Forbid implementations from extending the RegExp grammar.
I think it would be more worthwhile of we tried to draw a compatibility
boundary. Taking perlre as a baseline, for example, are there additional
characters we should escape in RegExp.escape so that implementations (and
the language itself) could add more perlre features without breaking
compatibility? The (?...) syntax (and flags) seems to be the de facto
extension point, can we protect that more narrowly?
This isn't really about RegExp.escape as an issue. We can always extend
RegExp.escape when we make additions to the RegExp grammar as a standard
that would not be a problematic issue since we can keep both parts in sync
relatively easily.
On the other hand currently implementations are allowed to diverge in their regular expressions which means there is no guarantee that they'll behave the same in some cases. This is really risky for standard behavior and if an implementation decides to use the clause it could create a big pain point for developers while keeping it compliant.
Luckily, implementors are insightful people and implementations don't do that because of precisely those usability implications for end developers.
What I'm suggesting is that we forbid implementations from extending the regular expressions grammar beyond the language specification and outside the process. Basically, we take the ECMAScript regular expression object as specified (minus allowing extensions) as our base line :)
Benji -- but you've just specifically mentioned that implementations are already using the flexibility provided by the spec to experiment with and implement ES6 features. Why are you going to foreclose that possibility for ES2016+?
The perl community has managed to compatibly extend their regex engine
to an almost absurd degree. There are plenty of ways to add features
to your regexp that don't break "standard-compliant" regexps. I think
that's the spirit of the existing language in the spec, and it
should be honored. I'm fine with narrowing the scope, so we know that
new flags and characters after (? are "reserved", for example, but I
don't see why we have to ban future change outright.
On Jul 5, 2015, at 10:56 PM, Benjamin Gruenbaum wrote:
So, following work on RegExp.escape [1] I found out that implementations may extend the regular expression grammar in JavaScript [2]. However, when asking esdiscuss and Stack Overflow about it [2][3] it doesn't look like any implementations currently do so (*).
Actually, almost all ES implementation extend/modify the ES RegExp pattern grammar. Annex B.1.4 ecma-international.org/ecma-262/6.0/#sec-regular-expressions-patterns attempts to describe the interoperable RegExp extensions that are common among browsers.
Can we please forbid implementations from extending the regular expression syntax? It seems like this could cause compatibility issues between implementations anyway. We have subclassable RegExp with hooks and symbols in place and implementations that want to provide an extended RegExp can subclass RegExp or propose an extension to the language itself.
Can't do it, won't work. If followed, a general probation of syntactic extensions, whether for the entire language or just for RegExp patterns,would block all future language innovation. But, it practice it would just be ignored.
We (think) we can get away with a few very targeted and well motivated extension prohibitions such a those listed in ecma-international.org/ecma-262/6.0/#sec-forbidden-extensions but broad a "no new syntax" prohibition would hold and isn't desirable.
So, following work on RegExp.escape [1] I found out that implementations may extend the regular expression grammar in JavaScript [2]. However, when asking esdiscuss and Stack Overflow about it [2][3] it doesn't look like any implementations currently do so (*).
Can we please forbid implementations from extending the regular expression syntax? It seems like this could cause compatibility issues between implementations anyway. We have subclassable RegExp with hooks and symbols in place and implementations that want to provide an extended RegExp can subclass RegExp or propose an extension to the language itself.
[1] benjamingr/RegExp.escape [2] esdiscuss.org/topic/why-are-implementations-allowed-to-extend-the-regular-expressions-syntax [3] stackoverflow.com/questions/30958288/what-ecmascript-implementations-extend-the-regexp-syntax
(*) some did it to implement ES2015 features before ES2015.