Regular expressions s (dotAll) flag

[GeoffreyBooth]

This adds support for ES2018’s s (dotAll) flag.

The syntax is only supported in Node 9+, so I added Node 9 to the list of versions we test in CI.

Merging this in would mean that we would need to expand the “Compatibility” section of the docs that currently say:

With the exception of modules and JSX, all the modern JavaScript features that CoffeeScript supports can run natively in Node 7.6+.

We would probably need to put a table there, listing the features required by certain Node versions (i.e. async functions: 7.6+, dotAll flag: 9+, etc.).

[aminland]

Should we wait for this to be stage 4 first? otherwise you have to use the plugin transform-modern-regexp unless we don't care about IE anymore...

[GeoffreyBooth]

This feature is at Stage 4: https://github.com/tc39/proposal-regexp-dotall-flag

[GeoffreyBooth]

@jashkenas @lydell @zdenko @connec I updated the docs to start listing features that CoffeeScript supports that are newer than Node 7.6. See this diff. Any feedback on this language?

Note also that Node’s new, native support for modules needs to be addressed. It was painful just writing the instructions for how to use .mjs files now; we should make this better. Please see #5018.

[jashkenas]

Looks good! I would, personally, omit the "Why doesn't CoffeeScript simply always transpile?" paragraph.

[GeoffreyBooth]

I would, personally, omit the “Why doesn’t CoffeeScript simply always transpile?” paragraph.

Yeah, I think that made more sense back when we were introducing CoffeeScript 2, but it isn’t needed anymore.