[swift-evolution] Prohibit invisible characters in identifier names

[John McCall]

> On Jun 20, 2016, at 5:22 PM, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
> IIRC, some languages require zero-width joiners (though not zero-width spaces, which are distinct) to properly encode some of their characters. I'd be very leery of having Swift land on a model where identifiers can be used with some languages and not others; that smacks of ethnocentrism.

None of those languages require zero-width characters between two Latin letters, or between a Latin letter and an Arabic numeral, or at the end of a word.  Since standard / system APIs will (barring some radical shift) use those code points exclusively, it's justifiable to give them some special attention.

John.

> 
> Jordan
> 
> 
>> On Jun 20, 2016, at 10:51, João Pinheiro via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> Recently there has been a screenshot going around Twitter about C++ allowing zero-width spaces in variable names. Swift also suffers from this problem which can be abused to create ambiguous, misleading, and potentially obfuscate nefarious code.
>> 
>> I would like to propose a change to prohibit the use of invisible characters in identifier names.
>> 
>> I'm including an example of problematic code at the bottom of this email.
>> 
>> Sincerely,
>> João Pinheiro
>> 
>> 
>> /* The output for this code is:
>> A
>> B
>> C
>> 1
>> 2
>> 3
>> */
>> 
>> func test() { print("A") }
>> func t​est() { print("B") }
>> func te​st() { print("C") }
>> 
>> let abc = 1
>> let a​bc = 2
>> let ab​c = 3
>> 
>> test()
>> t​est()
>> te​st()
>> 
>> print(abc)
>> print(a​bc)
>> print(ab​c)
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> 
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