Subject: Re: bug#41649: 27.0.91; beginning-of-defun doesn't work inside React markup in js-jsx-mode

From: Brian Leung <[email-masked]>
Date: Tue, 2 Jun 2020 10:27:38 -0700

> Daniel, what is going on, here?  Is this just a simple coding error,
> where the second c-init-language-vars should have been removed at some
> stage?

I wasn't sure if js-beginning-of-defun was preferred here since it does not
seem to detect ES2015 arrow functions like what is used here, whereas
c-beginning-of-defun handles them fine outside of ReactJS cases: if you try
M-: js-beginning-of-defun on my React example, point moves straight from
the class declaration to the imports, which is not desirable. Should I file
a separate ticket for that?

On Tue, Jun 2, 2020 at 10:12 AM Alan Mackenzie <[email-masked]> wrote:

> Hello Brian.
>
> In article <[email-masked]> you wrote:
> > [-- text/plain, encoding 7bit, charset: UTF-8, 44 lines --]
>
> > With a file App.js that looks like:
>
> > import * as React from "react";
> > import { render } from "react-dom";
>
> > const App = () => {
> >   return (
> >     <div>
> >       <h1 id="abc">hello</h1>
> >       <SearchParams />
> >     </div>
> >   );
> > };
>
> > render(<App />, document.getElementById("root"));
>
>
> > If you open the file in JS mode (Emacs 27), and move point inside of
> > "abc", calling
>
> > M-: (c-beginning-of-defun)
>
> That looks like a strange thing to do.  JS mode has its own
> js-beginning-of-defun.
>
> But wait - beginning-of-defun-function is set to c-beginning-of-defun,
> which is probably why you reported the bug the way you did.
>
> c-beginning-of-defun won't work, because a suitable member or derivative
> of CC Mode hasn't been fully initialised.
>
> > gives the following error:
>
> > Debugger entered--Lisp error: (wrong-type-argument hash-table-p nil)
> >   copy-hash-table(nil)
> >   c-forward-<>-arglist(nil)
> >   c-backward-<>-arglist(nil nil)
> >   c-looking-at-decl-block(99 nil)
> >   c-most-enclosing-decl-block((117 99 88 (40 . 50)))
> >   c-widen-to-enclosing-decl-scope((117 99 88 (40 . 50)) 1 234)
> >   c-beginning-of-defun()
> >   eval((c-beginning-of-defun) t)
> >   eval-expression((c-beginning-of-defun) nil nil 127)
> >   funcall-interactively(eval-expression (c-beginning-of-defun) nil nil
> 127)
> >   call-interactively(eval-expression nil nil)
> >   command-execute(eval-expression)
>
> > Manually invoking C-M-a inside the double quotes should end the same way.
>
> It does.
>
> The problem seems to stem from the top-level function #'js-mode.  Early
> on, it invokes
>
>     (c-init-language-vars js-mode)
>
> , which initialises the CC Mode language variables to (mostly) their
> Java Mode values.  js-mode continues by overwriting the local value of
> quite a few of these variables, including beginning-of-defun-function.
>
> js-mode then invokes
>
>     (c-init-language-vars js-mode)
>
> a second time, which initialises the language variables again, in
> particular, those variables which just got a local value, including
> beginning-of-defun-function.
>
> Daniel, what is going on, here?  Is this just a simple coding error,
> where the second c-init-language-vars should have been removed at some
> stage?
>
> > In GNU Emacs 27.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
> > Windowing system distributor 'The X.Org Foundation', version
> 11.0.12008000
> > System Description: NixOS 20.09 (Nightingale)
>
> --
> Alan Mackenzie (Nuremberg, Germany).
>
>