Honor delete branch on merge repo setting when using merge API (#35488) (#35726)

Backport #35488 by @kemzeb

Fix #35463.

---------

Co-authored-by: Kemal Zebari <60799661+kemzeb@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

models/git/protected_branch.go

@@ -5,7 +5,6 @@ package git
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"slices"
 	"strings"
@@ -25,7 +24,7 @@ import (
 	"xorm.io/builder"
 )
 
-var ErrBranchIsProtected = errors.New("branch is protected")
+var ErrBranchIsProtected = util.ErrorWrap(util.ErrPermissionDenied, "branch is protected")
 
 // ProtectedBranch struct
 type ProtectedBranch struct {

modules/util/error.go

@@ -6,6 +6,7 @@ package util
 import (
 	"errors"
 	"fmt"
+	"html/template"
 )
 
 // Common Errors forming the base of our error system
@@ -40,22 +41,6 @@ func (w errorWrapper) Unwrap() error {
 	return w.Err
 }
 
-type LocaleWrapper struct {
-	err    error
-	TrKey  string
-	TrArgs []any
-}
-
-// Error returns the message
-func (w LocaleWrapper) Error() string {
-	return w.err.Error()
-}
-
-// Unwrap returns the underlying error
-func (w LocaleWrapper) Unwrap() error {
-	return w.err
-}
-
 // ErrorWrap returns an error that formats as the given text but unwraps as the provided error
 func ErrorWrap(unwrap error, message string, args ...any) error {
 	if len(args) == 0 {
@@ -84,15 +69,39 @@ func NewNotExistErrorf(message string, args ...any) error {
 	return ErrorWrap(ErrNotExist, message, args...)
 }
 
-// ErrorWrapLocale wraps an err with a translation key and arguments
-func ErrorWrapLocale(err error, trKey string, trArgs ...any) error {
-	return LocaleWrapper{err: err, TrKey: trKey, TrArgs: trArgs}
+// ErrorTranslatable wraps an error with translation information
+type ErrorTranslatable interface {
+	error
+	Unwrap() error
+	Translate(ErrorLocaleTranslator) template.HTML
+}
+
+type errorTranslatableWrapper struct {
+	err    error
+	trKey  string
+	trArgs []any
+}
+
+type ErrorLocaleTranslator interface {
+	Tr(key string, args ...any) template.HTML
+}
+
+func (w *errorTranslatableWrapper) Error() string { return w.err.Error() }
+
+func (w *errorTranslatableWrapper) Unwrap() error { return w.err }
+
+func (w *errorTranslatableWrapper) Translate(t ErrorLocaleTranslator) template.HTML {
+	return t.Tr(w.trKey, w.trArgs...)
+}
+
+func ErrorWrapTranslatable(err error, trKey string, trArgs ...any) ErrorTranslatable {
+	return &errorTranslatableWrapper{err: err, trKey: trKey, trArgs: trArgs}
 }
 
-func ErrorAsLocale(err error) *LocaleWrapper {
-	var e LocaleWrapper
+func ErrorAsTranslatable(err error) ErrorTranslatable {
+	var e *errorTranslatableWrapper
 	if errors.As(err, &e) {
-		return &e
+		return e
 	}
 	return nil
 }

modules/util/error_test.go

@@ -0,0 +1,29 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package util
+
+import (
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestErrorTranslatable(t *testing.T) {
+	var err error
+
+	err = ErrorWrapTranslatable(io.EOF, "key", 1)
+	assert.ErrorIs(t, err, io.EOF)
+	assert.Equal(t, "EOF", err.Error())
+	assert.Equal(t, "key", err.(*errorTranslatableWrapper).trKey)
+	assert.Equal(t, []any{1}, err.(*errorTranslatableWrapper).trArgs)
+
+	err = ErrorWrap(err, "new msg %d", 100)
+	assert.ErrorIs(t, err, io.EOF)
+	assert.Equal(t, "new msg 100", err.Error())
+
+	errTr := ErrorAsTranslatable(err)
+	assert.Equal(t, "EOF", errTr.Error())
+	assert.Equal(t, "key", errTr.(*errorTranslatableWrapper).trKey)
+}

routers/api/v1/repo/pull.go

@@ -13,7 +13,6 @@ import (
 	"time"
 
 	activities_model "code.gitea.io/gitea/models/activities"
-	git_model "code.gitea.io/gitea/models/git"
 	issues_model "code.gitea.io/gitea/models/issues"
 	access_model "code.gitea.io/gitea/models/perm/access"
 	pull_model "code.gitea.io/gitea/models/pull"
@@ -938,7 +937,7 @@ func MergePullRequest(ctx *context.APIContext) {
 		} else if errors.Is(err, pull_service.ErrNoPermissionToMerge) {
 			ctx.APIError(http.StatusMethodNotAllowed, "User not allowed to merge PR")
 		} else if errors.Is(err, pull_service.ErrHasMerged) {
-			ctx.APIError(http.StatusMethodNotAllowed, "")
+			ctx.APIError(http.StatusMethodNotAllowed, "The PR is already merged")
 		} else if errors.Is(err, pull_service.ErrIsWorkInProgress) {
 			ctx.APIError(http.StatusMethodNotAllowed, "Work in progress PRs cannot be merged")
 		} else if errors.Is(err, pull_service.ErrNotMergeableState) {
@@ -989,8 +988,14 @@ func MergePullRequest(ctx *context.APIContext) {
 		message += "\n\n" + form.MergeMessageField
 	}
 
