Add type deduction for type aliases

refurb/checks/common.py

@@ -46,7 +46,7 @@
     UnaryExpr,
     Var,
 )
-from mypy.types import AnyType, CallableType, Instance, TupleType, Type
+from mypy.types import AnyType, CallableType, Instance, TupleType, Type, TypeAliasType
 
 from refurb import types
 from refurb.error import Error
@@ -572,6 +572,12 @@ def _is_same_type(ty: Type | SymbolNode | None, expected: TypeLike) -> bool:
     if ty is expected is None:
         return True
 
+    if isinstance(ty, TypeAliasType):
+        if not ty.alias:
+            return False  # pragma: no cover
+
+        return _is_same_type(ty.alias.target, expected)
+
     if isinstance(ty, TupleType) and expected is tuple:
         return True
 

test/data/type_deduce.py

@@ -36,5 +36,13 @@ async def return_bool() -> bool:
 _ = bool(cast(bool, 123))
 
 
+DictAlias = dict[str, str]
+
+# Must use function here so that `d` uses the `DictAlias` type alias. If an intermediate
+# object is used the alias will "resolve" and won't trigger the type alias check.
+def dict_alias_wrapper(d: DictAlias) -> None:
+    _ = dict(d)
+
+
 # These types are not able to be deduced (yet)
 _ = int(1 or 2)

test/data/type_deduce.txt

@@ -10,3 +10,4 @@ test/data/type_deduce.py:29:5 [FURB123]: Replace `int(+1)` with `+1`
 test/data/type_deduce.py:30:5 [FURB123]: Replace `int(~1)` with `~1`
 test/data/type_deduce.py:32:5 [FURB123]: Replace `bool(walrus := True)` with `walrus := True`
 test/data/type_deduce.py:36:5 [FURB123]: Replace `bool(cast(bool, 123))` with `cast(bool, 123)`
+test/data/type_deduce.py:44:9 [FURB123]: Replace `dict(d)` with `d.copy()`