Preserve semicolon after macro call inside foreign mod

[dtolnay]

Fixes #5281.

Before:

$ echo 'extern { x!(-); x!(x); }' | cargo run --bin rustfmt
extern "C" {
    x!(-)
    x!(x);
}

After:

$ echo 'extern { x!(-); x!(x); }' | cargo run --bin rustfmt
extern "C" {
    x!(-);
    x!(x);
}

[ytmimi]

Thanks for the PR! Changes look good to me. Just so I'm understanding this correctly, since we fail to parse the macro args (because we can't parse - or #) we end up calling return_macro_parse_failure_fallback, which was dropping the trailing ;. The fix seems pretty reasonable to me.

[calebcartwright]

Just so I'm understanding this correctly, since we fail to parse the macro args (because we can't parse - or #) we end up calling return_macro_parse_failure_fallback, which was dropping the trailing ;

Essentially yes, though I'd probably make one distinction in that the trailing semi isn't part of the maccall.

We still can't/don't do much with calls whose args can't be directly parsed as some valid Rust construct and the fallback behavior is to just leave the call itself however the author wrote it and that's working "correctly". However, there was a change upstream in rustc not too terribly long ago that removed the trailing semi from the various spans including that of the maccall.

We added a couple workarounds that account for that and recover the trailing semi, along with handling more absurd scenarios (like comments between the closing delim and semi), but those workarounds apparently aren't utilized on the call path for a maccall in a foreign item context.

[calebcartwright]

Thank you for the report and fix.

TBH I'm not too terribly keen on having yet another one of these semicolon workarounds, however, content to move forward with this anyway given the impact of the issue.

Mostly comments for our future selves, but at some point down the road I think we should probably reuse behavior leveraged in other contexts to look between the end of the mac call's span and the semi at the end of the containing foreign item's span