Retarget depending pulls when the parent branch is deleted (#28686)

Sometimes you need to work on a feature which depends on another (unmerged) feature.
In this case, you may create a PR based on that feature instead of the main branch.
Currently, such PRs will be closed without the possibility to reopen in case the parent feature is merged and its branch is deleted.
Automatic target branch change make life a lot easier in such cases.
Github and Bitbucket behave in such way.

Example:
$PR_1$: main <- feature1
$PR_2$: feature1 <- feature2

Currently, merging $PR_1$ and deleting its branch leads to $PR_2$ being closed without the possibility to reopen.
This is both annoying and loses the review history when you open a new PR.

With this change, $PR_2$ will change its target branch to main ($PR_2$: main <- feature2) after $PR_1$ has been merged and its branch has been deleted.

This behavior is enabled by default but can be disabled.
For security reasons, this target branch change will not be executed when merging PRs targeting another repo. 

Fixes #27062
Fixes #18408

---------

Co-authored-by: Denys Konovalov <kontakt@denyskon.de>
Co-authored-by: delvh <dev.lh@web.de>

3 files changed, 104 insertions, 24 deletions

diff --git a/tests/integration/pull_create_test.go b/tests/integration/pull_create_test.go
index a6ee0d9dfa..029ea65d71 100644
--- a/tests/integration/pull_create_test.go
+++ b/tests/integration/pull_create_test.go
@@ -17,7 +17,7 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func testPullCreate(t *testing.T, session *TestSession, user, repo, branch, title string) *httptest.ResponseRecorder {
+func testPullCreate(t *testing.T, session *TestSession, user, repo string, toSelf bool, targetBranch, sourceBranch, title string) *httptest.ResponseRecorder {
 	req := NewRequest(t, "GET", path.Join(user, repo))
 	resp := session.MakeRequest(t, req, http.StatusOK)
 
@@ -25,8 +25,21 @@ func testPullCreate(t *testing.T, session *TestSession, user, repo, branch, titl
 	htmlDoc := NewHTMLParser(t, resp.Body)
 	link, exists := htmlDoc.doc.Find("#new-pull-request").Attr("href")
 	assert.True(t, exists, "The template has changed")
-	if branch != "master" {
-		link = strings.Replace(link, ":master", ":"+branch, 1)
+
+	targetUser := strings.Split(link, "/")[1]
+	if toSelf && targetUser != user {
+		link = strings.Replace(link, targetUser, user, 1)
+	}
+
+	if targetBranch != "master" {
+		link = strings.Replace(link, "master...", targetBranch+"...", 1)
+	}
+	if sourceBranch != "master" {
+		if targetUser == user {
+			link = strings.Replace(link, "...master", "..."+sourceBranch, 1)
+		} else {
+			link = strings.Replace(link, ":master", ":"+sourceBranch, 1)
+		}
 	}
 
 	req = NewRequest(t, "GET", link)
@@ -49,7 +62,7 @@ func TestPullCreate(t *testing.T) {
 		session := loginUser(t, "user1")
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
-		resp := testPullCreate(t, session, "user1", "repo1", "master", "This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master", "This is a pull title")
 
 		// check the redirected URL
 		url := test.RedirectURL(resp)
@@ -77,7 +90,7 @@ func TestPullCreate_TitleEscape(t *testing.T) {
 		session := loginUser(t, "user1")
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
-		resp := testPullCreate(t, session, "user1", "repo1", "master", "<i>XSS PR</i>")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master", "<i>XSS PR</i>")
 
 		// check the redirected URL
 		url := test.RedirectURL(resp)
@@ -142,7 +155,7 @@ func TestPullBranchDelete(t *testing.T) {
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testCreateBranch(t, session, "user1", "repo1", "branch/master", "master1", http.StatusSeeOther)
 		testEditFile(t, session, "user1", "repo1", "master1", "README.md", "Hello, World (Edited)\n")
-		resp := testPullCreate(t, session, "user1", "repo1", "master1", "This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master1", "This is a pull title")
 
 		// check the redirected URL
 		url := test.RedirectURL(resp)
diff --git a/tests/integration/pull_merge_test.go b/tests/integration/pull_merge_test.go
index 35af47f802..2aa6742a56 100644
--- a/tests/integration/pull_merge_test.go
+++ b/tests/integration/pull_merge_test.go
@@ -35,16 +35,23 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func testPullMerge(t *testing.T, session *TestSession, user, repo, pullnum string, mergeStyle repo_model.MergeStyle) *httptest.ResponseRecorder {
+func testPullMerge(t *testing.T, session *TestSession, user, repo, pullnum string, mergeStyle repo_model.MergeStyle, deleteBranch bool) *httptest.ResponseRecorder {
 	req := NewRequest(t, "GET", path.Join(user, repo, "pulls", pullnum))
 	resp := session.MakeRequest(t, req, http.StatusOK)
 
 	htmlDoc := NewHTMLParser(t, resp.Body)
 	link := path.Join(user, repo, "pulls", pullnum, "merge")
-	req = NewRequestWithValues(t, "POST", link, map[string]string{
+
+	options := map[string]string{
 		"_csrf": htmlDoc.GetCSRF(),
 		"do":    string(mergeStyle),
-	})
+	}
+
+	if deleteBranch {
+		options["delete_branch_after_merge"] = "on"
+	}
+
+	req = NewRequestWithValues(t, "POST", link, options)
 	resp = session.MakeRequest(t, req, http.StatusOK)
 
 	respJSON := struct {
@@ -83,11 +90,11 @@ func TestPullMerge(t *testing.T) {
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
 
