fix GenericPlainRegistry getattr type

CHANGES

@@ -9,6 +9,7 @@ Pint Changelog
 - Added ℓ as alternative for liter
 - Support permille units and `‰` symbol (PR #2033, Issue #1963)
 - Switch from appdirs to platformdirs.
+- Fixes issues related to GenericPlainRegistry.__getattr__ type (PR #2038, Issues #1946 and #1804)
 
 
 0.24.1 (2024-06-24)

pint/facets/plain/registry.py

@@ -367,7 +367,7 @@ def __deepcopy__(self: Self, memo) -> type[Self]:
         new._init_dynamic_classes()
         return new
 
-    def __getattr__(self, item: str) -> QuantityT:
+    def __getattr__(self, item: str) -> UnitT:
         getattr_maybe_raise(self, item)
 
         # self.Unit will call parse_units

pint/testsuite/test_quantity.py

@@ -2014,3 +2014,11 @@ def test_offset_autoconvert_gt_zero(self):
         assert q2 > 0
         with pytest.raises(DimensionalityError):
             q1.__gt__(ureg.Quantity(0, ""))
+
+    def test_types(self):
+        quantity = self.Q_(1.0, "m")
+        assert isinstance(quantity, self.Q_)
+        assert isinstance(quantity.units, self.ureg.Unit)
+        assert isinstance(quantity.m, float)
+
+        assert isinstance(self.ureg.m, self.ureg.Unit)