bug#75224: RNG validation unnecessarily marks buffer as changed

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 31 Dec 2024 14:31:27 +0200
> From: Vili Aapro <vili.aapro@iki.fi>
> 
> I found a bug in RNG Validation mode in the file `nxml/rng-valid.el' that unnecessarily marks buffer as changed.  The bug can be fixed with a simple application of `with-silent-modifications' in the function `rng-do-some-validation-1'.  I've attached a patch that does so.  However, in the long run, in my opinion the application of `with-silent-modifications' should be moved to `rng-clear-cached-state'; that is where it properly belongs.  Perhaps this has been left undone because of efficiency reasons; perhaps there is work to be done to make `with-silent-modifications' less expensive.
> 
> To reproduce, visit a big enough RNG-validatable XML file, such as the included `rdfxml.rng'; goto and end-tag, say on line 22; kill it; undo.
> 
> Undo runs `after-change-functions' and thus `rng-after-change-function' and thus `rng-do-some-validation-1', reproducing the bug.

Thanks, I installed this on the master branch, and I'm therefore
closing the bug.