+	deleteBranchAfterMerge, err := pull_service.ShouldDeleteBranchAfterMerge(ctx, form.DeleteBranchAfterMerge, ctx.Repo.Repository, pr)
+	if err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+
 	if form.MergeWhenChecksSucceed {
-		scheduled, err := automerge.ScheduleAutoMerge(ctx, ctx.Doer, pr, repo_model.MergeStyle(form.Do), message, form.DeleteBranchAfterMerge)
+		scheduled, err := automerge.ScheduleAutoMerge(ctx, ctx.Doer, pr, repo_model.MergeStyle(form.Do), message, deleteBranchAfterMerge)
 		if err != nil {
 			if pull_model.IsErrAlreadyScheduledToAutoMerge(err) {
 				ctx.APIError(http.StatusConflict, err)
@@ -1035,47 +1040,10 @@ func MergePullRequest(ctx *context.APIContext) {
 	}
 	log.Trace("Pull request merged: %d", pr.ID)
 
-	// for agit flow, we should not delete the agit reference after merge
-	if form.DeleteBranchAfterMerge && pr.Flow == issues_model.PullRequestFlowGithub {
-		// check permission even it has been checked in repo_service.DeleteBranch so that we don't need to
-		// do RetargetChildrenOnMerge
-		if err := repo_service.CanDeleteBranch(ctx, pr.HeadRepo, pr.HeadBranch, ctx.Doer); err == nil {
-			// Don't cleanup when there are other PR's that use this branch as head branch.
-			exist, err := issues_model.HasUnmergedPullRequestsByHeadInfo(ctx, pr.HeadRepoID, pr.HeadBranch)
-			if err != nil {
-				ctx.APIErrorInternal(err)
-				return
-			}
-			if exist {
-				ctx.Status(http.StatusOK)
-				return
-			}
-
-			var headRepo *git.Repository
-			if ctx.Repo != nil && ctx.Repo.Repository != nil && ctx.Repo.Repository.ID == pr.HeadRepoID && ctx.Repo.GitRepo != nil {
-				headRepo = ctx.Repo.GitRepo
-			} else {
-				headRepo, err = gitrepo.OpenRepository(ctx, pr.HeadRepo)
-				if err != nil {
-					ctx.APIErrorInternal(err)
-					return
-				}
-				defer headRepo.Close()
-			}
-
-			if err := repo_service.DeleteBranch(ctx, ctx.Doer, pr.HeadRepo, headRepo, pr.HeadBranch, pr); err != nil {
-				switch {
-				case git.IsErrBranchNotExist(err):
-					ctx.APIErrorNotFound(err)
-				case errors.Is(err, repo_service.ErrBranchIsDefault):
-					ctx.APIError(http.StatusForbidden, errors.New("can not delete default branch"))
-				case errors.Is(err, git_model.ErrBranchIsProtected):
-					ctx.APIError(http.StatusForbidden, errors.New("branch protected"))
-				default:
-					ctx.APIErrorInternal(err)
-				}
-				return
-			}
+	if deleteBranchAfterMerge {
+		if err = repo_service.DeleteBranchAfterMerge(ctx, ctx.Doer, pr.ID, nil); err != nil {
+			// no way to tell users that what error happens, and the PR has been merged, so ignore the error
+			log.Debug("DeleteBranchAfterMerge: pr %d, err: %v", pr.ID, err)
 		}
 	}
 

routers/web/repo/actions/view.go

@@ -850,8 +850,8 @@ func Run(ctx *context_module.Context) {
 		return nil
 	})
 	if err != nil {
-		if errLocale := util.ErrorAsLocale(err); errLocale != nil {
-			ctx.Flash.Error(ctx.Tr(errLocale.TrKey, errLocale.TrArgs...))
+		if errTr := util.ErrorAsTranslatable(err); errTr != nil {
+			ctx.Flash.Error(errTr.Translate(ctx.Locale))
 			ctx.Redirect(redirectURL)
 		} else {
 			ctx.ServerError("DispatchActionWorkflow", err)

routers/web/repo/editor_apply_patch.go

@@ -41,7 +41,7 @@ func NewDiffPatchPost(ctx *context.Context) {
 		Committer:    parsed.GitCommitter,
 	})
 	if err != nil {
-		err = util.ErrorWrapLocale(err, "repo.editor.fail_to_apply_patch")
+		err = util.ErrorWrapTranslatable(err, "repo.editor.fail_to_apply_patch")
 	}
 	if err != nil {
 		editorHandleFileOperationError(ctx, parsed.NewBranchName, err)

routers/web/repo/editor_cherry_pick.go

@@ -74,7 +74,7 @@ func CherryPickPost(ctx *context.Context) {
 			opts.Content = buf.String()
 			_, err = files.ApplyDiffPatch(ctx, ctx.Repo.Repository, ctx.Doer, opts)
 			if err != nil {
-				err = util.ErrorWrapLocale(err, "repo.editor.fail_to_apply_patch")
+				err = util.ErrorWrapTranslatable(err, "repo.editor.fail_to_apply_patch")
 			}
 		}
 		if err != nil {

routers/web/repo/editor_error.go

@@ -38,8 +38,8 @@ func editorHandleFileOperationErrorRender(ctx *context_service.Context, message,
 }
 
 func editorHandleFileOperationError(ctx *context_service.Context, targetBranchName string, err error) {
-	if errAs := util.ErrorAsLocale(err); errAs != nil {
-		ctx.JSONError(ctx.Tr(errAs.TrKey, errAs.TrArgs...))
+	if errAs := util.ErrorAsTranslatable(err); errAs != nil {
+		ctx.JSONError(errAs.Translate(ctx.Locale))
 	} else if errAs, ok := errorAs[git.ErrNotExist](err); ok {
 		ctx.JSONError(ctx.Tr("repo.editor.file_modifying_no_longer_exists", errAs.RelPath))
 	} else if errAs, ok := errorAs[git_model.ErrLFSFileLocked](err); ok {

routers/web/repo/pull.go

@@ -1095,11 +1095,17 @@ func MergePullRequest(ctx *context.Context) {
 		message += "\n\n" + form.MergeMessageField
 	}
 
