[DRE-maint] Bug#903191: ruby-slack-notifier: FTBFS in buster/sid (dh_installdocs: Cannot find "readme.md")

[Santiago Vila]

Package: src:ruby-slack-notifier
Version: 1.5.1-1
Severity: serious
Tags: ftbfs

Dear maintainer:

I tried to build this package in buster but it failed:

--------------------------------------------------------------------------------
[...]
 debian/rules build-indep
dh build-indep --buildsystem=ruby --with ruby
   dh_update_autotools_config -i -O--buildsystem=ruby
   dh_auto_configure -i -O--buildsystem=ruby
	dh_ruby --configure
   dh_auto_build -i -O--buildsystem=ruby
	dh_ruby --build
   dh_ruby --build
   dh_auto_test -i -O--buildsystem=ruby
	dh_ruby --test
 fakeroot debian/rules binary-indep
dh binary-indep --buildsystem=ruby --with ruby
   dh_testroot -i -O--buildsystem=ruby
   dh_prep -i -O--buildsystem=ruby

[... snipped ...]

    handles mailto links in html
    when on ruby 2.1+ or have string-scrub installed
      handles invalid unicode sequences
      replaces invalid unicode sequences with the unicode replacement character

Slack::Notifier
  #initialize
    sets the given hook_url to the endpoint URI
    sets the default_payload options
    sets a custom http client
  #ping
    passes the message through LinkFormatter
    passes attachment messages through LinkFormatter
    allows sending only an attachment
    passes attachment messages through LinkFormatter, even if a single value is passed
    with a default channel set
      does not require a channel to ping
      uses default channel
      allows override channel to be set
    with default webhook
      posts with the correct endpoint & data
    with a custom http_client set
      uses it
  #channel=
    sets the given channel
  #username=
    sets the given username
  #escape
    escapes sequences of < > &, but not quotes

Finished in 0.02184 seconds (files took 0.10127 seconds to load)
29 examples, 0 failures


┌──────────────────────────────────────────────────────────────────────────────┐
│ dh_ruby --install finished                                                   │
└──────────────────────────────────────────────────────────────────────────────┘

   debian/rules override_dh_install
make[1]: Entering directory '/<<PKGBUILDDIR>>'
dh_install
rm -rf debian/ruby-slack-notifier/usr/bin
make[1]: Leaving directory '/<<PKGBUILDDIR>>'
   dh_installdocs -i -O--buildsystem=ruby
dh_installdocs: Cannot find (any matches for) "readme.md" (tried in .)

debian/rules:3: recipe for target 'binary-indep' failed
make: *** [binary-indep] Error 2
dpkg-buildpackage: error: fakeroot debian/rules binary-indep subprocess returned exit status 2
--------------------------------------------------------------------------------

The build was made with "dpkg-buildpackage -A" in my autobuilder
but it also fails in reproducible builds:

https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/ruby-slack-notifier.html

[ Note: There has been a recent change in debhelper behaviour, the current
  behaviour is the intended one. See Bug #903133 for details ].

Thanks.