Improve typing of jax.jit

- Fix for #23719

Signed-off-by: Fabrice Normandin <normandf@mila.quebec>

jax/_src/api.py

@@ -29,7 +29,7 @@
 import inspect
 import math
 import typing
-from typing import (Any, Literal, NamedTuple, TypeVar, overload,
+from typing import (Any, Literal, NamedTuple, ParamSpec, TypeVar, overload,
                     cast)
 import weakref
 
@@ -137,9 +137,11 @@ def _update_debug_special_thread_local(_):
 
 float0 = dtypes.float0
 
+_P = ParamSpec("_P")
+_OutT = TypeVar("_OutT", covariant=True)
 
 def jit(
-  fun: Callable,
+  fun: Callable[_P, _OutT],
   in_shardings=sharding_impls.UNSPECIFIED,
   out_shardings=sharding_impls.UNSPECIFIED,
   static_argnums: int | Sequence[int] | None = None,
@@ -151,7 +153,7 @@ def jit(
   backend: str | None = None,
   inline: bool = False,
   abstracted_axes: Any | None = None,
-) -> pjit.JitWrapped:
+) -> pjit.JitWrapped[_P, _OutT]:
   """Sets up ``fun`` for just-in-time compilation with XLA.
 
   Args:

jax/_src/pjit.py

@@ -22,7 +22,7 @@
 import logging
 import operator as op
 import weakref
-from typing import NamedTuple, Any, Union, cast
+from typing import NamedTuple, Any, ParamSpec, TypeVar, Union, cast
 import threading
 import warnings
 
@@ -807,8 +807,10 @@ def ax_leaf(l):
             isinstance(l, tuple) and all_leaves(l, lambda x: x is None))
   return broadcast_prefix(abstracted_axes, args, ax_leaf)
 
+_P = ParamSpec("_P")
+_OutT = TypeVar("_OutT", covariant=True)
 
-class JitWrapped(stages.Wrapped):
+class JitWrapped(stages.Wrapped[_P, _OutT]):
 
   def eval_shape(self, *args, **kwargs):
     """See ``jax.eval_shape``."""

jax/_src/stages.py

@@ -33,7 +33,7 @@
 import functools
 from collections.abc import Sequence
 from dataclasses import dataclass
-from typing import Any, NamedTuple, Protocol, Union, runtime_checkable
+from typing import Any, NamedTuple, ParamSpec, Protocol, TypeVar, Union, runtime_checkable
 
 import jax
 
@@ -751,9 +751,11 @@ def lower(self, *, lowering_platforms: tuple[str, ...] | None = None,
       raise ValueError(msg) from None
     return Lowered(lowering, self.args_info, self._out_tree)
 
+_P = ParamSpec("_P")
+_OutT = TypeVar("_OutT", covariant=True)
 
 @runtime_checkable
-class Wrapped(Protocol):
+class Wrapped(Protocol[_P, _OutT]):
   """A function ready to be traced, lowered, and compiled.
 
   This protocol reflects the output of functions such as
@@ -762,11 +764,11 @@ class Wrapped(Protocol):
   to compilation, and the result compiled prior to execution.
   """
 
-  def __call__(self, *args, **kwargs):
+  def __call__(self, *args: _P.args, **kwargs: _P.kwargs) -> _OutT:
     """Executes the wrapped function, lowering and compiling as needed."""
     raise NotImplementedError
 
-  def trace(self, *args, **kwargs) -> Traced:
+  def trace(self, *args: _P.args, **kwargs: _P.kwargs) -> Traced:
     """Trace this function explicitly for the given arguments.
 
     A traced function is staged out of Python and translated to a jaxpr. It is
@@ -777,7 +779,7 @@ def trace(self, *args, **kwargs) -> Traced:
     """
     raise NotImplementedError
 
-  def lower(self, *args, **kwargs) -> Lowered:
+  def lower(self, *args: _P.args, **kwargs: _P.kwargs) -> Lowered:
     """Lower this function explicitly for the given arguments.
 
     A lowered function is staged out of Python and translated to a