-		resp := testPullCreate(t, session, "user1", "repo1", "master", "This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master", "This is a pull title")
 
 		elem := strings.Split(test.RedirectURL(resp), "/")
 		assert.EqualValues(t, "pulls", elem[3])
-		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleMerge)
+		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleMerge, false)
 
 		hookTasks, err = webhook.HookTasks(db.DefaultContext, 1, 1)
 		assert.NoError(t, err)
@@ -105,11 +112,11 @@ func TestPullRebase(t *testing.T) {
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
 
-		resp := testPullCreate(t, session, "user1", "repo1", "master", "This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master", "This is a pull title")
 
 		elem := strings.Split(test.RedirectURL(resp), "/")
 		assert.EqualValues(t, "pulls", elem[3])
-		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleRebase)
+		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleRebase, false)
 
 		hookTasks, err = webhook.HookTasks(db.DefaultContext, 1, 1)
 		assert.NoError(t, err)
@@ -127,11 +134,11 @@ func TestPullRebaseMerge(t *testing.T) {
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
 
-		resp := testPullCreate(t, session, "user1", "repo1", "master", "This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master", "This is a pull title")
 
 		elem := strings.Split(test.RedirectURL(resp), "/")
 		assert.EqualValues(t, "pulls", elem[3])
-		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleRebaseMerge)
+		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleRebaseMerge, false)
 
 		hookTasks, err = webhook.HookTasks(db.DefaultContext, 1, 1)
 		assert.NoError(t, err)
@@ -150,11 +157,11 @@ func TestPullSquash(t *testing.T) {
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited!)\n")
 
-		resp := testPullCreate(t, session, "user1", "repo1", "master", "This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master", "This is a pull title")
 
 		elem := strings.Split(test.RedirectURL(resp), "/")
 		assert.EqualValues(t, "pulls", elem[3])
-		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleSquash)
+		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleSquash, false)
 
 		hookTasks, err = webhook.HookTasks(db.DefaultContext, 1, 1)
 		assert.NoError(t, err)
@@ -168,11 +175,11 @@ func TestPullCleanUpAfterMerge(t *testing.T) {
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testEditFileToNewBranch(t, session, "user1", "repo1", "master", "feature/test", "README.md", "Hello, World (Edited - TestPullCleanUpAfterMerge)\n")
 
-		resp := testPullCreate(t, session, "user1", "repo1", "feature/test", "This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "feature/test", "This is a pull title")
 
 		elem := strings.Split(test.RedirectURL(resp), "/")
 		assert.EqualValues(t, "pulls", elem[3])
-		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleMerge)
+		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleMerge, false)
 
 		// Check PR branch deletion
 		resp = testPullCleanUp(t, session, elem[1], elem[2], elem[4])
@@ -203,7 +210,7 @@ func TestCantMergeWorkInProgress(t *testing.T) {
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
 
-		resp := testPullCreate(t, session, "user1", "repo1", "master", "[wip] This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master", "[wip] This is a pull title")
 
