GNU bug report logs - #76546
30.1; Native compilation is corrupting lambdas/closures stored in variables after some time

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Message #8 received at 76546 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Christian Johansson <christian <at> cvj.se>, Andrea Corallo <acorallo <at> gnu.org>
Cc: 76546 <at> debbugs.gnu.org
Subject: Re: bug#76546: 30.1;
 Native compilation is corrupting lambdas/closures stored in variables
 after some time
Date: Wed, 26 Feb 2025 14:43:30 +0200

> Date: Tue, 25 Feb 2025 11:27:58 +0100
> From: Christian Johansson <christian <at> cvj.se>
> 
> There is something fishy going on, but it is a very slippery bug, I have 
> trouble reproducing it but it started to happen when native compilation 
> was introduced and it has significantly gotten worse with Emacs 30, I 
> never happened before native-compilation was introduced.
> 
> Maybe you can give me some tips in building a reproducible test case? I 
> will try to explain what happens. So prior to Emacs 30 there was only 
> one bug I stumbled upon:
> 
> 1. When a lambda is stored in a variable in a lexical scoped file it 
> stores a closure. After some time when native compilation has done its 
> magic on the variable you will get an error when you try to output it 
> like this:
> (format "%S" my-native-compiled-variable) and Emacs crashes.
> 
> This happened every time my parser-generator library ran for a long time 
> and then tried to output a parser file. The only solution to this was to 
> not byte-compile the file that contained the lambdas that was later 
> supposed to be printed to a file, this solution worked but it was a 
> workaround due to this bug.
> 
> 
> 2. After Emacs 30 it seems to corrupt strings with escape sequences 
> inside lambdas inside variables, like this:
> 
> (setq my-lambda (lambda() (looking-at "<\\?=")))
> 
> After native-compilation has performed its magic on the variable the 
> function body will become corrupted and it will become a invalid 
> function body. This happens now to my major my phps-mode, I have 
> reproduced the error on two machines with Emacs 30 and it has never 
> occurred before Emacs 30 and there has been no recent changes to the 
> plugin. If I just eval the function files anew the problem disappears so 
> it only happens in compiled files. It however does not happen in 
> byte-compiled files, only in native compiled files.

Andrea, any comments or suggestions?

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