Add checks for conduit filter order

- It's not allowed to have a reducer after a repeater -> taking the last of a repeated message is not useful
- It's not allowed to have a repeat filter after a pad filter -> it would repeat nil messages

Author: maarten-ic

ymmsl/v0_2/model.py

@@ -126,6 +126,21 @@ def __init__(
         self.__check_reference(self.sender)
         self.__check_reference(self.receiver)
 
+        # Check if filters are in the correct order:
+        err_msg = None
+        for i in range(len(self.filters) - 1):
+            pair = self.filters[i : i + 2]
+            if pair == [ConduitFilter.REPEAT, ConduitFilter.LAST]:
+                err_msg = "'repeat' filter must come after 'last'"
+                break
+            if pair == [ConduitFilter.PAD, ConduitFilter.LAST]:
+                err_msg = "'pad' filter must come after 'last'"
+                break
+            if pair == [ConduitFilter.PAD, ConduitFilter.REPEAT]:
+                err_msg = "'pad' filter must come after 'repeat'"
+        if err_msg is not None:
+            raise RuntimeError(f"Invalid conduit filter for {self}: {err_msg}.")
+
     def __str__(self) -> str:
         """Return a string representation of the object."""
         if not self.filters:

ymmsl/v0_2/tests/test_model.py

@@ -21,6 +21,21 @@ def test_conduit_filter() -> None:
     assert ConduitFilter.PAD.is_repeater()
 
 
+def test_conduit_order() -> None:
+    Conduit("a", "b", "last last")
+    Conduit("a", "b", "last pad")
+    Conduit("a", "b", "last repeat")
+    Conduit("a", "b", "repeat repeat")
+    Conduit("a", "b", "repeat pad")
+    Conduit("a", "b", "pad pad")
+    with pytest.raises(RuntimeError):
+        Conduit("a", "b", "repeat last")
+    with pytest.raises(RuntimeError):
+        Conduit("a", "b", "pad last")
+    with pytest.raises(RuntimeError):
+        Conduit("a", "b", "pad repeat")
+
+
 def test_conduit_access() -> None:
     conduit = Conduit("macro.out", "micro.in")