Bug#970234: consider dropping "No hard links in source packages"

[Guillem Jover]

Hi!

On Thu, 2022-09-22 at 19:20:00 -0700, Russ Allbery wrote:
> Russ Allbery <r...@debian.org> writes:
> > The fact that this has gone unnoticed in a source package in an existing
> > release makes a pretty strong argument that nothing in Debian cares and
> > we should just remove the constraint.
> 
> Here is a patch dropping the restriction on hard links in source packages
> that I think is ready for seconds.  I'm copying Guillem for his review, in
> case there's some dpkg concern.

I'm not really sure what the footnote really refers to, TBH, as I'm
not aware of any such check, or what would require a fair amount of
work. Besides the other potential issues mentioned on the bug, which
I agree we might not care much about, a case that comes to mind would
be that patching hard linked source files can end up being very
confusing, and might not really break the build but can end up not
producing what one might expect. I've quickly prepared the attached
tentative and completely untested patch, to add a warning in that case,
which I guess I might be targeting for dpkg 1.22.1 (once I've added
some tests).

But given that hard links in source packages do not seem prevalent
at all, and that the tooling or linters can be improved in that
direction I suppose it might make sense to lift this specific
restriction.

> >From 12b014c4b930577a728dfb1254b64aac6a5eb1e0 Mon Sep 17 00:00:00 2001
> From: Russ Allbery <r...@debian.org>
> Date: Thu, 22 Sep 2022 19:15:52 -0700
> Subject: [PATCH] Allow hard links in source packages
> 
> It's not clear why this restriction was in place, and Debian
> included a package containing hard links without anyone noticing
> in the last release.
> ---
>  policy/ch-source.rst | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/policy/ch-source.rst b/policy/ch-source.rst
> index c7415fc..a7df539 100644
> --- a/policy/ch-source.rst
> +++ b/policy/ch-source.rst
> @@ -282,8 +282,8 @@ source files in a package, as far as is reasonably 
> possible.  [#]_
>  Restrictions on objects in source packages
>  ------------------------------------------
>  
> -The source package must not contain any hard links,  [#]_ device special
> -files, sockets or setuid or setgid files.. [#]_
> +The source package must not contain device special files, sockets, or
> +setuid or setgid files. [#]_
>  
>  .. _s-debianrules:
>  
> @@ -918,13 +918,6 @@ must not exist a file ``debian/patches/foo.series`` for 
> any ``foo``.
>     would be nice if the modification time of the upstream source would
>     be preserved.
>  
> -.. [#]
> -   This is not currently detected when building source packages, but
> -   only when extracting them.
> -
> -   Hard links may be permitted at some point in the future, but would
> -   require a fair amount of work.
> -
>  .. [#]
>     Setgid directories are allowed.

Seconded.

Thanks,
Guillem

diff --git i/scripts/Dpkg/Source/Patch.pm w/scripts/Dpkg/Source/Patch.pm
index 0da35b9e5..99020885b 100644
--- i/scripts/Dpkg/Source/Patch.pm
+++ w/scripts/Dpkg/Source/Patch.pm
@@ -513,6 +513,11 @@ sub analyze {
 	    error(g_("diff '%s' patches something which is not a plain file"),
 	          $diff);
 	}
+        my $nlink = (stat _)[3];
+        if ($nlink > 1) {
+            warning(g_("diff '%s' patches hard link %s which can have " .
+                       "unintended consequences"), $diff, $fn);
+        }
 
 	if ($filepatched{$fn}) {
             $filepatched{$fn}++;

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