+	deleteBranchAfterMerge, err := pull_service.ShouldDeleteBranchAfterMerge(ctx, form.DeleteBranchAfterMerge, ctx.Repo.Repository, pr)
+	if err != nil {
+		ctx.ServerError("ShouldDeleteBranchAfterMerge", err)
+		return
+	}
+
 	if form.MergeWhenChecksSucceed {
 		// delete all scheduled auto merges
 		_ = pull_model.DeleteScheduledAutoMerge(ctx, pr.ID)
 		// schedule auto merge
-		scheduled, err := automerge.ScheduleAutoMerge(ctx, ctx.Doer, pr, repo_model.MergeStyle(form.Do), message, form.DeleteBranchAfterMerge)
+		scheduled, err := automerge.ScheduleAutoMerge(ctx, ctx.Doer, pr, repo_model.MergeStyle(form.Do), message, deleteBranchAfterMerge)
 		if err != nil {
 			ctx.ServerError("ScheduleAutoMerge", err)
 			return
@@ -1185,35 +1191,27 @@ func MergePullRequest(ctx *context.Context) {
 
 	log.Trace("Pull request merged: %d", pr.ID)
 
-	if !form.DeleteBranchAfterMerge {
-		ctx.JSONRedirect(issue.Link())
-		return
+	if deleteBranchAfterMerge {
+		deleteBranchAfterMergeAndFlashMessage(ctx, pr.ID)
+		if ctx.Written() {
+			return
+		}
 	}
+	ctx.JSONRedirect(issue.Link())
+}
 
-	// Don't cleanup when other pr use this branch as head branch
-	exist, err := issues_model.HasUnmergedPullRequestsByHeadInfo(ctx, pr.HeadRepoID, pr.HeadBranch)
-	if err != nil {
-		ctx.ServerError("HasUnmergedPullRequestsByHeadInfo", err)
+func deleteBranchAfterMergeAndFlashMessage(ctx *context.Context, prID int64) {
+	var fullBranchName string
+	err := repo_service.DeleteBranchAfterMerge(ctx, ctx.Doer, prID, &fullBranchName)
+	if errTr := util.ErrorAsTranslatable(err); errTr != nil {
+		ctx.Flash.Error(errTr.Translate(ctx.Locale))
 		return
-	}
-	if exist {
-		ctx.JSONRedirect(issue.Link())
+	} else if err == nil {
+		ctx.Flash.Success(ctx.Tr("repo.branch.deletion_success", fullBranchName))
 		return
 	}
-
-	var headRepo *git.Repository
-	if ctx.Repo != nil && ctx.Repo.Repository != nil && pr.HeadRepoID == ctx.Repo.Repository.ID && ctx.Repo.GitRepo != nil {
-		headRepo = ctx.Repo.GitRepo
-	} else {
-		headRepo, err = gitrepo.OpenRepository(ctx, pr.HeadRepo)
-		if err != nil {
-			ctx.ServerError(fmt.Sprintf("OpenRepository[%s]", pr.HeadRepo.FullName()), err)
-			return
-		}
-		defer headRepo.Close()
-	}
-	deleteBranch(ctx, pr, headRepo)
-	ctx.JSONRedirect(issue.Link())
+	// catch unknown errors
+	ctx.ServerError("DeleteBranchAfterMerge", err)
 }
 
 // CancelAutoMergePullRequest cancels a scheduled pr
@@ -1402,131 +1400,17 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 }
 
