[struct] Add struct.pack and struct.unpack polyfills (#156977)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/156977
Approved by: https://github.com/XuehaiPan, https://github.com/jansel
ghstack dependencies: #156975

torch/_dynamo/polyfills/__init__.py

@@ -30,6 +30,7 @@ if TYPE_CHECKING:
         operator as operator,
         os as os,
         pytree as pytree,
+        struct as struct,
         sys as sys,
     )
 

torch/_dynamo/polyfills/loader.py

@@ -19,6 +19,7 @@ POLYFILLED_MODULE_NAMES: tuple[str, ...] = (
     "operator",
     "os",
     "pytree",
+    "struct",
     "sys",
     "fx",
     "tensor",

torch/_dynamo/polyfills/struct.py

@@ -0,0 +1,27 @@
+"""
+Python polyfills for struct
+"""
+
+from __future__ import annotations
+
+import struct
+from typing import Any
+from typing_extensions import Buffer
+
+from ..decorators import substitute_in_graph
+
+
+__all__ = [
+    "pack",
+    "unpack",
+]
+
+
+@substitute_in_graph(struct.pack, can_constant_fold_through=True)  # type: ignore[arg-type]
+def pack(fmt: bytes | str, /, *v: Any) -> bytes:
+    return struct.pack(fmt, *v)
+
+
+@substitute_in_graph(struct.unpack, can_constant_fold_through=True)  # type: ignore[arg-type]
+def unpack(format: bytes | str, buffer: Buffer, /) -> tuple[Any, ...]:
+    return struct.unpack(format, buffer)