Make gogit Repository.GetBranchNames consistent

[AdamMajer]

nogogit GetBranchNames() lists branches sorted in reverse commit date order. On the other hand the gogit implementation doesn't apply any ordering resulting in unpredictable behaviour. In my case, the unit tests requiring particular order fail

repo_branch_test.go:24:
            Error Trace:
           ./gitea/modules/git/repo_branch_test.go:24
            Error:          elements differ

                            extra elements in list A:
                            ([]interface {}) (len=1) {
                             (string) (len=6) "master"
                            }

                            extra elements in list B:
                            ([]interface {}) (len=1) {
                             (string) (len=7) "branch1"
                            }

                            listA:
                            ([]string) (len=2) {
                             (string) (len=6) "master",
                             (string) (len=7) "branch2"
                            }

                            listB:
                            ([]string) (len=2) {
                             (string) (len=7) "branch1",
                             (string) (len=7) "branch2"
                            }
            Test:           TestRepository_GetBranches

To fix this, we sort branches based on their commit date in gogit implementation.

Fixes: #28318

[lng2020]

Have you tried using the Log function in go-git? After I checked the branches function in go-git, the code logic seemed cumbersome to me because the code iterates first to filter out the type branch and then sort.
I think using the Log function with an embedded heap sort to get the hash ref iterator and using the hash ref to see if it's a branch ref during the iteration would be a more effective way. Correct me if my understanding needs to be corrected because I'm not so familiar with the go-git package.

[AdamMajer]

I had no idea about the said Log function either (I generally don't use go-git), so I found this example,

https://github.com/go-git/go-git/blob/master/_examples/log/main.go

and the implementation,

https://github.com/go-git/go-git/blob/master/repository.go#L1236

It looks like Log is for getting commit history from a given point in time, not about fetching branches. The Branches() implementation is not too cumbersome,

https://github.com/go-git/go-git/blob/master/repository.go#L1379

since it goes through all the "References" (see refs/ directory in git repository). There generally are not a lot of these. But if that's not exactly true, it should be fixed in go-git instead of here.

[lng2020]

You are right. I think Log function mimics the behavior of the git log. Usually, the number of ref is way less than the number of commits. So your approach is better.

But if that's not exactly true, it should be fixed in go-git instead of here.

You are right. It seems that the API provided by go-git is not that flexible.