feat(config): add resource and propagator creation from declarative config

[MikeGoldsmith]

Description

Implements step 3 of the declarative configuration work (see below), resource and propagator creation from a parsed config file.

• Add declarative configuration prototype #3631

Adds:

• create_resource(config) — builds an SDK Resource from the declarative config model without reading OTEL_RESOURCE_ATTRIBUTES or running any resource detectors (matches Java/JS SDK behavior). Starts from SDK telemetry defaults (telemetry.sdk.*), merges attributes (with AttributeType coercion) and attributes_list (URL-decoded, lower priority), and adds service.name=unknown_service if not specified.
• create_propagator(config) — builds a CompositePropagator from the config's composite list and/or composite_list string. Deduplicates by propagator type. Returns an empty CompositePropagator (noop) when no propagator is configured.
• configure_propagator(config) — calls set_global_textmap to override Python's default env-var-based propagator setup.
• ConfigurationError moved to _exceptions.py to break a circular import introduced when file/__init__.py re-exports the new functions.

All functions are exported from opentelemetry.sdk._configuration.file.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

43 new unit tests covering:

• All AttributeType coercions (string, bool, int, double, and array variants)
• attributes_list parsing: priority vs explicit attributes, URL decoding, = in values, invalid pairs
• schema_url passthrough
• OTEL_RESOURCE_ATTRIBUTES env var is NOT read
• All four built-in propagators (tracecontext, baggage, b3, b3multi)
• composite + composite_list merging and deduplication
• none and empty entries in composite_list skipped
• Missing entry point raises ConfigurationError
• configure_propagator calls set_global_textmap

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

Assisted-by: Claude Sonnet 4.6

[pmcollins]

Looks great. Minor comments below.

[herin049]

Should the structured propagator list also support entrypoints?

[MikeGoldsmith]

The structured composite list is intentionally limited to the four types defined in the config schema (tracecontext, baggage, b3, b3multi) — the schema enforces maxProperties: 1 with fixed property names, so there's no way to specify an unknown third-party propagator via that path. For anything outside those four, composite_list (the comma-separated string) is the right mechanism, and that does use entry points. So I don't think we need entry point support in the structured path.

[pmcollins]

Thanks, LGTM once suggestions are addressed (I added a typing suggestion).

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: herin049 / name: Lukas Hering (15431b4)
• ✅ login: MikeGoldsmith / name: Mike Goldsmith (15431b4, 7d2379d, a7c17a0, b3a3980, e1c16a6, f708be9)

[MikeGoldsmith]

I think the Misc/tracecontext failure is a flakey test. Please can someone, re-run it for me?

[herin049]

Suggested change

	def _map_compression(
	value: Optional[str], compression_enum: type
	) -> Optional[object]:
	"""Map a compression string to the given Compression enum value."""
	if value is None or value.lower() == "none":
	return None
	if value.lower() == "gzip":
	return compression_enum.Gzip # type: ignore[attr-defined]
	raise ConfigurationError(
	f"Unsupported compression value '{value}'. Supported values: 'gzip', 'none'."
	)
	class CompressionT(Protocol[T]):
	@property
	def Gzip(self) -> T: ...
	def _map_compression(
	value: Optional[str], compression_enum: CompressionT[T]
	) -> Optional[T]:
	"""Map a compression string to the given Compression enum value."""
	if value is None or value.lower() == "none":
	return None
	if value.lower() == "gzip":
	return compression_enum.Gzip
	raise ConfigurationError(
	f"Unsupported compression value '{value}'. Supported values: 'gzip', 'none'."
	)

[MikeGoldsmith]

Thanks for the suggestion @herin049.

I tried using Protocol[T] but ran into a Pyright limitation: we pass the enum class itself (e.g. grpc.Compression) as compression_enum, not an instance of it.

This means:

• @Property def Gzip(self) -> T describes instance-level access, so Pyright rejects type[Compression] as incompatible
• ClassVar[T] would describe class-level access correctly, but Pyright doesn't allow TypeVars inside ClassVar

I reverted back to compression_enum: type with # type: ignore[attr-defined].

If you know a way to express this that Pyright accepts, happy to revisit — but I couldn't find a clean path.

Thanks