Display pull request head branch even the branch deleted or repository deleted (#10413)

* Display pull request head branch even the branch deleted or repository deleted

* Merge getHeadRepo/loadHeadRepo and getBaseRepo/loadBaseRepo on pull and fill repo when pr.Issue.Repo is available

* retrieve sha from pull head when pull request branch deleted and fix tests

* Fix test

* Ensure MustHeadRepoName returns empty string if no head repo

Co-authored-by: zeripath <art27@cantab.net>

2 files changed, 68 insertions, 63 deletions

diff --git a/modules/convert/pull.go b/modules/convert/pull.go
index cf2bf88aa8..ccf64ef3ea 100644
--- a/modules/convert/pull.go
+++ b/modules/convert/pull.go
@@ -22,7 +22,6 @@ func ToAPIPullRequest(pr *models.PullRequest) *api.PullRequest {
 		baseBranch *git.Branch
 		headBranch *git.Branch
 		baseCommit *git.Commit
-		headCommit *git.Commit
 		err        error
 	)
 
@@ -32,20 +31,14 @@ func ToAPIPullRequest(pr *models.PullRequest) *api.PullRequest {
 	}
 
 	apiIssue := ToAPIIssue(pr.Issue)
-	if pr.BaseRepo == nil {
-		pr.BaseRepo, err = models.GetRepositoryByID(pr.BaseRepoID)
-		if err != nil {
-			log.Error("GetRepositoryById[%d]: %v", pr.ID, err)
-			return nil
-		}
+	if err := pr.LoadBaseRepo(); err != nil {
+		log.Error("GetRepositoryById[%d]: %v", pr.ID, err)
+		return nil
 	}
-	if pr.HeadRepoID != 0 && pr.HeadRepo == nil {
-		pr.HeadRepo, err = models.GetRepositoryByID(pr.HeadRepoID)
-		if err != nil && !models.IsErrRepoNotExist(err) {
-			log.Error("GetRepositoryById[%d]: %v", pr.ID, err)
-			return nil
 
-		}
+	if err := pr.LoadHeadRepo(); err != nil {
+		log.Error("GetRepositoryById[%d]: %v", pr.ID, err)
+		return nil
 	}
 
 	apiPullRequest := &api.PullRequest{
@@ -69,70 +62,74 @@ func ToAPIPullRequest(pr *models.PullRequest) *api.PullRequest {
 		Deadline:  apiIssue.Deadline,
 		Created:   pr.Issue.CreatedUnix.AsTimePtr(),
 		Updated:   pr.Issue.UpdatedUnix.AsTimePtr(),
-	}
-	baseBranch, err = repo_module.GetBranch(pr.BaseRepo, pr.BaseBranch)
-	if err != nil {
-		if git.IsErrBranchNotExist(err) {
-			apiPullRequest.Base = nil
-		} else {
-			log.Error("GetBranch[%s]: %v", pr.BaseBranch, err)
-			return nil
-		}
-	} else {
-		apiBaseBranchInfo := &api.PRBranchInfo{
+
+		Base: &api.PRBranchInfo{
 			Name:       pr.BaseBranch,
 			Ref:        pr.BaseBranch,
 			RepoID:     pr.BaseRepoID,
 			Repository: pr.BaseRepo.APIFormat(models.AccessModeNone),
-		}
+		},
+		Head: &api.PRBranchInfo{
+			Name:   pr.HeadBranch,
+			Ref:    fmt.Sprintf("refs/pull/%d/head", pr.Index),
+			RepoID: -1,
+		},
+	}
+
+	baseBranch, err = repo_module.GetBranch(pr.BaseRepo, pr.BaseBranch)
+	if err != nil && !git.IsErrBranchNotExist(err) {
+		log.Error("GetBranch[%s]: %v", pr.BaseBranch, err)
+		return nil
+	}
+
+	if err == nil {
 		baseCommit, err = baseBranch.GetCommit()
-		if err != nil {
-			if git.IsErrNotExist(err) {
-				apiBaseBranchInfo.Sha = ""
-			} else {
-				log.Error("GetCommit[%s]: %v", baseBranch.Name, err)
-				return nil
-			}
-		} else {
-			apiBaseBranchInfo.Sha = baseCommit.ID.String()
+		if err != nil && !git.IsErrNotExist(err) {
+			log.Error("GetCommit[%s]: %v", baseBranch.Name, err)
+			return nil
+		}
+
+		if err == nil {
+			apiPullRequest.Base.Sha = baseCommit.ID.String()
 		}
-		apiPullRequest.Base = apiBaseBranchInfo
 	}
 
