Allow to fork repository into the same owner (#32819)

This feature is experimental, not fully tested, and may be changed in
the future.

It is only designed for users who really need it: set
`[repository].ALLOW_FORK_INTO_SAME_OWNER=true` in your app.ini

Doc: https://gitea.com/gitea/docs/pulls/122


![image](https://github.com/user-attachments/assets/38d08c23-9cfc-49d8-9321-ff81edf65395)

custom/conf/app.example.ini

@@ -1040,9 +1040,13 @@ LEVEL = Info
 ;; Don't allow download source archive files from UI
 ;DISABLE_DOWNLOAD_SOURCE_ARCHIVES = false
 
-;; Allow fork repositories without maximum number limit
+;; Allow to fork repositories without maximum number limit
 ;ALLOW_FORK_WITHOUT_MAXIMUM_LIMIT = true
 
+;; Allow to fork repositories into the same owner (user or organization)
+;; This feature is experimental, not fully tested, and may be changed in the future
+;ALLOW_FORK_INTO_SAME_OWNER = false
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;[repository.editor]

modules/repository/fork.go

@@ -9,14 +9,22 @@ import (
 	"code.gitea.io/gitea/models/organization"
 	repo_model "code.gitea.io/gitea/models/repo"
 	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/setting"
 )
 
+func CanUserForkBetweenOwners(id1, id2 int64) bool {
+	if id1 != id2 {
+		return true
+	}
+	return setting.Repository.AllowForkIntoSameOwner
+}
+
 // CanUserForkRepo returns true if specified user can fork repository.
 func CanUserForkRepo(ctx context.Context, user *user_model.User, repo *repo_model.Repository) (bool, error) {
 	if user == nil {
 		return false, nil
 	}
-	if repo.OwnerID != user.ID && !repo_model.HasForkedRepo(ctx, user.ID, repo.ID) {
+	if CanUserForkBetweenOwners(repo.OwnerID, user.ID) && !repo_model.HasForkedRepo(ctx, user.ID, repo.ID) {
 		return true, nil
 	}
 	ownedOrgs, err := organization.GetOrgsCanCreateRepoByUserID(ctx, user.ID)

modules/repository/fork_test.go

@@ -0,0 +1,25 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repository
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/test"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCanUserForkBetweenOwners(t *testing.T) {
+	defer test.MockVariableValue(&setting.Repository.AllowForkIntoSameOwner)
+
+	setting.Repository.AllowForkIntoSameOwner = true
+	assert.True(t, CanUserForkBetweenOwners(1, 1))
+	assert.True(t, CanUserForkBetweenOwners(1, 2))
+
+	setting.Repository.AllowForkIntoSameOwner = false
+	assert.False(t, CanUserForkBetweenOwners(1, 1))
+	assert.True(t, CanUserForkBetweenOwners(1, 2))
+}

modules/setting/repository.go

@@ -53,6 +53,7 @@ var (
 		AllowDeleteOfUnadoptedRepositories      bool
 		DisableDownloadSourceArchives           bool
 		AllowForkWithoutMaximumLimit            bool
+		AllowForkIntoSameOwner                  bool
 
 		// Repository editor settings
 		Editor struct {

routers/web/repo/fork.go

@@ -16,6 +16,7 @@ import (
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/optional"
+	"code.gitea.io/gitea/modules/repository"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/web"
@@ -48,7 +49,7 @@ func getForkRepository(ctx *context.Context) *repo_model.Repository {
 	ctx.Data["repo_name"] = forkRepo.Name
 	ctx.Data["description"] = forkRepo.Description
 	ctx.Data["IsPrivate"] = forkRepo.IsPrivate || forkRepo.Owner.Visibility == structs.VisibleTypePrivate
-	canForkToUser := forkRepo.OwnerID != ctx.Doer.ID && !repo_model.HasForkedRepo(ctx, ctx.Doer.ID, forkRepo.ID)
+	canForkToUser := repository.CanUserForkBetweenOwners(forkRepo.OwnerID, ctx.Doer.ID) && !repo_model.HasForkedRepo(ctx, ctx.Doer.ID, forkRepo.ID)
 
 	ctx.Data["ForkRepo"] = forkRepo
 
@@ -66,7 +67,7 @@ func getForkRepository(ctx *context.Context) *repo_model.Repository {
 
 	traverseParentRepo := forkRepo
 	for {
-		if ctx.Doer.ID == traverseParentRepo.OwnerID {
+		if !repository.CanUserForkBetweenOwners(ctx.Doer.ID, traverseParentRepo.OwnerID) {
 			canForkToUser = false
 		} else {
 			for i, org := range orgs {
@@ -162,7 +163,7 @@ func ForkPost(ctx *context.Context) {
 	var err error
 	traverseParentRepo := forkRepo
 	for {
-		if ctxUser.ID == traverseParentRepo.OwnerID {
+		if !repository.CanUserForkBetweenOwners(ctxUser.ID, traverseParentRepo.OwnerID) {
 			ctx.RenderWithErr(ctx.Tr("repo.settings.new_owner_has_same_repo"), tplFork, &form)
 			return
 		}