Deparse.pm: handle BEGIN { require expr }

Deparse examines BEGIN subs to see if they look like

    BEGIN { require Foo; ... }

and if so deparses them as 'use Foo' instead.

However, it can't cope when Foo is an expression rather than a constant,
such as

    BEGIN {
        require($ENV{PERL_CORE} ? '../../t/test.pl' : './t/test.pl');
    }

and crashes.

This commit makes it instead recognise such op trees as not being part of
a 'use'.

Under TEST -deparse, this fixes the following unexpectedly failing
script:

    dist/threads/t/kill3.t

and fixes the following expected-to-fail scripts:

    dist/IO/t/io_file_export.t
    dist/IO/t/io_multihomed.t
    dist/IO/t/io_udp.t
    dist/threads/t/err.t
    dist/threads/t/kill2.t
    dist/threads/t/libc.t

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/B/Deparse.pm b/lib/B/Deparse.pm
index 8e94ee6515..dd61739260 100644
--- a/lib/B/Deparse.pm
+++ b/lib/B/Deparse.pm
@@ -628,6 +628,9 @@ sub begin_is_use {
     my $req_op = $lineseq->first->sibling;
     return if $req_op->name ne "require";
 
+    # maybe it's C<require expr> rather than C<require 'foo'>
+    return if ($req_op->first->name ne 'const');
+
     my $module;
     if ($req_op->first->private & OPpCONST_BARE) {
 	# Actually it should always be a bareword