fix(config): align additional_properties typing

opentelemetry-sdk/codegen/dataclass.jinja2

@@ -3,7 +3,7 @@
    JSON Schema additionalProperties. When a schema type allows additional
    properties (e.g. Sampler, SpanExporter), this template adds:
    - @_additional_properties decorator (captures user-defined kwargs)
-   - additional_properties: ClassVar[dict[str, Any]] annotation (for type checkers)
+   - additional_properties instance field matching the decorator runtime behavior
 
    The template checks two context variables set by datamodel-codegen:
    - additionalProperties: set when the schema value is a boolean (true/false)
@@ -69,5 +69,5 @@ class {{ class_name }}:
     {%- endif %}
 {%- endfor -%}
 {%- if has_additional %}
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(default_factory=dict, init=False)
 {%- endif -%}

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

@@ -30,7 +30,7 @@ def _additional_properties(cls):
     """
     original_init = cls.__init__
     original_sig = inspect.signature(original_init)
-    known_fields = frozenset(f.name for f in dataclasses.fields(cls))
+    known_fields = frozenset(f.name for f in dataclasses.fields(cls) if f.init)
 
     def _init(self, **kwargs):
         known = {k: v for k, v in kwargs.items() if k in known_fields}
@@ -81,10 +81,8 @@ class _ComponentConfig(Protocol):
     for ``**kwargs`` splatting to the user-defined component class) or
     ``None`` (when the YAML uses ``my_plugin:`` or ``my_plugin: null``).
 
-    Note: the generated models declare ``additional_properties`` as a
-    ``ClassVar`` even though the decorator assigns it as an instance
-    attribute at runtime. This is tolerated by pyright in ``standard``
-    mode but flagged in ``strict`` mode. See #5268.
+    The generated models declare ``additional_properties`` as an instance
+    field to match the decorator's runtime assignment.
     """
 
     additional_properties: dict[str, dict[str, Any] | None]

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

@@ -172,17 +172,20 @@ def _run_detectors(
     The detected_attrs dict is updated in-place; later detectors overwrite
     earlier ones for the same key.
     """
-    for name in dataclasses.fields(detector_config):
-        value = getattr(detector_config, name.name, None)
+    for field in dataclasses.fields(detector_config):
+        if not field.init:
+            continue
+
+        value = getattr(detector_config, field.name, None)
         if value is None:
             continue
-        if name.name in _RESOURCE_DETECTOR_REGISTRY:
+        if field.name in _RESOURCE_DETECTOR_REGISTRY:
             detected_attrs.update(
-                _RESOURCE_DETECTOR_REGISTRY[name.name](value)
+                _RESOURCE_DETECTOR_REGISTRY[field.name](value)
             )
         else:
             cls = load_entry_point(
-                "opentelemetry_resource_detector", name.name
+                "opentelemetry_resource_detector", field.name
             )
             detected_attrs.update(cls(**(value or {})).detect().attributes)
 

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

@@ -4,9 +4,9 @@
 
 from __future__ import annotations
 
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from enum import Enum
-from typing import Any, ClassVar, TypeAlias
+from typing import Any, TypeAlias
 
