Add latest commit's SHA to content response

[Gusted]

• When requesting the contents of a filepath, add the latest commit's SHA to the requested file.
• Resolves API: please make commit hash/timestamp available with ​/repos​/{owner}​/{repo}​/contents​/{filepath} #12840

[zeripath]

I wonder if we should be hooking into the lastcommit cache here, but I guess the issue is we don't really want the cache to explode however, I'm going to assume that most of the time the user here is going to keep requesting the same object over and over to see if the last commit has changed which is eminently useful for caching.

The real problem with this underlying feature request is that it totally ignores the actual cost of finding out this information. It's very much not free on large repositories and can require significant calculation.

[zeripath]

Thinking on - we absolutely should be hooking in to the last commit cache here.

We may also need to consider if this information needs to be only for the default branch or for those who are logged in.

[zeripath]

I think we need #20444 before this is merged.

[Gusted]

Since #20444 is merged(which will handle the integration with lastcommitcache for us). @zeripath Do you have a strong opinion on the matter when we should return this information? I'm fine either way, as we don't really have use-case to go on, other than #12840 which only uses default branch.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (main@8b0e07e). Click here to learn what that means.
The diff coverage is 53.33%.

@@           Coverage Diff           @@
##             main   #20398   +/-   ##
=======================================
  Coverage        ?   46.98%           
=======================================
  Files           ?      978           
  Lines           ?   135426           
  Branches        ?        0           
=======================================
  Hits            ?    63628           
  Misses          ?    64000           
  Partials        ?     7798           

Impacted Files	Coverage Δ
modules/structs/repo_file.go	100.00% <ø> (ø)
routers/api/v1/utils/git.go	56.41% <33.33%> (ø)
modules/git/repo_commit.go	51.60% <53.84%> (ø)
services/repository/files/content.go	61.69% <57.14%> (ø)

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[zeripath]

I'm pretty certain that gitRepos you're using here won't have had a LastCommitCache set because that is only set once we know a reference commit to provide the reasoning for caching. (Yes I know that means that the LCC should be on the git.Commit not the git.Repo - that would mean that git.Repo should have a commit cache part - as they kinda do in the gogit variant - and then the LCC just wraps the calls to the system cache before asking the repo to get commits - which it can choose to get from its cache.)

You need to assign the lastcommitcache as per utils.ResolveRefOrSha

	if ctx.Repo.GitRepo != nil && ctx.Repo.GitRepo.LastCommitCache == nil {
		commitsCount, err := cache.GetInt64(ctx.Repo.Repository.GetCommitsCountCacheKey(ref, true), func() (int64, error) {
			commit, err := ctx.Repo.GitRepo.GetCommit(sha)
			if err != nil {
				return 0, err
			}
			return commit.CommitsCount()
		})
		if err != nil {
			log.Error("Unable to get commits count for %s in %s. Error: %v", sha, ctx.Repo.Repository.FullName(), err)
			return sha
		}
		ctx.Repo.GitRepo.LastCommitCache = git.NewLastCommitCache(commitsCount, ctx.Repo.Repository.FullName(), ctx.Repo.GitRepo, cache.GetCache())
	}

[zeripath]

Build failures were due to the fact that this function needs to be shared across both gogit and nogogit variants.

I've fixed that.

[wxiaoguang]

LGTM

(curious about why the NewLastCommitCache(count ...) must have the count argument. It seems that NewLastCommitCache may be possible to handle the count internally?)

[lunny]

make L-G-T-M work