 // CleanUpPullRequest responses for delete merged branch when PR has been merged
+// Used by "DeleteBranchLink" for "delete branch" button
 func CleanUpPullRequest(ctx *context.Context) {
 	issue, ok := getPullInfo(ctx)
 	if !ok {
 		return
 	}
-
-	pr := issue.PullRequest
-
-	// Don't cleanup unmerged and unclosed PRs and agit PRs
-	if !pr.HasMerged && !issue.IsClosed && pr.Flow != issues_model.PullRequestFlowGithub {
-		ctx.NotFound(nil)
-		return
-	}
-
-	// Don't cleanup when there are other PR's that use this branch as head branch.
-	exist, err := issues_model.HasUnmergedPullRequestsByHeadInfo(ctx, pr.HeadRepoID, pr.HeadBranch)
-	if err != nil {
-		ctx.ServerError("HasUnmergedPullRequestsByHeadInfo", err)
-		return
-	}
-	if exist {
-		ctx.NotFound(nil)
-		return
-	}
-
-	if err := pr.LoadHeadRepo(ctx); err != nil {
-		ctx.ServerError("LoadHeadRepo", err)
-		return
-	} else if pr.HeadRepo == nil {
-		// Forked repository has already been deleted
-		ctx.NotFound(nil)
-		return
-	} else if err = pr.LoadBaseRepo(ctx); err != nil {
-		ctx.ServerError("LoadBaseRepo", err)
-		return
-	} else if err = pr.HeadRepo.LoadOwner(ctx); err != nil {
-		ctx.ServerError("HeadRepo.LoadOwner", err)
-		return
-	}
-
-	if err := repo_service.CanDeleteBranch(ctx, pr.HeadRepo, pr.HeadBranch, ctx.Doer); err != nil {
-		if errors.Is(err, util.ErrPermissionDenied) {
-			ctx.NotFound(nil)
-		} else {
-			ctx.ServerError("CanDeleteBranch", err)
-		}
-		return
-	}
-
-	fullBranchName := pr.HeadRepo.Owner.Name + "/" + pr.HeadBranch
-
-	var gitBaseRepo *git.Repository
-
-	// Assume that the base repo is the current context (almost certainly)
-	if ctx.Repo != nil && ctx.Repo.Repository != nil && ctx.Repo.Repository.ID == pr.BaseRepoID && ctx.Repo.GitRepo != nil {
-		gitBaseRepo = ctx.Repo.GitRepo
-	} else {
-		// If not just open it
-		gitBaseRepo, err = gitrepo.OpenRepository(ctx, pr.BaseRepo)
-		if err != nil {
-			ctx.ServerError(fmt.Sprintf("OpenRepository[%s]", pr.BaseRepo.FullName()), err)
-			return
-		}
-		defer gitBaseRepo.Close()
-	}
-
-	// Now assume that the head repo is the same as the base repo (reasonable chance)
-	gitRepo := gitBaseRepo
-	// But if not: is it the same as the context?
-	if pr.BaseRepoID != pr.HeadRepoID && ctx.Repo != nil && ctx.Repo.Repository != nil && ctx.Repo.Repository.ID == pr.HeadRepoID && ctx.Repo.GitRepo != nil {
-		gitRepo = ctx.Repo.GitRepo
-	} else if pr.BaseRepoID != pr.HeadRepoID {
-		// Otherwise just load it up
-		gitRepo, err = gitrepo.OpenRepository(ctx, pr.HeadRepo)
-		if err != nil {
-			ctx.ServerError(fmt.Sprintf("OpenRepository[%s]", pr.HeadRepo.FullName()), err)
-			return
-		}
-		defer gitRepo.Close()
-	}
-
-	defer func() {
-		ctx.JSONRedirect(issue.Link())
-	}()
-
-	// Check if branch has no new commits
-	headCommitID, err := gitBaseRepo.GetRefCommitID(pr.GetGitHeadRefName())
-	if err != nil {
-		log.Error("GetRefCommitID: %v", err)
-		ctx.Flash.Error(ctx.Tr("repo.branch.deletion_failed", fullBranchName))
-		return
-	}
-	branchCommitID, err := gitRepo.GetBranchCommitID(pr.HeadBranch)
-	if err != nil {
-		log.Error("GetBranchCommitID: %v", err)
-		ctx.Flash.Error(ctx.Tr("repo.branch.deletion_failed", fullBranchName))
-		return
-	}
-	if headCommitID != branchCommitID {
-		ctx.Flash.Error(ctx.Tr("repo.branch.delete_branch_has_new_commits", fullBranchName))
-		return
-	}
-
-	deleteBranch(ctx, pr, gitRepo)
-}
-
-func deleteBranch(ctx *context.Context, pr *issues_model.PullRequest, gitRepo *git.Repository) {
-	fullBranchName := pr.HeadRepo.FullName() + ":" + pr.HeadBranch
-
-	if err := repo_service.DeleteBranch(ctx, ctx.Doer, pr.HeadRepo, gitRepo, pr.HeadBranch, pr); err != nil {
-		switch {
-		case git.IsErrBranchNotExist(err):
-			ctx.Flash.Error(ctx.Tr("repo.branch.deletion_failed", fullBranchName))
-		case errors.Is(err, repo_service.ErrBranchIsDefault):
-			ctx.Flash.Error(ctx.Tr("repo.branch.deletion_failed", fullBranchName))
-		case errors.Is(err, git_model.ErrBranchIsProtected):
-			ctx.Flash.Error(ctx.Tr("repo.branch.deletion_failed", fullBranchName))
-		default:
-			log.Error("DeleteBranch: %v", err)
-			ctx.Flash.Error(ctx.Tr("repo.branch.deletion_failed", fullBranchName))
-		}
+	deleteBranchAfterMergeAndFlashMessage(ctx, issue.PullRequest.ID)
+	if ctx.Written() {
 		return
 	}
-
-	ctx.Flash.Success(ctx.Tr("repo.branch.deletion_success", fullBranchName))
+	ctx.JSONRedirect(issue.Link())
 }
 
