erepo: set up more logging (#3403)

dvc/external_repo.py

@@ -208,6 +208,7 @@ def _cached_clone(url, rev, for_write=False):
 
     # Copy to a new dir to keep the clone clean
     repo_path = tempfile.mkdtemp("dvc-erepo")
+    logger.debug("erepo: making a copy of {} clone", url)
     copy_tree(clone_path, repo_path)
 
     # Check out the specified revision
@@ -233,8 +234,10 @@ def _clone_default_branch(url, rev):
             git = Git(clone_path)
             # Do not pull for known shas, branches and tags might move
             if not Git.is_sha(rev) or not git.has_rev(rev):
+                logger.debug("erepo: git pull {}", url)
                 git.pull()
         else:
+            logger.debug("erepo: git clone {} to a temporary dir", url)
             clone_path = tempfile.mkdtemp("dvc-clone")
             git = Git.clone(url, clone_path)
             CLONES[url] = clone_path
@@ -246,6 +249,7 @@ def _clone_default_branch(url, rev):
 
 
 def _git_checkout(repo_path, rev):
+    logger.debug("erepo: git checkout {}@{}", repo_path, rev)
     git = Git(repo_path)
     try:
         git.checkout(rev)