Invalid character escape returns error in regress but is accepted in other JS engines

[jasonwilliams]

In Boa we had an issue of

const a = /,\;/`

causing a panic, due to regress triggering a "Invalid character escape" panic.
However this seems to be acceptable in other JS engines, running the above in chrome for example is allowed.

Is there somewhere in the specification that does not allow invalid escapes?
Linked to Boa PR: boa-dev/boa#1027

[ridiculousfish]

Apologies for the delay. regress assumes the JS Unicode flag 'u' is set, which does not allow this escape:

> const a = /,\;/u
Uncaught SyntaxError: Invalid regular expression: /,\;/: Invalid escape

How would you like to proceed? If we need to tweak the syntax, or add a new flag I can do that.

[AnnikaCodes]

Probably we should disable the Unicode support unless the /u flag is set. Is that possible to do within Regress?

[ridiculousfish]

There's no support for non-Unicode in regress today. Non-Unicode regexes per the JS spec have a lot of terrible semantics: only supports BMP, its case folding is crazy.

But probably regress can have a mode that supports the non-Unicode syntax (including this escape) but still supports the Unicode semantics. I can work on adding that.

[jasonwilliams]

Sounds good @ridiculousfish 👍