fix(remote): assert fetch respec is set

It turns out we can't deal do fetches if no refspec is set as git
will change the format of the fetch return values, providing less
information than usual.

A test was added to show that such a case will fail, and an assertion
will assure we don't attempt to fetch/pull if there is no refspec
for 'fetch'.

Closes #296

Author: Byron

Diff for: git/remote.py

@@ -604,6 +604,18 @@ def stdout_handler(line):
                 raise
         return output
 
+    def _assert_refspec(self):
+        """Turns out we can't deal with remotes if the refspec is missing"""
+        config = self.config_reader
+        try:
+            if config.get_value('fetch', default=type) is type:
+                msg = "Remote '%s' has no refspec set.\n"
+                msg += "You can set it as follows:"
+                msg += " 'git config --add \"remote.%s.fetch +refs/heads/*:refs/heads/*\"'." % self.name
+                raise AssertionError(msg)
+        finally:
+            config.release()
+
     def fetch(self, refspec=None, progress=None, **kwargs):
         """Fetch the latest changes for this remote
 
@@ -631,6 +643,7 @@ def fetch(self, refspec=None, progress=None, **kwargs):
         :note:
             As fetch does not provide progress information to non-ttys, we cannot make
             it available here unfortunately as in the 'push' method."""
+        self._assert_refspec()
         kwargs = add_progress(kwargs, self.repo.git, progress)
         if isinstance(refspec, list):
             args = refspec
@@ -651,6 +664,7 @@ def pull(self, refspec=None, progress=None, **kwargs):
         :param progress: see 'push' method
         :param kwargs: Additional arguments to be passed to git-pull
         :return: Please see 'fetch' method """
+        self._assert_refspec()
         kwargs = add_progress(kwargs, self.repo.git, progress)
         proc = self.repo.git.pull(self, refspec, with_extended_output=True, as_process=True, v=True, **kwargs)
         res = self._get_fetch_info_from_stderr(proc, progress or RemoteProgress())

Diff for: git/test/test_remote.py

@@ -494,6 +494,11 @@ def test_fetch_info(self):
         fetch_info_line_fmt = "c437ee5deb8d00cf02f03720693e4c802e99f390	not-for-merge	%s '0.3' of "
         fetch_info_line_fmt += "git://github.com/gitpython-developers/GitPython"
         remote_info_line_fmt = "* [new branch]      nomatter     -> %s"
+
+        self.failUnlessRaises(ValueError, FetchInfo._from_line, self.rorepo,
+                              remote_info_line_fmt % "refs/something/branch",
+                              "269c498e56feb93e408ed4558c8138d750de8893\t\t/Users/ben/test/foo\n")
+
         fi = FetchInfo._from_line(self.rorepo,
                                   remote_info_line_fmt % "local/master",
                                   fetch_info_line_fmt % 'remote-tracking branch')