GNU bug report logs - #79124
emacs -Q doesn't give me a clean slate

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: rpluim <at> gmail.com, 79124 <at> debbugs.gnu.org, rms <at> gnu.org
Subject: bug#79124: emacs -Q doesn't give me a clean slate
Date: Sat, 2 Aug 2025 11:53:19 -0700

On 2025-07-31 22:54, Eli Zaretskii wrote:
> I explained why -nw matters: Emacs needs to load lisp/term/xterm.el
> (or some other terminal-specific library).  Since those libraries are
> not preloaded, Emacs looks up their *.eln files, and if it doesn't
> find them, it will load xterm.elc and attempt to natively-compile
> xterm.el into xterm.eln, putting xterm.eln in ~/.emacs.d/eln-cache's
> subdirectory (and then load it).  That's what JIT compilation is
> about.

That's all fine, but the main point is that, -nw or not, everything 
works for me despite there being no eln cache. Nothing goes wrong. Emacs 
works fine other than spurious diagnostics that a new flag would 
suppress. So I'm still puzzled as to why the eln cache is essential for 
Emacs to operate.

Even if something (but what?) goes wrong for interactive use, my main 
use case is -batch (for testing) where terminal-specific libraries 
largely don't matter.

> if you modify native-comp-eln-load-path to
> replace the first element by some temporary writable directory.  This
> should be done very early

That's doable and fairly simple, though I'm still puzzled as to why it's 
needed.

Alternatively, Emacs could be taught to not trust any existing files in 
the eln cache. That should be a simple change. Emacs probably has a 
"don't trust" mode already for files generated by older versions, and 
the mode just needs to be enabled for reproducible testing.

> I don't know what could be in ~/.terminfo, so I don't understand the
> implications of that.

I know what could be in ~/.terminfo, and it's definitely not important 
for reproducible testing. It's worse than not important: it's 
counterproductive.

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