Function analyze_sub_for_inlining 

pub fn analyze_sub_for_inlining(
    source: &str,
    sub_name: &str,
) -> Result<InlineAbility, InlineError>

Analyse whether a named subroutine can be inlined.

Returns Ok(InlineAbility::Ok { … }) when safe to inline, or an InlineError when the subroutine must not be inlined.