bug#63345: 28.2; provided-mode-derived-p doesn't work when passed an alias in MODES

bug#63345: 28.2; provided-mode-derived-p doesn't work when passed an alias in MODES

[Damien Cassou]

Hi,

The function `provided-mode-derived-p` (used by `derived-mode-p`) has
the code below. The first 3 lines of the function takes care of
converting the first argument MODE if it is an alias (as
`javascript-mode` is an alias for `js-mode`). This works great when
calling the function this way:

  (provided-mode-derived-p 'javascript-mode 'prog-mode)
    ⇒ prog-mode

But if the second argument MODES contains an alias, the code has no
conversion mechanism and the line below returns nil even though I
expect it to return non-nil:

  (provided-mode-derived-p 'javacript-mode 'javascript-mode)
    ⇒ nil

Is that a bug?

(defun provided-mode-derived-p (mode &rest modes)
  "Non-nil if MODE is derived from one of MODES.
Uses the `derived-mode-parent' property of the symbol to trace backwards.
If you just want to check `major-mode', use `derived-mode-p'."
  ;; If MODE is an alias, then look up the real mode function first.
  (when-let ((alias (symbol-function mode)))
    (when (symbolp alias)
      (setq mode alias)))
  (while
      (and
       (not (memq mode modes))
       (let* ((parent (get mode 'derived-mode-parent))
              (parentfn (symbol-function parent)))
         (setq mode (if (and parentfn (symbolp parentfn)) parentfn parent)))))
  mode)

-- 
Damien Cassou

"Success is the ability to go from one failure to another without
losing enthusiasm." --Winston Churchill

bug#63345: 28.2; provided-mode-derived-p doesn't work when passed an alias in MODES

[Eli Zaretskii]

> From: Damien Cassou <damien@cassou.me>
> Date: Sun, 07 May 2023 11:49:37 +0200
> 
> The function `provided-mode-derived-p` (used by `derived-mode-p`) has
> the code below. The first 3 lines of the function takes care of
> converting the first argument MODE if it is an alias (as
> `javascript-mode` is an alias for `js-mode`). This works great when
> calling the function this way:
> 
>   (provided-mode-derived-p 'javascript-mode 'prog-mode)
>     ⇒ prog-mode
> 
> But if the second argument MODES contains an alias, the code has no
> conversion mechanism and the line below returns nil even though I
> expect it to return non-nil:
> 
>   (provided-mode-derived-p 'javacript-mode 'javascript-mode)
>     ⇒ nil
> 
> Is that a bug?

Adding Stefan.

bug#63345: 28.2; provided-mode-derived-p doesn't work when passed an alias in MODES

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Hi Damien,

>>   (provided-mode-derived-p 'javacript-mode 'javascript-mode)
>>     ⇒ nil
>> Is that a bug?

I'd put it into "not a bug" because there really is a difference between
a mode and an alias to a mode (e.g. you can expect a mode to have
matching `<mode>-map`, `<mode>-hook`, ... vars).

But admittedly, this is a messy area.

What was the original scenario where you bumped into this problem?


        Stefan

bug#63345: 28.2; provided-mode-derived-p doesn't work when passed an alias in MODES

[Damien Cassou]

Stefan Monnier <monnier@iro.umontreal.ca> writes:
> What was the original scenario where you bumped into this problem?

The jinx package defines 'jinx-camel-modes [1], a list of major modes
for languages using camel case or pascal case. This variable is passed
to 'derived-mode-p. Before my PR #64 [2], this variable used to contain
'javascript-mode (the alias) instead of 'js-mode (the function). For a
file using 'js-mode, the equivalent of the code below was executed:

  (derived-mode-p 'js-mode 'javascript-mode)
    ⇒ nil

I was expecting a non-nil value. My PR replaced 'javascript-mode with
'js-mode in 'jinx-camel-modes thus working around the problem.

[1] https://github.com/minad/jinx/blob/0.8/jinx.el#L96
[2] https://github.com/minad/jinx/pull/64

-- 
Damien Cassou

"Success is the ability to go from one failure to another without
losing enthusiasm." --Winston Churchill

bug#63345: 28.2; provided-mode-derived-p doesn't work when passed an alias in MODES

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Damien Cassou [2023-05-07 16:35:38] wrote:
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>> What was the original scenario where you bumped into this problem?
>
> The jinx package defines 'jinx-camel-modes [1], a list of major modes
> for languages using camel case or pascal case. This variable is passed
> to 'derived-mode-p. Before my PR #64 [2], this variable used to contain
> 'javascript-mode (the alias) instead of 'js-mode (the function). For a
> file using 'js-mode, the equivalent of the code below was executed:
>
>   (derived-mode-p 'js-mode 'javascript-mode)
>     ⇒ nil

I see, thanks.

> I was expecting a non-nil value. My PR replaced 'javascript-mode with
> 'js-mode in 'jinx-camel-modes thus working around the problem.

`js-mode` is the right value to use there, indeed.


        Stefan

bug#63345: 28.2; provided-mode-derived-p doesn't work when passed an alias in MODES

[Damien Cassou]

Stefan Monnier <monnier@iro.umontreal.ca> writes:
> `js-mode` is the right value to use there, indeed.

Very good, thank you. In this case I would close the issue.

-- 
Damien Cassou

"Success is the ability to go from one failure to another without
losing enthusiasm." --Winston Churchill

bug#63345: 28.2; provided-mode-derived-p doesn't work when passed an alias in MODES

[Eli Zaretskii]

> From: Damien Cassou <damien@cassou.me>
> Cc: 63345@debbugs.gnu.org, Eli Zaretskii <eliz@gnu.org>
> Date: Mon, 08 May 2023 06:56:05 +0200
> 
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
> > `js-mode` is the right value to use there, indeed.
> 
> Very good, thank you. In this case I would close the issue.

Thanks, done.