[BUG] Fix pull request reopen conditions

- Move the conditions code around, such that the existence of the head
and base is first checked (so a clear error can be given, instead of a
possible server error). This makes it easier to read this code. As the
logic is now grouped together.
- Adds integration testing that simulates the deletion of the base and
head branch and ensures the pull request cannot be opened. The 'normal'
testcase also 'informally' ensures that the previous incorrect condition
is not there, because the branch `base-branch` doesn't exist on the head
repository.
- Resolves #2321

options/locale/locale_en-US.ini

@@ -1859,6 +1859,8 @@ pulls.cmd_instruction_merge_title = Merge
 pulls.cmd_instruction_merge_desc = Merge the changes and update on Forgejo.
 pulls.clear_merge_message = Clear merge message
 pulls.clear_merge_message_hint = Clearing the merge message will only remove the commit message content and keep generated git trailers such as "Co-Authored-By …".
+pulls.reopen_failed.head_branch = The pull request cannot be reopened, because the head branch doesn't exist anymore.
+pulls.reopen_failed.base_branch = The pull request cannot be reopened, because the base branch doesn't exist anymore.
 
 pulls.auto_merge_button_when_succeed = (When checks succeed)
 pulls.auto_merge_when_succeed = Auto merge when all checks succeed

routers/web/repo/issue.go

@@ -3028,27 +3028,34 @@ func NewComment(ctx *context.Context) {
 				// check whether the ref of PR <refs/pulls/pr_index/head> in base repo is consistent with the head commit of head branch in the head repo
 				// get head commit of PR
 				if pull.Flow == issues_model.PullRequestFlowGithub {
-					prHeadRef := pull.GetGitRefName()
 					if err := pull.LoadBaseRepo(ctx); err != nil {
 						ctx.ServerError("Unable to load base repo", err)
 						return
 					}
+					if err := pull.LoadHeadRepo(ctx); err != nil {
+						ctx.ServerError("Unable to load head repo", err)
+						return
+					}
+
+					// Check if the base branch of the pull request still exists.
+					if ok := git.IsBranchExist(ctx, pull.BaseRepo.RepoPath(), pull.BaseBranch); !ok {
+						ctx.JSONError(ctx.Tr("repo.pulls.reopen_failed.base_branch"))
+						return
+					}
+
+					// Check if the head branch of the pull request still exists.
+					if ok := git.IsBranchExist(ctx, pull.HeadRepo.RepoPath(), pull.HeadBranch); !ok {
+						ctx.JSONError(ctx.Tr("repo.pulls.reopen_failed.head_branch"))
+						return
+					}
+
+					prHeadRef := pull.GetGitRefName()
 					prHeadCommitID, err := git.GetFullCommitID(ctx, pull.BaseRepo.RepoPath(), prHeadRef)
 					if err != nil {
 						ctx.ServerError("Get head commit Id of pr fail", err)
 						return
 					}
 
-					// get head commit of branch in the head repo
-					if err := pull.LoadHeadRepo(ctx); err != nil {
-						ctx.ServerError("Unable to load head repo", err)
-						return
-					}
-					if ok := git.IsBranchExist(ctx, pull.HeadRepo.RepoPath(), pull.BaseBranch); !ok {
-						// todo localize
-						ctx.JSONError("The origin branch is delete, cannot reopen.")
-						return
-					}
 					headBranchRef := pull.GetGitHeadBranchRefName()
 					headBranchCommitID, err := git.GetFullCommitID(ctx, pull.HeadRepo.RepoPath(), headBranchRef)
 					if err != nil {

