perl.c - move PL_restartop assert out of perl_run()

In dd66b1d793 we added an assert to perl_run() that PL_restartop should
never be true when perl_run() is called after perl_parse(). Looked at
from the point of the internals, which calls perl_parse() and perl_run()
exactly once, this made sense.

It turns out however that there is at least one XS module out there that
expects to be able to set PL_restartop and then call perl_run(). If that
works out for them then we shouldn't block it, as we aren't really
trying to say "perl_run() should never be called with PL_restartop set"
(at least this assert wasn't trying to say that really), we are trying
to assert "between the top level transition from perl_parse() to
perl_run() we shouldnt leak any PL_restartop".

One could argue the assert maybe should go at the end of perl_parse(),
but I chose to put it in Miniperl.pm and thus into perlmain.c and
miniperlmain.c as I am not certain that perl_parse() should never be
called with PL_restartop set already, and putting it in the main code
really does more closely reflect the intent of this assert anyway.

This was reported as Blead Breaks CPAN Github Issue #20557.

1 files changed, 23 insertions, 2 deletions

diff --git a/ext/ExtUtils-Miniperl/lib/ExtUtils/Miniperl.pm b/ext/ExtUtils-Miniperl/lib/ExtUtils/Miniperl.pm
index 38a37244e2..18627f8a5e 100644
--- a/ext/ExtUtils-Miniperl/lib/ExtUtils/Miniperl.pm
+++ b/ext/ExtUtils-Miniperl/lib/ExtUtils/Miniperl.pm
@@ -5,7 +5,7 @@ use Exporter 'import';
 use ExtUtils::Embed 1.31, qw(xsi_header xsi_protos xsi_body);
 
 our @EXPORT = qw(writemain);
-our $VERSION = '1.12';
+our $VERSION = '1.13';
 
 # blead will run this with miniperl, hence we can't use autodie or File::Temp
 my $temp;
@@ -135,8 +135,29 @@ main(int argc, char **argv, char **env)
 	PL_perl_destruct_level = 0;
     }
     PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
-    if (!perl_parse(my_perl, xs_init, argc, argv, (char **)NULL))
+    if (!perl_parse(my_perl, xs_init, argc, argv, (char **)NULL)) {
+
+        /* perl_parse() may end up starting its own run loops, which
+         * might end up "leaking" PL_restartop from the parse phase into
+         * the run phase which then ends up confusing run_body(). This
+         * leakage shouldn't happen and if it does its a bug.
+         *
+         * Note we do not do this assert in perl_run() or perl_parse()
+         * as there are modules out there which explicitly set
+         * PL_restartop before calling perl_run() directly from XS code
+         * (Coro), and it is conceivable PL_restartop could be set prior
+         * to calling perl_parse() by XS code as well.
+         *
+         * What we want to check is that the top level perl_parse(),
+         * perl_run() pairing does not allow a leaking PL_restartop, as
+         * that indicates a bug in perl. By putting the assert here we
+         * can validate that Perl itself is operating correctly without
+         * risking breakage to XS code under DEBUGGING. - Yves
+         */
+        assert(!PL_restartop);
+
         perl_run(my_perl);
+    }
 
 #ifndef PERL_MICRO
     /* Unregister our signal handler before destroying my_perl */