At Sun, 17 May 2015 10:32:15 +0100, Laurent wrote:
> The following recent change breaks rwind/x11 [1, 2]:
> https://github.com/plt/racket/commit/ad899173b97ce2ca51612a496d17ea32db45ecdc#di
> ff-4f20ebf5b6abb6ab4c0b80b41efa1614R819
>
> Now when running rwind, it fails with:
> _enum: key is not a symbol
> symbols: '(2)
> key: 2
> value: 3
> context...:
> /usr/share/racket-6.2.0.3/collects/ffi/unsafe.rkt:832:2: loop
> /usr/share/racket-6.2.0.3/collects/ffi/unsafe.rkt:821:0: unpack63
> /home/orseau/Unison/Prog/Racket/x11/x11/x11.rkt: [running body]
> /home/orseau/Unison/Prog/Racket/rwind/color.rkt: [traversing imports]
> /home/orseau/Unison/Prog/Racket/rwind/rwind.rkt: [traversing imports]
>
> Unfortunately, I couldn't get a better error stacktrace, even with `racket
> --no-jit -l errortrace`.
>
> I'm having trouble debugging this, as it's hidden under piles of FFI calls,
> but would allowing for integers in place of symbols be really a bad idea
> here?
The old treatment of integers in `_enum` was not intentional, but I
think it would count as a bad idea if it had been intentional:
> (cast 'a (_enum '(a 17 b)) _int)
0
> (cast 17 (_enum '(a 17 b)) _int)
1
> (cast 'b (_enum '(a 17 b)) _int)
2
In other words, with the old `_enum`, an integer was treated like a
symbol on input and converted to a different integer (based on the
position of the original integer in the `_enum` sequence).
The problem code in "x11.rkt" is
(define EventQueue
(_enum '(QueuedAlready = 0
QueuedAfterReading = 1
QueuedAfterFlush 2)))
where a `=` is omitted accidentally. Since the default numbering of
`QueduedAfterFLush` is 2 anyway, the consequence of the typo is minor;
a 2 would be allowed where only one of three symbols was intended to be
allowed, and the 2 would be silently converted to a 3! Still, it's not
a case where an integer element of an enumeration was intended.
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