for<> is erased from macro calls

[WaffleLapkin]

Given this input:

a!(for<> A);
a!(for<A> A);
a!(for<A: A> A);
a!(for<A: ?A> A);

rustfmt produces the following output:

a!(A);
a!(A);
a!(A);
a!(A);

Which is incorrect since macros can depend on the for<...>. (playground)

[ytmimi]

Thanks for the report!

Seems like this could be related to #4631 as both deal with dropping tokens in macro calls.

EDIT: upon further investigation these issues don't seem to be related. #4631 deals more with adding tokens to macro calls. specifically adding commas ,.

[ytmimi]

I wonder if the advice from #4631 (comment) would help? I know that rustfmt doesn't typically format macros that use {}.

[ytmimi]

Doing some testing and it seems like #5301 will fix some of the examples you outlined, but the first case a!(for<> A); is still an issue even after testing this snippet on that branch.

[ytmimi]

I believe all but the first issue were resolved by #5848. @compiler-errors do you have any interest in digging into the empty for<> case?