Use git ls-tree to autodetect build system

The cost of one git ls-tree call is roughly the same as one
git cat-file call. Therefore, when autodetecting the build system,
it is much faster to list the tree once and then search for the
required files than to call git cat-file for every possible one.

1 files changed, 4 insertions, 15 deletions

diff --git a/morphlib/morphologyfactory.py b/morphlib/morphologyfactory.py
index 89288b33..c03d541e 100644
--- a/morphlib/morphologyfactory.py
+++ b/morphlib/morphologyfactory.py
@@ -72,26 +72,15 @@ class MorphologyFactory(object):
             raise NotcachedError(reponame)
 
     def _autodetect_text(self, reponame, sha1, filename):
-        # TODO get lists of files from the cache to reduce round trips
         if self._lrc.has_repo(reponame):
             repo = self._lrc.get_repo(reponame)
-
-            def has_file(filename):
-                try:
-                    repo.cat(sha1, filename)
-                    return True
-                except IOError:
-                    return False
+            file_list = repo.ls_tree(sha1)
         elif self._rrc is not None:
-            def has_file(filename):
-                try:
-                    text = self._rrc.cat_file(reponame, sha1, filename)
-                    return True
-                except morphlib.remoterepocache.CatFileError:
-                    return False
+            file_list = self._rrc.ls_tree(reponame, sha1)
         else:
             raise NotcachedError(reponame)
-        bs = morphlib.buildsystem.detect_build_system(has_file)
+
+        bs = morphlib.buildsystem.detect_build_system(file_list)
         if bs is None:
             raise AutodetectError(reponame, sha1)
         # TODO consider changing how morphs are located to be by morph