If cit is run with an unknown tool, print usage rather than throwing an exception

BUG=
TBR=hinoka

Review-Url: https://codereview.chromium.org/2181413004

cit.py

@@ -99,8 +99,28 @@ def get_available_tools():
   return (sorted(infra_tools), sorted(cipd_tools))
 
 
+def usage():
+  infra_tools, cipd_tools = get_available_tools()
+  print """usage: cit.py <name of tool> [args for tool]
+
+  Wrapper for maintaining and calling tools in:
+    "infra.git/run.py infra.tools.*"
+    "infra.git/cipd/*"
+
+  Available infra tools are:"""
+  for tool in infra_tools:
+    print '  * %s' % tool
+
+  print """
+  Available cipd tools are:"""
+  for tool in cipd_tools:
+    print '  * %s' % tool
+
+
 def run(args):
-  if args:
+  if not args:
+    return usage()
+
   tool_name = args[0]
   # Check to see if it is a infra tool first.
   infra_dir = os.path.join(
@@ -115,28 +135,14 @@ def run(args):
         'infra.tools.%s' % tool_name]
   elif os.path.isfile(cipd_file) and is_exe(cipd_file):
     cmd = [cipd_file]
+  else:
+    print >>sys.stderr, 'Unknown tool "%s"' % tool_name
+    return usage()
 
   # Add the remaining arguments.
   cmd.extend(args[1:])
   return subprocess.call(cmd)
 
-  infra_tools, cipd_tools = get_available_tools()
-  print """usage: cit.py <name of tool> [args for tool]
-
-  Wrapper for maintaining and calling tools in:
-    "infra.git/run.py infra.tools.*"
-    "infra.git/cipd/*"
-
-  Available infra tools are:"""
-  for tool in infra_tools:
-    print '  * %s' % tool
-
-  print """
-  Available cipd tools are:"""
-  for tool in cipd_tools:
-    print '  * %s' % tool
-
-
 
 def main():
   parser = argparse.ArgumentParser("Chrome Infrastructure CLI.")