NoScopeStatement violates C compatibility principal.

[Kenji Hara]

I think this is a corner case bug of current dmd parser.

Kenji Hara


2013/5/28 monarch_dodra <monarchdodra at gmail.com>

> I have created before two threads about the weird semantics of labeled
> block statements. In a word: putting a label before a block means that
> block does not create a scope, and the variables created inside that scope
> will "leak" to the outside of said scope. I've found this to be problematic
> on several points:
>
> 1. No use case for this
> 2. You can accidentally break code by placing a label before a block (but
> without meaning to label the actual block)
> 3. Deviates from C.
>
> What kind of bothers me most is the combination 1 & 3: Why??? I've
> complained about this before, and the answer was: "According to spec", but
> to the question "why are the specs like this", I have yet to get an answer.
>
> ----------------
> The reason I'm bringing this up (again), is that it bit me in the ass very
> recently. According to TDPL:
>
> "If a numeric expression compiles in the C language and also compiles in
> D, its
> type will be the same in both languages (note that not all C expressions
> must be
> accepted by D)."
>
> Followed by
>
> "Rule 1 makes things just a tad more complicated than they would otherwise
> be, but D overlaps enough with C and C++ to inspire people to simply copy
> and paste entire functions into D programs. Now it’s all right if D
> occasionally refuses to compile certain constructs for safety or
> portability reasons; but if it compiled that 2000-line encryption package
> and ran it with different results, life would definitely not be good for
> the hapless victim."
>
> So basically, this is saying "If your C code compiles in D, you'll get the
> same result. I guarantee it :)"
>
> Here's a (reduced) C program:
>
> ----
> int i = 3;
>
> void main()
> {
>   {
>     int some_condition = 1;
>     if ( some_condition )
>       goto block_end;
>
>     /* dummy code */
>   } block_end:
>
>   {
>     int i = 7;
>     printf("%i", i);
>   }
>
>   printf("%i", i);
> }
> ----
> C prints: "70"
> D prints: "77"
>
> Oops!
>
> I realize 99% of people don't use goto or labels too much, but this
> doesn't mean it shouldn't be addressed. For me, D has been about being a
> "smooth experience", and this makes so little sense to me it infuriates me.
>
> I don't see how this could help anyone, but I do see how it can create
> bugs, and these kinds of cases are what D strives to avoid. "Fixing" would
> probably break nothing.
>
> -------------------
> I'd like to make a push to get the specs changed in regards to this. I'd
> like to get others' opinion on the matter, in particular, if anybody can
> think of a rationale for the current behavior. And if there is no
> rationale, how much support there is for changing it. (in which case I'll
> file the corresponding ER).
>
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