Switched from parameter in can_cast to from_. (#126030)

Fixes #126012.

`from` is a reserved keyword in Python, thus we can't make the C++ impl available with `from` as function parameter. This PR changes the name to `from_` and also adjusts the docs.

If we want to preserve backwards compatibility, we can leave the C++ name as-is and only fix the docs. However, `torch.can_cast(from_=torch.int, to=torch.int)` won't work then.

Pull Request resolved: #126030
Approved by: https://github.com/albanD

aten/src/ATen/native/TypeProperties.cpp

@@ -191,8 +191,8 @@ ScalarType result_type(const Scalar& scalar1, const Scalar& scalar2) {
   return result_type(state);
 }
 
-bool can_cast(const at::ScalarType from, const at::ScalarType to) {
-  return at::canCast(from, to);
+bool can_cast(const at::ScalarType from_, const at::ScalarType to) {
+  return at::canCast(from_, to);
 }
 
 ScalarType promote_types(ScalarType type1, ScalarType type2) {

aten/src/ATen/native/native_functions.yaml

@@ -7702,7 +7702,7 @@
 
 - func: result_type.Scalar_Scalar(Scalar scalar1, Scalar scalar2) -> ScalarType
 
-- func: can_cast(ScalarType from, ScalarType to) -> bool
+- func: can_cast(ScalarType from_, ScalarType to) -> bool
   variants: function
 
 - func: promote_types(ScalarType type1, ScalarType type2) -> ScalarType

test/forward_backward_compatibility/check_forward_backward_compatibility.py

@@ -147,6 +147,8 @@
     ("aten::_aminmax.dim", datetime.date(2024, 12, 31)),
     ("aten::_aminmax.out", datetime.date(2024, 12, 31)),
     ("aten::_aminmax.dim_out", datetime.date(2024, 12, 31)),
+    # BC-breaking change in can_cast signature: 'from' -> 'from_'
+    ("aten::can_cast", datetime.date(2024, 5, 31)),
 ]
 
 ALLOW_LIST_COMPILED = [

torch/_torch_docs.py

@@ -2195,13 +2195,13 @@ def merge_dicts(*dicts):
 add_docstr(
     torch.can_cast,
     r"""
-can_cast(from, to) -> bool
+can_cast(from_, to) -> bool
 
 Determines if a type conversion is allowed under PyTorch casting rules
 described in the type promotion :ref:`documentation <type-promotion-doc>`.
 
 Args:
-    from (dtype): The original :class:`torch.dtype`.
+    from\_ (dtype): The original :class:`torch.dtype`.
     to (dtype): The target :class:`torch.dtype`.
 
 Example::