[perl #130637] Odd segfaults with a small grammar

[brian d foy]

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This program consistently segfaults for me:

    grammar Grammar::Foo {
        rule TOP {
            'z' | <unicode_escape>
            }
        token unicode_escape { '\\u' :i <[0..9a..f]> ** 4 }
        }

    my $res = Grammar::Foo.parse( '\u2603' );


This one blows up and writes a bunch of long hex numbers to the terminal:

    grammar Grammar::Foo {
        rule TOP {
            'z' | <unicode_escape>
            }
        token unicode_escape { 'u' :i <[0..9a..f]> ** 4 }
        }

    my $res = Grammar::Foo.parse( 'u2603' );

I stripped this down from a much larger thing I was working on, and
if I remove anything else I don't have the problem.


And, some details:

    $ perl6 -v
    This is Rakudo version 2016.11 built on MoarVM version 2016.11
    implementing Perl 6.c.
    $ uname -a
    Darwin macpro.local 14.5.0 Darwin Kernel Version 14.5.0