tests/integration/pull_reopen_test.go

@@ -0,0 +1,214 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+	"time"
+
+	"code.gitea.io/gitea/models/db"
+	git_model "code.gitea.io/gitea/models/git"
+	issues_model "code.gitea.io/gitea/models/issues"
+	unit_model "code.gitea.io/gitea/models/unit"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	gitea_context "code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/translation"
+	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"
+)
+
+func TestPullrequestReopen(t *testing.T) {
+	onGiteaRun(t, func(t *testing.T, u *url.URL) {
+		user2 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+		org26 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 26})
+
+		// Create an base repository.
+		baseRepo, _, f := CreateDeclarativeRepo(t, user2, "reopen-base",
+			[]unit_model.Type{unit_model.TypePullRequests}, nil, nil,
+		)
+		defer f()
+
+		// Create a new branch on the base branch, so it can be deleted later.
+		_, err := files_service.ChangeRepoFiles(git.DefaultContext, baseRepo, user2, &files_service.ChangeRepoFilesOptions{
+			Files: []*files_service.ChangeRepoFile{
+				{
+					Operation:     "update",
+					TreePath:      "README.md",
+					ContentReader: strings.NewReader("New README.md"),
+				},
+			},
+			Message:   "Modify README for base",
+			OldBranch: "main",
+			NewBranch: "base-branch",
+			Author: &files_service.IdentityOptions{
+				Name:  user2.Name,
+				Email: user2.Email,
+			},
+			Committer: &files_service.IdentityOptions{
+				Name:  user2.Name,
+				Email: user2.Email,
+			},
+			Dates: &files_service.CommitDateOptions{
+				Author:    time.Now(),
+				Committer: time.Now(),
+			},
+		})
+		assert.NoError(t, err)
+
+		// Create an head repository.
+		headRepo, err := repo_service.ForkRepository(git.DefaultContext, user2, org26, repo_service.ForkRepoOptions{
+			BaseRepo: baseRepo,
+			Name:     "reopen-head",
+		})
+		assert.NoError(t, err)
+		assert.NotEmpty(t, headRepo)
+
+		// Add a change to the head repository, so a pull request can be opened.
+		_, err = files_service.ChangeRepoFiles(git.DefaultContext, headRepo, user2, &files_service.ChangeRepoFilesOptions{
+			Files: []*files_service.ChangeRepoFile{
+				{
+					Operation:     "update",
+					TreePath:      "README.md",
+					ContentReader: strings.NewReader("Updated README.md"),
+				},
+			},
+			Message:   "Modify README for head",
+			OldBranch: "main",
+			NewBranch: "head-branch",
+			Author: &files_service.IdentityOptions{
+				Name:  user2.Name,
+				Email: user2.Email,
+			},
+			Committer: &files_service.IdentityOptions{
+				Name:  user2.Name,
+				Email: user2.Email,
+			},
+			Dates: &files_service.CommitDateOptions{
+				Author:    time.Now(),
+				Committer: time.Now(),
+			},
+		})
+		assert.NoError(t, err)
+
+		// Create the pull reuqest.
+		pullIssue := &issues_model.Issue{
+			RepoID:   baseRepo.ID,
+			Title:    "Testing reopen functionality",
+			PosterID: user2.ID,
+			Poster:   user2,
+			IsPull:   true,
+		}
+		pullRequest := &issues_model.PullRequest{
+			HeadRepoID: headRepo.ID,
+			BaseRepoID: baseRepo.ID,
+			HeadBranch: "head-branch",
+			BaseBranch: "base-branch",
+			HeadRepo:   headRepo,
+			BaseRepo:   baseRepo,
+			Type:       issues_model.PullRequestGitea,
+		}
+		err = pull_service.NewPullRequest(git.DefaultContext, baseRepo, pullIssue, nil, nil, pullRequest, nil)
