wire host resource detector in declarative config

Makes _HostResourceDetector public as HostResourceDetector and wires
it to detection_development.detectors[].host in _run_detectors().

Assisted-by: Claude Sonnet 4.6

Author: MikeGoldsmith

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

@@ -29,6 +29,7 @@
 from opentelemetry.sdk.resources import (
     _DEFAULT_RESOURCE,
     SERVICE_NAME,
+    HostResourceDetector,
     Resource,
 )
 
@@ -152,6 +153,8 @@ def _run_detectors(
     is updated in-place; later detectors overwrite earlier ones for the
     same key.
     """
+    if detector_config.host is not None:
+        detected_attrs.update(HostResourceDetector().detect().attributes)
 
 
 def _filter_attributes(

opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py

@@ -490,10 +490,8 @@ def detect(self) -> "Resource":
         )
 
 
-class _HostResourceDetector(ResourceDetector):  # type: ignore[reportUnusedClass]
-    """
-    The HostResourceDetector detects the hostname and architecture attributes.
-    """
+class HostResourceDetector(ResourceDetector):
+    """Detects host.name (hostname) and host.arch (CPU architecture)."""
 
     def detect(self) -> "Resource":
         return Resource(

opentelemetry-sdk/tests/_configuration/test_resource.py

@@ -13,16 +13,22 @@
 # limitations under the License.
 
 import os
+import socket
 import unittest
 from unittest.mock import patch
 
 from opentelemetry.sdk._configuration._resource import create_resource
 from opentelemetry.sdk._configuration.models import (
     AttributeNameValue,
     AttributeType,
+    ExperimentalResourceDetection,
+    ExperimentalResourceDetector,
+    IncludeExclude,
 )
 from opentelemetry.sdk._configuration.models import Resource as ResourceConfig
 from opentelemetry.sdk.resources import (
+    HOST_ARCH,
+    HOST_NAME,
     SERVICE_NAME,
     TELEMETRY_SDK_LANGUAGE,
     TELEMETRY_SDK_NAME,
@@ -295,3 +301,73 @@ def test_attributes_list_invalid_pair_skipped(self):
         self.assertEqual(resource.attributes["foo"], "bar")
         self.assertNotIn("no-equals", resource.attributes)
         self.assertTrue(any("no-equals" in msg for msg in cm.output))
+
+
+class TestHostResourceDetector(unittest.TestCase):
+    def _config_with_host(self) -> ResourceConfig:
+        return ResourceConfig(
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(host={})]
+            )
+        )
+
+    def test_host_detector_adds_host_attributes(self):
+        resource = create_resource(self._config_with_host())
+        self.assertIn(HOST_NAME, resource.attributes)
+        self.assertEqual(resource.attributes[HOST_NAME], socket.gethostname())
+        self.assertIn(HOST_ARCH, resource.attributes)
+
+    def test_host_detector_also_includes_sdk_defaults(self):
+        resource = create_resource(self._config_with_host())
+        self.assertEqual(resource.attributes[TELEMETRY_SDK_LANGUAGE], "python")
+        self.assertIn(TELEMETRY_SDK_VERSION, resource.attributes)
+
+    def test_host_detector_not_run_when_absent(self):
+        resource = create_resource(ResourceConfig())
+        self.assertNotIn(HOST_NAME, resource.attributes)
+        self.assertNotIn(HOST_ARCH, resource.attributes)
+
+    def test_host_detector_not_run_when_detection_development_is_none(self):
+        resource = create_resource(ResourceConfig(detection_development=None))
+        self.assertNotIn(HOST_NAME, resource.attributes)
+
+    def test_host_detector_not_run_when_detectors_list_empty(self):
+        config = ResourceConfig(
+            detection_development=ExperimentalResourceDetection(detectors=[])
+        )
+        resource = create_resource(config)
+        self.assertNotIn(HOST_NAME, resource.attributes)
+
+    def test_explicit_attributes_override_host_detector(self):
+        config = ResourceConfig(
+            attributes=[
+                AttributeNameValue(name="host.name", value="custom-host")
+            ],
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(host={})]
+            ),
+        )
+        resource = create_resource(config)
+        self.assertEqual(resource.attributes[HOST_NAME], "custom-host")
+
+    def test_included_filter_limits_host_attributes(self):
+        config = ResourceConfig(
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(host={})],
+                attributes=IncludeExclude(included=["host.name"]),
+            )
+        )
+        resource = create_resource(config)
+        self.assertIn(HOST_NAME, resource.attributes)
+        self.assertNotIn(HOST_ARCH, resource.attributes)
+
+    def test_excluded_filter_removes_host_attributes(self):
+        config = ResourceConfig(
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(host={})],
+                attributes=IncludeExclude(excluded=["host.name"]),
+            )
+        )
+        resource = create_resource(config)
+        self.assertNotIn(HOST_NAME, resource.attributes)
+        self.assertIn(HOST_ARCH, resource.attributes)