Subject: bug#60974: 30.0.50; byte-compile-preprocess mutates self evaluating forms in expanded macro bodies

From: Vibhav Pant <[email-masked]>
Date: Thu, 02 Feb 2023 18:45:56 +0530

On Thu, 2023-02-02 at 13:39 +0100, Mattias Engdegård wrote:
> [ trimmed emacs-devel ]
> 
> 2 feb. 2023 kl. 13.35 skrev Vibhav Pant <[email-masked]>:
> 
> > Sure. Do we need to install this to the release branch? The bug
> > doesn't
> > really break anything AFAIK, so I dont think it's really a release
> > blocker.
> 
> In any case there should be a test. (Not implying that you needed to
> be reminded, of course.)
> 

I had thought of adding a test a while back, but I'm not sure how we'd
do it. The immutability of self evaluating literals is only enforced
for data in purespace. One potential way to achieve this would be a
test-case that depends on a macro defined in purespace, which expands
to a body that is not byte-compiled, but that doesn't sound like a
great approach.

Alternatively, we could define a macro, store its expanded form in a
variable and run it through `cconv-closure-convert`, checking
afterwards whether the original value changed or not. It feels a little
more reliable, but writing it might be a little tricky.

(Shameless plug for scratch/comp-static-data, which does enforce
immutability in natively compiled code, and has new tests that check
for exactly this).

-- 
Vibhav Pant
[email-masked]
GPG: 7ED1 D48C 513C A024 BE3A  785F E3FB 28CB 6AB5 9598