Make a typing dependency that is not in older PyTorch backwards compatible. (#2948)

This was found in a downstream that is pegged to an older PyTorch
version.

python/torch_mlir/extras/fx_importer.py

@@ -16,7 +16,18 @@ import operator
 import re
 from dataclasses import dataclass
 from types import BuiltinMethodType, BuiltinFunctionType
-from typing import Any, Callable, Dict, List, Optional, Sequence, Set, Tuple, Union
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    List,
+    Optional,
+    Sequence,
+    Set,
+    Tuple,
+    TYPE_CHECKING,
+    Union,
+)
 import weakref
 
 import numpy as np
@@ -45,6 +56,16 @@ from torch.fx import (
     Node,
 )
 
+try:
+    from torch.export.graph_signature import InputSpec as TypingInputSpec
+except ModuleNotFoundError:
+    # PyTorch prior to 2.3 is missing certain things we use in typing
+    # signatures. Just make them be Any.
+    if not TYPE_CHECKING:
+        TypingInputSpec = Any
+    else:
+        raise
+
 try:
     import ml_dtypes
 except ModuleNotFoundError:
@@ -299,7 +320,7 @@ class InputInfo:
     """Provides additional metadata when resolving inputs."""
 
     program: torch.export.ExportedProgram
-    input_spec: torch.export.graph_signature.InputSpec
+    input_spec: TypingInputSpec
     node: Node
     ir_type: IrType
     mutable_producer_node_name: Optional[str] = None