Add Bool special form.

Author: dnwpark

typemap/type_eval/_eval_operators.py

@@ -14,6 +14,7 @@
 from typemap.type_eval._eval_typing import _eval_types
 from typemap.typing import (
     Attrs,
+    Bool,
     Capitalize,
     DropAnnotations,
     FromUnion,
@@ -223,6 +224,11 @@ def _eval_Iter(tp, *, ctx):
         )
 
 
+@type_eval.register_evaluator(Bool)
+def _eval_Bool(tp, *, ctx):
+    return _eval_types(tp, ctx)
+
+
 # N.B: These handle unions on their own
 
 

typemap/type_eval/_special_form.py

@@ -2,6 +2,7 @@
 import typing
 from typing import _GenericAlias  # type: ignore
 
+from . import _typing_inspect
 
 _SpecialForm: typing.Any = typing._SpecialForm
 
@@ -21,10 +22,19 @@ def __iter__(self):
             return iter(typing.TypeVarTuple("_IterDummy"))
 
 
-class _IsGenericAlias(_GenericAlias, _root=True):  # type: ignore[call-arg]
+class _BoolGenericAlias(_GenericAlias, _root=True):  # type: ignore[call-arg]
+    """A special form for boolean expressions.
+    Converts Literal[bool] to bool for use in boolean contexts.
+    """
     def __bool__(self):
         evaluator = _special_form_evaluator.get()
         if evaluator:
-            return evaluator(self)
+            result = evaluator(self)
+            if isinstance(result, bool):
+                return result
+            elif _typing_inspect.is_literal(result):
+                return typing.get_args(result)[0]
+
+            raise RuntimeError(f"Expected bool or Literal[bool], got {result}")
         else:
             return False

typemap/typing.py

@@ -3,7 +3,7 @@
 
 from .type_eval._special_form import (
     _IterGenericAlias,
-    _IsGenericAlias,
+    _BoolGenericAlias,
     _SpecialForm,
 )
 
@@ -183,14 +183,19 @@ def Iter(self, tp):
     return _IterGenericAlias(self, (tp,))
 
 
+@_SpecialForm
+def Bool(self, tps):
+    return _BoolGenericAlias(self, tps)
+
+
 @_SpecialForm
 def IsSubtype(self, tps):
-    return _IsGenericAlias(self, tps)
+    return _BoolGenericAlias(self, tps)
 
 
 @_SpecialForm
 def IsSubSimilar(self, tps):
-    return _IsGenericAlias(self, tps)
+    return _BoolGenericAlias(self, tps)
 
 
 Sub = IsSubSimilar