From @masak

<masak> r​: sub infix​:<@​>($a, $b) is assoc<non> { $a + $b }; say 1 @​ 2 @​ 3
<p6eval> rakudo 930369​: OUTPUT«6␤»
<masak> like that, but it isn't enforced.
* masak submits rakudobug
<masak> std​: 1 <=> 2 <=> 3
<p6eval> std a8bc48f​: OUTPUT«===SORRY!===␤"<=>" and "<=>" are
non-associative and require parens [...] Check failed␤FAILED 00​:00
42m␤»
<masak> r​: 1 <=> 2 <=> 3
<p6eval> rakudo 930369​: ( no output )
<masak> seems non-associativity in general, even among built-in
operators, isn't enforced.

From @moritz

fixed by jnthn++, and tested in S06-traits/is-assoc.t.

@moritz - Status changed from 'new' to 'resolved'