mutlitconcat: fix non-folding adjacent consts

RT ##132646

v5.27.6-120-gbcc30fd changed multiconcat so that adjacent constants
weren't folded, so that ($overloaded . "a" . "b") is invoked as
    $overloaded->concat("a")->concat("b")
rather than
    $overloaded->concat("ab")

It did this by 'demoting' every second adjacent const as a real arg rather
than adding it to the const string. However, that could leave a
multiconcat op with more than the maximum allowed args.

So include demotion candidates as part of the arg count.

1 files changed, 31 insertions, 1 deletions

diff --git a/t/opbasic/concat.t b/t/opbasic/concat.t
index 55965c1702..42851d23b9 100644
--- a/t/opbasic/concat.t
+++ b/t/opbasic/concat.t
@@ -39,7 +39,7 @@ sub is {
     return $ok;
 }
 
-print "1..251\n";
+print "1..252\n";
 
 ($a, $b, $c) = qw(foo bar);
 
@@ -810,3 +810,33 @@ ok(ref(CORE::state $y = "a $o b") eq 'o',
         is($got, $expected, "long concat chain $i");
     }
 }
+
+# RT #132646
+# with adjacent consts, the second const is treated as an arg rather than a
+# consts. Make sure this doesn't exceeed the maximum allowed number of
+# args
+{
+    my $x = 'X';
+    my $got =
+          'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        . 'A' . $x . 'B' . 'C' . $x . 'D'
+        ;
+    is ($got,
+        "AXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXDAXBCXD",
+        "RT #132646");
+}