Bug#865427: devscripts: dcmd should exit non-zero on special failures like permission denied

[Ximin Luo]

Package: devscripts
Version: 2.17.6
Severity: normal

Dear Maintainer,

$ chmod -r dpkg_1.18.24.dsc 
$ dcmd --diff echo dpkg_1.18.24.dsc
/usr/bin/dcmd: 76: /usr/bin/dcmd: cannot open dpkg_1.18.24.dsc: Permission denied
dpkg_1.18.24.dsc
$ echo $?
0

By contrast, on a normal error it exits 1:

$ chmod +r dpkg_1.18.24.dsc 
$ dcmd --diff echo dpkg_1.18.24.dsc
$ echo $?
1

-- Package-specific info:

--- /etc/devscripts.conf ---

--- ~/.devscripts ---
export DEBSIGN_PROGRAM="gpg2"

-- System Information:
Debian Release: 9.0
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable-debug'), (500, 'testing-debug'), (500, 'buildd-unstable'), (300, 'unstable'), (100, 'experimental'), (1, 'experimental-debug')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.9.0-3-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_GB.utf8, LC_CTYPE=en_GB.utf8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages devscripts depends on:
ii  dpkg-dev              1.18.24
ii  libc6                 2.24-11
ii  libfile-homedir-perl  1.00-1
ii  perl                  5.24.1-3
ii  python3               3.5.3-1

Versions of packages devscripts recommends:
ii  apt                         1.4.6
ii  at                          3.1.20-3
ii  curl                        7.52.1-5
ii  dctrl-tools                 2.24-2+b1
ii  debian-keyring              2017.05.28
ii  dput                        0.12.1
ii  equivs                      2.0.9+nmu1
ii  fakeroot                    1.21-3.1
ii  file                        1:5.30-1
ii  gnupg                       2.1.18-6
ii  gnupg2                      2.1.18-6
ii  libdistro-info-perl         0.14
ii  libdpkg-perl                1.18.24
ii  libencode-locale-perl       1.05-1
ii  libgit-wrapper-perl         0.047-1
ii  liblist-compare-perl        0.53-1
ii  liblwp-protocol-https-perl  6.06-2
ii  libsoap-lite-perl           1.20-1
ii  liburi-perl                 1.71-1
ii  libwww-perl                 6.15-1
ii  licensecheck                3.0.29-1
ii  lintian                     2.5.50.4
ii  man-db                      2.7.6.1-2
ii  patch                       2.7.5-1+b2
ii  patchutils                  0.3.4-2
ii  python3-debian              0.1.30
ii  python3-magic               1:5.30-1
ii  sensible-utils              0.0.9
ii  strace                      4.15-2
ii  unzip                       6.0-21
ii  wdiff                       1.2.2-2
ii  wget                        1.18-5
ii  xz-utils                    5.2.2-1.2+b1

Versions of packages devscripts suggests:
ii  adequate                     0.15.1
ii  autopkgtest                  4.4
pn  bls-standalone               <none>
ii  bsd-mailx [mailx]            8.1.2-0.20160123cvs-4
ii  build-essential              12.3
pn  check-all-the-things         <none>
pn  cvs-buildpackage             <none>
pn  devscripts-el                <none>
ii  diffoscope                   78
ii  disorderfs                   0.5.1-1+b1
pn  dose-extra                   <none>
pn  duck                         <none>
ii  faketime                     0.9.6-7+b1
ii  gnuplot                      5.0.5+dfsg1-6
ii  gpgv                         2.1.18-6
ii  how-can-i-help               15
ii  libauthen-sasl-perl          2.1600-1
ii  libfile-desktopentry-perl    0.22-1
pn  libnet-smtps-perl            <none>
pn  libterm-size-perl            <none>
ii  libtimedate-perl             2.3000-2
ii  libyaml-syck-perl            1.29-1+b2
ii  mozilla-devscripts           0.47
ii  mutt                         1.7.2-1
ii  openssh-client [ssh-client]  1:7.4p1-10
ii  piuparts                     0.77
pn  ratt                         <none>
ii  reprotest                    0.6.2
pn  svn-buildpackage             <none>
pn  w3m                          <none>

-- no debconf information