[swift-dev] Breaking change in lexing operators next to comments

[Simon Pilkington]

It seems to make more sense to treat comments as this if they are not present.

As a related question, should the presence/absence of whitespace be important at all? It seems fragile if it is.

-Simon


> On 14 Dec 2015, at 9:42 PM, Chris Lattner via swift-dev <swift-dev at swift.org> wrote:
> 
>> 
>> On Dec 14, 2015, at 8:15 PM, Jesse Rusak via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>> 
>> Hi all,
>> 
>> I’m investigating this bug: https://bugs.swift.org/browse/SR-186 <https://bugs.swift.org/browse/SR-186>
>> 
>> Which appears to be a result of the fact that the logic that determines if an operator is prefix/postfix/binary does not treat comments as whitespace. So, for example:
>> 
>> /* comment */!foo
>> 
>> does not lex as expected because the “!" thinks it has an something on both sides and so is treated as a binary operator. 
>> 
>> Fixing this (by treating comments as whitespace here) will break existing code which relies on the current behavior, such as:
>> 
>> foo/* comment */!
>> 
>> which currently treats the “!” as a postfix operator but will change to binary. I expect these cases would be rare (maybe in some generated code?), but the results might be pretty confusing. 
>> 
>> Any objections to fixing this or other thoughts? 
> 
> There are two defensible models here:
> 
> 1) comments should be treated as whitespace.
> 2) comments should be treated as if they were not present.
> 
> The later model seems more ideal to me (because you can put whitespace on either side of the comment after all), but I don’t have a strong opinion about that.  What do others think?
> 
> -Chris
> 
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