Fix to ticket #2310: make loadConfig check for a configfile path in t…

…he .tac file if the default location doesn't exist

master/buildbot/config.py

@@ -117,6 +117,14 @@ def loadConfig(cls, basedir, filename):
                 "basedir '%s' does not exist" % (basedir,),
             ])
         filename = os.path.join(basedir, filename)
+        if not os.path.exists(filename):
+            # execute the .tac file to see if its configfile location exists
+            tacFile = os.path.join(basedir, 'buildbot.tac')
+            # don't mess with the global namespace
+            if os.path.exists(tacFile):
+                tacGlobals = {}
+                execfile(tacFile, tacGlobals)
+                filename = tacGlobals["configfile"]
         if not os.path.exists(filename):
             raise ConfigErrors([
                 "configuration file '%s' does not exist" % (filename,),
@@ -276,7 +284,7 @@ def copy_str_param(name, alt_key=None):
             error("codebaseGenerator must be a callable accepting a dict and returning a str")
         else:
             self.codebaseGenerator = codebaseGenerator
-            
+
         prioritizeBuilders = config_dict.get('prioritizeBuilders')
         if prioritizeBuilders is not None and not callable(prioritizeBuilders):
             error("prioritizeBuilders must be a callable")