core: make BaseAttr inferrable (#3491)

As discussed in #3477 

Fixes #3483

tests/irdl/test_attr_constraint.py

@@ -3,7 +3,7 @@
 import pytest
 
 from xdsl.dialects.builtin import StringAttr
-from xdsl.ir import Attribute, ParametrizedAttribute
+from xdsl.ir import Attribute, Data, ParametrizedAttribute
 from xdsl.irdl import (
     AllOf,
     AnyAttr,
@@ -105,3 +105,35 @@ class WrapAttr(BaseWrapAttr): ...
         ),
     )
     assert not base_constr.can_infer(set())
+
+
+def test_base_attr_constraint_inference():
+    class BaseNoParamAttr(ParametrizedAttribute):
+        name = "no_param"
+
+    @irdl_attr_definition
+    class WithParamAttr(ParametrizedAttribute):
+        name = "with_param"
+
+        inner: ParameterDef[Attribute]
+
+    @irdl_attr_definition
+    class DataAttr(Data[int]):
+        name = "data"
+
+    @irdl_attr_definition
+    class NoParamAttr(BaseNoParamAttr): ...
+
+    constr = BaseAttr(NoParamAttr)
+
+    assert constr.can_infer(set())
+    assert constr.infer({}) == NoParamAttr()
+
+    base_constr = BaseAttr(BaseNoParamAttr)
+    assert not base_constr.can_infer(set())
+
+    with_param_constr = BaseAttr(WithParamAttr)
+    assert not with_param_constr.can_infer(set())
+
+    data_constr = BaseAttr(DataAttr)
+    assert not data_constr.can_infer(set())

xdsl/irdl/constraints.py

@@ -296,6 +296,18 @@ def verify(
                 f"{attr} should be of base attribute {self.attr.name}"
             )
 
+    def can_infer(self, var_constraint_names: Set[str]) -> bool:
+        return (
+            is_runtime_final(self.attr)
+            and issubclass(self.attr, ParametrizedAttribute)
+            and not self.attr.get_irdl_definition().parameters
+        )
+
+    def infer(self, variables: dict[str, ConstraintVariableType]) -> AttributeCovT:
+        assert issubclass(self.attr, ParametrizedAttribute)
+        attr = self.attr.new(())
+        return attr
+
     def get_unique_base(self) -> type[Attribute] | None:
         if is_runtime_final(self.attr):
             return self.attr