Re: Backwards compatibility and U+2E2F in `Identifier`s

[Mathias Bynens]

On 18 Sep 2013, at 21:05, Anne van Kesteren  wrote:

> On Mon, Aug 19, 2013 at 5:25 AM, Mathias Bynens  wrote:
>> After comparing the output, I noticed that both regular expressions are 
>> identical except for the following: ECMAScript 5 allows U+2E2F VERTICAL 
>> TILDE in `IdentifierStart` and `IdentifierPart`, but ECMAScript 6 / Unicode 
>> TR31 doesn’t.
> 
> Per ES6 identifiers start with code points whose category is ID_Start
> which per http://www.unicode.org/reports/tr31/ includes Lm which per
> http://www.unicode.org/Public/UNIDATA/UnicodeData.txt is true for
> U+2E2F. So why exactly is it disallowed?

`ID_Start` includes code points in the `Lm` category indeed, but then later 
explicitly disallows `Pattern_Syntax` and `Pattern_White_Space` code points. As 
it says on the page you linked to:

> In set notation, this is 
> [[:L:][:Nl:]--[:Pattern_Syntax:]--[:Pattern_White_Space:]] plus stability 
> extensions.

U+2E2F has the `Pattern_Syntax` property and is thus not a valid `ID_Start` 
code point.

___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Backwards compatibility and U+2E2F in `Identifier`s

[Anne van Kesteren]

On Mon, Aug 19, 2013 at 5:25 AM, Mathias Bynens  wrote:
> After comparing the output, I noticed that both regular expressions are 
> identical except for the following: ECMAScript 5 allows U+2E2F VERTICAL TILDE 
> in `IdentifierStart` and `IdentifierPart`, but ECMAScript 6 / Unicode TR31 
> doesn’t.

Per ES6 identifiers start with code points whose category is ID_Start
which per http://www.unicode.org/reports/tr31/ includes Lm which per
http://www.unicode.org/Public/UNIDATA/UnicodeData.txt is true for
U+2E2F. So why exactly is it disallowed?

Unless I'm missing something, the discussion we had in TC39 yesterday
was moot, and these bugs are invalid:

https://bugs.ecmascript.org/show_bug.cgi?id=1802
https://bugzilla.mozilla.org/show_bug.cgi?id=917436
https://bugs.webkit.org/show_bug.cgi?id=121541
https://code.google.com/p/v8/issues/detail?id=2892

And IE10 and maybe IE11 have a bug in not allowing it.


-- 
http://annevankesteren.nl/
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Backwards compatibility and U+2E2F in `Identifier`s

[Mathias Bynens]

> I had no intentions specific to U+2E2F when I proposed relying on UTR 31 - 
> the change is simply the effect of the character properties that the Unicode 
> Technical Committee assigned to this character.
> 
> I don't think there's a real problem. U+2E2F was added in Unicode version 
> 5.1. ECMAScript 5.1 requires only support for Unicode 3.0, and warns "If 
> portability is a concern, programmers should only employ identifier 
> characters defined in Unicode 3.0" (section 7.6). IE 10 throws a SyntaxError 
> if the character is used in an identifier.
> 
> BTW, if that's the only difference between the regular expressions for ES 5.1 
> and ES 6, then at least one of them is wrong - ES 6 allows supplementary 
> characters in identifiers, while ES 5.1 doesn't.

It’s the only difference in the BMP range. (Like you said, differences in the 
astral range are to be expected, since astral symbols weren’t allowed in ES5. 
No back-compat issues there.)
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Backwards compatibility and U+2E2F in `Identifier`s

[Norbert Lindenberg]

I had no intentions specific to U+2E2F when I proposed relying on UTR 31 - the 
change is simply the effect of the character properties that the Unicode 
Technical Committee assigned to this character.

I don't think there's a real problem. U+2E2F was added in Unicode version 5.1. 
ECMAScript 5.1 requires only support for Unicode 3.0, and warns "If portability 
is a concern, programmers should only employ identifier characters defined in 
Unicode 3.0" (section 7.6). IE 10 throws a SyntaxError if the character is used 
in an identifier.