 // DownloadPullDiff render a pull's raw diff

services/actions/workflow.go

@@ -49,14 +49,14 @@ func EnableOrDisableWorkflow(ctx *context.APIContext, workflowID string, isEnabl
 
 func DispatchActionWorkflow(ctx reqctx.RequestContext, doer *user_model.User, repo *repo_model.Repository, gitRepo *git.Repository, workflowID, ref string, processInputs func(model *model.WorkflowDispatch, inputs map[string]any) error) error {
 	if workflowID == "" {
-		return util.ErrorWrapLocale(
+		return util.ErrorWrapTranslatable(
 			util.NewNotExistErrorf("workflowID is empty"),
 			"actions.workflow.not_found", workflowID,
 		)
 	}
 
 	if ref == "" {
-		return util.ErrorWrapLocale(
+		return util.ErrorWrapTranslatable(
 			util.NewNotExistErrorf("ref is empty"),
 			"form.target_ref_not_exist", ref,
 		)
@@ -66,7 +66,7 @@ func DispatchActionWorkflow(ctx reqctx.RequestContext, doer *user_model.User, re
 	cfgUnit := repo.MustGetUnit(ctx, unit.TypeActions)
 	cfg := cfgUnit.ActionsConfig()
 	if cfg.IsWorkflowDisabled(workflowID) {
-		return util.ErrorWrapLocale(
+		return util.ErrorWrapTranslatable(
 			util.NewPermissionDeniedErrorf("workflow is disabled"),
 			"actions.workflow.disabled",
 		)
@@ -85,7 +85,7 @@ func DispatchActionWorkflow(ctx reqctx.RequestContext, doer *user_model.User, re
 		runTargetCommit, err = gitRepo.GetBranchCommit(ref)
 	}
 	if err != nil {
-		return util.ErrorWrapLocale(
+		return util.ErrorWrapTranslatable(
 			util.NewNotExistErrorf("ref %q doesn't exist", ref),
 			"form.target_ref_not_exist", ref,
 		)
@@ -126,7 +126,7 @@ func DispatchActionWorkflow(ctx reqctx.RequestContext, doer *user_model.User, re
 	}
 
 	if entry == nil {
-		return util.ErrorWrapLocale(
+		return util.ErrorWrapTranslatable(
 			util.NewNotExistErrorf("workflow %q doesn't exist", workflowID),
 			"actions.workflow.not_found", workflowID,
 		)
@@ -164,7 +164,7 @@ func DispatchActionWorkflow(ctx reqctx.RequestContext, doer *user_model.User, re
 	}
 
 	if len(workflows) == 0 {
-		return util.ErrorWrapLocale(
+		return util.ErrorWrapTranslatable(
 			util.NewNotExistErrorf("workflow %q doesn't exist", workflowID),
 			"actions.workflow.not_found", workflowID,
 		)

services/automerge/automerge.go

@@ -205,18 +205,6 @@ func handlePullRequestAutoMerge(pullID int64, sha string) {
 		return
 	}
 
-	var headGitRepo *git.Repository
-	if pr.BaseRepoID == pr.HeadRepoID {
-		headGitRepo = baseGitRepo
-	} else {
-		headGitRepo, err = gitrepo.OpenRepository(ctx, pr.HeadRepo)
-		if err != nil {
-			log.Error("OpenRepository %-v: %v", pr.HeadRepo, err)
-			return
-		}
-		defer headGitRepo.Close()
-	}
-
 	switch pr.Flow {
 	case issues_model.PullRequestFlowGithub:
 		headBranchExist := pr.HeadRepo != nil && gitrepo.IsBranchExist(ctx, pr.HeadRepo, pr.HeadBranch)
@@ -276,9 +264,12 @@ func handlePullRequestAutoMerge(pullID int64, sha string) {
 		return
 	}
 
-	if pr.Flow == issues_model.PullRequestFlowGithub && scheduledPRM.DeleteBranchAfterMerge {
-		if err := repo_service.DeleteBranch(ctx, doer, pr.HeadRepo, headGitRepo, pr.HeadBranch, pr); err != nil {
-			log.Error("DeletePullRequestHeadBranch: %v", err)
+	deleteBranchAfterMerge, err := pull_service.ShouldDeleteBranchAfterMerge(ctx, &scheduledPRM.DeleteBranchAfterMerge, pr.BaseRepo, pr)
+	if err != nil {
+		log.Error("ShouldDeleteBranchAfterMerge: %v", err)
+	} else if deleteBranchAfterMerge {
+		if err = repo_service.DeleteBranchAfterMerge(ctx, doer, pr.ID, nil); err != nil {
+			log.Error("DeleteBranchAfterMerge: %v", err)
 		}
 	}
 }

services/forms/repo_form.go

@@ -540,7 +540,7 @@ type MergePullRequestForm struct {
 	HeadCommitID           string `json:"head_commit_id,omitempty"`
 	ForceMerge             bool   `json:"force_merge,omitempty"`
 	MergeWhenChecksSucceed bool   `json:"merge_when_checks_succeed,omitempty"`
-	DeleteBranchAfterMerge bool   `json:"delete_branch_after_merge,omitempty"`
+	DeleteBranchAfterMerge *bool  `json:"delete_branch_after_merge,omitempty"`
 }
 
 // Validate validates the fields

services/pull/merge.go

@@ -730,3 +730,24 @@ func SetMerged(ctx context.Context, pr *issues_model.PullRequest, mergedCommitID
 		return true, nil
 	})
 }
+
+func ShouldDeleteBranchAfterMerge(ctx context.Context, userOption *bool, repo *repo_model.Repository, pr *issues_model.PullRequest) (bool, error) {
+	if pr.Flow != issues_model.PullRequestFlowGithub {
+		// only support GitHub workflow (branch-based)
+		// for agit workflow, there is no branch, so nothing to delete
+		// TODO: maybe in the future, it should delete the "agit reference (refs/for/xxxx)"?
+		return false, nil
+	}
+
+	// if user has set an option, respect it
+	if userOption != nil {
+		return *userOption, nil
+	}
+
+	// otherwise, use repository default
+	prUnit, err := repo.GetUnit(ctx, unit.TypePullRequests)
+	if err != nil {
+		return false, err
+	}
+	return prUnit.PullRequestsConfig().DefaultDeleteBranchAfterMerge, nil
+}

services/repository/branch.go

@@ -485,10 +485,7 @@ func RenameBranch(ctx context.Context, repo *repo_model.Repository, doer *user_m
 	return "", nil
 }
 
