bug#8576: 23.2; js-mode doesn't support multi-line variable declarations

[Felix H. Dahlke]

Quoting Stefan Monnier <monnier@IRO.UMontreal.CA>:

> Thank you for your efforts trying to find a good fix for this problem.
> I'd like to install your changes (or some future version of them once
> the wrinkles are worked out), but it's sufficiently non-trivial that
> we need you to sign some copyright paperwork.

I already sent a signed CA to the FSF, it should arrive shortly.

> > const a = 5,
> >     b = 6;
>
> Yup, that'd be a bug.

Depends, IMO. Do we want to indent on the column, or by the configured  
indentation level? I personally want to indent on column, so that  
would indeed be a problem for me (never noticed because I use a tab  
size of 4 and no const keyword). Should this be configurable?

If we don't make it configurable, I'd vote for going with Dmitry's  
variant, as that seems to be the more popular style.

> > I meant that nobody will care, most likely. But the implementation
> > shouldn't be too hard either - add a function to `post-command-hook'
> > which would check if the command is `self-insert-command', check if we
> > inserted a comma, skip backward to the previous non-whitespace char, see
> > if it's } or ], etc.
>
> Rather than a post-command-hook, that would be a post-self-insert-hook.
> And that would need to be conditional on some js-electric-foo variable
> (or better yet, be made to work with electric-indent-mode).
>
> Note that looking forward during indentation, while occasionally
> annoying, is not that big of a problem in practice: contrary to popular
> belief, we don't write code quite as linearly as one might think.
> We at least as frequently edit code in place.
>
> BTW, rather than a post-self-insert-hook, you could put a special
> text-property `js--indent-depends-on-next-line' on the line, and then
> when indenting a line, you could check if the previous line has that
> property and if so indent both lines.  I'm not claiming it's a better
> approach, just an alternative one.

Thanks for the hints Dmitry and Stefan, as you undoubtly noticed, I am  
quite new to Emacs development, but willing to learn :)

But I'd rather get this patch in in the simple form first, and enhance  
the behaviour with another one.

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