add propagator plugin loading to declarative config via entry points

TextMapPropagator is changed from @DataClass to TypeAlias = dict[str, Any]
in models.py, preserving unknown propagator names (plugin names) as dict
keys through the config pipeline — same approach as Sampler.

_propagators_from_textmap_config() now iterates the dict's key-value pairs
directly. Known names (tracecontext, baggage) are bootstrapped from
_PROPAGATOR_REGISTRY. All other names — including b3, b3multi, and custom
plugin propagators — fall back to load_entry_point("opentelemetry_propagator",
name), matching the spec's PluginComponentProvider mechanism.

Assisted-by: Claude Sonnet 4.6

Author: MikeGoldsmith

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
+  ([#5070](https://github.com/open-telemetry/opentelemetry-python/pull/5070))
 - `opentelemetry-sdk`: add `load_entry_point` shared utility to declarative file configuration for loading plugins via entry points; refactor propagator loading to use it
   ([#5093](https://github.com/open-telemetry/opentelemetry-python/pull/5093))
 - `opentelemetry-sdk`: Add `create_logger_provider`/`configure_logger_provider` to declarative file configuration, enabling LoggerProvider instantiation from config files without reading env vars

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

@@ -24,32 +24,33 @@
 from opentelemetry.sdk._configuration.models import (
     Propagator as PropagatorConfig,
 )
-from opentelemetry.sdk._configuration.models import (
-    TextMapPropagator as TextMapPropagatorConfig,
-)
 from opentelemetry.trace.propagation.tracecontext import (
     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,
+    config: dict,
 ) -> list[TextMapPropagator]:
-    """Resolve a single TextMapPropagator config entry to a list of propagators."""
+    """Resolve a TextMapPropagator config dict to a list of propagators.
+
+    Each key in the dict names a propagator. Known names (tracecontext, baggage)
+    are bootstrapped directly. All other names — including b3, b3multi, and
+    custom plugin propagators — are loaded via the ``opentelemetry_propagator``
+    entry point group, matching the spec's PluginComponentProvider mechanism.
+    """
     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, prop_config in config.items():
+        if name in _PROPAGATOR_REGISTRY:
+            result.append(_PROPAGATOR_REGISTRY[name](prop_config))
+        else:
+            result.append(load_entry_point("opentelemetry_propagator", name)())
     return result
 
 
@@ -85,7 +86,7 @@ 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/src/opentelemetry/sdk/_configuration/models.py

@@ -573,12 +573,10 @@ class SpanProcessor:
     simple: SimpleSpanProcessor | None = None
 
 
-@dataclass
-class TextMapPropagator:
-    tracecontext: TraceContextPropagator | None = None
-    baggage: BaggagePropagator | None = None
-    b3: B3Propagator | None = None
-    b3multi: B3MultiPropagator | None = None
+# Diverges from codegen: TextMapPropagator is typed as dict[str, Any] rather
+# than a dataclass so that unknown propagator names (plugin/custom propagators)
+# are preserved as dict keys through the config pipeline.
+TextMapPropagator: TypeAlias = dict[str, Any]
 
 
 @dataclass

opentelemetry-sdk/tests/_configuration/test_propagator.py

@@ -30,9 +30,6 @@
 from opentelemetry.sdk._configuration.models import (
     Propagator as PropagatorConfig,
 )
-from opentelemetry.sdk._configuration.models import (
-    TextMapPropagator as TextMapPropagatorConfig,
-)
 from opentelemetry.trace.propagation.tracecontext import (
     TraceContextTextMapPropagator,
 )
@@ -50,9 +47,7 @@ def test_empty_config_returns_empty_composite(self):
         self.assertEqual(result._propagators, [])  # type: ignore[attr-defined]
 
     def test_tracecontext_only(self):
-        config = PropagatorConfig(
-            composite=[TextMapPropagatorConfig(tracecontext={})]
-        )
+        config = PropagatorConfig(composite=[{"tracecontext": {}}])
         result = create_propagator(config)
         self.assertEqual(len(result._propagators), 1)  # type: ignore[attr-defined]
         self.assertIsInstance(
@@ -61,18 +56,16 @@ def test_tracecontext_only(self):
         )
 
