dc_util owns parameter declaration; nav2_util stays a dependency

Before this decision, parameter declaration in dc_measurements/dc_group was three patterns at once: most Measurement/Condition plugins called nav2_util::declare_parameter_if_not_declared directly, duplicating the same declare-then-get_parameter-then-fatal-on-failure boilerplate in each onConfigure(); measurement_server.cpp mixed that with a handful of raw declare_parameter calls for its own node-level parameters (which throw on redeclaration instead of being idempotent); and a dc_util::get_*_type_param() helper family existed but was only used in ~20 of the roughly 90 plugin-parameter call sites, wrapping nav2_util::declare_parameter_if_not_declared for the rest without most callers going through it.

Decision

  • nav2_util stays a dependency. MeasurementServer already inherits nav2_util::LifecycleNode for the bond/lifecycle machinery dc_lifecycle_manager orchestrates — dropping nav2_util isn't on the table regardless of how parameter declaration is handled, so re-implementing declare_parameter_if_not_declared's idempotent-declare logic inside dc_util would only add a second implementation of the same thing for no dependency-removal benefit.
  • dc_util::get_*_type_param() / get_*_param() become the single sanctioned way to declare a parameter in dc_measurements/dc_group C++ code. Plugin authors call these, never declare_parameter or nav2_util::declare_parameter_if_not_declared directly (documented in doc/src/dc/contributing.md). Internally these helpers still call nav2_util::declare_parameter_if_not_declared — dc_util/include/dc_util/node_utils.hpp is now the only file in dc_measurements/dc_group allowed to reference nav2_util for parameter declaration — so the dependency is kept, but callers no longer see it or hand-roll its error handling.
  • The helper family was extended to cover every parameter type actually declared across the plugins (double, and mandatory vector<bool>/vector<int64_t>/vector<double> were missing) plus a node-level (unprefixed) variant for MeasurementServer's own parameters, so the raw declare_parameter calls in its constructor could move to the same idempotent pattern as everything else.
  • dc_group (Python/rclpy) keeps its existing plain self.declare_parameter(...) calls. There is no Python equivalent of nav2_util::declare_parameter_if_not_declared in this codebase, and none is needed: every GroupServer parameter is declared exactly once, in init_parameters(), never re-entered — the idempotent-declare problem the C++ helpers solve (multiple plugins/onConfigure() calls potentially racing to declare a shared namespace) doesn't exist on the group-server side. Introducing a declare-if-not-declared wrapper there would be solving a problem this file doesn't have.

Consequences

  • A new plugin parameter is one dc_util::get_*_type_param() call, not a declare-if-not-declared pair plus a manual fatal-on-missing check.
  • Two pre-existing bugs surfaced while converting call sites — bool_equal.cpp's value_ field is double despite the parameter being declared PARAMETER_BOOL, and distance_traveled.cpp declares transform_tolerance but reads back the different, undeclared name transform_timeout — were deliberately left as direct nav2_util::declare_parameter_if_not_declared/get_parameter calls rather than folded into the new helpers, so as not to silently change behavior while unifying the declaration pattern. Both are noted inline and are follow-up work, not part of this change.