feat(config): propagator plugin loading via entry points for declarative config

CHANGELOG.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- `opentelemetry-sdk`: add propagator plugin loading to declarative file configuration via the `opentelemetry_propagator` entry point group, matching the spec's PluginComponentProvider mechanism
+  ([#5098](https://github.com/open-telemetry/opentelemetry-python/pull/5098))
 - `opentelemetry-sdk`: add `additional_properties` support to generated config models via custom `datamodel-codegen` template, enabling plugin/custom component names to flow through typed dataclasses
   ([#5131](https://github.com/open-telemetry/opentelemetry-python/pull/5131))
 - Fix incorrect code example in `create_tracer()` docstring

opentelemetry-sdk/src/opentelemetry/sdk/_configuration/_propagator.py

@@ -31,25 +31,37 @@
     TraceContextTextMapPropagator,
 )
 
-
-def _load_entry_point_propagator(name: str) -> TextMapPropagator:
-    """Load and instantiate a propagator by name."""
-    return load_entry_point("opentelemetry_propagator", name)()
+# Propagators bundled with the SDK — no entry point lookup needed.
+_PROPAGATOR_REGISTRY: dict = {
+    "tracecontext": lambda _: TraceContextTextMapPropagator(),
+    "baggage": lambda _: W3CBaggagePropagator(),
+}
 
 
 def _propagators_from_textmap_config(
     config: TextMapPropagatorConfig,
 ) -> list[TextMapPropagator]:
-    """Resolve a single TextMapPropagator config entry to a list of propagators."""
+    """Resolve a TextMapPropagator config to a list of propagators.
+
+    Known names (tracecontext, baggage) are bootstrapped directly via
+    _PROPAGATOR_REGISTRY. Known schema fields not in the registry (b3, b3multi)
+    and unknown plugin names from additional_properties are loaded via the
+    ``opentelemetry_propagator`` entry point group.
+    """
     result: list[TextMapPropagator] = []
-    if config.tracecontext is not None:
-        result.append(TraceContextTextMapPropagator())
-    if config.baggage is not None:
-        result.append(W3CBaggagePropagator())
-    if config.b3 is not None:
-        result.append(_load_entry_point_propagator("b3"))
-    if config.b3multi is not None:
-        result.append(_load_entry_point_propagator("b3multi"))
+    for name in _PROPAGATOR_REGISTRY:
+        if getattr(config, name, None) is not None:
+            result.append(_PROPAGATOR_REGISTRY[name](getattr(config, name)))
+
+    # Known schema fields not in registry (b3, b3multi) — loaded via entry point
+    for name in ("b3", "b3multi"):
+        if getattr(config, name, None) is not None:
+            result.append(load_entry_point("opentelemetry_propagator", name)())
+
+    # Plugin propagators from additional_properties
+    for name in config.additional_properties:
+        result.append(load_entry_point("opentelemetry_propagator", name)())
+
     return result
 
 
@@ -85,7 +97,7 @@ def create_propagator(
             name = name.strip()
             if not name or name.lower() == "none":
                 continue
-            propagator = _load_entry_point_propagator(name)
+            propagator = load_entry_point("opentelemetry_propagator", name)()
             propagators.setdefault(type(propagator), propagator)
 
     return CompositePropagator(list(propagators.values()))

opentelemetry-sdk/tests/_configuration/test_propagator.py

@@ -236,6 +236,40 @@ def test_unknown_composite_list_propagator_raises(self):
             with self.assertRaises(ConfigurationError):
                 create_propagator(config)
 
+    def test_plugin_propagator_via_entry_point(self):
+        mock_propagator = MagicMock()
+        mock_ep = MagicMock()
+        mock_ep.load.return_value = lambda: mock_propagator
+
+        with patch(
+            "opentelemetry.sdk._configuration._common.entry_points",
+            return_value=[mock_ep],
+        ):
+            config = PropagatorConfig(
+                composite=[
+                    # pylint: disable=unexpected-keyword-arg
+                    TextMapPropagatorConfig(my_custom_propagator={})
+                ]
+            )
+            result = create_propagator(config)
+
+        self.assertEqual(len(result._propagators), 1)  # type: ignore[attr-defined]
+        self.assertIs(result._propagators[0], mock_propagator)  # type: ignore[attr-defined]
+
+    def test_unknown_composite_propagator_raises(self):
+        with patch(
+            "opentelemetry.sdk._configuration._common.entry_points",
+            return_value=[],
+        ):
+            config = PropagatorConfig(
+                composite=[
+                    # pylint: disable=unexpected-keyword-arg
+                    TextMapPropagatorConfig(nonexistent={})
+                ]
+            )
+            with self.assertRaises(ConfigurationError):
+                create_propagator(config)
+
 
 class TestConfigurePropagator(unittest.TestCase):
     def test_configure_propagator_calls_set_global_textmap(self):