-// enmuerates all branch related errors
-var (
-	ErrBranchIsDefault = errors.New("branch is default")
-)
+var ErrBranchIsDefault = util.ErrorWrap(util.ErrPermissionDenied, "branch is default")
 
 func CanDeleteBranch(ctx context.Context, repo *repo_model.Repository, branchName string, doer *user_model.User) error {
 	if branchName == repo.DefaultBranch {
@@ -748,3 +745,89 @@ func GetBranchDivergingInfo(ctx reqctx.RequestContext, baseRepo *repo_model.Repo
 	info.BaseHasNewCommits = info.HeadCommitsBehind > 0
 	return info, nil
 }
+
+func DeleteBranchAfterMerge(ctx context.Context, doer *user_model.User, prID int64, outFullBranchName *string) error {
+	pr, err := issues_model.GetPullRequestByID(ctx, prID)
+	if err != nil {
+		return err
+	}
+	if err = pr.LoadIssue(ctx); err != nil {
+		return err
+	}
+	if err = pr.LoadBaseRepo(ctx); err != nil {
+		return err
+	}
+	if err := pr.LoadHeadRepo(ctx); err != nil {
+		return err
+	}
+	if pr.HeadRepo == nil {
+		// Forked repository has already been deleted
+		return util.ErrorWrapTranslatable(util.ErrNotExist, "repo.branch.deletion_failed", "(deleted-repo):"+pr.HeadBranch)
+	}
+	if err = pr.HeadRepo.LoadOwner(ctx); err != nil {
+		return err
+	}
+
+	fullBranchName := pr.HeadRepo.FullName() + ":" + pr.HeadBranch
+	if outFullBranchName != nil {
+		*outFullBranchName = fullBranchName
+	}
+
+	errFailedToDelete := func(err error) error {
+		return util.ErrorWrapTranslatable(err, "repo.branch.deletion_failed", fullBranchName)
+	}
+
+	// Don't clean up unmerged and unclosed PRs and agit PRs
+	if !pr.HasMerged && !pr.Issue.IsClosed && pr.Flow != issues_model.PullRequestFlowGithub {
+		return errFailedToDelete(util.ErrUnprocessableContent)
+	}
+
+	// Don't clean up when there are other PR's that use this branch as head branch.
+	exist, err := issues_model.HasUnmergedPullRequestsByHeadInfo(ctx, pr.HeadRepoID, pr.HeadBranch)
+	if err != nil {
+		return err
+	}
+	if exist {
+		return errFailedToDelete(util.ErrUnprocessableContent)
+	}
+
+	if err := CanDeleteBranch(ctx, pr.HeadRepo, pr.HeadBranch, doer); err != nil {
+		if errors.Is(err, util.ErrPermissionDenied) {
+			return errFailedToDelete(err)
+		}
+		return err
+	}
+
+	gitBaseRepo, gitBaseCloser, err := gitrepo.RepositoryFromContextOrOpen(ctx, pr.BaseRepo)
+	if err != nil {
+		return err
+	}
+	defer gitBaseCloser.Close()
+
+	gitHeadRepo, gitHeadCloser, err := gitrepo.RepositoryFromContextOrOpen(ctx, pr.HeadRepo)
+	if err != nil {
+		return err
+	}
+	defer gitHeadCloser.Close()
+
+	// Check if branch has no new commits
+	headCommitID, err := gitBaseRepo.GetRefCommitID(pr.GetGitHeadRefName())
+	if err != nil {
+		log.Error("GetRefCommitID: %v", err)
+		return errFailedToDelete(err)
+	}
+	branchCommitID, err := gitHeadRepo.GetBranchCommitID(pr.HeadBranch)
+	if err != nil {
+		log.Error("GetBranchCommitID: %v", err)
+		return errFailedToDelete(err)
+	}
+	if headCommitID != branchCommitID {
+		return util.ErrorWrapTranslatable(util.ErrUnprocessableContent, "repo.branch.delete_branch_has_new_commits", fullBranchName)
+	}
+
+	err = DeleteBranch(ctx, doer, pr.HeadRepo, gitHeadRepo, pr.HeadBranch, pr)
+	if errors.Is(err, util.ErrPermissionDenied) || errors.Is(err, util.ErrNotExist) {
+		return errFailedToDelete(err)
+	}
+	return err
+}

templates/repo/issue/view_content/pull_merge_box.tmpl

@@ -51,7 +51,7 @@
 							</div>
 						</div>
 						<div class="item-section-right">
-							<button class="delete-button ui button" data-url="{{.DeleteBranchLink}}">{{ctx.Locale.Tr "repo.branch.delete_html"}}</button>
+							<button class="ui button link-action delete-branch-after-merge" data-url="{{.DeleteBranchLink}}">{{ctx.Locale.Tr "repo.branch.delete_html"}}</button>
 						</div>
 					</div>
 				{{end}}
@@ -69,7 +69,7 @@
 					</div>
 					{{if and .IsPullBranchDeletable (not .IsPullRequestBroken)}}
 						<div class="item-section-right">
-							<button class="delete-button ui button" data-url="{{.DeleteBranchLink}}">{{ctx.Locale.Tr "repo.branch.delete_html"}}</button>
+							<button class="ui button link-action delete-branch-after-merge" data-url="{{.DeleteBranchLink}}">{{ctx.Locale.Tr "repo.branch.delete_html"}}</button>
 						</div>
 					{{end}}
 				</div>

tests/integration/api_issue_config_test.go

@@ -129,7 +129,7 @@ func TestAPIRepoIssueConfigPaths(t *testing.T) {
 				configData, err := yaml.Marshal(configMap)
 				assert.NoError(t, err)
 