 from opentelemetry.sdk._configuration._common import _additional_properties
 
@@ -359,7 +359,9 @@ class SpanExporter:
     otlp_grpc: OtlpGrpcExporter | None = None
     otlp_file_development: ExperimentalOtlpFileExporter | None = None
     console: ConsoleExporter | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 class SpanKind(Enum):
@@ -511,7 +513,9 @@ class ExperimentalResourceDetector:
     host: ExperimentalHostResourceDetector | None = None
     process: ExperimentalProcessResourceDetector | None = None
     service: ExperimentalServiceResourceDetector | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @dataclass
@@ -537,21 +541,27 @@ class LogRecordExporter:
     otlp_grpc: OtlpGrpcExporter | None = None
     otlp_file_development: ExperimentalOtlpFileExporter | None = None
     console: ConsoleExporter | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @_additional_properties
 @dataclass
 class MetricProducer:
     opencensus: OpenCensusMetricProducer | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @_additional_properties
 @dataclass
 class PullMetricExporter:
     prometheus_development: ExperimentalPrometheusMetricExporter | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @dataclass
@@ -568,7 +578,9 @@ class PushMetricExporter:
     otlp_grpc: OtlpGrpcMetricExporter | None = None
     otlp_file_development: ExperimentalOtlpFileMetricExporter | None = None
     console: ConsoleMetricExporter | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @dataclass
@@ -586,7 +598,9 @@ class SimpleSpanProcessor:
 class SpanProcessor:
     batch: BatchSpanProcessor | None = None
     simple: SimpleSpanProcessor | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @_additional_properties
@@ -596,7 +610,9 @@ class TextMapPropagator:
     baggage: BaggagePropagator | None = None
     b3: B3Propagator | None = None
     b3multi: B3MultiPropagator | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @dataclass
@@ -662,7 +678,9 @@ class ExperimentalResourceDetection:
 class LogRecordProcessor:
     batch: BatchLogRecordProcessor | None = None
     simple: SimpleLogRecordProcessor | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @dataclass
@@ -731,7 +749,9 @@ class OpenTelemetryConfiguration:
     resource: Resource | None = None
     instrumentation_development: ExperimentalInstrumentation | None = None
     distribution: Distribution | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @dataclass
@@ -773,7 +793,9 @@ class ExperimentalComposableSampler:
     )
     probability: ExperimentalComposableProbabilitySampler | None = None
     rule_based: ExperimentalComposableRuleBasedSampler | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @dataclass
@@ -802,7 +824,9 @@ class Sampler:
     parent_based: ParentBasedSampler | None = None
     probability_development: ExperimentalProbabilitySampler | None = None
     trace_id_ratio_based: TraceIdRatioBasedSampler | None = None
-    additional_properties: ClassVar[dict[str, Any]]
+    additional_properties: dict[str, dict[str, Any] | None] = field(
+        default_factory=dict, init=False
+    )
 
 
 @dataclass

opentelemetry-sdk/tests/_configuration/test_common.py

@@ -3,9 +3,9 @@
 
 import inspect
 import unittest
-from dataclasses import dataclass
+from dataclasses import dataclass, field, fields
 from types import SimpleNamespace
-from typing import Any, ClassVar
+from typing import Any
 from unittest.mock import MagicMock, patch
 
 from opentelemetry.sdk._configuration._common import (
@@ -213,7 +213,9 @@ def setUp(self):
         class _SampleConfig:
             known_field: dict | None = None
             another_field: str | None = None
-            additional_properties: ClassVar[dict[str, Any]]
+            additional_properties: dict[str, dict[str, Any] | None] = field(
+                default_factory=dict, init=False
+            )
 
         self.cls = _SampleConfig
 
@@ -265,11 +267,23 @@ class TestGeneratedModelsHaveAdditionalProperties(unittest.TestCase):
     def _assert_supports_additional_properties(self, model_cls):
         # pylint: disable=unexpected-keyword-arg
         obj = model_cls(_test_plugin_key={})
+        other = model_cls()
         self.assertTrue(
             hasattr(obj, "additional_properties"),
             f"{model_cls.__name__} missing additional_properties attribute",
         )
         self.assertIn("_test_plugin_key", obj.additional_properties)
+        self.assertEqual(other.additional_properties, {})
+        self.assertIsNot(
+            obj.additional_properties, other.additional_properties
+        )
+
+        additional_properties_field = next(
+            field
+            for field in fields(model_cls)
+            if field.name == "additional_properties"
+        )
+        self.assertFalse(additional_properties_field.init)
 
     def test_sampler(self):
         self._assert_supports_additional_properties(Sampler)
@@ -299,7 +313,9 @@ def setUp(self):
         class _Config:
             builtin_a: dict | None = None
             builtin_b: str | None = None
-            additional_properties: ClassVar[dict[str, Any]]
+            additional_properties: dict[str, dict[str, Any] | None] = field(
+                default_factory=dict, init=False
+            )
 
         self.cls = _Config
         self.registry = {