Test infix:<∘> and infix:<o> keep RHS's .arity and .count

RT#130891: https://rt.perl.org/Ticket/Display.html?id=130891
Rakudo fix: rakudo/rakudo@032b283d5a

S03-operators/composition.t

@@ -2,7 +2,7 @@ use v6;
 
 use Test;
 
-plan 10;
+plan 12;
 
 sub double ($x) { $x * 2 };
 sub invert ($x) { 1 / $x };
@@ -23,3 +23,46 @@ is (* o *)(* + 1, * * 2)(3), 7, "can autocurry with Whatever on both sides";
 
 is ((* + *) o { $_ + 7, $_ * 6 })(5), 42, "can compose functions that pass two arguments";
 is ({ [+] @_ } o *.map(* * 2))(1..10), 110, "can compose functions that pass multiple arguments";
+
+# RT #130891
+{
+    subtest 'infix:<∘> preserves .count and .arity of RHS' => {
+        plan 4;
+        my &one = sub { $^a.uc } ∘ sub { "$^a:$^b" };
+        is-deeply <a b c d e f g h>.map(&one).List,
+            ("A:B", "C:D", "E:F", "G:H"),
+            'can 2-at-a-time map with a composed routine';
+
+        my &two = sub { $^a.flip } ∘ &one;
+        is-deeply <a b c d e f g h>.map(&two).List,
+            ("B:A", "D:C", "F:E", "H:G"),
+            'can 2-at-a-time map with a double-composed routine';
+
+        my &grepper = sub { $^a.not } ∘ sub { ($^a + $^b) %% 2 }
+        is-deeply (1, 1,  2, 3,  4, 5).grep(&grepper).List, ((2, 3), (4, 5)),
+            'can 2-at-a-time grep with a composed routine';
+
+        is-deeply ([∘] {$_ xx 2} xx 2)(3).List, ((3, 3), (3, 3)),
+            'Can use infix:<∘> as a meta';
+    }
+
+    subtest 'infix:<o> preserves .count and .arity of RHS' => {
+        plan 4;
+        my &one = sub { $^a.uc } o sub { "$^a:$^b" };
+        is-deeply <a b c d e f g h>.map(&one).List,
+            ("A:B", "C:D", "E:F", "G:H"),
+            'can 2-at-a-time map with a composed routine';
+
+        my &two = sub { $^a.flip } o &one;
+        is-deeply <a b c d e f g h>.map(&two).List,
+            ("B:A", "D:C", "F:E", "H:G"),
+            'can 2-at-a-time map with a double-composed routine';
+
+        my &grepper = sub { $^a.not } o sub { ($^a + $^b) %% 2 }
+        is-deeply (1, 1,  2, 3,  4, 5).grep(&grepper).List, ((2, 3), (4, 5)),
+            'can 2-at-a-time grep with a composed routine';
+
+        is-deeply ([o] {$_ xx 2} xx 2)(3).List, ((3, 3), (3, 3)),
+            'Can use infix:<o> as a meta';
+    }
+}