[perl #98954] [BUG] Nested indexing semantics changed from Beijing to nom in Rakudo

[Carl Mäsak]

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<masak> b: my @a = [1], [2], [3]; say (map { @a[1 - $_][0] }, 0 .. 3).perl
<p6eval> b 1b7dd1: OUTPUT«(2, 1, Any, Any)␤»
<masak> nom: my @a = [1], [2], [3]; say (map { @a[1 - $_][0] }, 0 .. 3).perl
<p6eval> nom 08ef94: OUTPUT«(2, 1).list␤»
* masak submits rakudobug
<tadzik> here we go again
<masak> tadzik: this change in semantics causes connect-4 to give the
first player the win on the first move.
<tadzik> masak: serious business
<masak> tadzik: seems connect-4's winning condition relied on being
able to do negative indexing.
<masak> tadzik: I have no trouble believing that this isn't spectested.
<masak> and I have no horse in this race. I'll gladly rewrite that
part of connect-4 if need be.
<masak> but until there's a verdict, it goes into RT.
<masak> niecza: my @a = [1], [2], [3]; say (map { @a[1 - $_][0] }, 0 .. 3).perl
<p6eval> niecza v9-23-g1a8efca: OUTPUT«(2, 1, Any, Any).list␤»  [23:52]
<masak> there'a another data point, I guess.
<jnthn> nom: my @a = [1], [2], [3]; say (map { say @a[1 - $_][0].WHAT;
@a[1 - $_][0] }, 0 .. 3).perl
<p6eval> nom 08ef94: OUTPUT«Int()␤Int()␤Nil␤Nil␤(2, 1).list␤»
<jnthn> nom: say (map { Nil }, 0 .. 3).perl
<p6eval> nom 08ef94: OUTPUT«().list␤»
<jnthn> masak: There's the underlying thing.
<masak> jnthn: I suspected that.
<masak> jnthn: why Nil and not Any?
<jnthn> masak: I can believe that's actually correct. But I'm not
quite sure if the Nil you got before is wrong.
<jnthn> masak: That is, it's not map's fault..but @a[1 - $_][0]
returning Nil may be wrong.
<masak> aye.
<masak> I know.
<jnthn> Well, so that golfs if. :)

Does the spec say that one should get Nil in this case? I was fine
with getting Any. Note also that Niecza agrees.