Function lookup_alias 

pub fn lookup_alias(
    context: &GitContext,
    global: &[OsString],
    name: &OsString,
) -> Option<Vec<u8>>

What: An alias value in either of Git’s spellings, alias.<name> first. Why: lookupAlias.

In TS you’d write (pseudocode):

async function lookupAlias({ gitPath, globalArgs, name }): Promise<string | typeof ALIAS_UNSET>;