Compiler crashes on malformed macro

[Binero]

A simple malformed macro makes the compiler crash.

Code:

macro_rules! code_block {
    $c:block => $c
}

Playpen error:

<anon>:1:1: 3:2 error: internal compiler error: wrong-structured lhs for follow check (didn't find a TtDelimited or TtSequence)
<anon>:1 macro_rules! code_block {
<anon>:2     $c:block => $c
<anon>:3 }
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>', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:130

Playpen: http://is.gd/COoZe7

[vi]

Another case:
macro_rules! q { ($($w:ident,$t:$ident)*) => {}} q!();

Playpen: http://is.gd/CYZPiW

[ehiggs]

I had a crash in a bad macro which hits the same bug as @vi. Note that his/her error has the following which is a different stack trace:

error: internal compiler error: unexpected panic
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 'Cannot fill in a NT', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/ext/tt/macro_parser.rs:236


playpen: application terminated with error code 101

I'm on the latest beta; not nightly.

[Nashenas88]

@ehiggs I think you and I are getting a different panic from this bug. I've opened #27092 since the panic is in a different location in the code.