Ensure free floating connections are cleared

CHANGES.rst

@@ -33,6 +33,10 @@ Release History
 
 **Fixed**
 
+- Fixed a bug where an exception within an ``ActionSelection`` block would
+  lead to every subsequent ``ActionSelection`` block to raise an exception.
+  (`#230 <https://github.com/nengo/nengo_spa/issues/230>`__,
+  `#231 <https://github.com/nengo/nengo_spa/pull/231>`__)
 - Nengo SPA is now compatible with pytest 4. Support for earlier versions has
   been dropped.
   (`#227 <https://github.com/nengo/nengo_spa/pull/227>`__)

nengo_spa/action_selection.py

@@ -92,6 +92,7 @@ def __exit__(self, exc_type, exc_value, traceback):
         ActionSelection.active = None
         ModuleInput.routed_mode = False
         if exc_type is not None:
+            RoutedConnection.free_floating.clear()
             return
         self._build()
 

nengo_spa/tests/test_action_selection.py

@@ -390,3 +390,18 @@ def test_action_selection_keys_corner_cases():
         with ActionSelection() as action_sel:
             spa.ifmax(0.)
     assert list(action_sel.keys()) == [0]
+
+
+def test_action_selection_is_side_effect_free_if_exception_is_raised():
+    with spa.Network():
+        state_a = spa.State(32)
+        state_b = spa.State(32)
+        state_c = spa.State(64)
+
+        with pytest.raises(SpaTypeError):
+            with ActionSelection():
+                spa.ifmax(1, state_a >> state_b, state_a >> state_c)
+
+        with ActionSelection():
+            pass
+            # should not raise