     def test_baggage_only(self):
-        config = PropagatorConfig(
-            composite=[TextMapPropagatorConfig(baggage={})]
-        )
+        config = PropagatorConfig(composite=[{"baggage": {}}])
         result = create_propagator(config)
         self.assertEqual(len(result._propagators), 1)  # type: ignore[attr-defined]
         self.assertIsInstance(result._propagators[0], W3CBaggagePropagator)  # type: ignore[attr-defined]
 
     def test_tracecontext_and_baggage(self):
         config = PropagatorConfig(
             composite=[
-                TextMapPropagatorConfig(tracecontext={}),
-                TextMapPropagatorConfig(baggage={}),
+                {"tracecontext": {}},
+                {"baggage": {}},
             ]
         )
         result = create_propagator(config)
@@ -92,9 +85,7 @@ def test_b3_via_entry_point(self):
             "opentelemetry.sdk._configuration._common.entry_points",
             return_value=[mock_ep],
         ):
-            config = PropagatorConfig(
-                composite=[TextMapPropagatorConfig(b3={})]
-            )
+            config = PropagatorConfig(composite=[{"b3": {}}])
             result = create_propagator(config)
 
         self.assertEqual(len(result._propagators), 1)  # type: ignore[attr-defined]
@@ -109,9 +100,7 @@ def test_b3multi_via_entry_point(self):
             "opentelemetry.sdk._configuration._common.entry_points",
             return_value=[mock_ep],
         ):
-            config = PropagatorConfig(
-                composite=[TextMapPropagatorConfig(b3multi={})]
-            )
+            config = PropagatorConfig(composite=[{"b3multi": {}}])
             result = create_propagator(config)
 
         self.assertEqual(len(result._propagators), 1)  # type: ignore[attr-defined]
@@ -121,9 +110,7 @@ def test_b3_not_installed_raises_configuration_error(self):
             "opentelemetry.sdk._configuration._common.entry_points",
             return_value=[],
         ):
-            config = PropagatorConfig(
-                composite=[TextMapPropagatorConfig(b3={})]
-            )
+            config = PropagatorConfig(composite=[{"b3": {}}])
             with self.assertRaises(ConfigurationError) as ctx:
                 create_propagator(config)
         self.assertIn("b3", str(ctx.exception))
@@ -214,7 +201,7 @@ def test_deduplication_across_composite_and_composite_list(self):
             return_value=[mock_ep],
         ):
             config = PropagatorConfig(
-                composite=[TextMapPropagatorConfig(tracecontext={})],
+                composite=[{"tracecontext": {}}],
                 composite_list="tracecontext",
             )
             result = create_propagator(config)
@@ -236,6 +223,30 @@ 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=[{"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=[{"nonexistent": {}}])
+            with self.assertRaises(ConfigurationError):
+                create_propagator(config)
+
 
 class TestConfigurePropagator(unittest.TestCase):
     def test_configure_propagator_calls_set_global_textmap(self):
@@ -248,9 +259,7 @@ def test_configure_propagator_calls_set_global_textmap(self):
             self.assertIsInstance(arg, CompositePropagator)
 
     def test_configure_propagator_with_config(self):
-        config = PropagatorConfig(
-            composite=[TextMapPropagatorConfig(tracecontext={})]
-        )
+        config = PropagatorConfig(composite=[{"tracecontext": {}}])
         with patch(
             "opentelemetry.sdk._configuration._propagator.set_global_textmap"
         ) as mock_set:
@@ -263,9 +272,7 @@ def test_configure_propagator_with_config(self):
     @patch.dict(environ, {OTEL_PROPAGATORS: "baggage"})
     def test_otel_propagators_env_var_ignored(self):
         """OTEL_PROPAGATORS env var must not influence configure_propagator output."""
-        config = PropagatorConfig(
-            composite=[TextMapPropagatorConfig(tracecontext={})]
-        )
+        config = PropagatorConfig(composite=[{"tracecontext": {}}])
         with patch(
             "opentelemetry.sdk._configuration._propagator.set_global_textmap"
         ) as mock_set: