Issue 1777 - ensure_dependencies.py fails to detect unknown Git revisions

ensure_dependencies.py

Index: ensure_dependencies.py
===================================================================
--- a/ensure_dependencies.py
+++ b/ensure_dependencies.py
@@ -84,18 +84,23 @@ class Git():
 
   def clone(self, source, target):
     source = source.rstrip("/")
     if not source.endswith(".git"):
       source += ".git"
     subprocess.check_call(["git", "clone", "--quiet", source, target])
 
   def get_revision_id(self, repo, rev="HEAD"):
-    command = ["git", "rev-parse", "--revs-only", rev]
-    return subprocess.check_output(command, cwd=repo).strip()
+    command = ["git", "rev-list", "--remotes=*", "--max-count=1", rev]

[Wladimir Palant, 2015/01/11 23:10:22]

Note that I don't really know how to use Git, and its command line interface is
quite a mess. So far that's the only command I found that will resolve tags into
revision IDs, keep existing revision IDs unchanged and complain about
non-existing ones.

[Wladimir Palant, 2015/01/11 23:39:28]

I noticed that the rev-list with --remotes specified will resolve HEAD
incorrectly (remote HEAD taken). On the other hand, without --remotes it will
refuse to work on fetched revisions above HEAD. It seems however that rev-parse
will produce the desired results if type is specified explicitly:
<rev>^{commit}. So I went with this solution now.

+    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, cwd=repo)
+
+    # Ignore stderr output and return code here: if revision lookup failed we
+    # should simply return an empty string.
+    result = process.communicate()[0]
+    return result.strip()
 
   def pull(self, repo):
     subprocess.check_call(["git", "fetch", "--quiet", "--all", "--tags"], cwd=repo)
 
   def update(self, repo, rev):
     subprocess.check_call(["git", "checkout", "--quiet", rev], cwd=repo)
 
   def ignore(self, target, repo):