fix(backgrounds): clear backgrounds that point at files used elsewhere

A migration clears the background of projects whose background file is
also a task attachment, an avatar, a data export, a pending import upload
or another project's background. Of projects sharing a file, the oldest
keeps it.

The Unsplash and upload providers now remove the old background through
DeleteBackgroundFileIfExists.

pkg/migration/20261105115436.go

@@ -0,0 +1,70 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package migration
+
+import (
+	"code.vikunja.io/api/pkg/log"
+
+	"src.techknowlogick.com/xormigrate"
+	"xorm.io/builder"
+	"xorm.io/xorm"
+)
+
+// Of projects sharing a background file, the oldest keeps it.
+var sharedBackgroundCond20261105115436 = builder.And(
+	builder.Gt{"background_file_id": 0},
+	builder.Or(
+		builder.In("background_file_id", builder.Select("file_id").From("task_attachments")),
+		builder.In("background_file_id", builder.Select("avatar_file_id").From("users")),
+		builder.In("background_file_id", builder.Select("export_file_id").From("users")),
+		builder.In("background_file_id", builder.Select("upload_file_id").From("migration_status")),
+		builder.Expr("EXISTS (SELECT 1 FROM projects other WHERE other.background_file_id = projects.background_file_id AND other.id < projects.id)"),
+	),
+)
+
+func init() {
+	migrations = append(migrations, &xormigrate.Migration{
+		ID:          "20261105115436",
+		Description: "Clear project backgrounds that point at files used elsewhere",
+		Migrate: func(tx *xorm.Engine) error {
+			ids := []int64{}
+			if err := tx.Table("projects").Cols("id").Where(sharedBackgroundCond20261105115436).Find(&ids); err != nil {
+				return err
+			}
+			if len(ids) == 0 {
+				return nil
+			}
+
+			// Usually none; any hit means the background was set to someone else's file.
+			log.Warningf("Clearing the background of %d projects whose background file is used elsewhere: %v", len(ids), ids)
+			for start := 0; start < len(ids); start += 500 {
+				chunk := ids[start:min(start+500, len(ids))]
+				_, err := tx.Table("projects").In("id", chunk).Update(map[string]any{
+					"background_file_id":   0,
+					"background_blur_hash": "",
+				})
+				if err != nil {
+					return err
+				}
+			}
+			return nil
+		},
+		Rollback: func(tx *xorm.Engine) error {
+			return nil
+		},
+	})
+}

