regexec: don't increment recursion counter for non-postponed EVAL

It wasn't intended to be part of the recursion logic, and doesn't get
decremented again (GH 17490).

(cherry picked from commit af6880c950bceae5aa17dc228f139d0b4e797594)

2 files changed, 11 insertions, 2 deletions

diff --git a/regexec.c b/regexec.c
index bc18396b5f..fc4dbffa72 100644
--- a/regexec.c
+++ b/regexec.c
@@ -7243,7 +7243,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
             /* NOTREACHED */
 
         case EVAL:  /*   /(?{...})B/   /(??{A})B/  and  /(?(?{...})X|Y)B/   */
-            if (cur_eval && cur_eval->locinput==locinput) {
+            if (logical == 2 && cur_eval && cur_eval->locinput==locinput) {
 		if ( ++nochange_depth > max_nochange_depth )
                     Perl_croak(aTHX_ "EVAL without pos change exceeded limit in regex");
             } else {
diff --git a/t/re/pat.t b/t/re/pat.t
index 4ece584840..9338dcc98e 100644
--- a/t/re/pat.t
+++ b/t/re/pat.t
@@ -25,7 +25,7 @@ BEGIN {
 skip_all('no re module') unless defined &DynaLoader::boot_DynaLoader;
 skip_all_without_unicode_tables();
 
-plan tests => 867;  # Update this when adding/deleting tests.
+plan tests => 869;  # Update this when adding/deleting tests.
 
 run_tests() unless caller;
 
@@ -2132,6 +2132,15 @@ SKIP:
                         "Assertion failure matching /il on single char folding to multi");
     }
 
+    # gh17490: test recursion check
+    {
+        my $eval = '(?{1})';
+        my $re = sprintf '(?&FOO)(?(DEFINE)(?<FOO>%sfoo))', $eval x 20;
+        my $result = eval qq{"foo" =~ /$re/};
+        is($@ // '', '', "many evals did not die");
+        ok($result, "regexp correctly matched");
+    }
+
 } # End of sub run_tests
 
 1;