Handle /@a/ array expansion within regex engine

Previously /a@{b}c/ would be parsed as

    regcomp('a', join($", @b), 'c')

This means that the array was flattened and its contents stringified before
hitting the regex engine.

Change it so that it is parsed as

    regcomp('a', @b, 'c')

(but where the array isn't flattened, but rather just the AV itself is
pushed onto the stack, c.f. push @b, ....).

This means that the regex engine itself can process any qr// objects
within the array, and correctly extract out any previously-compiled
code blocks (thus preserving the correct closure behaviour). This is
an improvement on 5.16.x behaviour, and brings it into line with the
newish 5.17.x behaviour for *scalar* vars where they happen to hold
regex objects.

It also fixes a regression from 5.16.x, which meant that you suddenly
needed a 'use re eval' in scope if any of the elements of the array were
a qr// object with code blocks (RT #115004).

It also means that 'qr' overloading is now handled within interpolated
arrays as well as scalars:

    use overload 'qr' => sub { return  qr/a/ };
    my $o = bless [];
    my @a = ($o);
    "a" =~ /^$o$/; # always worked
    "a" =~ /^@a$/; # now works too

1 files changed, 17 insertions, 1 deletions

diff --git a/op.c b/op.c
index c502d3fe0d..a46d68b181 100644
--- a/op.c
+++ b/op.c
@@ -4545,11 +4545,21 @@ Perl_pmruntime(pTHX_ OP *o, OP *expr, bool isreg, I32 floor)
 
     LINKLIST(expr);
 
-    /* fix up DO blocks; treat each one as a separate little sub */
+    /* fix up DO blocks; treat each one as a separate little sub;
+     * also, mark any arrays as LIST/REF */
 
     if (expr->op_type == OP_LIST) {
 	OP *o;
 	for (o = cLISTOPx(expr)->op_first; o; o = o->op_sibling) {
+
+            if (o->op_type == OP_PADAV || o->op_type == OP_RV2AV) {
+                assert( !(o->op_flags  & OPf_WANT));
+                /* push the array rather than its contents. The regex
+                 * engine will retrieve and join the elements later */
+                o->op_flags |= (OPf_WANT_LIST | OPf_REF);
+                continue;
+            }
+
 	    if (!(o->op_type == OP_NULL && (o->op_flags & OPf_SPECIAL)))
 		continue;
 	    o->op_next = NULL; /* undo temporary hack from above */
@@ -4583,6 +4593,12 @@ Perl_pmruntime(pTHX_ OP *o, OP *expr, bool isreg, I32 floor)
 		finalize_optree(o);
 	}
     }
+    else if (expr->op_type == OP_PADAV || expr->op_type == OP_RV2AV) {
+        assert( !(expr->op_flags  & OPf_WANT));
+        /* push the array rather than its contents. The regex
+         * engine will retrieve and join the elements later */
+        expr->op_flags |= (OPf_WANT_LIST | OPf_REF);
+    }
 
     PL_hints |= HINT_BLOCK_SCOPE;
     pm = (PMOP*)o;