Compare branches, commits and tags with each other

[saitho]

Resolves #4567

Currently the comparing branches and commits is two separate routes and the logic is spread on multiple files. This pull request puts that logic in one place and allows comparing commits, branches and tags among each other (e.g. compare a branch with a commit, compare a tag with a branch, etc).

When comparing two branches there will be a button "Create pull request" (similarly to GitHub) which will show the pull request form.

Screenshots

Comparing branches (=> Pull Request)

Comparing commit and tag

Comparing tag and branch

[codecov-io]

Codecov Report

Merging #6991 into master will increase coverage by 0.05%.
The diff coverage is 57.84%.

@@            Coverage Diff             @@
##           master    #6991      +/-   ##
==========================================
+ Coverage   41.58%   41.64%   +0.05%     
==========================================
  Files         446      447       +1     
  Lines       60873    60888      +15     
==========================================
+ Hits        25317    25358      +41     
+ Misses      32271    32243      -28     
- Partials     3285     3287       +2

Impacted Files	Coverage Δ
routers/repo/commit.go	29.43% <0%> (+5.2%)	⬆️
models/pull.go	49.76% <0%> (+0.04%)	⬆️
routers/routes/routes.go	82.85% <100%> (-0.07%)	⬇️
routers/repo/pull.go	31.05% <50%> (-5.31%)	⬇️
routers/repo/compare.go	53.67% <53.67%> (ø)
routers/api/v1/repo/pull.go	37.89% <85.71%> (ø)	⬆️
modules/git/repo_commit.go	48.1% <85.71%> (+1.02%)	⬆️
modules/git/repo_compare.go	66.66% <88.46%> (ø)
models/unit.go	62.16% <0%> (-5.41%)	⬇️
routers/repo/view.go	42.02% <0%> (-1.02%)	⬇️
... and 3 more

---

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[zeripath]

I'm not a fan of polluting the main repository and sticking objects within its object database. (Although this is not your fault.)

I think we should be either, creating a new temporary repository with references to the head branches and then pulling the changes there, or setting:

gitea/modules/private/hook.go

Lines 18 to 19 in cf857fa

	GitAlternativeObjectDirectories = "GIT_ALTERNATE_OBJECT_DIRECTORIES"
	GitObjectDirectory = "GIT_OBJECT_DIRECTORY"

appropriately as per:

gitea/routers/private/hook.go

Lines 64 to 68 in cf857fa

	env := append(os.Environ(),
	private.GitAlternativeObjectDirectories+"="+gitAlternativeObjectDirectories,
	private.GitObjectDirectory+"="+gitObjectDirectory,
	private.GitQuarantinePath+"="+gitObjectDirectory,
	)

And fetch into a non-reffed branch.

Now this doesn't have to be done in this PR, but we should do it.

[saitho]

I'm not a fan of polluting the main repository and sticking objects within its object database.
...
Now this doesn't have to be done in this PR, but we should do it.

We should create a new issue for that. :)

[richmahn]

Can we compare commits with their 9 character hash that we usually see in lists of commits? I can't do this: http://localhost:3000/root/test/compare/3c5db14a4...d2f998efb but can do this: http://localhost:3000/root/test/compare/3c5db140a4f6778cd4a50217fafd3a0a0d3d6481...d42f998efbe325b5d4431ec1e56d227a94cb777a. On Github I can do it with the short hash that they show
(e.g. richmahn/test@ff58894...a877a10)

While we show 9 characters of the commit SHA and GitHub shows only 7, Gitea commit URL allows for 7, so would be great if compare also took 7 or more characters to find the commit SHA to compare.

[saitho]

Can we compare commits with their 9 character hash that we usually see in lists of commits?

No, we can't. Gitea uses go-git to interact with Git repositories. As I explained in #4567, go-git does not support short hashes at the moment.

[richmahn]

@saitho Ah, thanks for that explanation. Didn't know.

[richmahn]

@saitho Moving our conversation from the issue to here. I know from https://github.com/go-gitea/gitea/blob/master/routers/repo/commit.go#L200 that this is what figures out the commit ID for a short hash or a branch name if the string isn't 40 characters long. Uses rev-parse of the git command, such as git rev-parse 9406344 => 940634488e90fc72315bba52795806a942f0622d. Would think and hope that can be used?

[saitho]

Now this doesn't have to be done in this PR, but we should do it.

We should do that here, because the temporary branch I created when head repository is a fork shows up in the branch list. Even if we deleted it afterwards a user might still be able to check it out. ^^

EDIT: At least I was left with a temporary branch still being visible in Gitea...

[saitho]

We should do that here, because the temporary branch I created when head repository is a fork shows up in the branch list.

Might have been a leftover from development. Removed it once and it didn't come back when I tested the compare functionality.
The temporary branch even belongs to the remote repository which is removed after comparing. So that should be okay for now.