment.Assignee.ID)
+		})
+	}
+}

models/issues/issue_list.go

@@ -79,7 +79,7 @@ func (issues IssueList) LoadPosters(ctx context.Context) error {
 	}
 
 	posterIDs := container.FilterSlice(issues, func(issue *Issue) (int64, bool) {
-		return issue.PosterID, issue.Poster == nil && issue.PosterID > 0
+		return issue.PosterID, issue.Poster == nil && user_model.IsValidUserID(issue.PosterID)
 	})
 
 	posterMaps, err := getPostersByIDs(ctx, posterIDs)
@@ -89,7 +89,7 @@ func (issues IssueList) LoadPosters(ctx context.Context) error {
 
 	for _, issue := range issues {
 		if issue.Poster == nil {
-			issue.Poster = getPoster(issue.PosterID, posterMaps)
+			issue.PosterID, issue.Poster = user_model.GetUserFromMap(issue.PosterID, posterMaps)
 		}
 	}
 	return nil
@@ -115,20 +115,6 @@ func getPostersByIDs(ctx context.Context, posterIDs []int64) (map[int64]*user_mo
 	return posterMaps, nil
 }
 
-func getPoster(posterID int64, posterMaps map[int64]*user_model.User) *user_model.User {
-	if posterID == user_model.ActionsUserID {
-		return user_model.NewActionsUser()
-	}
-	if posterID <= 0 {
-		return nil
-	}
-	poster, ok := posterMaps[posterID]
-	if !ok {
-		return user_model.NewGhostUser()
-	}
-	return poster
-}
-
 func (issues IssueList) getIssueIDs() []int64 {
 	ids := make([]int64, 0, len(issues))
 	for _, issue := range issues {

models/issues/issue_list_test.go

@@ -9,9 +9,11 @@ import (
 	"code.gitea.io/gitea/models/db"
 	issues_model "code.gitea.io/gitea/models/issues"
 	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/setting"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestIssueList_LoadRepositories(t *testing.T) {
@@ -78,3 +80,50 @@ func TestIssueList_LoadAttributes(t *testing.T) {
 		assert.Equal(t, issue.ID == 1, issue.IsRead, "unexpected is_read value for issue[%d]", issue.ID)
 	}
 }
+
+func TestIssueListLoadUser(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	issue := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{})
+	doer := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1})
+
+	for _, testCase := range []struct {
+		poster int64
+		user   *user_model.User
+	}{
+		{
+			poster: user_model.ActionsUserID,
+			user:   user_model.NewActionsUser(),
+		},
+		{
+			poster: user_model.GhostUserID,
+			user:   user_model.NewGhostUser(),
+		},
+		{
+			poster: doer.ID,
+			user:   doer,
+		},
+		{
+			poster: 0,
+			user:   user_model.NewGhostUser(),
+		},
+		{
+			poster: -200,
+			user:   user_model.NewGhostUser(),
+		},
+		{
+			poster: 200,
+			user:   user_model.NewGhostUser(),
+		},
+	} {
+		t.Run(testCase.user.Name, func(t *testing.T) {
+			list := issues_model.IssueList{issue}
+
+			issue.PosterID = testCase.poster
+			issue.Poster = nil
+			assert.NoError(t, list.LoadPosters(db.DefaultContext))
+			require.NotNil(t, issue.Poster)
+			assert.Equal(t, testCase.user.ID, issue.Poster.ID)
+		})
+	}
+}

models/user/user.go

@@ -906,6 +906,20 @@ func GetUserByIDs(ctx context.Context, ids []int64) ([]*User, error) {
 	return users, err
 }
 
+func IsValidUserID(id int64) bool {
+	return id > 0 || id == GhostUserID || id == ActionsUserID
+}
+
+func GetUserFromMap(id int64, idMap map[int64]*User) (int64, *User) {
+	if user, ok := idMap[id]; ok {
+		return id, user
+	}
+	if id == ActionsUserID {
+		return ActionsUserID, NewActionsUser()
+	}
+	return GhostUserID, NewGhostUser()
+}
+
 // GetPossibleUserByID returns the user if id > 0 or return system usrs if id < 0
 func GetPossibleUserByID(ctx context.Context, id int64) (*User, error) {
 	switch id {

models/user/user_test.go

@@ -35,6 +35,39 @@ func TestOAuth2Application_LoadUser(t *testing.T) {
 	assert.NotNil(t, user)
 }
 
+func TestIsValidUserID(t *testing.T) {
+	assert.False(t, user_model.IsValidUserID(-30))
+	assert.False(t, user_model.IsValidUserID(0))
+	assert.True(t, user_model.IsValidUserID(user_model.GhostUserID))
+	assert.True(t, user_model.IsValidUserID(user_model.ActionsUserID))
+	assert.True(t, user_model.IsValidUserID(200))
+}
+
+func TestGetUserFromMap(t *testing.T) {
+	id := int64(200)
+	idMap := map[int64]*user_model.User{
+		id: {ID: id},
+	}
+
+	ghostID := int64(user_model.GhostUserID)
+	actionsID := int64(user_model.ActionsUserID)
+	actualID, actualUser := user_model.GetUserFromMap(-20, idMap)
+	assert.Equal(t, ghostID, actualID)
+	assert.Equal(t, ghostID, actualUser.ID)
+
+	actualID, actualUser = user_model.GetUserFromMap(0, idMap)
+	assert.Equal(t, ghostID, actualID)
+	assert.Equal(t, ghostID, actualUser.ID)
+
+	actualID, actualUser = user_model.GetUserFromMap(ghostID, idMap)
+	assert.Equal(t, ghostID, actualID)
+	assert.Equal(t, ghostID, actualUser.ID)
+
+	actualID, actualUser = user_model.GetUserFromMap(actionsID, idMap)
+	assert.Equal(t, actionsID, actualID)
+	assert.Equal(t, actionsID, actualUser.ID)
+}
+
 func TestGetUserByName(t *testing.T) {
 	defer tests.AddFixtures("models/user/fixtures/")()
 	assert.NoError(t, unittest.PrepareTestDatabase())