Function rustc_expand::mbe::transcribe::lockstep_iter_size

fn lockstep_iter_size(
    tree: &TokenTree,
    interpolations: &FxHashMap<MacroRulesNormalizedIdent, NamedMatch>,
    repeats: &[(usize, usize)]
) -> LockstepIterSize

Given a tree, make sure that all sequences have the same length as the matches for the appropriate meta-vars in interpolations.

Note that if repeats does not match the exact correct depth of a meta-var, lookup_cur_matched will return None, which is why this still works even in the presence of multiple nested matcher sequences.

Example: $($($x $y)+*);+ – we need to make sure that x and y repeat the same amount as each other at the given depth when the macro was invoked. If they don’t it might mean they were declared at depths which weren’t equal or there was a compiler bug. For example, if we have 3 repetitions of the outer sequence and 4 repetitions of the inner sequence for x, we should have the same for y; otherwise, we can’t transcribe them both at the given depth.