fix: only warn about asyncio_default_fixture_loop_scope when needed

changelog.d/1344.fixed.rst

@@ -0,0 +1 @@
+Only warn about an unset ``asyncio_default_fixture_loop_scope`` configuration option when an async fixture is actually used.

pytest_asyncio/plugin.py

@@ -52,6 +52,7 @@
     PytestCollectionWarning,
     PytestDeprecationWarning,
     PytestPluginManager,
+    StashKey,
 )
 
 if sys.version_info >= (3, 11):
@@ -293,11 +294,19 @@ def _validate_scope(scope: str | None, option_name: str) -> None:
         )
 
 
+_DEFAULT_FIXTURE_LOOP_SCOPE_WARNING_EMITTED: StashKey[bool] = StashKey()
+
+
+def _warn_default_fixture_loop_scope_unset(config: Config) -> None:
+    if config.stash.get(_DEFAULT_FIXTURE_LOOP_SCOPE_WARNING_EMITTED, False):
+        return
+    config.stash[_DEFAULT_FIXTURE_LOOP_SCOPE_WARNING_EMITTED] = True
+    warnings.warn(PytestDeprecationWarning(_DEFAULT_FIXTURE_LOOP_SCOPE_UNSET))
+
+
 def pytest_configure(config: Config) -> None:
     default_fixture_loop_scope = config.getini("asyncio_default_fixture_loop_scope")
     _validate_scope(default_fixture_loop_scope, "asyncio_default_fixture_loop_scope")
-    if not default_fixture_loop_scope:
-        warnings.warn(PytestDeprecationWarning(_DEFAULT_FIXTURE_LOOP_SCOPE_UNSET))
 
     default_test_loop_scope = config.getini("asyncio_default_test_loop_scope")
     _validate_scope(default_test_loop_scope, "asyncio_default_test_loop_scope")
@@ -926,11 +935,10 @@ def pytest_fixture_setup(fixturedef: FixtureDef, request) -> object | None:
         if not _is_coroutine_or_asyncgen(fixturedef.func):
             return (yield)
     default_loop_scope = request.config.getini("asyncio_default_fixture_loop_scope")
-    loop_scope = (
-        getattr(fixturedef.func, "_loop_scope", None)
-        or default_loop_scope
-        or fixturedef.scope
-    )
+    fixture_loop_scope = getattr(fixturedef.func, "_loop_scope", None)
+    loop_scope = fixture_loop_scope or default_loop_scope or fixturedef.scope
+    if not default_loop_scope and not fixture_loop_scope:
+        _warn_default_fixture_loop_scope_unset(request.config)
     runner_fixture_id = f"_{loop_scope}_scoped_runner"
     runner = request.getfixturevalue(runner_fixture_id)
     # Prevent the runner closing before the fixture's async teardown.

tests/test_fixture_loop_scopes.py

@@ -126,3 +126,48 @@ def test_invalid_default_fixture_loop_scope_raises_error(pytester: Pytester):
             "function, class, module, package, session."
         ]
     )
+
+
+def test_no_warning_for_unset_default_fixture_loop_scope_without_async_fixtures(
+    pytester: Pytester,
+):
+    """Regression test for #1344."""
+    pytester.makeini(dedent("""\
+        [pytest]
+        asyncio_mode = strict
+        """))
+    pytester.makepyfile(dedent("""\
+        def test_no_async():
+            pass
+        """))
+    result = pytester.runpytest_subprocess("-Werror")
+    result.assert_outcomes(passed=1)
+
+
+def test_warning_for_unset_default_fixture_loop_scope_with_async_fixture(
+    pytester: Pytester,
+):
+    pytester.makeini(dedent("""\
+        [pytest]
+        asyncio_mode = strict
+        """))
+    pytester.makepyfile(dedent("""\
+        import pytest
+        import pytest_asyncio
+
+        @pytest_asyncio.fixture
+        async def async_fixture():
+            return 42
+
+        @pytest.mark.asyncio
+        async def test_async(async_fixture):
+            assert async_fixture == 42
+        """))
+    result = pytester.runpytest_subprocess("-Wdefault")
+    result.assert_outcomes(passed=1, warnings=1)
+    result.stdout.fnmatch_lines(
+        [
+            "*PytestDeprecationWarning: The configuration option "
+            '"asyncio_default_fixture_loop_scope" is unset.*'
+        ]
+    )