Re: Use (eval-when-compile 'treesit) to save us from writing declare-function forms

[Yuan Fu <casouri@gmail.com>]

> On Dec 8, 2024, at 7:27 AM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
> 
>> +(eval-when-compile
>> +  (treesit-declare-c-functions))
> 
> `treesit-declare-c-functions` is a macro, that expands to
> `declare-function`s, i.e. to "no-ops".
> Why wrap it within `eval-when-compile`?

I thought that might be TRT since they’re only needed for compiling the file.

> 
> If it works within an `eval-when-compile`, it's only by accident (just
> like the fact that (eval-when-compile (defvar foo)) "works" is an
> accident): code shouldn't rely on it.
> 
> It's not the evaluation of `defvar` or `declare-function` that is needed
> (because such an evaluation should have no effect, as you can see if
> you look at the definition of `declare-function`), but instead the
> "calls" to `defvar` or `declare-function` need to be seen/processed by
> the compiler.  By wrapping them within an `eval-when-compile` you risk
> *hiding* them from the compiler.

I thought eval-when-compile is more of a “include if compiling” macro, should’ve checked :)

We can also go with Dmitry’s idea, and just define all the functions in treesit.el if Emacs is not built with tree-sitter. We can detect that with treesit-available-p.

Yuan