More helpful record_full_arg errors

msprime/ancestry.py

@@ -901,6 +901,16 @@ def _parse_sim_ancestry(
     is_dtwf = isinstance(models[0], DiscreteTimeWrightFisher)
     is_pedigree = any(isinstance(model, FixedPedigree) for model in models)
 
+    if record_full_arg:
+        if is_dtwf:
+            raise ValueError(
+                "Full ARG recording not supported in DiscreteTimeWrightFisher simulation"
+            )
+        if is_pedigree:
+            raise ValueError(
+                "Full ARG recording not supported in FixedPedigree simulation"
+            )
+
     if is_pedigree:
         if demography is not None:
             raise ValueError("Cannot specify demography for FixedPedigree simulation")
@@ -919,10 +929,6 @@ def _parse_sim_ancestry(
             raise ValueError(
                 "Gene conversion not supported in FixedPedigree simulation"
             )
-        if record_full_arg:
-            raise ValueError(
-                "Full ARG recording not supported in FixedPedigree simulation"
-            )
         if record_migrations:
             raise ValueError(
                 "Migration recording not supported in FixedPedigree simulation"

tests/test_models.py

@@ -559,6 +559,20 @@ class TestUnsupportedFullArg:
     """
 
     def test_dtwf(self):
+        for model in [msprime.DiscreteTimeWrightFisher()]:
+            with pytest.raises(
+                ValueError, match="not supported in DiscreteTimeWrightFisher"
+            ):
+                msprime.sim_ancestry(
+                    10,
+                    model=model,
+                    record_full_arg=True,
+                )
+
+    def test_dtwf_simulate(self):
+        """
+        Old "simulate" command gives a less descriptive error message
+        """
         for model in [msprime.DiscreteTimeWrightFisher()]:
             with pytest.raises(_msprime.LibraryError):
                 msprime.simulate(