Fix pull requests API convert panic when head repository is deleted. (go-gitea#34685)

Fix go-gitea#34682

Author: lunny

services/convert/pull.go

@@ -419,6 +419,9 @@ func ToAPIPullRequests(ctx context.Context, baseRepo *repo_model.Repository, prs
 		if baseBranch != nil {
 			apiPullRequest.Base.Sha = baseBranch.CommitID
 		}
+		if pr.HeadRepoID == pr.BaseRepoID {
+			apiPullRequest.Head.Repository = apiPullRequest.Base.Repository
+		}
 
 		// pull request head branch, both repository and branch could not exist
 		if pr.HeadRepo != nil {
@@ -431,22 +434,19 @@ func ToAPIPullRequests(ctx context.Context, baseRepo *repo_model.Repository, prs
 			if exist {
 				apiPullRequest.Head.Ref = pr.HeadBranch
 			}
+			if pr.HeadRepoID != pr.BaseRepoID {
+				p, err := access_model.GetUserRepoPermission(ctx, pr.HeadRepo, doer)
+				if err != nil {
+					log.Error("GetUserRepoPermission[%d]: %v", pr.HeadRepoID, err)
+					p.AccessMode = perm.AccessModeNone
+				}
+				apiPullRequest.Head.Repository = ToRepo(ctx, pr.HeadRepo, p)
+			}
 		}
 		if apiPullRequest.Head.Ref == "" {
 			apiPullRequest.Head.Ref = pr.GetGitRefName()
 		}
 
-		if pr.HeadRepoID == pr.BaseRepoID {
-			apiPullRequest.Head.Repository = apiPullRequest.Base.Repository
-		} else {
-			p, err := access_model.GetUserRepoPermission(ctx, pr.HeadRepo, doer)
-			if err != nil {
-				log.Error("GetUserRepoPermission[%d]: %v", pr.HeadRepoID, err)
-				p.AccessMode = perm.AccessModeNone
-			}
-			apiPullRequest.Head.Repository = ToRepo(ctx, pr.HeadRepo, p)
-		}
-
 		if pr.Flow == issues_model.PullRequestFlowAGit {
 			apiPullRequest.Head.Name = ""
 		}

services/convert/pull_test.go

@@ -46,4 +46,11 @@ func TestPullRequest_APIFormat(t *testing.T) {
 	assert.NotNil(t, apiPullRequest)
 	assert.Nil(t, apiPullRequest.Head.Repository)
 	assert.EqualValues(t, -1, apiPullRequest.Head.RepoID)
+
+	apiPullRequests, err := ToAPIPullRequests(git.DefaultContext, pr.BaseRepo, []*issues_model.PullRequest{pr}, nil)
+	assert.NoError(t, err)
+	assert.Len(t, apiPullRequests, 1)
+	assert.NotNil(t, apiPullRequests[0])
+	assert.Nil(t, apiPullRequests[0].Head.Repository)
+	assert.EqualValues(t, -1, apiPullRequests[0].Head.RepoID)
 }