Improve sort with non-constant keys error message (#151193)

Fixes https://github.com/pytorch/pytorch/issues/143505

Test Plan:
- new test

Pull Request resolved: https://github.com/pytorch/pytorch/pull/151193
Approved by: https://github.com/jansel, https://github.com/anijain2305, https://github.com/williamwen42

test/dynamo/test_error_messages.py

@@ -126,6 +126,33 @@ from user code:
     return torch.equal(x, x)""",
             )
 
+    def test_sort_with_nonconstant_keys(self):
+        lst = [
+            torch.tensor(4),
+            torch.tensor(1),
+            torch.tensor(2),
+            torch.tensor(3),
+        ]
+
+        def fn(lst):
+            return sorted(lst)
+
+        self.assertExpectedInlineMunged(
+            Unsupported,
+            lambda: torch.compile(fn, backend="eager", fullgraph=True)(lst),
+            """\
+sort with non-constant keys
+  Explanation: Cannot perform sort with non-constant key. First non-constant key type: <class 'torch.Tensor'>. Most notably, we cannot sort with Tensor or SymInt keys, but we can sort ints.
+  Hint: Use something else as the key.
+
+  Developer debug context: TensorVariable()
+
+
+from user code:
+   File "test_error_messages.py", line N, in fn
+    return sorted(lst)""",
+        )
+
     def test_super_call_method(self):
         def fn(it):
             return [x + 1 for x in it]

torch/_dynamo/variables/lists.py

@@ -485,7 +485,23 @@ class ListVariable(CommonListMethodsVariable):
                 keys = [key_fn_var.call_function(tx, [x], {}) for x in self.items]
 
             if not all(k.is_python_constant() for k in keys):
-                unimplemented("sort with non-constant keys")
+                first_non_constant_key = None
+                for k in keys:
+                    if not k.is_python_constant():
+                        first_non_constant_key = k
+                assert first_non_constant_key is not None
+
+                unimplemented_v2(
+                    gb_type="sort with non-constant keys",
+                    context=str(first_non_constant_key),
+                    explanation=(
+                        f"Cannot perform sort with non-constant key. "
+                        f"First non-constant key type: {first_non_constant_key.python_type()}. "
+                        f"Most notably, we cannot sort with Tensor or SymInt keys, but we can "
+                        f"sort ints."
+                    ),
+                    hints=["Use something else as the key."],
+                )
 
             tx.output.side_effects.mutation(self)
             sorted_items_with_keys = sorted(