Make LightningModule torch.jit.script-able again (#15947)

* Make LightningModule torch.jit.script-able again
* remove skip

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: awaelchli

src/pytorch_lightning/CHANGELOG.md

@@ -91,6 +91,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed `fit_loop.restarting` to be `False` for lr finder ([#15620](https://github.com/Lightning-AI/lightning/pull/15620))
 
 
+- Fixed `torch.jit.script`-ing a LightningModule causing an unintended error message about deprecated `use_amp` property ([#15947](https://github.com/Lightning-AI/lightning/pull/15947))
+
+
 ## [1.8.3] - 2022-11-22
 
 ### Changed

src/pytorch_lightning/_graveyard/core.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 from typing import Any
 
-from pytorch_lightning import LightningDataModule, LightningModule
+from pytorch_lightning import LightningDataModule
 
 
 def _on_save_checkpoint(_: LightningDataModule, __: Any) -> None:
@@ -32,28 +32,6 @@ def _on_load_checkpoint(_: LightningDataModule, __: Any) -> None:
     )
 
 
-def _use_amp(_: LightningModule) -> None:
-    # Remove in v2.0.0 and the skip in `__jit_unused_properties__`
-    if not LightningModule._jit_is_scripting:
-        # cannot use `AttributeError` as it messes up with `nn.Module.__getattr__`
-        raise RuntimeError(
-            "`LightningModule.use_amp` was deprecated in v1.6 and is no longer accessible as of v1.8."
-            " Please use `Trainer.amp_backend`.",
-        )
-
-
-def _use_amp_setter(_: LightningModule, __: bool) -> None:
-    # Remove in v2.0.0
-    # cannot use `AttributeError` as it messes up with `nn.Module.__getattr__`
-    raise RuntimeError(
-        "`LightningModule.use_amp` was deprecated in v1.6 and is no longer accessible as of v1.8."
-        " Please use `Trainer.amp_backend`.",
-    )
-
-
-# Properties
-LightningModule.use_amp = property(fget=_use_amp, fset=_use_amp_setter)
-
 # Methods
 LightningDataModule.on_save_checkpoint = _on_save_checkpoint
 LightningDataModule.on_load_checkpoint = _on_load_checkpoint

src/pytorch_lightning/core/module.py

@@ -88,7 +88,6 @@ class LightningModule(
             "automatic_optimization",
             "truncated_bptt_steps",
             "trainer",
-            "use_amp",  # from graveyard
         ]
         + _DeviceDtypeModuleMixin.__jit_unused_properties__
         + HyperparametersMixin.__jit_unused_properties__

tests/tests_pytorch/core/test_lightning_module.py

@@ -425,6 +425,17 @@ def test_proper_refcount():
     assert sys.getrefcount(torch_module) == sys.getrefcount(lightning_module)
 
 
+def test_lightning_module_scriptable():
+    """Test that the LightningModule is `torch.jit.script`-able.
+
+    Regression test for #15917.
+    """
+    model = BoringModel()
+    trainer = Trainer()
+    model.trainer = trainer
+    torch.jit.script(model)
+
+
 def test_trainer_reference_recursively():
     ensemble = LightningModule()
     inner = LightningModule()

tests/tests_pytorch/graveyard/test_core.py

@@ -53,18 +53,3 @@ def on_load_checkpoint(self, checkpoint):
         match="`LightningDataModule.on_load_checkpoint`.*no longer supported as of v1.8.",
     ):
         trainer.fit(model, OnLoadDataModule())
-
-
-def test_v2_0_0_lightning_module_unsupported_use_amp():
-    model = BoringModel()
-    with pytest.raises(
-        RuntimeError,
-        match="`LightningModule.use_amp`.*no longer accessible as of v1.8.",
-    ):
-        model.use_amp
-
-    with pytest.raises(
-        RuntimeError,
-        match="`LightningModule.use_amp`.*no longer accessible as of v1.8.",
-    ):
-        model.use_amp = False