Re: Regarding Emacs, js.el, template-strings and syntax-tables

[Anders Lindgren <andlind@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 3718 bytes --]

Hi!

I've been playing around with constructs like that for quite some time,
here are some thoughts on the matter:

--------

If you use a string face with, say, both a background and a foreground
color, it will matter if you *replace* the existing face as opposed to
*prepend* a new face on top of it.

For example, the default Ruby mode replace the face, which doesn't look
good when the string face has a background color:

"Hello #{name}"

With *prepend* it would have looked like:

"Hello #{name}"

In other words, the font-lock rule should use "prepend" and not "t" as the
override flag. (I've got it on my todo-list to change a lot of "t":s to
"prepend" but haven't had time to do it yet.)

--------

One question is if the delimiters around the expression should be
highlighted as well? In Ruby they are highlighted. In my cmake-font-lock[1]
package I have opted not to highlight them, as it makes it easier to read
the variable name:

"Hello ${name}"

Another reason for this is that CMake supports nested such constructs,
which look better this way:

"Hello ${name${tail}}"

[1] https://github.com/Lindydancer/cmake-font-lock

--------

> how should font-lock display `name`.  Should it have a normal face as if
it weren't inside a string?  Or should have a kind of combination of
string-face and something else?

In all cases I've seen, the content is displayed using
`font-lock-variable-name-face', even for the cases where the content is
more complex than a plain variable. I would say that this is OK, as they
stand out and, most of the time, it is a plain variable anyway.

As I said above, using *prepend*, the end result will be a mix of
font-lock-variable-name-face and font-lock-string-face.

--------

> several parts of Emacs like to know if we're inside
>  code/string/comment (usually using (nth [3|4|8] (syntax-ppss))).
>  Should these all consider "name" as being inside code?
>  Or inside string?  Or should we revisit all those cases one-by-one?

I see this as a pure syntax highlighting thing, so I would say that
syntax-ppss should treat them as strings.

--------

A side note: I've started to make an inventory of syntax highlighting in
various modes in Emacs, as part of a font-lock regression test suite I've
accumulated over the years. The suite and the inventory is far from
complete, but it might be worth looking into:


https://github.com/Lindydancer/font-lock-regression-suite/blob/master/doc/CommentsOnMajorModes.org

One mode that stands out in this respect is "bat" mode, it handles "%alpha"
but not "%alpha_beta", and doesn't support the construct in strings at all.

    -- Anders

On Thu, Aug 24, 2017 at 12:53 PM, Stefan Monnier <monnier@iro.umontreal.ca>
wrote:

> >> function getGreeting(name) {
> >> let greeting = `Hello, ${name}!`;
> >> return greeting;
> >> }
>
> Indeed this problem has been with us in sh-script.el for many years.
> There are several different aspects at play:
> - how should font-lock display `name`.  Should it have a normal face as
>   if it weren't inside a string?  Or should have a kind of combination
>   of string-face and something else?
> - how should we handle nestings of such constructs.
> - several parts of Emacs like to know if we're inside
>   code/string/comment (usually using (nth [3|4|8] (syntax-ppss))).
>   Should these all consider "name" as being inside code?
>   Or inside string?  Or should we revisit all those cases one-by-one?
>
> In sh-script, we use syntax-propertize to make sure the whole string and
> its contents is all considered as a string and nothing else.  This was
> the simplest solution and probably corresponds to the current behavior
> of js.el (and typescript.el) as well.
>
>
>         Stefan
>
>
>

[-- Attachment #2: Type: text/html, Size: 6287 bytes --]