Fix configuration validation error message in Lite CLI (#16334)

src/lightning_fabric/CHANGELOG.md

@@ -71,6 +71,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Restored sampling parity between PyTorch and Fabric dataloaders when using the `DistributedSampler` ([#16101](https://github.com/Lightning-AI/lightning/issues/16101))
 
+- Fixes an issue where the error message wouldn't tell the user the real value that was passed through the CLI ([#16334](https://github.com/Lightning-AI/lightning/issues/16334))
+
 
 ## [1.8.6] - 2022-12-21
 

src/lightning_fabric/connector.py

@@ -539,7 +539,7 @@ def _argument_from_env(name: str, current: Any, default: Any) -> Any:
         if env_value is not None and env_value != str(current) and str(current) != str(default):
             raise ValueError(
                 f"Your code has `Fabric({name}={current!r}, ...)` but it conflicts with the value "
-                f"`--{name}={current}` set through the CLI. "
+                f"`--{name}={env_value}` set through the CLI. "
                 " Remove it either from the CLI or from the Lightning Fabric object."
             )
         if env_value is None:

tests/tests_fabric/test_connector.py

@@ -13,7 +13,6 @@
 # limitations under the License
 
 import os
-from re import escape
 from typing import Any, Dict
 from unittest import mock
 
@@ -808,27 +807,23 @@ def test_devices_from_environment(*_):
 def test_arguments_from_environment_collision():
     """Test that the connector raises an error when the CLI settings conflict with settings in the code."""
     with mock.patch.dict(os.environ, {"LT_ACCELERATOR": "cpu"}):
-        with pytest.raises(
-            ValueError, match=escape("Your code has `Fabric(accelerator='cuda', ...)` but it conflicts")
-        ):
+        with pytest.raises(ValueError, match="`Fabric\\(accelerator='cuda', ...\\)` but .* `--accelerator=cpu`"):
             _Connector(accelerator="cuda")
 
     with mock.patch.dict(os.environ, {"LT_STRATEGY": "ddp"}):
-        with pytest.raises(
-            ValueError, match=escape("Your code has `Fabric(strategy='ddp_spawn', ...)` but it conflicts")
-        ):
+        with pytest.raises(ValueError, match="`Fabric\\(strategy='ddp_spawn', ...\\)` but .* `--strategy=ddp`"):
             _Connector(strategy="ddp_spawn")
 
     with mock.patch.dict(os.environ, {"LT_DEVICES": "2"}):
-        with pytest.raises(ValueError, match=escape("Your code has `Fabric(devices=3, ...)` but it conflicts")):
+        with pytest.raises(ValueError, match="`Fabric\\(devices=3, ...\\)` but .* `--devices=2`"):
             _Connector(devices=3)
 
     with mock.patch.dict(os.environ, {"LT_NUM_NODES": "3"}):
-        with pytest.raises(ValueError, match=escape("Your code has `Fabric(num_nodes=2, ...)` but it conflicts")):
+        with pytest.raises(ValueError, match="`Fabric\\(num_nodes=2, ...\\)` but .* `--num_nodes=3`"):
             _Connector(num_nodes=2)
 
     with mock.patch.dict(os.environ, {"LT_PRECISION": "16"}):
-        with pytest.raises(ValueError, match=escape("Your code has `Fabric(precision=64, ...)` but it conflicts")):
+        with pytest.raises(ValueError, match="`Fabric\\(precision=64, ...\\)` but .* `--precision=16`"):
             _Connector(precision=64)