+		assert.NoError(t, err)
+
+		issue := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{Title: "Testing reopen functionality"})
+
+		// Close the PR.
+		err = issue_service.ChangeStatus(db.DefaultContext, issue, user2, "", true)
+		assert.NoError(t, err)
+
+		session := loginUser(t, "user2")
+
+		reopenPR := func(t *testing.T, expectedStatus int) *httptest.ResponseRecorder {
+			t.Helper()
+
+			link := fmt.Sprintf("%s/pulls/%d/comments", baseRepo.FullName(), issue.Index)
+			req := NewRequestWithValues(t, "POST", link, map[string]string{
+				"_csrf":  GetCSRF(t, session, fmt.Sprintf("%s/pulls/%d", baseRepo.FullName(), issue.Index)),
+				"status": "reopen",
+			})
+			return session.MakeRequest(t, req, expectedStatus)
+		}
+
+		restoreBranch := func(t *testing.T, repoName, branchName string, branchID int64) {
+			t.Helper()
+
+			link := fmt.Sprintf("/%s/branches", repoName)
+			req := NewRequestWithValues(t, "POST", fmt.Sprintf("%s/restore?branch_id=%d&name=%s", link, branchID, branchName), map[string]string{
+				"_csrf": GetCSRF(t, session, link),
+			})
+			session.MakeRequest(t, req, http.StatusOK)
+
+			flashCookie := session.GetCookie(gitea_context.CookieNameFlash)
+			assert.NotNil(t, flashCookie)
+			assert.Contains(t, flashCookie.Value, "success%3DBranch%2B%2522"+branchName+"%2522%2Bhas%2Bbeen%2Brestored.")
+		}
+
+		deleteBranch := func(t *testing.T, repoName, branchName string) {
+			t.Helper()
+
+			link := fmt.Sprintf("/%s/branches", repoName)
+			req := NewRequestWithValues(t, "POST", fmt.Sprintf("%s/delete?name=%s", link, branchName), map[string]string{
+				"_csrf": GetCSRF(t, session, link),
+			})
+			session.MakeRequest(t, req, http.StatusOK)
+
+			flashCookie := session.GetCookie(gitea_context.CookieNameFlash)
+			assert.NotNil(t, flashCookie)
+			assert.Contains(t, flashCookie.Value, "success%3DBranch%2B%2522"+branchName+"%2522%2Bhas%2Bbeen%2Bdeleted.")
+		}
+
+		type errorJSON struct {
+			Error string `json:"errorMessage"`
+		}
+
+		t.Run("Base branch deleted", func(t *testing.T) {
+			defer tests.PrintCurrentTest(t)()
+
+			branch := unittest.AssertExistsAndLoadBean(t, &git_model.Branch{Name: "base-branch", RepoID: baseRepo.ID})
+			defer func() {
+				restoreBranch(t, baseRepo.FullName(), branch.Name, branch.ID)
+			}()
+
+			deleteBranch(t, baseRepo.FullName(), branch.Name)
+			resp := reopenPR(t, http.StatusBadRequest)
+
+			var errorResp errorJSON
+			DecodeJSON(t, resp, &errorResp)
+			assert.EqualValues(t, translation.NewLocale("en-US").Tr("repo.pulls.reopen_failed.base_branch"), errorResp.Error)
+		})
+
+		t.Run("Head branch deleted", func(t *testing.T) {
+			defer tests.PrintCurrentTest(t)()
+
+			branch := unittest.AssertExistsAndLoadBean(t, &git_model.Branch{Name: "head-branch", RepoID: headRepo.ID})
+			defer func() {
+				restoreBranch(t, headRepo.FullName(), branch.Name, branch.ID)
+			}()
+
+			deleteBranch(t, headRepo.FullName(), branch.Name)
+			resp := reopenPR(t, http.StatusBadRequest)
+
+			var errorResp errorJSON
+			DecodeJSON(t, resp, &errorResp)
+			assert.EqualValues(t, translation.NewLocale("en-US").Tr("repo.pulls.reopen_failed.head_branch"), errorResp.Error)
+		})
+
+		t.Run("Normal", func(t *testing.T) {
+			defer tests.PrintCurrentTest(t)()
+
+			reopenPR(t, http.StatusOK)
+		})
+	})
+}