Add support for main as the default branch

[rastersize]

GitHub and others are moving to use main as the default branch name. In fact newly created repositories use it by default now. The most recent version/commit of Mint fails to clone tools that don’t have any tags and uses main:

$ mint run rastersize/apollo-codegen
🌱 Finding latest version of apollo-codegen
🌱 Cloning apollo-codegen master
Cloning into 'github.com_rastersize_apollo-codegen'...
warning: Could not find remote branch master to clone.
fatal: Remote branch master not found in upstream origin
🌱 Encountered error during "git clone --depth 1 -b master https://github.com/rastersize/apollo-codegen.git github.com_rastersize_apollo-codegen". Use --verbose to see full output
🌱  Couldn't clone https://github.com/rastersize/apollo-codegen.git master

This PR aims to resolve that by adding support for both main and master. It should in theory support any name for the default branch as it uses git to look up the name of the branch.

With this patch the invocation above succeeds:

$ .build/debug/mint run rastersize/apollo-codegen apollo-codegen --help
🌱 Finding latest version of apollo-codegen
🌱 Cloning apollo-codegen main
🌱 Resolving package
🌱 Building package
🌱 Installed apollo-codegen main
🌱 Running apollo-codegen main...
OVERVIEW: A utility for performing Apollo GraphQL related tasks.

[...]

[rastersize]

Heya @yonaskolb! Just wanted to check if you had time to look at this, or had any comments/questions about it. Thank you 🙂

[yonaskolb]

Thanks @rastersize, great change. Note sure it always works though.
Could you also please add a changelog entry

[yonaskolb]

Suggested change

	An optional version can be specified by appending @version to the repo, otherwise the newest tag will be used (or main, then master if no tags are found.)
	An optional version can be specified by appending @version to the repo, otherwise the newest tag will be used, or the default branch if untagged

[yonaskolb]

Could you also update the same message in the Readme, under Package reference

[yonaskolb]

Are you sure this always works? I tried locally in some repos. Some I got an access error if though they have public remotes:

[email protected]: Permission denied (publickey).
fatal: Could not read from remote repository.

And some I just got a list of the branches in the repo, and not just the default branch. I'm on Git 2.24.3 and zsh 5.8

[Cyberbeni]

I use this in my zsh function, it's a bit different: defaultBranch=$(git ls-remote --symref "$remoteUrl" HEAD | grep "^ref: " | sed 's@^ref: refs/heads/\([^[:space:]]*\).*@\1@')

[Cyberbeni]

Assuming pipefail is on, my version will result in an error in the rare case where the default branch is not set, while the original code will probably not result in an error. (I'm not on my dev machine, so I can't check but I'm 99% sure about this)

related git docs: https://git-scm.com/docs/git-remote#Documentation/git-remote.txt-emset-headem

[gwynne]

If it's assume both 1) that the repo was cloned, not created locally, and 2) that the first (or only) remote is the one that matters), this should be as good as it seems to be possible to get within the bounds of what's practical (I know the string extraction is a bit tortured; while either sed or the new regex support in Swift 5.7 could do this less painfully, sed is not always dependable between platforms, and 5.7 is a bit of a jump from this project's current minimum supported version of 5.0):

let symref = try Task.capture(bash: "git ls-remote --symref . 'refs/remotes/*/HEAD'")
if symref.starts(with: "ref:") { return symref
    .prefix { !$0.isNewline }    // "ref: refs/remotes/origin/main    refs/remotes/origin/HEAD"
    .dropFirst(17)               // "origin/main    refs/remotes/origin/HEAD"
    .drop { $0 != "/" }          // "/main    refs/remotes/origin/HEAD"
    .dropFirst()                 // "main    refs/remotes/origin/HEAD"
    .prefix { !$0.isWhitespace } // "main"
} else {
    // no remote configured?
    return "HEAD" // fall back to current checked out revision
}