feat(config): sampler 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 sampler plugin loading to declarative file configuration via the `opentelemetry_sampler` entry point group, matching the spec's PluginComponentProvider mechanism
+  ([#5095](https://github.com/open-telemetry/opentelemetry-python/pull/5095))
 - `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/_tracer_provider.py

@@ -18,7 +18,10 @@
 from typing import Optional
 
 from opentelemetry import trace
-from opentelemetry.sdk._configuration._common import _parse_headers
+from opentelemetry.sdk._configuration._common import (
+    _parse_headers,
+    load_entry_point,
+)
 from opentelemetry.sdk._configuration._exceptions import ConfigurationError
 from opentelemetry.sdk._configuration.models import (
     OtlpGrpcExporter as OtlpGrpcExporterConfig,
@@ -184,7 +187,13 @@ def _create_span_processor(
 
 
 def _create_sampler(config: SamplerConfig) -> Sampler:
-    """Create a sampler from config."""
+    """Create a sampler from config.
+
+    Known sampler types are checked via typed fields on the Sampler
+    dataclass. Unknown sampler names captured in additional_properties
+    by the @_additional_properties decorator are loaded via the
+    ``opentelemetry_sampler`` entry point group.
+    """
     if config.always_on is not None:
         return ALWAYS_ON
     if config.always_off is not None:
@@ -194,6 +203,9 @@ def _create_sampler(config: SamplerConfig) -> Sampler:
         return TraceIdRatioBased(ratio if ratio is not None else 1.0)
     if config.parent_based is not None:
         return _create_parent_based_sampler(config.parent_based)
+    if config.additional_properties:
+        name = next(iter(config.additional_properties))
+        return load_entry_point("opentelemetry_sampler", name)()
     raise ConfigurationError(
         f"Unknown or unsupported sampler type in config: {config!r}. "
         "Supported types: always_on, always_off, trace_id_ratio_based, parent_based."

opentelemetry-sdk/tests/_configuration/test_tracer_provider.py

@@ -69,6 +69,7 @@
     ALWAYS_OFF,
     ALWAYS_ON,
     ParentBased,
+    Sampler,
     TraceIdRatioBased,
 )
 
@@ -219,9 +220,27 @@ def test_parent_based_with_delegate_samplers(self):
 
     def test_unknown_sampler_raises_configuration_error(self):
         with self.assertRaises(ConfigurationError):
-            create_tracer_provider(
-                TracerProviderConfig(processors=[], sampler=SamplerConfig())
-            )
+            self._make_provider(SamplerConfig())
+
+    def test_plugin_sampler_loaded_via_entry_point(self):
+        mock_sampler = MagicMock(spec=Sampler)
+        mock_class = MagicMock(return_value=mock_sampler)
+        with patch(
+            "opentelemetry.sdk._configuration._common.entry_points",
+            return_value=[MagicMock(**{"load.return_value": mock_class})],
+        ):
+            # pylint: disable=unexpected-keyword-arg
+            provider = self._make_provider(SamplerConfig(my_custom_sampler={}))
+        self.assertIs(provider.sampler, mock_sampler)
+
+    def test_unknown_plugin_raises_configuration_error(self):
+        with patch(
+            "opentelemetry.sdk._configuration._common.entry_points",
+            return_value=[],
+        ):
+            with self.assertRaises(ConfigurationError):
+                # pylint: disable=unexpected-keyword-arg
+                self._make_provider(SamplerConfig(no_such_sampler={}))
 
 
 class TestCreateSpanExporterAndProcessor(unittest.TestCase):