help: if groff is not found, try mandoc

This will allow 'help' to work on BSDs, Illumos and Linux
distributions using the mandoc formatter.

awscli/help.py

@@ -106,9 +106,12 @@ class PosixHelpRenderer(PagingHelpRenderer):
 
  def _convert_doc_content(self, contents):
  man_contents = publish_string(contents, writer=manpage.Writer())
- if not self._exists_on_path('groff'):
- raise ExecutableNotFoundError('groff')
- cmdline = ['groff', '-m', 'man', '-T', 'ascii']
+ if self._exists_on_path('groff'):
+ cmdline = ['groff', '-m', 'man', '-T', 'ascii']
+ elif self._exists_on_path('mandoc'):
+ cmdline = ['mandoc', '-T', 'ascii']
+ else:
+ raise ExecutableNotFoundError('groff or mandoc')
  LOG.debug("Running command: %s", cmdline)
  p3 = self._popen(cmdline, stdin=PIPE, stdout=PIPE, stderr=PIPE)
  groff_output = p3.communicate(input=man_contents)[0]

tests/unit/test_help.py

@@ -99,8 +99,8 @@ def test_pager_with_args(self):
  def test_no_groff_exists(self):
  renderer = FakePosixHelpRenderer()
  renderer.exists_on_path['groff'] = False
- expected_error = 'Could not find executable named "groff"'
- with self.assertRaisesRegex(ExecutableNotFoundError, expected_error):
+ expected_error = 'Could not find executable named "groff or mandoc"'
+ with self.assertRaisesRegexp(ExecutableNotFoundError, expected_error):
  renderer.render('foo')
 
  @skip_if_windows('Requires POSIX system.')