Module fetcher 

Git-based package fetcher.

The Fetcher trait abstracts over different fetch backends (git, luarocks, http). GitFetcher implements the git backend using libgit2 via the git2 crate. No subprocess git invocations are used.

Cache layout

<cache_root>/git/<host>/<path…>/<sha>/

For example, https://github.com/ynishi/lshape at SHA abc123 becomes:

<cache_root>/git/github.com/ynishi/lshape/abc123/

Cache hit without a clone

Before cloning, the ref is resolved cheaply:

pin	network needed to resolve
rev = full 40-hex SHA	none
tag (exact or prefix) / branch / no pin	one ls-remote (ref listing, no objects)
rev = short SHA / revspec	falls through to a clone

If <cache_root>/git/<host>/<path…>/<sha>/ already exists for the resolved SHA, that directory is returned as is and no clone happens. Only a cache miss pays for a full clone (into a temp dir, then renamed into place).

Authentication

GitFetcher uses a RemoteCallbacks-based credential cascade:

1. SSH agent (Cred::ssh_key_from_agent) — tried only when the remote advertises SSH_KEY in allowed_types.
2. Credential helper (Cred::credential_helper) — tried when USER_PASS_PLAINTEXT is advertised.
3. Cred::default() — last resort.

The callback tracks attempted credential types to avoid infinite retry loops.

Structs

FetchedPkg

Result of a successful Fetcher::fetch call.

GitFetcher

Fetcher implementation backed by libgit2.

Traits

Fetcher

Abstraction over package fetch backends.