Function is_short_pattern 

pub(crate) fn is_short_pattern(
    context: &RewriteContext<'_>,
    pat: &Pat,
    pat_str: &str,
) -> bool

Returns true if the given pattern is “short”. A short pattern is defined by the following grammar:

[small, ntp]: - single token - &[single-line, ntp]

[small]: - [small, ntp] - unary tuple constructor ([small, ntp]) - &[small]