 		req := NewRequest(t, "GET", test.RedirectURL(resp))
 		resp = session.MakeRequest(t, req, http.StatusOK)
@@ -435,3 +442,63 @@ func TestConflictChecking(t *testing.T) {
 		assert.False(t, conflictingPR.Mergeable(db.DefaultContext))
 	})
 }
+
+func TestPullRetargetChildOnBranchDelete(t *testing.T) {
+	onGiteaRun(t, func(t *testing.T, giteaURL *url.URL) {
+		session := loginUser(t, "user1")
+		testEditFileToNewBranch(t, session, "user2", "repo1", "master", "base-pr", "README.md", "Hello, World\n(Edited - TestPullRetargetOnCleanup - base PR)\n")
+		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
+		testEditFileToNewBranch(t, session, "user1", "repo1", "base-pr", "child-pr", "README.md", "Hello, World\n(Edited - TestPullRetargetOnCleanup - base PR)\n(Edited - TestPullRetargetOnCleanup - child PR)")
+
+		respBasePR := testPullCreate(t, session, "user2", "repo1", true, "master", "base-pr", "Base Pull Request")
+		elemBasePR := strings.Split(test.RedirectURL(respBasePR), "/")
+		assert.EqualValues(t, "pulls", elemBasePR[3])
+
+		respChildPR := testPullCreate(t, session, "user1", "repo1", false, "base-pr", "child-pr", "Child Pull Request")
+		elemChildPR := strings.Split(test.RedirectURL(respChildPR), "/")
+		assert.EqualValues(t, "pulls", elemChildPR[3])
+
+		testPullMerge(t, session, elemBasePR[1], elemBasePR[2], elemBasePR[4], repo_model.MergeStyleMerge, true)
+
+		// Check child PR
+		req := NewRequest(t, "GET", test.RedirectURL(respChildPR))
+		resp := session.MakeRequest(t, req, http.StatusOK)
+
+		htmlDoc := NewHTMLParser(t, resp.Body)
+		targetBranch := htmlDoc.doc.Find("#branch_target>a").Text()
+		prStatus := strings.TrimSpace(htmlDoc.doc.Find(".issue-title-meta>.issue-state-label").Text())
+
+		assert.EqualValues(t, "master", targetBranch)
+		assert.EqualValues(t, "Open", prStatus)
+	})
+}
+
+func TestPullDontRetargetChildOnWrongRepo(t *testing.T) {
+	onGiteaRun(t, func(t *testing.T, giteaURL *url.URL) {
+		session := loginUser(t, "user1")
+		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
+		testEditFileToNewBranch(t, session, "user1", "repo1", "master", "base-pr", "README.md", "Hello, World\n(Edited - TestPullDontRetargetChildOnWrongRepo - base PR)\n")
+		testEditFileToNewBranch(t, session, "user1", "repo1", "base-pr", "child-pr", "README.md", "Hello, World\n(Edited - TestPullDontRetargetChildOnWrongRepo - base PR)\n(Edited - TestPullDontRetargetChildOnWrongRepo - child PR)")
+
+		respBasePR := testPullCreate(t, session, "user1", "repo1", false, "master", "base-pr", "Base Pull Request")
+		elemBasePR := strings.Split(test.RedirectURL(respBasePR), "/")
+		assert.EqualValues(t, "pulls", elemBasePR[3])
+
+		respChildPR := testPullCreate(t, session, "user1", "repo1", true, "base-pr", "child-pr", "Child Pull Request")
+		elemChildPR := strings.Split(test.RedirectURL(respChildPR), "/")
+		assert.EqualValues(t, "pulls", elemChildPR[3])
+
+		testPullMerge(t, session, elemBasePR[1], elemBasePR[2], elemBasePR[4], repo_model.MergeStyleMerge, true)
+
+		// Check child PR
+		req := NewRequest(t, "GET", test.RedirectURL(respChildPR))
+		resp := session.MakeRequest(t, req, http.StatusOK)
+
+		htmlDoc := NewHTMLParser(t, resp.Body)
+		targetBranch := htmlDoc.doc.Find("#branch_target>a").Text()
+		prStatus := strings.TrimSpace(htmlDoc.doc.Find(".issue-title-meta>.issue-state-label").Text())
+
+		assert.EqualValues(t, "base-pr", targetBranch)
+		assert.EqualValues(t, "Closed", prStatus)
+	})
+}
diff --git a/tests/integration/repo_activity_test.go b/tests/integration/repo_activity_test.go
index c8d0c46d64..792554db4b 100644
--- a/tests/integration/repo_activity_test.go
+++ b/tests/integration/repo_activity_test.go
@@ -22,16 +22,16 @@ func TestRepoActivity(t *testing.T) {
 		// Create PRs (1 merged & 2 proposed)
 		testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
 		testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
-		resp := testPullCreate(t, session, "user1", "repo1", "master", "This is a pull title")
+		resp := testPullCreate(t, session, "user1", "repo1", false, "master", "master", "This is a pull title")
 		elem := strings.Split(test.RedirectURL(resp), "/")
 		assert.EqualValues(t, "pulls", elem[3])
-		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleMerge)
+		testPullMerge(t, session, elem[1], elem[2], elem[4], repo_model.MergeStyleMerge, false)
 
 		testEditFileToNewBranch(t, session, "user1", "repo1", "master", "feat/better_readme", "README.md", "Hello, World (Edited Again)\n")
-		testPullCreate(t, session, "user1", "repo1", "feat/better_readme", "This is a pull title")
+		testPullCreate(t, session, "user1", "repo1", false, "master", "feat/better_readme", "This is a pull title")
 
 		testEditFileToNewBranch(t, session, "user1", "repo1", "master", "feat/much_better_readme", "README.md", "Hello, World (Edited More)\n")
-		testPullCreate(t, session, "user1", "repo1", "feat/much_better_readme", "This is a pull title")
+		testPullCreate(t, session, "user1", "repo1", false, "master", "feat/much_better_readme", "This is a pull title")
 
 		// Create issues (3 new issues)
 		testNewIssue(t, session, "user2", "repo1", "Issue 1", "Description 1")