Early error on '0' followed by '8' or '9' in numeric literals does not seem to be web-compatible

Mark S. Miller erights at google.com
Thu Aug 7 09:06:48 PDT 2014


On Aug 7, 2014 8:52 AM, "Alex Kocharin" <alex at kocharin.ru> wrote:
>
>
> So strict mode is mandatory in classes and modules, and can't be turned
off.

Yes, classes and modules are optional. If you want to use with or 05, don't
use classes or modules.

> Since it is mandatory, it is no longer "strict mode" like it is in perl.
You can't opt out of it if you want to. Therefore all legacy constructs
should be allowed there unless they are guaranteed to break the code in the
future.
>
> Sooner or later people will migrate their legacy code into es6 modules.
We would want to make this migration as easy as possible. And saying that
"02468" is fine in es3, forbidden in es6, and allowed again in es8 with
*exactly the same meaning* isn't helping.
>
>
> 07.08.2014, 19:32, "Mark S. Miller" <erights at google.com>:
>>
>> The web seems unable to shed its past. In the absence of opt-in (either
"use strict";, classes, or modules) legacy web code will probably be sloppy
forever. In sloppy mode, you can probably use "with" forever as well.
>>
>>
>>
>> On Thu, Aug 7, 2014 at 8:23 AM, Alex Kocharin <alex at kocharin.ru> wrote:
>>>
>>>
>>> 07.08.2014, 18:51, "Mark S. Miller" <erights at google.com>:
>>>>
>>>> On Thu, Aug 7, 2014 at 7:08 AM, Alex Kocharin <alex at kocharin.ru> wrote:
>>>>>
>>>>>
>>>>> 07.08.2014, 09:49, "Mathias Bynens" <mathias at qiwi.be>:
>>>>> > On 7 Aug 2014, at 02:46, Bill Frantz <frantz at pwpconsult.com> wrote:
>>>>> >>  On Tue, Aug 5, 2014 at 7:56 AM, Mathias Bynens <mathias at qiwi.be>
wrote:
>>>>> >>
>>>>> >>  ...
>>>>> >>>  In section 11.8.3 (Numeric Literals), the definition for
>>>>> >>>  `DecimalIntegerLiteral` should somehow be tweaked to match that
of
>>>>> >>>  `DecimalDigits`, with the exception that if the first digit is
`0` and all
>>>>> >>>  other digits are octal digits (0-7) it must be treated as a
legacy octal
>>>>> >>>  literal.
>>>>> >>  So this horrible footgun, changing the value of a constant
changes its radix, is only lurking in sloppy mode.
>>>>> >
>>>>> > It affects strict mode code too in existing implementations: there
you go from not throwing on e.g. `0123456789` (which is not an octal
literal because of the `8` and `9`) to suddenly throwing a syntax error
when the value changes to `0` followed by only octal digits (as then it is
an octal literal). See my previous posts in this thread.
>>>>> Throw if value is ambiguous (i.e. `052`), don't throw if value is
unambiguous (i.e. `05`, `082`). Looks good to me.
>>>>>
>>>>> It is not compiler job to prevent bad code style, it's what linters
should do.
>>>>
>>>>
>>>> It is partially the job of strict mode to prevent some egregiously
confusing constructs. There is a line to draw between what strict mode
prohibits and what linters warn about. But there's no one line statement of
principle that captures this. Strict mode prohibits "with" and some other
constructs that make it especially hard to reason about programs.
>>>>
>>>
>>>
>>> Well, then the question is this. Is strict mode optional or mandatory
to use? Will a developer always have a choice not to use it?
>>>
>>> If it is optional like it is now, that's fine.
>>>
>>> But if it is going to become the only es mode in the future, it should
be extended as much as possible, leaving linting job to linters. Including
confusing "with", because it have its uses in template engines.
>>>
>>
>>
>>
>>
>> --
>>     Cheers,
>>     --MarkM
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