RT #119125: continue /[#$x]/x not interpolating

the earlier fix for /[#](?{})/x, although correct, as a
side-effect fixed another long-standing bug where /[#$x]/x
didn't interpolate the var $x. Although fixing that is good,
it's too big a change for maint, so keep the old buggy behaviour
for now.

t/re/pat.t

@@ -20,7 +20,7 @@ BEGIN {
     require './test.pl';
 }
 
-plan tests => 470;  # Update this when adding/deleting tests.
+plan tests => 472;  # Update this when adding/deleting tests.
 
 run_tests() unless caller;
 
@@ -1363,6 +1363,23 @@ EOP
         like($c, $re, "mixed up-/downgraded pattern matches upgraded string");
     }
 
+    {
+	# RT #119125
+	# the earlier fix for /[#](?{})/x, although correct, as a
+	# side-effect fixed another long-standing bug where /[#$x]/x
+	# didn't interpolate the var $x. Although fixing that is good,
+	# it's too big a change for maint, so keep the old buggy behaviour
+	# for now.
+
+	my $b = 'cd';
+	my $s = 'abcd$%#&';
+	$s =~ s/[a#$b%]/X/g;
+	is ($s, 'XbXX$XX&', 'RT #119125 without /x');
+	$s = 'abcd$%#&';
+	$s =~ s/[a#$b%]/X/gx;
+	is ($s, 'XXcdXXX&', 'RT #119125 with /x');
+    }
+
 } # End of sub run_tests
 
 1;

toke.c

@@ -3177,10 +3177,23 @@ S_scan_const(pTHX_ char *start)
 	}
 
 	/* likewise skip #-initiated comments in //x patterns */
-	else if (*s == '#' && PL_lex_inpat && !in_charclass &&
+	else if (*s == '#' && PL_lex_inpat &&
 	  ((PMOP*)PL_lex_inpat)->op_pmflags & RXf_PMf_EXTENDED) {
-	    while (s+1 < send && *s != '\n')
+	    while (s+1 < send && *s != '\n') {
+                /* for maint-5.18, half-fix #-in-charclass bug:
+                 *   *do* recognise codeblocks: /[#](?{})/
+                 *   *don't* recognise interpolated vars: /[#$x]/
+                 */
+                if (in_charclass && !PL_lex_casemods && s+3 < send &&
+		     s[0] == '(' &&
+		     s[1] == '?' &&
+		     (    s[2] == '{'
+		      || (s[2] == '?' && s[3] == '{')))
+                    break;
 		*d++ = NATIVE_TO_NEED(has_utf8,*s++);
+            }
+            if (s+ 1 < send && *s != '\n')
+                break; /* we stopped on (?{}), not EOL */
 	}
 
 	/* no further processing of single-quoted regex */