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Re: Finalizing 'inhibit-automatic-native-compilation'

From: Aymeric Agon-Rambosson
Subject: Re: Finalizing 'inhibit-automatic-native-compilation'
Date: Wed, 15 Feb 2023 23:39:19 +0100
User-agent: mu4e 1.6.10; emacs 28.1

Le mardi 14 février 2023 à 15:51, Eli Zaretskii <eliz@gnu.org> a écrit :

When will this be useful, and why the existing features don't already
support whatever use case you had in mind?

The use case we want to have supported is for instance when there is no writable home directory, like in the bug report Sean posted in the other branch of this conversation.

As people here pointed out just recently, if Emacs cannot write a .eln file, it will still work correctly by using the corresponding .elc

I could be wrong, but it does not seem to be the case for trampolines. In the current state of master, if no writable directory can be found for the output of the .eln file containing the trampoline, emacs errors out.

So why do we need a subtle feature of depositing *.eln files in
a temporary directory

The temporary directory ("/tmp/" on POSIX systems) can potentially be the only user-writable directory. So being able to write there as a last resort can guarantee that a trampoline compilation will not produce an error.

(which on many systems is ephemeral, or is
regularly purged)?

(In the case of POSIX systems at least, a program can still expect the content of /tmp to be preserved for the duration of its current invocation, according to https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch03s18.html). I admit I do not know the semantics of the equivalent for Windows.

By the very nature of temporary files and directories created by
Emacs, you cannot know their exact name, and so putting a file there would be almost completely useless. So I'm asking when will this be useful. I'd like to avoid adding features whose usability is not well understood and whose justification is not solid enough. We have too
many subtle knobs in native-compilation already.

The commit added by Andrea (ce4a066ed1e) on the inhibit-native-comp-cleanup branch implements the following behaviour : if no writable directory is found in either `native-comp-target-directory' or in the output of `comp-eln-load-path-eff', a filename in the directory `temporary-file-directory' is returned. This file is guaranteed to be creatable, which is what we wanted to ensure, and we know its exact name (you had a good point there). This is I guess equivalent to what I wanted to ensure with 'compile-but-no-output, so personnally I'm good. But what actually matters are the results of Sean's tests, of course.

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