[swift-evolution] Prohibit invisible characters in identifier names

João Pinheiro joao at joaopinheiro.org
Mon Jun 20 14:17:38 CDT 2016

Nice feature in the IBM Swift Sandbox. Xcode doesn't display zero-width spaces either so the identifier names look exactly the same.

The issue with left-to-right and right-to-left markers is interesting and has previously been exploited in email phishing attacks.

It would be possible to highlight invisible characters in Xcode as a stopgap measure, but that doesn't solve the problem for developers using other editors or in other platforms. I think it would be a better idea to sanitise the set of allowed (or prohibited) characters for identifiers at the language level.

João Pinheiro

> On 20 Jun 2016, at 19:26, Vladimir.S <svabox at gmail.com> wrote:
> Very interesting.
> Btw, IBM Swift Sandbox shows these spaces:
> https://swiftlang.ng.bluemix.net/
> But my mail client does not - i.e. I saw exactly the same "test"&"abc"
> Also, I read about some issues with left-to-right and right-to-left markers that also somehow change the actual text of source - i.e. you see one text, but when it compiles - it works not as expected. I.e. viewer/editor processes these special codes and show you one text, but compiler treats text in another way.
> I believe it is a potential security problem that all unicode chars are allowed for variables/func names in Swift. IMO We definitely should limit allowed charset for identifiers in sources.
> On 20.06.2016 20:51, João Pinheiro via swift-evolution 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)
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution

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