Description

Adds pull metric reader support to declarative file configuration, including Prometheus metric reader via the prometheus_development config field.

Previously, _create_metric_reader() raised ConfigurationError for any pull reader config. Now it dispatches to new factory functions that handle both the built-in Prometheus reader and plugin-based pull readers.

How it works

Prometheus (prometheus_development):

• Dynamically imports PrometheusMetricReader and start_http_server from opentelemetry-exporter-prometheus (same try/except pattern as OTLP exporters)
• Maps config fields: without_target_info_development → disable_target_info, host/port → start_http_server()
• Warns for unsupported fields: without_scope_info, with_resource_constant_labels

Plugin pull readers:

• Unknown exporter names in additional_properties are loaded via load_entry_point("opentelemetry_pull_metric_exporter", name)(**(config or {}))

Not yet supported (warnings logged):

• producers — SDK doesn't have MetricProducer support yet (feat(config): add pull metric reader support to declarative config #5074)
• cardinality_limits — deferred

Design note

Pull "exporters" like Prometheus are combined reader+exporter objects — PrometheusMetricReader IS a MetricReader. The _create_pull_metric_exporter() function returns a MetricReader, matching the config schema's terminology while reflecting the SDK's class hierarchy.

Example config

meter_provider:
  readers:
    - pull:
        exporter:
          prometheus_development:
            host: "0.0.0.0"
            port: 9090
            without_target_info_development: true

Tests

8 new tests covering: prometheus creation with config, defaults, missing package, no exporter, plugin loading, plugin not found, producers warning, cardinality_limits warning.

Closes #5073