-				_, err = createFileInBranch(owner, repo, fullPath, repo.DefaultBranch, string(configData))
+				_, err = createFile(owner, repo, fullPath, string(configData))
 				assert.NoError(t, err)
 
 				issueConfig := getIssueConfig(t, owner.Name, repo.Name)

tests/integration/api_pull_test.go

@@ -17,19 +17,23 @@ import (
 	issues_model "code.gitea.io/gitea/models/issues"
 	"code.gitea.io/gitea/models/perm"
 	repo_model "code.gitea.io/gitea/models/repo"
+	unit_model "code.gitea.io/gitea/models/unit"
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/setting"
 	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/services/convert"
 	"code.gitea.io/gitea/services/forms"
 	"code.gitea.io/gitea/services/gitdiff"
 	issue_service "code.gitea.io/gitea/services/issue"
 	pull_service "code.gitea.io/gitea/services/pull"
+	repo_service "code.gitea.io/gitea/services/repository"
 	files_service "code.gitea.io/gitea/services/repository/files"
 	"code.gitea.io/gitea/tests"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestAPIViewPulls(t *testing.T) {
@@ -186,6 +190,76 @@ func TestAPIMergePullWIP(t *testing.T) {
 	MakeRequest(t, req, http.StatusMethodNotAllowed)
 }
 
+func TestAPIMergePull(t *testing.T) {
+	onGiteaRun(t, func(t *testing.T, giteaURL *url.URL) {
+		repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+		owner := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: repo.OwnerID})
+		apiCtx := NewAPITestContext(t, repo.OwnerName, repo.Name, auth_model.AccessTokenScopeWriteRepository)
+
+		checkBranchExists := func(t *testing.T, branchName string, status int) {
+			req := NewRequest(t, "GET", fmt.Sprintf("/api/v1/repos/%s/%s/branches/%s", owner.Name, repo.Name, branchName)).AddTokenAuth(apiCtx.Token)
+			MakeRequest(t, req, status)
+		}
+
+		createTestBranchPR := func(t *testing.T, branchName string) *api.PullRequest {
+			testCreateFileInBranch(t, owner, repo, createFileInBranchOptions{NewBranch: branchName}, map[string]string{"a-new-file-" + branchName + ".txt": "dummy content"})
+			prDTO, err := doAPICreatePullRequest(apiCtx, repo.OwnerName, repo.Name, repo.DefaultBranch, branchName)(t)
+			require.NoError(t, err)
+			return &prDTO
+		}
+
+		performMerge := func(t *testing.T, prIndex int64, params map[string]any, optExpectedStatus ...int) {
+			req := NewRequestWithJSON(t, http.MethodPost, fmt.Sprintf("/api/v1/repos/%s/%s/pulls/%d/merge", owner.Name, repo.Name, prIndex), params).AddTokenAuth(apiCtx.Token)
+			expectedStatus := util.OptionalArg(optExpectedStatus, http.StatusOK)
+			MakeRequest(t, req, expectedStatus)
+		}
+
+		t.Run("Normal", func(t *testing.T) {
+			newBranch := "test-pull-1"
+			prDTO := createTestBranchPR(t, newBranch)
+			performMerge(t, prDTO.Index, map[string]any{"do": "merge"})
+			checkBranchExists(t, newBranch, http.StatusOK)
+			// try to merge again, make sure we cannot perform a merge on the same PR
+			performMerge(t, prDTO.Index, map[string]any{"do": "merge"}, http.StatusMethodNotAllowed)
+		})
+
+		t.Run("DeleteBranchAfterMergePassedByFormField", func(t *testing.T) {
+			newBranch := "test-pull-2"
+			prDTO := createTestBranchPR(t, newBranch)
+			performMerge(t, prDTO.Index, map[string]any{"do": "merge", "delete_branch_after_merge": true})
+			checkBranchExists(t, newBranch, http.StatusNotFound)
+		})
+
+		updateRepoUnitDefaultDeleteBranchAfterMerge := func(t *testing.T, repo *repo_model.Repository, value bool) {
+			prUnit, err := repo.GetUnit(t.Context(), unit_model.TypePullRequests)
+			require.NoError(t, err)
+
+			prUnit.PullRequestsConfig().DefaultDeleteBranchAfterMerge = value
+			require.NoError(t, repo_service.UpdateRepositoryUnits(t.Context(), repo, []repo_model.RepoUnit{{
+				RepoID: repo.ID,
+				Type:   unit_model.TypePullRequests,
+				Config: prUnit.PullRequestsConfig(),
+			}}, nil))
+		}
+
+		t.Run("DeleteBranchAfterMergePassedByRepoSettings", func(t *testing.T) {
+			newBranch := "test-pull-3"
+			prDTO := createTestBranchPR(t, newBranch)
+			updateRepoUnitDefaultDeleteBranchAfterMerge(t, repo, true)
+			performMerge(t, prDTO.Index, map[string]any{"do": "merge"})
+			checkBranchExists(t, newBranch, http.StatusNotFound)
+		})
+
+		t.Run("DeleteBranchAfterMergeFormFieldIsSetButNotRepoSettings", func(t *testing.T) {
+			newBranch := "test-pull-4"
+			prDTO := createTestBranchPR(t, newBranch)
+			updateRepoUnitDefaultDeleteBranchAfterMerge(t, repo, false)
+			performMerge(t, prDTO.Index, map[string]any{"do": "merge", "delete_branch_after_merge": true})
+			checkBranchExists(t, newBranch, http.StatusNotFound)
+		})
+	})
+}
+
 func TestAPICreatePullSuccess(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
 	repo10 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 10})

