Fix a panic bug when head repository deleting (#30674) (#30676)

Backport #30674 & #30679 by @lunny

When visiting a pull request files which head repository has been
deleted, it will panic because headrepo is nil.

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/repo/pull.go

@@ -865,21 +865,21 @@ func viewPullFiles(ctx *context.Context, specifiedStartCommit, specifiedEndCommi
 
 		if pull.HeadRepo != nil {
 			ctx.Data["SourcePath"] = pull.HeadRepo.Link() + "/src/branch/" + util.PathEscapeSegments(pull.HeadBranch)
-		}
 
-		if !pull.HasMerged && ctx.Doer != nil {
-			perm, err := access_model.GetUserRepoPermission(ctx, pull.HeadRepo, ctx.Doer)
-			if err != nil {
-				ctx.ServerError("GetUserRepoPermission", err)
-				return
-			}
+			if !pull.HasMerged && ctx.Doer != nil {
+				perm, err := access_model.GetUserRepoPermission(ctx, pull.HeadRepo, ctx.Doer)
+				if err != nil {
+					ctx.ServerError("GetUserRepoPermission", err)
+					return
+				}
 
-			if perm.CanWrite(unit.TypeCode) || issues_model.CanMaintainerWriteToBranch(ctx, perm, pull.HeadBranch, ctx.Doer) {
-				ctx.Data["CanEditFile"] = true
-				ctx.Data["EditFileTooltip"] = ctx.Tr("repo.editor.edit_this_file")
-				ctx.Data["HeadRepoLink"] = pull.HeadRepo.Link()
-				ctx.Data["HeadBranchName"] = pull.HeadBranch
-				ctx.Data["BackToLink"] = setting.AppSubURL + ctx.Req.URL.RequestURI()
+				if perm.CanWrite(unit.TypeCode) || issues_model.CanMaintainerWriteToBranch(ctx, perm, pull.HeadBranch, ctx.Doer) {
+					ctx.Data["CanEditFile"] = true
+					ctx.Data["EditFileTooltip"] = ctx.Tr("repo.editor.edit_this_file")
+					ctx.Data["HeadRepoLink"] = pull.HeadRepo.Link()
+					ctx.Data["HeadBranchName"] = pull.HeadBranch
+					ctx.Data["BackToLink"] = setting.AppSubURL + ctx.Req.URL.RequestURI()
+				}
 			}
 		}
 	}

tests/integration/pull_compare_test.go

@@ -4,9 +4,17 @@
 package integration
 
 import (
+	"fmt"
 	"net/http"
+	"net/url"
 	"testing"
 
+	"code.gitea.io/gitea/models/db"
+	issues_model "code.gitea.io/gitea/models/issues"
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	repo_service "code.gitea.io/gitea/services/repository"
 	"code.gitea.io/gitea/tests"
 
 	"github.com/stretchr/testify/assert"
@@ -32,4 +40,36 @@ func TestPullCompare(t *testing.T) {
 	doc := NewHTMLParser(t, resp.Body)
 	editButtonCount := doc.doc.Find(".diff-file-header-actions a[href*='/_edit/']").Length()
 	assert.Greater(t, editButtonCount, 0, "Expected to find a button to edit a file in the PR diff view but there were none")
+
+	onGiteaRun(t, func(t *testing.T, u *url.URL) {
+		defer tests.PrepareTestEnv(t)()
+
+		session := loginUser(t, "user1")
+		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")
+		testPullCreate(t, session, "user1", "repo1", false, "master", "master1", "This is a pull title")
+
+		repo1 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{OwnerName: "user2", Name: "repo1"})
+		issueIndex := unittest.AssertExistsAndLoadBean(t, &issues_model.IssueIndex{GroupID: repo1.ID}, unittest.OrderBy("group_id ASC"))
+		prFilesURL := fmt.Sprintf("/user2/repo1/pulls/%d/files", issueIndex.MaxIndex)
+		req = NewRequest(t, "GET", prFilesURL)
+		resp = session.MakeRequest(t, req, http.StatusOK)
+		doc := NewHTMLParser(t, resp.Body)
+		editButtonCount := doc.doc.Find(".diff-file-header-actions a[href*='/_edit/']").Length()
+		assert.Greater(t, editButtonCount, 0, "Expected to find a button to edit a file in the PR diff view but there were none")
+
+		repoForked := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{OwnerName: "user1", Name: "repo1"})
+		user2 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+
+		// delete the head repository and revisit the PR diff view
+		err := repo_service.DeleteRepositoryDirectly(db.DefaultContext, user2, repoForked.ID)
+		assert.NoError(t, err)
+
+		req = NewRequest(t, "GET", prFilesURL)
+		resp = session.MakeRequest(t, req, http.StatusOK)
+		doc = NewHTMLParser(t, resp.Body)
+		editButtonCount = doc.doc.Find(".diff-file-header-actions a[href*='/_edit/']").Length()
+		assert.EqualValues(t, editButtonCount, 0, "Expected not to find a button to edit a file in the PR diff view because head repository has been deleted")
+	})
 }