Bad syntax in macro_rules! macro definition causes an ICE in beta and nightly, but not stable

[niconii]

This code:

macro_rules! foo {
    $($t:tt)* => (1);
}

fn main() {
    foo!();
}

gives the following error on 1.5 stable (which is correct, though where it points is perhaps a little odd):

<anon>:6:5: 6:12 error: malformed macro lhs
<anon>:6     foo!();
             ^~~~~~~

but this error on 1.6 beta and the current nightly:

<anon>:6:5: 6:12 error: internal compiler error: malformed macro lhs
<anon>:6     foo!();
             ^~~~~~~
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', ../src/libsyntax/diagnostic.rs:175

[jonas-schievink]

The culprit seems to be cce7b8b, which changes the check from span_fatal to span_bug

cc @sanxiyn

[GuillaumeGomez]

I'll take a look if no one is on it.

[Sean1708]

Possibly related, this code causes an ICE on nightly, but not on beta or stable.

[jonas-schievink]

@Sean1708 Looks like a different bug to me

[Sean1708]

@jonas-schievink Thanks, I'll open a new issue then.

[brson]

@Sean1708 When you do can you link it from here? It needs to be tagged as a regression.

[jonas-schievink]

@brson It was #30715, which was already fixed in #30723

[GuillaumeGomez]

@jonas-schievink: I just fixed the regression and added a test, not the supposed improvement.

[brson]

Thanks @GuillaumeGomez!

[brson]

Oh, wait, this hasn't been backported yet. I'll leave it open a bit.

[nikomatsakis]

What precisely should be backported here? I cant' figure out through all the comments :)

[nikomatsakis]

Seems like #30708 has been backported?

[nikomatsakis]

(In #30853.)

So I think we can close?

[GuillaumeGomez]

@nikomatsakis: I think as well. The purpose here was to fix the regression, which is done. Unless @brson has another reason?