[swift-evolution] Prohibit invisible characters in identifier names

[Xiaodi Wu]

On Mon, Jun 20, 2016 at 8:58 PM, John McCall via swift-evolution <
swift-evolution at swift.org> wrote:

> 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.
>

Although the practical implementation may need to be more limited in scope,
the general principle doesn't need to privilege Latin letters and Arabic
numerals. If, in any context, the presence or absence of a zero-width glyph
cannot possibly be distinguished by a human reading the text, then the
compiler should also be indifferent to its presence or absence (or,
alternatively, its presence should be a compile-time error).



> John.
>
>
> Jordan
>
>
> On Jun 20, 2016, at 10:51, João Pinheiro via swift-evolution <
> 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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