 	if pr.HeadRepo != nil {
-		headBranch, err = repo_module.GetBranch(pr.HeadRepo, pr.HeadBranch)
+		apiPullRequest.Head.RepoID = pr.HeadRepo.ID
+		apiPullRequest.Head.Repository = pr.HeadRepo.APIFormat(models.AccessModeNone)
+
+		headGitRepo, err := git.OpenRepository(pr.HeadRepo.RepoPath())
 		if err != nil {
-			if git.IsErrBranchNotExist(err) {
-				apiPullRequest.Head = nil
-			} else {
-				log.Error("GetBranch[%s]: %v", pr.HeadBranch, err)
+			log.Error("OpenRepository[%s]: %v", pr.HeadRepo.RepoPath(), err)
+			return nil
+		}
+		defer headGitRepo.Close()
+
+		headBranch, err = headGitRepo.GetBranch(pr.HeadBranch)
+		if err != nil && !git.IsErrBranchNotExist(err) {
+			log.Error("GetBranch[%s]: %v", pr.HeadBranch, err)
+			return nil
+		}
+
+		if git.IsErrBranchNotExist(err) {
+			headCommitID, err := headGitRepo.GetRefCommitID(apiPullRequest.Head.Ref)
+			if err != nil && !git.IsErrNotExist(err) {
+				log.Error("GetCommit[%s]: %v", headBranch.Name, err)
 				return nil
 			}
+			if err == nil {
+				apiPullRequest.Head.Sha = headCommitID
+			}
 		} else {
-			apiHeadBranchInfo := &api.PRBranchInfo{
-				Name:       pr.HeadBranch,
-				Ref:        pr.HeadBranch,
-				RepoID:     pr.HeadRepoID,
-				Repository: pr.HeadRepo.APIFormat(models.AccessModeNone),
+			commit, err := headBranch.GetCommit()
+			if err != nil && !git.IsErrNotExist(err) {
+				log.Error("GetCommit[%s]: %v", headBranch.Name, err)
+				return nil
 			}
-			headCommit, err = headBranch.GetCommit()
-			if err != nil {
-				if git.IsErrNotExist(err) {
-					apiHeadBranchInfo.Sha = ""
-				} else {
-					log.Error("GetCommit[%s]: %v", headBranch.Name, err)
-					return nil
-				}
-			} else {
-				apiHeadBranchInfo.Sha = headCommit.ID.String()
+			if err == nil {
+				apiPullRequest.Head.Ref = pr.HeadBranch
+				apiPullRequest.Head.Sha = commit.ID.String()
 			}
-			apiPullRequest.Head = apiHeadBranchInfo
-		}
-	} else {
-		apiPullRequest.Head = &api.PRBranchInfo{
-			Name:   pr.HeadBranch,
-			Ref:    fmt.Sprintf("refs/pull/%d/head", pr.Index),
-			RepoID: -1,
 		}
 	}
 
diff --git a/modules/convert/pull_test.go b/modules/convert/pull_test.go
index fe82a61bd4..b78bbe87c9 100644
--- a/modules/convert/pull_test.go
+++ b/modules/convert/pull_test.go
@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/structs"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -15,12 +16,19 @@ import (
 func TestPullRequest_APIFormat(t *testing.T) {
 	//with HeadRepo
 	assert.NoError(t, models.PrepareTestDatabase())
+	headRepo := models.AssertExistsAndLoadBean(t, &models.Repository{ID: 1}).(*models.Repository)
 	pr := models.AssertExistsAndLoadBean(t, &models.PullRequest{ID: 1}).(*models.PullRequest)
 	assert.NoError(t, pr.LoadAttributes())
 	assert.NoError(t, pr.LoadIssue())
 	apiPullRequest := ToAPIPullRequest(pr)
 	assert.NotNil(t, apiPullRequest)
-	assert.Nil(t, apiPullRequest.Head)
+	assert.EqualValues(t, &structs.PRBranchInfo{
+		Name:       "branch1",
+		Ref:        "refs/pull/2/head",
+		Sha:        "4a357436d925b5c974181ff12a994538ddc5a269",
+		RepoID:     1,
+		Repository: headRepo.APIFormat(models.AccessModeNone),
+	}, apiPullRequest.Head)
 
 	//withOut HeadRepo
 	pr = models.AssertExistsAndLoadBean(t, &models.PullRequest{ID: 1}).(*models.PullRequest)