Support gitrevset in args that accept commits

[bcongdon]

It looks like git-branchless already has a dependency on https://github.com/quark-zju/gitrevset

Allowing revset expressions to be used as values to args/flags that accept commits would be nice.

e.g. being able to do git hide descendants(abcd1234) would be handy

[arxanas]

That's the plan!

In my assessment, we would be able to reuse the parser, but probably not the evaluator (see quark-zju/gitrevset#1, quark-zju/gitrevset#2). Originally, I was trying to integrate directly with gitrevset, but their models for updating the DAG are rather different. For example, we have an event log which tells us which commits are obsolete, while the gitrevset library attempts to infer somehow else (from the reflog?).

The place to add a call to evaluate a revset would be in Dag::resolve_commits:

git-branchless/src/git/dag.rs

Lines 531 to 560 in 279e754

	/// Parse strings which refer to commits, such as:
	///
	/// - Full OIDs.
	/// - Short OIDs.
	/// - Reference names.
	#[instrument]
	pub fn resolve_commits<'repo>(
	effects: &Effects,
	repo: &'repo Repo,
	dag: &mut Dag,
	hashes: Vec<String>,
	) -> eyre::Result<ResolveCommitsResult<'repo>> {
	let mut commits = Vec::new();
	for hash in hashes {
	let commit = match repo.revparse_single_commit(&hash)? {
	Some(commit) => commit,
	None => return Ok(ResolveCommitsResult::CommitNotFound { commit: hash }),
	};
	commits.push(commit)
	}
	let commit_oids = commits.iter().map(|commit| commit.get_oid()).collect_vec();
	dag.sync_from_oids(
	effects,
	repo,
	CommitSet::empty(),
	CommitSet::from_iter(commit_oids.into_iter().map(CommitVertex::from).map(Ok)),
	)?;
	Ok(ResolveCommitsResult::Ok { commits })
	}

It'll require some refactoring since current it operates on a list of OIDs instead of individual OIDs (for historical reasons), and it returns a Vec<Commit>. Instead, it should accept a revset expression and return a CommitSet. If you plan to add revset support yourself, then open an issue and assign it to yourself, so that I don't duplicate your work at some point in the future.