Implicit returns with multiple #cfg[...] cause compilation errors

[Susurrus]

If there are two different #cfg[...] one after each other and they utilize implicit returns (don't have a trailing ';'), then a compilation error will occur.

Example of the error: https://is.gd/fiScoc
Fixed: https://is.gd/Z87TE0

I believe this is a compiler bug because in the fixed version there's still an implicit return as part of the last #cfg[...] and there isn't an error about it.

[sinkuu]

/* #[cfg(unix)]    */ return Ok("unix".to_string());
/* #[cfg(windows)] */ Ok("windows".to_string())

is syntactically valid, while this is not:

/* #[cfg(unix)]    */ Ok("unix".to_string())
/* #[cfg(windows)] */ Ok("windows".to_string())

As stated in #29850 (comment), the current implementation doesn't implicitly fix such code.

[cyplo]

Still a problem on rustc 1.23.0-nightly (8b22e70 2017-10-31)

[Mark-Simulacrum]

This seems like expected behavior to me so I'm going to go ahead and close. Expressions can't be adjacent like this without some separator in general (and cfg is after parsing, not before/during).