Aligned the signature of new_slot with functools.partial.__new__

Specifically, both `cls` and `func` are now positional-only parameters.

PiperOrigin-RevId: 830922244

Author: superbobry

pytype/overlays/functools_overlay.py

@@ -47,7 +47,7 @@ def __init__(self, ctx: "context.Context", module: str):
     self._pytd_new = self.pytd_cls.Lookup("__new__")
 
   def new_slot(
-      self, node, cls, *args, **kwargs
+      self, node, cls, func, /, *args, **kwargs
   ) -> tuple[cfg.CFGNode, cfg.Variable]:
     # Make sure the call is well typed before binding the partial
     new = self.ctx.convert.convert_pytd_function(self._pytd_new)
@@ -56,7 +56,7 @@ def new_slot(
         node,
         new.to_variable(node),
         function.Args(
-            (cls, *args),
+            (cls, func, *args),
             kwargs,
             call_context.starargs,
             call_context.starstarargs,
@@ -67,19 +67,19 @@ def new_slot(
     type_arg = specialized_obj.get_formal_type_parameter("_T")
     [cls] = cls.data
     cls = abstract.ParameterizedClass(cls, {"_T": type_arg}, self.ctx)
-    obj = bind_partial(node, cls, args, kwargs, self.ctx)
+    obj = bind_partial(node, cls, func, args, kwargs, self.ctx)
     return node, obj.to_variable(node)
 
   def get_own_new(self, node, value) -> tuple[cfg.CFGNode, cfg.Variable]:
     new = NativeFunction("__new__", self.new_slot, self.ctx)
     return node, new.to_variable(node)
 
 
-def bind_partial(node, cls, args, kwargs, ctx) -> BoundPartial:
+def bind_partial(node, cls, func, args, kwargs, ctx) -> BoundPartial:
   del node  # Unused.
   obj = BoundPartial(ctx, cls)
-  obj.underlying = args[0]
-  obj.args = args[1:]
+  obj.underlying = func
+  obj.args = args
   obj.kwargs = kwargs
   obj.starargs = call_context.starargs
   obj.starstarargs = call_context.starstarargs

pytype/tests/test_functions1.py

@@ -1079,6 +1079,17 @@ def f(a, b=None):
       partial_f(0)
     """)
 
+  def test_functools_partial_cls(self):
+    # This is a smoke test that **kwargs do not interfere with the receiver
+    # in partial.__new__.
+    self.Check("""
+      import functools
+      def f(cls):
+        return cls
+      partial_f = functools.partial(f, cls=int)
+      partial_f()
+    """)
+
   def test_functools_partial_starstar(self):
     self.Check("""
       import functools
@@ -1180,7 +1191,7 @@ def __init__(self, a, b=None):
   def test_functools_partial_bad_call(self):
     errors = self.CheckWithErrors("""
       import functools
-      functools.partial()  # missing-parameter
+      functools.partial()  # wrong-arg-count
       functools.partial(42)  # wrong-arg-types[e]
     """)
     self.assertErrorRegexes(errors, {"e": r"Callable.*int"})