Ensure no variable intent conflict when building a model (#57)

* ensure no variable intent conflict when building a model

* fix missing import

* update what's new

doc/whats_new.rst

@@ -6,6 +6,13 @@ Release Notes
 v0.3.0 (Unreleased)
 -------------------
 
+Enhancements
+~~~~~~~~~~~~
+
+- Ensure that there is no ``intent`` conflict between the variables
+  declared in a model. This check is explicit at Model creation and a
+  more meaningful error message is shown when it fails (:issue:`57`).
+
 
 v0.2.1 (7 November 2018)
 ------------------------

xsimlab/model.py

@@ -145,6 +145,34 @@ def set_process_keys(self):
                 if od_key is not None:
                     p_obj.__xsimlab_od_keys__[var.name] = od_key
 
+    def ensure_no_intent_conflict(self):
+        """Raise an error if more than one variable with
+        intent='out' targets the same variable.
+
+        """
+        filter_out = lambda var: (
+            var.metadata['intent'] == VarIntent.OUT and
+            var.metadata['var_type'] != VarType.ON_DEMAND
+        )
+
+        targets = defaultdict(list)
+
+        for p_name, p_obj in self._processes_obj.items():
+            for var in filter_variables(p_obj, func=filter_out).values():
+                target_key = p_obj.__xsimlab_store_keys__.get(var.name)
+                targets[target_key].append((p_name, var.name))
+
+        conflicts = {k: v for k, v in targets.items() if len(v) > 1}
+
+        if conflicts:
+            conflicts_str = {k: ' and '.join(["'{}.{}'".format(*i) for i in v])
+                             for k, v in conflicts.items()}
+            msg = '\n'.join(["'{}.{}' set by: {}".format(*k, v)
+                             for k, v in conflicts_str.items()])
+
+            raise ValueError(
+                "Conflict(s) found in given variable intents:\n" + msg)
+
     def get_all_variables(self):
         """Get all variables in the model as a list of
         ``(process_name, var_name)`` tuples.
@@ -364,6 +392,8 @@ def __init__(self, processes):
         self._all_vars = builder.get_all_variables()
         self._all_vars_dict = None
 
+        builder.ensure_no_intent_conflict()
+
         self._input_vars = builder.get_input_variables()
         self._input_vars_dict = None
 

xsimlab/tests/test_model.py

@@ -1,7 +1,7 @@
 import pytest
 
 import xsimlab as xs
-from xsimlab.tests.fixture_model import AddOnDemand, InitProfile
+from xsimlab.tests.fixture_model import AddOnDemand, InitProfile, Profile
 
 
 class TestModelBuilder(object):
@@ -52,6 +52,15 @@ def test_get_all_variables(self, model):
         assert all([p_name in model for p_name, _ in model.all_vars])
         assert ('profile', 'u') in model.all_vars
 
+    def test_ensure_no_intent_conflict(self, model):
+        @xs.process
+        class Foo(object):
+            u = xs.foreign(Profile, 'u', intent='out')
+
+        with pytest.raises(ValueError) as excinfo:
+            invalid_model = model.update_processes({'foo': Foo})
+        assert "Conflict(s)" in str(excinfo.value)
+
     def test_get_input_variables(self, model):
         expected = {('init_profile', 'n_points'),
                     ('roll', 'shift'),