BTW, if that's the only difference between the regular expressions for ES 5.1 
and ES 6, then at least one of them is wrong - ES 6 allows supplementary 
characters in identifiers, while ES 5.1 doesn't.

Norbert


On Aug 19, 2013, at 2:25 , Mathias Bynens  wrote:

> I wrote a (new) script that generates a regular expression that matches valid 
> JavaScript identifiers as per ECMAScript 5.1 / Unicode v6.2.0. 
> http://mathiasbynens.be/demo/javascript-identifier-regex
> 
> Then, I made it do the same thing according to the latest ECMAScript 6 draft, 
> which refers to Unicode Standard Annex #31: Unicode Identifier and Pattern 
> Syntax (http://www.unicode.org/reports/tr31/).
> 
> After comparing the output, I noticed that both regular expressions are 
> identical except for the following: ECMAScript 5 allows U+2E2F VERTICAL TILDE 
> in `IdentifierStart` and `IdentifierPart`, but ECMAScript 6 / Unicode TR31 
> doesn’t.
> 
> Was this potentially breaking change intentional? I’m fine with disallowing 
> U+2E2F, but only if we’re sure it doesn’t break any existing code.
> 
> Mathias
> http://mathiasbynens.be/
> ___
> es-discuss mailing list
> es-discuss@mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss

___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Backwards compatibility and U+2E2F in `Identifier`s

[Brendan Eich]

Thanks for filing. I don't recall any reason for this and it seems bad 
to break compatibility.


It may be that Norbert and Allen just missed your post on Monday; cc'ing 
them.


/be

Mathias Bynens wrote:

On 19 Aug 2013, at 11:25, Mathias Bynens  wrote:


After comparing the output, I noticed that both regular expressions are 
identical except for the following: ECMAScript 5 allows U+2E2F VERTICAL TILDE 
in `IdentifierStart` and `IdentifierPart`, but ECMAScript 6 / Unicode TR31 
doesn’t.

Was this potentially breaking change intentional? I’m fine with disallowing 
U+2E2F, but only if we’re sure it doesn’t break any existing code.


Follow-up: since this thread is being ignored, I 
filed.
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss


___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Re: Backwards compatibility and U+2E2F in `Identifier`s

[Mathias Bynens]

On 19 Aug 2013, at 11:25, Mathias Bynens  wrote:

> After comparing the output, I noticed that both regular expressions are 
> identical except for the following: ECMAScript 5 allows U+2E2F VERTICAL TILDE 
> in `IdentifierStart` and `IdentifierPart`, but ECMAScript 6 / Unicode TR31 
> doesn’t.
> 
> Was this potentially breaking change intentional? I’m fine with disallowing 
> U+2E2F, but only if we’re sure it doesn’t break any existing code.

Follow-up: since this thread is being ignored, I filed 
.
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss

Backwards compatibility and U+2E2F in `Identifier`s

[Mathias Bynens]

I wrote a (new) script that generates a regular expression that matches valid 
JavaScript identifiers as per ECMAScript 5.1 / Unicode v6.2.0. 
http://mathiasbynens.be/demo/javascript-identifier-regex

Then, I made it do the same thing according to the latest ECMAScript 6 draft, 
which refers to Unicode Standard Annex #31: Unicode Identifier and Pattern 
Syntax (http://www.unicode.org/reports/tr31/).

After comparing the output, I noticed that both regular expressions are 
identical except for the following: ECMAScript 5 allows U+2E2F VERTICAL TILDE 
in `IdentifierStart` and `IdentifierPart`, but ECMAScript 6 / Unicode TR31 
doesn’t.

Was this potentially breaking change intentional? I’m fine with disallowing 
U+2E2F, but only if we’re sure it doesn’t break any existing code.

Mathias
http://mathiasbynens.be/
___
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss