bug#61014: 29.0.60; flymake-mode stderr warning is confusing when edit the init.el or eary-init.el

["João Távora" <joaotavora@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> 1. create a new .emacs.d folder in the HOME directory
>> 2. create an empty init.e and eary-init.el file in the .emacs.d folder
>> 3. Start Emacs and C-x, C-f open the init.el or early.el
>> 4. M-x flymake-mode, add some blank lines in the init.el or early.el
>> 5. C-x b, Switch to buffer:  *stderr of elisp-flymake-byte-compile*
>> Now you will see the warnings.
>
> João, any comments?  The warning comes from startup.el, but it is
> triggered by what Flymake does, AFAICT.

Sorry for taking so long.

Yes, I have comments.

First of all, let's make it clear that this warning happens in a hidden
Flymake buffer, an implementation detail which stores the stderr output
of the subprocess(es) invoked.  It does not appear in the interactive
seeion's *Warnings* buffer.  Unless I've missed something, the user is
never confronted with it or hindered by it in any way.  It seems to be
largely benign.

The warning only become visible when switching to a specific hidden
buffer, like Eason did, and that operation is more accurately described
as an introspection feature intended for developers, not for users.

So, to summarize, the warning is coming from the subprocess
non-interactive Emacs spawned by the interactive Emacs where
flymake-mode is turned on.  In the interactive Emacs session, nothing
special is going on.

The reason elisp-flymake-byte-compile-load-path has a default value of
"./" is to help with the primary use case for the
elisp-flymake-byte-compile Flymake backend: developing libraries that
`require` other .el libraries.  Such .el files often live in the same
directory of the file/buffer you are editing with flymake-mode turned
on.  So when you're editing x/y/z/foo.el and you type

  (require 'foo-utils)

elisp-flymake-byte-compile will understand that to syntax-check foo.el
with the byte-compiler it needs to load "x/u/z/foo-utils.el".

In Eason's case, the user happens to be editing a .el file in a special
Emacs directory where such a use case is unlikely (though not
impossible).  So every few changes the user does to the buffer,
flymake-mdoe will invoke a Emacs subprocess and give it this particular
load-path initialization, that, in the specific acse of ~/.emacs.d, is
slightly non-orthodox.  And thus the subprocess emacs complains with
this warning which is recorded in the special hidden buffer.

If we're really worries about this, we could special-case this directory
elisp-mode.el.  But I also don't see what the harm could be.  So my
advice is to only do this when someone describes real harm.

João