GenericAnalyzer: expected matcher never populates expected_ (analyzer fails to initialise) #656

Summary

GenericAnalyzer's expected matcher is non-functional: an analyzer whose only matcher is expected fails to initialise, and even alongside another matcher, expected never matches anything.

Root cause

In generic_analyzer.cpp, the expected branch of GenericAnalyzer::init only pre-seeds the base-class items_ map (via addItem()); it never populates the expected_ vector:

} else if (pname.compare("expected") == 0) {
  ...
  for (auto exp : pvalue.as_string_array()) {
    auto item = std::make_shared<StatusItem>(exp);
    this->addItem(exp, item);          // -> items_, never expected_
  }
}

But expected_ is what the rest of the class relies on:

• the init guard — startswith_.size() == 0 && name_.size() == 0 && contains_.size() == 0 && expected_.size() == 0 && regex_.size() == 0 — decides "was not initialized with any way of checking diagnostics";
• match() — iterates expected_ (name == expected_[i]);
• report() — iterates expected_ for missing-item detection.

expected_ is never written anywhere in the file, so:

1. an expected-only analyzer trips the init guard and is dropped, leaving its AnalyzerGroup empty (Group '<x>' doesn't contain any analyzers, can't match); and
2. even combined with another matcher, expected contributes nothing, since match()/report() read the empty expected_.

This is a regression from the ROS 1 implementation, which populated the vector via getParamVals(expected, expected_) before creating the pre-seeded items (noetic-devel generic_analyzer.cpp).

Reproduction

Config (aggregator_node --ros-args --params-file expected.yaml):

/**:
  ros__parameters:
    path: Test
    loctest:
      type: diagnostic_aggregator/GenericAnalyzer
      path: LocTest
      expected: ['some/expected/status_name']
      timeout: 5.0

Actual: node logs GenericAnalyzer 'LocTest' was not initialized with any way of checking diagnostics and Group 'Test' doesn't contain any analyzers, can't match. Swapping expected for startswith/contains/regex works.

Expected: the analyzer initialises and matches statuses whose names are in expected (and reports missing expected items as stale, per the ROS 1 behaviour).

Affected versions

Present in the installed Jazzy build (diagnostic_aggregator 4.2.7) and the current ros2 (rolling) branch.

Fix

A fix (restore expected_ population) plus a regression test is proposed in #655.