bisect-alike src-code change fuzzer

gcc-try.pl

#!/usr/bin/perl

=pod

Change every single occurence of PARROT_CANNOT_RETURN_NULL in all .c files (not .h, as 
those declarations are autogenerated by make headerizer) to the opposite 
PARROT_CAN_RETURN_NULL declaration.
One by one.

Should find two gcc problems in parrot, as of commit 3a3d785:

1. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64459 which is a
parrot bug. gcc just was the only compiler I tested (clang, msvc)
which did the proper optimization.

test: ./parrot runtime/parrot/library/parrotlib.pir
=> some IO error with exit code > 0

result:
src/schedule.c:244 Parrot_cx_check_scheduler(), which had a wrong 
if (Parrot_cx_check_scheduler(...) == 0) check in core.ops, and consequently
this 0 branch was removed by gcc.

2. wrong IO output in the extend API.
test: prove t/src/extend.t errors

This will find the single wrong function returns_null attribute, if
it's the only one.  99.9% fails, only one pass.

If there are more wrong functions, the opposite approach needs to
done. Disable all returns_null and enable it one-by-one until it
fails.

=cut

use strict;
my @lines=`git grep -n ^PARROT_CANNOT_RETURN_NULL src compilers | grep .[cy]:`;
# @lines = @lines[470..$#lines];

system "perl Configure.pl --silent 2>/dev/null >/dev/null" and warn "failed to execute: Configure.pl $?\n";
sleep 1.0;

for (@lines) {
  chomp;
  my ($file, $line) = m/^(.+):(\d+):PARROT_CANNOT_RETURN_NULL/;
  print "\n$file:$line ";
  system "git checkout $file";
  do_patch($file, $line);
  do_test();
  print $? ? "fail $?\n" : "pass\n";
  system "git checkout $file";
  unlink "parrot";
}

sub do_test {
  system "make -s headerizer >/dev/null 2>/dev/null";
  system "make -s -j4 parrot >/dev/null 2>/dev/null" and warn "error make parrot: $?\n";
  sleep 0.1;
  system "./parrot -o runtime/parrot/include/parrotlib.pbc runtime/parrot/library/parrotlib.pir";
  #system "prove -Q t/src/extend.t 2>/dev/null";
}

sub do_patch {
  my ($file, $line) = @_;
  open my $in, "<", $file or die $!;
  open my $out, ">", $file.".tmp" or die $!;
  while (<$in>) {
    if ($line == $.) {
      s{PARROT_CANNOT_RETURN_NULL}{PARROT_CAN_RETURN_NULL};
    }
    print $out $_;
  }
  close $in;
  close $out;
  sleep 0.03;
  system "mv $file.tmp $file";
}