fix get branch

Author: wxiaoguang

models/git/branch.go

@@ -166,12 +166,10 @@ func GetBranch(ctx context.Context, repoID int64, branchName string) (*Branch, e
 			RepoID:     repoID,
 			BranchName: branchName,
 		}
-	} else if branch.IsDeleted {
-		return nil, ErrBranchNotExist{
-			RepoID:     repoID,
-			BranchName: branchName,
-		}
 	}
+	// FIXME: this design is not right: it doesn't check `branch.IsDeleted`, it doesn't make sense to make callers to check IsDeleted again and again.
+	// It causes inconsistency with `GetBranches` and `git.GetBranch`, and will lead to strange bugs
+	// In the future, there should be 2 functions: `GetBranchExisting` and `GetBranchWithDeleted`
 	return &branch, nil
 }
 

services/repository/branch.go

@@ -684,11 +684,20 @@ func GetBranchDivergingInfo(ctx reqctx.RequestContext, baseRepo *repo_model.Repo
 	if err != nil {
 		return nil, err
 	}
-
+	if headGitBranch.IsDeleted {
+		return nil, git_model.ErrBranchNotExist{
+			BranchName: headBranch,
+		}
+	}
 	baseGitBranch, err := git_model.GetBranch(ctx, baseRepo.ID, baseBranch)
 	if err != nil {
 		return nil, err
 	}
+	if baseGitBranch.IsDeleted {
+		return nil, git_model.ErrBranchNotExist{
+			BranchName: baseBranch,
+		}
+	}
 
 	info := &BranchDivergingInfo{}
 	if headGitBranch.CommitID == baseGitBranch.CommitID {