Function push 

pub fn push(branch_name: &str, repo: Option<&Repository>) -> Result<()>

Pushes a branch to the default remote.

Uses the default remote (determined by the first valid refs/remotes/{remote}/HEAD reference) to push the specified branch.

Errors

• Repository discovery fails.
• No default remote can be determined.
• The default remote cannot be found.
• Pushing the branch fails.