Fetch only the master branch when doing a hard reset

This avoids fetching the snapshot branches. The `+` prefix is added to
the refspec to ensure that the ref is updated even if it isn't a
fast-forward.

Author: jtgeibel

src/git.rs

@@ -158,7 +158,7 @@ impl Repository {
                 repo.remote_with_fetch(
                     name,
                     url,
-                    &format!("refs/heads/master:refs/remotes/{}/master", name),
+                    &format!("+refs/heads/master:refs/remotes/{}/master", name),
                 )
             })
             .clone(
@@ -261,7 +261,11 @@ impl Repository {
         let mut origin = self.repository.find_remote("origin")?;
         let original_head = self.head_oid()?;
         origin.fetch(
-            &["refs/heads/*:refs/heads/*"],
+            // Force overwrite (`+` prefix) local master branch with the server's master branch.
+            // The git CLI will refuse to fetch into the current branch of a non-bare repo
+            // but libgit2 doesn't seem to prevent this potential footgun.
+            // The entire point is to do a hard reset, so this footgun is not a concern.
+            &["+refs/heads/master:refs/heads/master"],
             Some(&mut Self::fetch_options(&self.credentials)),
             None,
         )?;