Test deprecation warnings

Tests/test_features.py

@@ -18,7 +18,11 @@ def test_check() -> None:
     for codec in features.codecs:
         assert features.check_codec(codec) == features.check(codec)
     for feature in features.features:
-        assert features.check_feature(feature) == features.check(feature)
+        if "webp" in feature:
+            with pytest.warns(DeprecationWarning):
+                assert features.check_feature(feature) == features.check(feature)
+        else:
+            assert features.check_feature(feature) == features.check(feature)
 
 
 def test_version() -> None:
@@ -43,19 +47,26 @@ def test(name: str, function: Callable[[str], str | None]) -> None:
     for codec in features.codecs:
         test(codec, features.version_codec)
     for feature in features.features:
-        test(feature, features.version_feature)
+        if "webp" in feature:
+            with pytest.warns(DeprecationWarning):
+                test(feature, features.version_feature)
+        else:
+            test(feature, features.version_feature)
 
 
 def test_webp_transparency() -> None:
-    assert features.check("transp_webp") == features.check_module("webp")
+    with pytest.warns(DeprecationWarning):
+        assert features.check("transp_webp") == features.check_module("webp")
 
 
 def test_webp_mux() -> None:
-    assert features.check("webp_mux") == features.check_module("webp")
+    with pytest.warns(DeprecationWarning):
+        assert features.check("webp_mux") == features.check_module("webp")
 
 
 def test_webp_anim() -> None:
-    assert features.check("webp_anim") == features.check_module("webp")
+    with pytest.warns(DeprecationWarning):
+        assert features.check("webp_anim") == features.check_module("webp")
 
 
 @skip_unless_feature("libjpeg_turbo")

src/PIL/features.py

@@ -180,7 +180,17 @@ def get_supported_features() -> list[str]:
     """
     :returns: A list of all supported features.
     """
-    return [f for f in features if check_feature(f)]
+    supported_features = []
+    for f, (module, flag, _) in features.items():
+        if flag is True:
+            for feature, (feature_module, _) in modules.items():
+                if feature_module == module:
+                    if check_module(feature):
+                        supported_features.append(f)
+                    break
+        elif check_feature(f):
+            supported_features.append(f)
+    return supported_features
 
 
 def check(feature: str) -> bool | None: