Fix /a++(?{})+$code_block/

This I would expect:

$ perl5.16.0 -wMre=eval -e '$x = "(?{})"; /a++(?{})+$x/x'
(?{})+ matches null string many times in regex; marked by <-- HERE in m/a++(?{})+ <-- HERE (?{})/ at -e line 1.
Use of uninitialized value $_ in pattern match (m//) at -e line 1.

It warns, but it still runs.

This I would not,

$ perl5.17.5 -wMre=eval -e '$x = "(?{})"; /a++(?{})+$x/x'
Nested quantifiers in regex; marked by <-- HERE in m/a++     + <-- HERE (?{})/ at (eval 1) line 1.

were it not for the fact that I know how it works. :-)

To compile the blocks in $x without recompiling the blocks directly
inside /.../, the regexp compiler blanks out the ‘outer’ blocks with
spaces, and compiles qr'a++     +(?{})'x.  But /x can see through
those spaces, resulting in a change in behaviour.  So use under-
scores instead.

1 files changed, 2 insertions, 2 deletions

diff --git a/regcomp.c b/regcomp.c
index 3bd847568d..4979b6a85e 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -5005,7 +5005,7 @@ S_has_runtime_code(pTHX_ RExC_state_t * const pRExC_state, OP *expr,
  *
  * becomes
  *
- *    qr'a\\bc                       def\'ghi\\\\jkl(?{"this is runtime"})mno'
+ *    qr'a\\bc_______________________def\'ghi\\\\jkl(?{"this is runtime"})mno'
  *
  * After eval_sv()-ing that, grab any new code blocks from the returned qr
  * and merge them with any code blocks of the original regexp.
@@ -5058,7 +5058,7 @@ S_compile_runtime_code(pTHX_ RExC_state_t * const pRExC_state,
 		/* blank out literal code block */
 		assert(pat[s] == '(');
 		while (s <= pRExC_state->code_blocks[n].end) {
-		    *p++ = ' ';
+		    *p++ = '_';
 		    s++;
 		}
 		s--;