Merge pull request #892 from swails/catch_chamber

Better error catch for using chamber prmtops

wrappers/python/simtk/openmm/app/internal/amber_file_parser.py

@@ -127,6 +127,10 @@ class PrmtopLoader(object):
                         tag, self._prmtopVersion = line.rstrip().split(None, 1)
                     elif line.startswith('%FLAG'):
                         tag, flag = line.rstrip().split(None, 1)
+                        if flag == 'CTITLE':
+                            raise TypeError('CHAMBER-style topology files are not supported here. '
+                                            'Consider using the CHARMM files directly with CharmmPsfFile '
+                                            'or ParmEd (where CHAMBER topologies are supported)')
                         self._flags.append(flag)
                         self._raw_data[flag] = []
                     elif line.startswith('%FORMAT'):

wrappers/python/tests/TestAmberPrmtopFile.py

@@ -316,7 +316,17 @@ class TestAmberPrmtopFile(unittest.TestCase):
         simulation.reporters.append(DCDReporter(fname, 1))  # This is an explicit test for the bugs in issue #850
         simulation.step(5)
         os.remove(fname)
-        
+
+    def testChamber(self):
+        """ Tests that Chamber prmtops fail with proper error message """
+        self.assertRaises(TypeError, lambda: AmberPrmtopFile('systems/ala3_solv.parm7'))
+        try:
+            parm = AmberPrmtopFile('systems/ala3_solv.parm7')
+            # Should not make it past here
+            self.assertTrue(False)
+        except TypeError as e:
+            # Make sure it says something about chamber
+            self.assertTrue('chamber' in str(e).lower())
 
 if __name__ == '__main__':
     unittest.main()