(perl #124368) make /foo/o; /$null/ act consistently

Previously the /o would be inherited by the second match if the first
match was successful, but only on non-threaded builds.

The op-tree rewriting done on non-threaded builds could also confuse
the interpreter, possibly resulting in the match op receiving
the argument intended for the regcomp op.

2 files changed, 18 insertions, 9 deletions

diff --git a/pp_ctl.c b/pp_ctl.c
index f91bb4dd38..b16e12de60 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -163,15 +163,9 @@ PP(pp_regcomp)
     /* handle the empty pattern */
     if (!RX_PRELEN(PM_GETRE(pm)) && PL_curpm) {
         if (PL_curpm == PL_reg_curpm) {
-            if (PL_curpm_under) {
-                if (PL_curpm_under == PL_reg_curpm) {
-                    Perl_croak(aTHX_ "Infinite recursion via empty pattern");
-                } else {
-                    pm = PL_curpm_under;
-                }
+            if (PL_curpm_under && PL_curpm_under == PL_reg_curpm) {
+                Perl_croak(aTHX_ "Infinite recursion via empty pattern");
             }
-        } else {
-            pm = PL_curpm;
         }
     }
 
diff --git a/t/re/pat.t b/t/re/pat.t
index fb6d4c4a69..cf97ecdf07 100644
--- a/t/re/pat.t
+++ b/t/re/pat.t
@@ -23,7 +23,7 @@ BEGIN {
     skip_all('no re module') unless defined &DynaLoader::boot_DynaLoader;
     skip_all_without_unicode_tables();
 
-plan tests => 837;  # Update this when adding/deleting tests.
+plan tests => 843;  # Update this when adding/deleting tests.
 
 run_tests() unless caller;
 
@@ -138,6 +138,21 @@ sub run_tests {
         $null = "";
         $xyz =~ /$null/;
         is($&, $xyz, $message);
+
+        # each entry: regexp, match string, $&, //o match success
+        my @tests =
+          (
+           [ "", "xy", "x", 1 ],
+           [ "y", "yz", "y", !1 ],
+          );
+        for my $test (@tests) {
+            my ($re, $str, $matched, $omatch) = @$test;
+            $xyz =~ /x/o;
+            ok($str =~ /$re/, "$str matches /$re/");
+            is($&, $matched, "on $matched");
+            $xyz =~ /x/o;
+            is($str =~ /$re/o, $omatch, "$str matches /$re/o (or not)");
+        }
     }
 
     {