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

[Anders Lindgren]

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

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> 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 <address@hidden> 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