declarative config: support Inferred spans

[zeitlinger]

The declarative config bridge has been copied from the agent - eventually, we can use only one, but that's a later step.

Fixes #2029

[zeitlinger]

@JonasKunz please have a look

[zeitlinger]

@jaydeluca please have a look

[zeitlinger]

@jaydeluca please check again

[trask]

(testing out the copilot-instructions.md)

[Copilot]

Pull Request Overview

This PR refactors the inferred spans configuration to support declarative YAML configuration and consolidates configuration logic. The changes enable the experimental_inferred_spans processor to be configured via OpenTelemetry's declarative configuration format, while maintaining backward compatibility with the existing autoconfiguration approach.

Key changes:

• Adds support for declarative YAML configuration through a new InferredSpansSpanProcessorProvider
• Extracts shared configuration logic from InferredSpansAutoConfig into a new InferredSpansConfig class
• Adds an enabled field to InferredSpansConfiguration to support conditional processor creation
• Improves test isolation by using JUnit 5's @TempDir for temporary file management

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
InferredSpansSpanProcessorProvider.java	New provider class that enables declarative configuration support for the inferred spans processor
InferredSpansConfig.java	Extracted configuration logic from InferredSpansAutoConfig to enable reuse across configuration approaches
InferredSpansAutoConfig.java	Refactored to delegate configuration logic to InferredSpansConfig
InferredSpansProcessorBuilder.java	Added profilerEnabled method to support the new enabled configuration field
InferredSpansProcessor.java	Updated constructor call to include new tempDir parameter
SamplingProfiler.java	Added tempDir field and early exit logic when profiling is disabled
InferredSpansConfiguration.java	Added enabled field and corresponding getter method
SamplingProfilerTest.java	Refactored to use @TempDir for better test isolation
InferredSpansAutoConfigTest.java	Updated test references from InferredSpansAutoConfig constants to InferredSpansConfig constants
InferredSpansSpanProcessorProviderTest.java	New test file for declarative configuration functionality
build.gradle.kts	Added dependencies required for declarative configuration support
README.md	Added documentation section explaining declarative configuration usage

Comments suppressed due to low confidence (1)

inferred-spans/README.md:37

• Corrected spelling: 'he frequency' should be 'The frequency'.

| otel.inferred.spans.sampling.interval <br/> OTEL_INFERRED_SPANS_SAMPLING_INTERVAL             | `50ms`                                                                                                                                                                                                                                                            | he frequency at which stack traces are gathered within a profiling session. The lower you set it, the more accurate the durations will be. This comes at the expense of higher overhead and more spans for potentially irrelevant operations. The minimal duration of a profiling-inferred span is the same as the value of this setting.                                                                                                                                                                                                                                                                                         |

[Copilot]

The comment states 'true by default' for declarative configuration, but the code in InferredSpansSpanProcessorProvider.java line 42 shows properties.getBoolean(InferredSpansConfig.ENABLED_OPTION, true), which indeed defaults to true. However, this creates a confusing inconsistency with autoconfiguration which defaults to false. Consider clarifying this difference more prominently in the documentation, perhaps in a separate note or warning box, to prevent user confusion about the different default behaviors.

[Copilot]

The YAML example should also include the enabled property in the list of available options. While it's shown in the example, the declarative configuration section doesn't mention that all autoconfiguration options (including enabled, logging_enabled, backup_diagnostic_files, etc.) are available. Consider adding a note or explicitly mentioning the full list of available properties.