tests/integration/api_repo_file_create_test.go

@@ -133,7 +133,7 @@ func BenchmarkAPICreateFileSmall(b *testing.B) {
 		b.ResetTimer()
 		for n := 0; b.Loop(); n++ {
 			treePath := fmt.Sprintf("update/file%d.txt", n)
-			_, _ = createFileInBranch(user2, repo1, treePath, repo1.DefaultBranch, treePath)
+			_, _ = createFile(user2, repo1, treePath)
 		}
 	})
 }
@@ -149,7 +149,7 @@ func BenchmarkAPICreateFileMedium(b *testing.B) {
 		for n := 0; b.Loop(); n++ {
 			treePath := fmt.Sprintf("update/file%d.txt", n)
 			copy(data, treePath)
-			_, _ = createFileInBranch(user2, repo1, treePath, repo1.DefaultBranch, treePath)
+			_, _ = createFile(user2, repo1, treePath)
 		}
 	})
 }

tests/integration/api_repo_file_helpers.go

@@ -6,26 +6,36 @@ package integration
 import (
 	"context"
 	"strings"
+	"testing"
 
 	repo_model "code.gitea.io/gitea/models/repo"
 	user_model "code.gitea.io/gitea/models/user"
 	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/util"
 	files_service "code.gitea.io/gitea/services/repository/files"
+
+	"github.com/stretchr/testify/require"
 )
 
-func createFileInBranch(user *user_model.User, repo *repo_model.Repository, treePath, branchName, content string) (*api.FilesResponse, error) {
+type createFileInBranchOptions struct {
+	OldBranch, NewBranch string
+}
+
+func testCreateFileInBranch(t *testing.T, user *user_model.User, repo *repo_model.Repository, createOpts createFileInBranchOptions, files map[string]string) *api.FilesResponse {
+	resp, err := createFileInBranch(user, repo, createOpts, files)
+	require.NoError(t, err)
+	return resp
+}
+
+func createFileInBranch(user *user_model.User, repo *repo_model.Repository, createOpts createFileInBranchOptions, files map[string]string) (*api.FilesResponse, error) {
 	ctx := context.TODO()
-	opts := &files_service.ChangeRepoFilesOptions{
-		Files: []*files_service.ChangeRepoFile{
-			{
-				Operation:     "create",
-				TreePath:      treePath,
-				ContentReader: strings.NewReader(content),
-			},
-		},
-		OldBranch: branchName,
-		Author:    nil,
-		Committer: nil,
+	opts := &files_service.ChangeRepoFilesOptions{OldBranch: createOpts.OldBranch, NewBranch: createOpts.NewBranch}
+	for path, content := range files {
+		opts.Files = append(opts.Files, &files_service.ChangeRepoFile{
+			Operation:     "create",
+			TreePath:      path,
+			ContentReader: strings.NewReader(content),
+		})
 	}
 	return files_service.ChangeRepoFiles(ctx, repo, user, opts)
 }
@@ -53,10 +63,12 @@ func createOrReplaceFileInBranch(user *user_model.User, repo *repo_model.Reposit
 		return err
 	}
 
-	_, err = createFileInBranch(user, repo, treePath, branchName, content)
+	_, err = createFileInBranch(user, repo, createFileInBranchOptions{OldBranch: branchName}, map[string]string{treePath: content})
 	return err
 }
 
-func createFile(user *user_model.User, repo *repo_model.Repository, treePath string) (*api.FilesResponse, error) {
-	return createFileInBranch(user, repo, treePath, repo.DefaultBranch, "This is a NEW file")
+// TODO: replace all usages of this function with testCreateFileInBranch or testCreateFile
+func createFile(user *user_model.User, repo *repo_model.Repository, treePath string, optContent ...string) (*api.FilesResponse, error) {
+	content := util.OptionalArg(optContent, "This is a NEW file") // some tests need this default content because its SHA is hardcoded
+	return createFileInBranch(user, repo, createFileInBranchOptions{}, map[string]string{treePath: content})
 }

tests/integration/pull_merge_test.go

@@ -79,7 +79,7 @@ func testPullCleanUp(t *testing.T, session *TestSession, user, repo, pullnum str
 
 	// Click the little button to create a pull
 	htmlDoc := NewHTMLParser(t, resp.Body)
-	link, exists := htmlDoc.doc.Find(".timeline-item .delete-button").Attr("data-url")
+	link, exists := htmlDoc.doc.Find(".timeline-item .delete-branch-after-merge").Attr("data-url")
 	assert.True(t, exists, "The template has changed, can not find delete button url")
 	req = NewRequestWithValues(t, "POST", link, map[string]string{
 		"_csrf": htmlDoc.GetCSRF(),