From be0ae065967e5c06e860c88271a906551da475b9 Mon Sep 17 00:00:00 2001
From: Abhishek Singh <abhi0singh1@gmail.com>
Date: Wed, 7 Aug 2024 20:17:36 +0530
Subject: [PATCH] Add `ddp_find_unused_parameters_true` alias in Fabric's
 DDPStrategy (#20125)

---
 src/lightning/fabric/strategies/ddp.py         | 7 +++++++
 tests/tests_fabric/strategies/test_registry.py | 1 +
 tests/tests_fabric/test_cli.py                 | 3 ++-
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/lightning/fabric/strategies/ddp.py b/src/lightning/fabric/strategies/ddp.py
index 0ec5df1a6b..c38780655c 100644
--- a/src/lightning/fabric/strategies/ddp.py
+++ b/src/lightning/fabric/strategies/ddp.py
@@ -200,6 +200,13 @@ class DDPStrategy(ParallelStrategy):
                 description=f"DDP strategy with `start_method={start_method!r}`",
                 start_method=start_method,
             )
+        strategy_registry.register(
+            "ddp_find_unused_parameters_true",
+            cls,
+            description="Alias for `find_unused_parameters_true` and `start_method='popen'`",
+            find_unused_parameters=True,
+            start_method="popen",
+        )
 
     def _setup_distributed(self) -> None:
         self._set_world_ranks()
diff --git a/tests/tests_fabric/strategies/test_registry.py b/tests/tests_fabric/strategies/test_registry.py
index 1865328cf5..8efd19541a 100644
--- a/tests/tests_fabric/strategies/test_registry.py
+++ b/tests/tests_fabric/strategies/test_registry.py
@@ -42,6 +42,7 @@ def test_strategy_registry_with_new_strategy():
 def test_available_strategies_in_registry():
     expected = {
         "ddp",
+        "ddp_find_unused_parameters_true",
         "deepspeed",
         "deepspeed_stage_1",
         "deepspeed_stage_1_offload",
diff --git a/tests/tests_fabric/test_cli.py b/tests/tests_fabric/test_cli.py
index 0e58acb3c7..a57f413ff6 100644
--- a/tests/tests_fabric/test_cli.py
+++ b/tests/tests_fabric/test_cli.py
@@ -71,8 +71,9 @@ def test_run_env_vars_strategy(_, strategy, monkeypatch, fake_script):
 def test_run_get_supported_strategies():
     """Test to ensure that when new strategies get added, we must consider updating the list of supported ones in the
     CLI."""
-    assert len(_get_supported_strategies()) == 7
+    assert len(_get_supported_strategies()) == 8
     assert "fsdp" in _get_supported_strategies()
+    assert "ddp_find_unused_parameters_true" in _get_supported_strategies()
 
 
 @pytest.mark.parametrize("strategy", ["ddp_spawn", "ddp_fork", "ddp_notebook", "deepspeed_stage_3_offload"])