tests/test-gendoc-el.t

copies-rust: pass closures and iterators instead of `&ChangedFiles`

… to some functions that only use one method.
This will makes it easier to unit-test them.

Differential Revision: https://phab.mercurial-scm.org/D10070

#require docutils gettext

  $ $TESTDIR/check-gendoc el
  checking for parse errors