pkg/migration/20261105115436_test.go

@@ -0,0 +1,115 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package migration
+
+import (
+	"slices"
+	"testing"
+
+	"code.vikunja.io/api/pkg/db"
+
+	"github.com/stretchr/testify/require"
+	"src.techknowlogick.com/xormigrate"
+)
+
+type project20261105115436 struct {
+	ID                 int64  `xorm:"bigint autoincr not null unique pk"`
+	BackgroundFileID   int64  `xorm:"null"`
+	BackgroundBlurHash string `xorm:"varchar(50) null"`
+}
+
+func (project20261105115436) TableName() string { return "projects" }
+
+type taskAttachment20261105115436 struct {
+	ID     int64 `xorm:"bigint autoincr not null unique pk"`
+	FileID int64 `xorm:"bigint not null"`
+}
+
+func (taskAttachment20261105115436) TableName() string { return "task_attachments" }
+
+type user20261105115436 struct {
+	ID           int64 `xorm:"bigint autoincr not null unique pk"`
+	AvatarFileID int64 `xorm:"null"`
+	ExportFileID int64 `xorm:"bigint null"`
+}
+
+func (user20261105115436) TableName() string { return "users" }
+
+type migrationStatus20261105115436 struct {
+	ID           int64  `xorm:"bigint autoincr not null unique pk"`
+	UploadFileID *int64 `xorm:"bigint null"`
+}
+
+func (migrationStatus20261105115436) TableName() string { return "migration_status" }
+
+func TestClearSharedBackgrounds20261105115436(t *testing.T) {
+	x, err := db.CreateTestEngine()
+	require.NoError(t, err)
+
+	tables := []any{
+		project20261105115436{},
+		taskAttachment20261105115436{},
+		user20261105115436{},
+		migrationStatus20261105115436{},
+	}
+	t.Cleanup(func() {
+		require.NoError(t, x.DropTables(tables...))
+	})
+	require.NoError(t, x.DropTables(tables...))
+	require.NoError(t, x.Sync2(tables...))
+
+	upload := int64(14)
+	_, err = x.Insert(
+		&taskAttachment20261105115436{ID: 1, FileID: 11},
+		&user20261105115436{ID: 1, AvatarFileID: 12, ExportFileID: 13},
+		&migrationStatus20261105115436{ID: 1, UploadFileID: &upload},
+		&migrationStatus20261105115436{ID: 2},
+		&project20261105115436{ID: 1, BackgroundFileID: 11, BackgroundBlurHash: "a"},
+		&project20261105115436{ID: 2, BackgroundFileID: 12, BackgroundBlurHash: "b"},
+		&project20261105115436{ID: 3, BackgroundFileID: 13, BackgroundBlurHash: "c"},
+		&project20261105115436{ID: 4, BackgroundFileID: 14, BackgroundBlurHash: "d"},
+		&project20261105115436{ID: 5, BackgroundFileID: 15, BackgroundBlurHash: "e"},
+		&project20261105115436{ID: 6, BackgroundFileID: 15, BackgroundBlurHash: "f"},
+		&project20261105115436{ID: 7, BackgroundFileID: 16, BackgroundBlurHash: "g"},
+		&project20261105115436{ID: 8},
+	)
+	require.NoError(t, err)
+
+	idx := slices.IndexFunc(migrations, func(m *xormigrate.Migration) bool { return m.ID == "20261105115436" })
+	require.NotEqual(t, -1, idx)
+	require.NoError(t, migrations[idx].Migrate(x))
+
+	projects := []*project20261105115436{}
+	require.NoError(t, x.OrderBy("id").Find(&projects))
+	got := map[int64]int64{}
+	for _, p := range projects {
+		got[p.ID] = p.BackgroundFileID
+		if p.BackgroundFileID == 0 {
+			require.Emptyf(t, p.BackgroundBlurHash, "project %d kept its blur hash", p.ID)
+		}
+	}
+	require.Equal(t, map[int64]int64{
+		1: 0,  // task attachment
+		2: 0,  // avatar
+		3: 0,  // data export
+		4: 0,  // pending import upload
+		5: 15, // oldest of two projects sharing a file
+		6: 0,
+		7: 16, // own file
+		8: 0,
+	}, got)
+}

pkg/modules/background/unsplash/unsplash.go

@@ -333,18 +333,8 @@ func (p *Provider) Set(s *xorm.Session, image *background.Image, project *models
 		return
 	}
 
-	// Remove the old background if one exists
-	if project.BackgroundFileID != 0 {
-		file := files.File{ID: project.BackgroundFileID}
-		err = file.Delete(s)
-		if err != nil && !files.IsErrFileDoesNotExist(err) {
-			return err
-		}
-
-		err = models.RemoveUnsplashPhoto(s, project.BackgroundFileID)
-		if err != nil && !files.IsErrFileDoesNotExist(err) {
-			return err
-		}
+	if err := project.DeleteBackgroundFileIfExists(s); err != nil {
+		return err
 	}
 
 	// Save the relation that we got it from unsplash

pkg/modules/background/upload/upload.go

@@ -54,13 +54,8 @@ func (p *Provider) Search(_ *xorm.Session, _ string, _ int64) (result []*backgro
 // @Failure 500 {object} models.Message "Internal error"
 // @Router /projects/{id}/backgrounds/upload [put]
 func (p *Provider) Set(s *xorm.Session, img *background.Image, project *models.Project, _ web.Auth) (err error) {
-	// Remove the old background if one exists
-	if project.BackgroundFileID != 0 {
-		file := files.File{ID: project.BackgroundFileID}
-		err := file.Delete(s)
-		if err != nil && !files.IsErrFileDoesNotExist(err) {
-			return err
-		}
+	if err := project.DeleteBackgroundFileIfExists(s); err != nil {
+		return err
 	}
 
 	file := &files.File{}