[perl #107492] [BUG] Modulo with negative numbers doesn't work right anymore in Rakudo

[Carl Mäsak]

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<az5112> printf "%d\n", (9 % (-9)) produces -9 in rakudo -- is this a bug?
<masak> az5112: was just going to eval that :)
<masak> az5112: welcome ;)
<masak> nom: say 9 % -9
<p6eval> nom ea0311: OUTPUT«0␤»
<masak> nom: say (9 % (-9))
<p6eval> nom ea0311: OUTPUT«-9␤»
<masak> hm.
<masak> why do those two even differ?
<masak> so the result should still be 0, right?
<TimToady> masak: sure, looks like a nom bug to me
* masak submits rakudobug
<TimToady> nom: say 0 % (-9)
<p6eval> nom ea0311: OUTPUT«-9␤»
<masak> b: say 9 % -9; say 9 % (-9)
<p6eval> b 1b7dd1: OUTPUT«0␤0␤»
<masak> yep. definitely a bug.
<masak> az5112++
<masak> az5112: I'm always very happy when p6cc contestants catch bugs for us :)

Looking at it more closely, I see both a parsing bug and an arithmetic bug here.

* Parsing bug: C<9 % -9> differs from C<9 % (-9)>. It shouldn't.
* Arithmetic bug: C<9 % (-9)> yields -9 rather than the correct
answer, 0. -9 is even outside of the range of *possible* values for
C<$x % (-9)>.