Update on "Deprecate old TORCH_VERSION variables"

**Summary:** This commit deprecates the following variables:

```
# Always True
TORCH_VERSION_AT_LEAST_2_6
TORCH_VERSION_AT_LEAST_2_5
TORCH_VERSION_AT_LEAST_2_4
TORCH_VERSION_AT_LEAST_2_3
TORCH_VERSION_AT_LEAST_2_2
# TORCH_VERSION_AFTER* was confusing to users
TORCH_VERSION_AFTER_2_5
TORCH_VERSION_AFTER_2_4
TORCH_VERSION_AFTER_2_3
TORCH_VERSION_AFTER_2_2
```

As of this commit, the latest released version of PyTorch is 2.8, which means the oldest pytorch version we support is now 2.6 since we only support 3 of the latest releases.

The next commit will remove usages of all of these variables from within torchao.

**Test Plan:**
```
python test/test_utils.py -k torch_version_deprecation
```

[ghstack-poisoned]

Author: andrewor14

test/test_utils.py

@@ -38,8 +38,8 @@ def test_torch_version_at_least(self):
 
     def test_torch_version_deprecation(self):
         """
-        Test that TORCH_VERSION_AT_LEAST_2_6 and before and TORCH_VERSION_AFTER*
-        trigger a deprecation warning.
+        Test that TORCH_VERSION_AT_LEAST* and TORCH_VERSION_AFTER*
+        trigger deprecation warnings on use, not on import.
         """
         # Reset deprecation warning state, otherwise we won't log warnings here
         warnings.resetwarnings()
@@ -56,9 +56,13 @@ def test_torch_version_deprecation(self):
                 TORCH_VERSION_AT_LEAST_2_4,
                 TORCH_VERSION_AT_LEAST_2_5,
                 TORCH_VERSION_AT_LEAST_2_6,
+                TORCH_VERSION_AT_LEAST_2_7,
+                TORCH_VERSION_AT_LEAST_2_8,
             )
 
             deprecated_api_to_name = [
+                (TORCH_VERSION_AT_LEAST_2_8, "TORCH_VERSION_AT_LEAST_2_8"),
+                (TORCH_VERSION_AT_LEAST_2_7, "TORCH_VERSION_AT_LEAST_2_7"),
                 (TORCH_VERSION_AT_LEAST_2_6, "TORCH_VERSION_AT_LEAST_2_6"),
                 (TORCH_VERSION_AT_LEAST_2_5, "TORCH_VERSION_AT_LEAST_2_5"),
                 (TORCH_VERSION_AT_LEAST_2_4, "TORCH_VERSION_AT_LEAST_2_4"),

torchao/utils.py

@@ -379,6 +379,10 @@ def torch_version_at_least(min_version):
 
 
 def _deprecated_torch_version_at_least(version_str: str) -> str:
+    """
+    Wrapper for existing TORCH_VERSION_AT_LEAST* variables that will log
+    a deprecation warning if the variable is used.
+    """
     version_str_var_name = "_".join(version_str.split(".")[:2])
     deprecation_msg = f"TORCH_VERSION_AT_LEAST_{version_str_var_name} is deprecated and will be removed in torchao 0.14.0"
     return _BoolDeprecationWrapper(
@@ -388,6 +392,10 @@ def _deprecated_torch_version_at_least(version_str: str) -> str:
 
 
 def _deprecated_torch_version_after(version_str: str) -> str:
+    """
+    Wrapper for existing TORCH_VERSION_AFTER* variables that will log
+    a deprecation warning if the variable is used.
+    """
     bool_value = is_fbcode() or version("torch") >= version_str
     version_str_var_name = "_".join(version_str.split(".")[:2])
     deprecation_msg = f"TORCH_VERSION_AFTER_{version_str_var_name} is deprecated and will be removed in torchao 0.14.0"
@@ -411,10 +419,9 @@ def __eq__(self, other):
         return bool(self) == bool(other)
 
 
-TORCH_VERSION_AT_LEAST_2_8 = torch_version_at_least("2.8.0")
-TORCH_VERSION_AT_LEAST_2_7 = torch_version_at_least("2.7.0")
-
-# Deprecated
+# Deprecated, use `torch_version_at_least` directly instead
+TORCH_VERSION_AT_LEAST_2_8 = _deprecated_torch_version_at_least("2.8.0")
+TORCH_VERSION_AT_LEAST_2_7 = _deprecated_torch_version_at_least("2.7.0")
 TORCH_VERSION_AT_LEAST_2_6 = _deprecated_torch_version_at_least("2.6.0")
 TORCH_VERSION_AT_LEAST_2_5 = _deprecated_torch_version_at_least("2.5.0")
 TORCH_VERSION_AT_LEAST_2_4 = _deprecated_torch_version_at_least("2.4.0")