When I use "C" (View a package's changelog) on clang-15 from the
aptitude TUI, I get a warning that is immediately erased, so that
it is impossible to read it.

I suppose that aptitude should redirect stderr from
aptitude-changelog-parser so that it can display its contents
(when non empty) in a clear way.

Enabling the terminal's logs allows me to get the text of this
warning:

aptitude-changelog-parser: warning: /tmp/aptitude-root.7707:EXkCUB/aptitude-download-4-bORTciGPJi,..uo2EeQnZD7WBcD+L6_aptitude-download-cbF3RCIRNjR7d%D7+V.DiRimX__YaCHL(l105): found start of entry where expected more change data or trailer

This text seems to come from /usr/share/perl5/Dpkg/Changelog/Debian.pm:

            unless ($expect eq FIRST_HEADING || $expect eq NEXT_OR_EOF) {
                $self->parse_error($file, $.,
                    sprintf(g_('found start of entry where expected %s'),
                    $expect), "$_");
            }

About this unexpected warning, there may be some other bug.
But note that "apt changelog clang-15" is fine.

It should prevent these errors from showing up in the first place.
See #967911, which has been tagged "pending" almost three years ago. :-(

Yes, the clang-15 changelog entry for version 1:15.0.7-2 is not properly
terminated.

Cheers,
       Sven

If aptitude knows what to do (or may ignore the issue), yes.

I forgot about this one.

OK, I've just reported a bug for this:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1042997

I was a bit imprecise, actually I meant that aptitude-changelog-parser
should not emit these warnings to stderr, which is what #967911 is about.

Since the screen flashes created by aptitude-changelog-parser's warnings
have been annoying me for so long, I have now created a merge request to
cherry-pick the fix for unstable:

https://salsa.debian.org/apt-team/aptitude/-/merge_requests/20

Cheers,
       Sven

[...]

First, I don't understand

  But we cannot currently change that verbose default when using
  changelog_parse() from Dpkg::Changelog::Parse.

in the patch. The following works as expected:

--- a/aptitude-changelog-parser	2022-08-06 05:45:53.000000000 +0200
+++ b/aptitude-changelog-parser	2023-08-05 10:55:39.291911672 +0200
@@ -15,6 +15,7 @@
 # Usage: aptitude-changelog-parser [<filename> [<from-version>]]

 my %opts;
+$opts{verbose} = 0;
 if (scalar @ARGV >= 1) {
     $opts{file} = shift @ARGV;
 }

This silences warnings from

sub parse_error {
    my ($self, $file, $line_nr, $error, $line) = @_;

    push @{$self->{parse_errors}}, [ $file, $line_nr, $error, $line ];

    if ($self->{verbose}) {
        if ($line) {
            warning("%20s(l$line_nr): $error\nLINE: $line", $file);
        } else {
            warning("%20s(l$line_nr): $error", $file);
        }
    }
}

in /usr/share/perl5/Dpkg/Changelog.pm.

Now, silenting such warnings for changelog_parse() will fix issues
like this one, but it will not fix the general problem with warnings
and errors.

For instance, aptitude-changelog-parser has

eval {
    require Dpkg::Changelog::Parse;
    Dpkg::Changelog::Parse->import();
    1;
} or do {
    warn "warning: Dpkg::Changelog::Parse not present, install libdpkg-perl\n";
    exit 0;
};

at the beginning, and this warning, which is important and must still
be output, will still quickly disappear. BTW, the "exit 0;" is also
incorrect, but that's another issue (bug 1043050, which I've just
reported).

And concerning errors, /usr/share/perl5/Dpkg/Changelog/Parse.pm has

    error(g_('changelog format %s is unknown: %s'), $format, $@) if $@;
    error(g_('changelog format %s is not a Dpkg::Changelog class'), $format)
        unless $changes->isa('Dpkg::Changelog');

and

        error(g_('unknown output format %s'), $options{format});

In /usr/share/perl5/Dpkg/ErrorHandling.pm, this corresponds to

sub error($;@)
{
    die report(REPORT_ERROR, @_);
}

This will not be silenced by "$SIG{__WARN__} = sub {};" like in your
patch. I don't think these fatal errors should be silenced at all,
but currently, they will also quickly disappear.

Ah yes, Guillem implemented the "verbose" option three years ago in
reaction to #967911.  And it could not be used back then because the
dpkg version offering it was only uploaded several months later, but now
it certainly can be used. :-)

Would you like to submit a merge request on salsa for the master branch?

Cheers,
       Sven

https://salsa.debian.org/apt-team/aptitude/-/merge_requests/21

Thanks, I have updated
https://salsa.debian.org/apt-team/aptitude/-/merge_requests/20
accordingly.

Cheers,
       Sven