dh_compress doesn't handle already compressed manpages with .so links

[Andreas Hasenack]

debhelper 11.1.6ubuntu1 from bionic

I'm preparing pmdk packages (upstream: https://github.com/pmem/pmdk) in my git repo (https://code.launchpad.net/~ahasenack/ubuntu/+source/pmdk/+git/pmdk/+ref/rename-pmdk-1.4) and noticed that dh_compress is adding another .gz suffix to manpages that are already compressed if they have just ".so" macros inside pointing elsewhere.

Attached is a full build log with DH_VERBOSE set.

Here is the gist of it: https://pastebin.ubuntu.com/p/TmyKycSkGK/

rm -f debian/libpmemlog-dev/usr/share/man/man3/pmemlog_open.3.gz debian/libpmemlog-dev/usr/share/man/man3/pmemlog_open.3.gz.gz
ln -s pmemlog_create.3.gz debian/libpmemlog-dev/usr/share/man/man3/pmemlog_open.3.gz.gz

Upstream already produces compressed manpages. Using pmemlog_open as an example again:
(rename-pmdk-1.4)ubuntu@bionic-pmdk:~/pmdk/pmdk-git$ rm -rf /tmp/pmdk
(rename-pmdk-1.4)ubuntu@bionic-pmdk:~/pmdk/pmdk-git$ mkdir /tmp/pmdk
(rename-pmdk-1.4)ubuntu@bionic-pmdk:~/pmdk/pmdk-git$ make DESTDIR=/tmp/pmdk install
(...)

(rename-pmdk-1.4)ubuntu@bionic-pmdk:~/pmdk/pmdk-git$ find /tmp/pmdk/ -name pmemlog_open.3* -ls -o -name pmemlog_create.3* -ls
   115952 1 -rw-r--r-- 1 ubuntu ubuntu 56 Apr 20 21:09 /tmp/pmdk/usr/local/share/man/man3/pmemlog_open.3.gz
   115890 5 -rw-r--r-- 1 ubuntu ubuntu 2931 Apr 20 21:09 /tmp/pmdk/usr/local/share/man/man3/pmemlog_create.3.gz
(rename-pmdk-1.4)ubuntu@bionic-pmdk:~/pmdk/pmdk-git$ zcat /tmp/pmdk/usr/local/share/man/man3/pmemlog_open.3.gz
.so pmemlog_create.3
(rename-pmdk-1.4)ubuntu@bionic-pmdk:~/pmdk/pmdk-git$

The double gzipped symlinks end up in the debs like this:
ubuntu@bionic-pmdk:~/pmdk$ for n in lib*.deb; do dpkg --contents $n|grep -E '\.gz\.gz'; done
lrwxrwxrwx root/root 0 2018-04-17 20:57 ./usr/share/man/man3/pmem_check_version.3.gz.gz -> ../man7/libpmem.7.gz
lrwxrwxrwx root/root 0 2018-04-17 20:57 ./usr/share/man/man3/pmem_deep_drain.3.gz.gz -> pmem_flush.3.gz
lrwxrwxrwx root/root 0 2018-04-17 20:57 ./usr/share/man/man3/pmem_deep_flush.3.gz.gz -> pmem_flush.3.gz
lrwxrwxrwx root/root 0 2018-04-17 20:57 ./usr/share/man/man3/pmem_deep_persist.3.gz.gz -> pmem_flush.3.gz
lrwxrwxrwx root/root 0 2018-04-17 20:57 ./usr/share/man/man3/pmem_drain.3.gz.gz -> pmem_flush.3.gz
lrwxrwxrwx root/root 0 2018-04-17 20:57 ./usr/share/man/man3/pmem_errormsg.3.gz.gz -> ../man7/libpmem.7.gz
(...)

[Launchpad Janitor (janitor)]

This bug was fixed in the package debhelper - 11.3.2ubuntu1

---------------
debhelper (11.3.2ubuntu1) cosmic; urgency=medium

  * Merge from Debian testing. Remaining changes:
    - Generate ddebs from debhelper instead of pkg-create-dbgsym
      + Make debhelper Conflict/Replace pkg-create-dbgsym to force it off.
      + Set DBGSYM_PACKAGE_TYPE to ddeb to get correct debian/files output.
    - dh_installchangelogs: Do not install upstream changelog in compat
      level 7 and higher to avoid pointlessly bloating installed packages.

debhelper (11.3.2) unstable; urgency=medium

  * dh_installchangelogs: Fix a second regression that made
    dh_installchangelogs ignore upstream changelogs in the
    source directories. Thanks to gregor herrmann for
    reporting the imcomplete fix. (Closes: #899248)

debhelper (11.3.1) unstable; urgency=medium

  * dh_installchangelogs: Fix logic error that made
    dh_installchangelogs incorrectly ignore explicitly passed
    changelogs. Thanks to Sven Joachim and Rene Engelhard
    for reporting the bug. (Closes: #899248)

debhelper (11.3) unstable; urgency=medium

  [ Niels Thykier ]
  * Buildsystem.pm: Fix use of undefined variable in certain
    error conditions.
  * dh_makeshlibs: Support -VUpstream-Version and -VNone as
    alternative to passing -V or omitting -V respectively.
  * dh_makeshlibs: Make -VUpstream-Version the default in
    compat 12 when -V is omitted. (Closes: #896464)
  * dh_makeshlibs: Correct handling of an explicit -V when
    a source builds multiple library packages and provides
    explicit shlibs files for a subset of them. Previously,
    the -V option could have been ignored for some of the
    packages containing libraries.
  * Dh_Lib.pm: Fall back to a regular mv(1) when rename fails
    with EXDEV (cross mount point moves). This restores
    debhelper's ability to move files between mount points,
    which can happen in dh_builddeb has to correct the
    extension of a binary package built by dpkg-deb.
    Thanks to Evan Krall for the report. (Closes: #897569)
  * dh_missing.1: Consistently mention that dh_missing
    defaults to --list-missing in compat 12. Thanks to
    Robie Basak for spotting the contradicting documentation.
    (Closes: #898161)
  * dh_compress: Avoid adding a duplicate ".gz" extension on
    a symlink if it already has it. This can happen e.g. with
    dh_installman recompresses a manpage that was compressed and
    had a valid symlink to it. Thanks to Andreas Hasenack for
    reporting the bug. (Closes: LP: #1765851)
  * debian/control: Depend on dwz for dh_dwz.
  * dh_dwz: Generate a per-package multifile by default. This
    feature can be disabled by --no-dwz-multifile.
  * dh: Run dh_dwz by default in compat 12.
  * dh_dwz: Remove warning about the dwz feature being experimental.
  * dwz.pm: Ditto.
  * dh_installsystemd: Use the basename of the "tmpfiles" config
    files. This makes "systemd-tmpfiles --create" search for it
    in both /usr/lib/tmpfiles.d and in /etc/tmpfiles.d. With
    this change the system administrator can now override the
    "tmpfiles" config shipped by the package in
    /usr/libtmpfiles.d. Thanks to ...