# HG changeset patch
# User Pierre-Yves David <pierre-yves.david@octobus.net>
# Date 1555420216 -7200
# Node ID b970fece153dd118593542f306adff386c08295a
# Parent  f0203c3406e7729338d504fe144da90a61ad3b56
compression: only declare revlog support for available engine

Even if we know that an engine support revlog compression, the Mercurial process
still won't support it if the compression engine is not available.

diff -r f0203c3406e7 -r b970fece153d mercurial/localrepo.py
--- a/mercurial/localrepo.py	Mon Apr 15 19:21:41 2019 +0300
+++ b/mercurial/localrepo.py	Tue Apr 16 15:10:16 2019 +0200
@@ -643,7 +643,7 @@
     # Add derived requirements from registered compression engines.
     for name in util.compengines:
         engine = util.compengines[name]
-        if engine.revlogheader():
+        if engine.available() and engine.revlogheader():
             supported.add(b'exp-compression-%s' % name)
 
     return supported