Subject: Re: bug#79380: 31.0.50; Flymake does not check Elisp code anymore

From: Spencer Baugh <[email-masked]>
Date: Thu, 04 Sep 2025 12:34:43 -0400

Daniel Mendler <[email-masked]> writes:

> Thanks for taking a look at this problem!
>
> Spencer Baugh <[email-masked]> writes:
>> On Thu, Sep 4, 2025, 12:03 PM Eli Zaretskii <[email-masked]> wrote:
>>> > From: Spencer Baugh <[email-masked]>
>>> > Date: Thu, 4 Sep 2025 11:45:12 -0400
>>> > Cc: [email-masked], [email-masked]
>>> >
>>> >  Shouldn't the tests of the value of the user option use stringp
>>> >  instead of null?
>>> >
>>> > Is that the convention?  I always feel like it's better to test for null
>>> explicitly, so that if the user sets the
>>> > variable to a symbol or list or something they get an error which can
>>> help them track down their mistake.
>>>
>>> I don't think this is about conventions.  In this specific case, any
>>> value that is not a string will signal an error in
>>> elisp-flymake-byte-compile--executable, exactly like nil did in the
>>> patch that was installed.  So I think any value that is not a string
>>> should be handled as nil (in addition to the checking of strings that
>>> the code already does).
>>>
>>
>> Yes, my suggestion is that signaling an error is good because it shows that
>> the user's configuration is wrong.
>
> I agree that signaling an error would be good. As an alternative you
> could do it explicitly. Check against nil to use the defaults, check
> stringp for a user defined path and throw an explicit error in the other
> cases.

Right, even better.  Like this:

>From 7801088c56a2c06fd3cd598f64343598911b76da Mon Sep 17 00:00:00 2001
From: Spencer Baugh <[email-masked]>
Date: Thu, 4 Sep 2025 10:36:17 -0400
Subject: [PATCH] Fix null values of elisp-flymake-byte-compile-executable

* lisp/progmodes/elisp-mode.el
(elisp-flymake-byte-compile-executable): Improve defcustom type.
(elisp-flymake-byte-compile--executable): Properly check for
nil. (bug#79380)
---
 lisp/progmodes/elisp-mode.el | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/lisp/progmodes/elisp-mode.el b/lisp/progmodes/elisp-mode.el
index e8344852829..b660eb74c05 100644
--- a/lisp/progmodes/elisp-mode.el
+++ b/lisp/progmodes/elisp-mode.el
@@ -2292,7 +2292,7 @@ elisp-flymake-byte-compile-executable
 If nil, or if the file named by this does not exist, Flymake will
 use the same executable as the running Emacs, as specified by the
 variables `invocation-name' and `invocation-directory'."
-  :type 'file
+  :type '(choice (const :tag "Running Emacs executable" nil) file)
   :group 'lisp
   :version "31.1")
 
@@ -2301,13 +2301,16 @@ elisp-flymake-byte-compile--executable
   "Return absolute file name of the Emacs executable for flymake byte-compilation."
   (let ((filename
          (cond
-          ((file-name-absolute-p elisp-flymake-byte-compile-executable)
-           elisp-flymake-byte-compile-executable)
+          ((null elisp-flymake-byte-compile-executable) nil)
           ((stringp elisp-flymake-byte-compile-executable)
-           (when-let* ((pr (project-current)))
-             (file-name-concat (project-root pr)
-                               elisp-flymake-byte-compile-executable))))))
-    (if (file-executable-p filename)
+           (if (file-name-absolute-p elisp-flymake-byte-compile-executable)
+               elisp-flymake-byte-compile-executable
+             (when-let* ((pr (project-current)))
+               (file-name-concat (project-root pr)
+                                 elisp-flymake-byte-compile-executable))))
+          (t (error "Invalid `elisp-flymake-byte-compile-executable': %s"
+                    elisp-flymake-byte-compile-executable)))))
+    (if (and filename (file-executable-p filename))
         filename
       (when elisp-flymake-byte-compile-executable
         (message "No such `elisp-flymake-byte-compile-executable': %s"
-- 
2.43.7