[R-pkg-team] Bug#1042406: dh-r: throws "Use of uninitialized value $dep_line in substitution" warnings with some packages

[Nilesh Patra]

Package: dh-r
Version: 20230722
Severity: important
Tags: patch

Dear Maintainer,

As discussed on matrix chan, it seems that during build of some R
packages, there's output such as this:

Use of uninitialized value $dep_line in substitution (s///) at /usr/share/perl5/Dpkg/Deps.pm line 300.
Use of uninitialized value $dep_line in substitution (s///) at /usr/share/perl5/Dpkg/Deps.pm line 302.
Use of uninitialized value $dep_line in substitution (s///) at /usr/share/perl5/Dpkg/Deps.pm line 303.
Use of uninitialized value $dep_line in split at /usr/share/perl5/Dpkg/Deps.pm line 306.

shown on the build log. As seen in https://salsa.debian.org/r-pkg-team/r-bioc-rtracklayer/-/jobs/4478926#L1890

On checking further, it seems to be stemming from the recommends line in
dh-r code[1]. This is because recommendsinput variable is being directly
set from desc->{Recommends}, and a check of whether this field is empty
is *after* the said initialization[3]. This can lead to `recommendsinput`
being set as `undef` and hence the unintialized errors from debhelper.

The reason that we don't see such problems in for instance
r-bioc-bsgenome is because it has some values in the testdepends and
recommendsinput ends up having some value[4].

I have attached a patch to fix this, please check.

** Please test properly before you merge and upload, do NOT upload
blindly **

PS: Please mention my contribution in d/ch if you take this patch.

[1]: https://salsa.debian.org/r-pkg-team/dh-r/-/blob/debian/20230722/dh/R.pm#L229
[2]: https://salsa.debian.org/r-pkg-team/dh-r/-/blob/debian/20230722/dh/R.pm#L201
[3]: https://salsa.debian.org/r-pkg-team/dh-r/-/blob/debian/20230722/dh/R.pm#L224
[4]: https://salsa.debian.org/r-pkg-team/dh-r/-/blob/debian/20230722/dh/R.pm#L221

-- System Information:
Debian Release: 12.0
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 6.1.0-9-amd64 (SMP w/8 CPU threads; PREEMPT)
Locale: LANG=en_IN, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to en_US.UTF-8), LANGUAGE=en_US.UTF-8
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages dh-r depends on:
ii  dctrl-tools              2.24-3+b1
ii  debhelper                13.11.4
ii  libfile-which-perl       1.27-2
pn  libswitch-perl           <none>
pn  libwww-curl-simple-perl  <none>
ii  r-base-dev               4.2.2.20221110-2

Versions of packages dh-r recommends:
ii  cme               1.038-1
ii  devscripts        2.23.3
ii  git-buildpackage  0.9.30

Versions of packages dh-r suggests:
pn  postgresql-client-common  <none>
-------------- next part --------------
>From 91285e0d6e725892d2b66f1f890850eb98ddc0bc Mon Sep 17 00:00:00 2001
From: Nilesh Patra <nilesh at nileshpatra.info>
Date: Thu, 27 Jul 2023 18:07:43 +0000
Subject: [PATCH] Fix Recommends properly

---
 dh/R.pm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/dh/R.pm b/dh/R.pm
index e7682ef..0b35e94 100644
--- a/dh/R.pm
+++ b/dh/R.pm
@@ -198,6 +198,7 @@ sub install {
     my %apthash;
     @apthash{@aptavail} = ();
 
+    if ( ! $desc->{Recommends} ) { $desc->{Recommends} = ""; }
     my $recommendsinput = $desc->{Recommends};
     # Add DEP8 test dependencies to Recommends to enable running test suite once the package is installed
     if ( $testdepends ) {
@@ -218,10 +219,11 @@ sub install {
        }
        $newsuggests =~ s/^, // ;
        $desc->{Suggests} = $newsuggests ;
+
        $recommendsinput = $recommendsinput . ', ' .  $testdepends ;
+       $recommendsinput =~ s/^, // ;
     }
     if ( ! $desc->{Depends} ) { $desc->{Depends} = ""; }
-    if ( ! $desc->{Recommends} ) { $desc->{Recommends} = ""; }
     if ( ! $desc->{Suggests} ) { $desc->{Suggests} = ""; }
     if ( ! $desc->{Imports} ) { $desc->{Imports} = ""; }
     if ( ! $desc->{LinkingTo} ) { $desc->{LinkingTo} = ""; }
-- 
2.40.1