fix: --reporter-option on CLI overrides values from config (#5532)

[devareddy05]

PR Checklist

• Addresses an existing open issue: fixes Bug: command line reporter-options parameter doesn't override .mocharc.yml #5532
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

--reporter-option (--reporter-options, -O) given on the CLI did not override the same key declared in .mocharc.* or package.json. The config-file value won instead. Regression observed since v8.3.0, still present in v11.7.5+. The maintainer comment on the issue narrowed it to "Mocha not recognizing the clashing options as 'clashing'".

Root cause

In lib/cli/options.mjs, the second call to parse(...) passes CLI args, env, RC, and package.json as configObjects in priority-HIGH→LOW order. yargs-parser's combine-arrays: true concatenates the reporter-option array from every source in that order: [CLI, env, rc, pkg]. The downstream coerce in lib/cli/run.js (around L223-L243) then reduces this array left-to-right with last-writer-wins — so the lowest-priority source ends up taking precedence, which is the inverse of the intended priority order.

Fix

After the second parse, re-emit reporter-option in priority-LOW→HIGH order (pkg, rc, env, CLI). The coerce's existing last-writer-wins reduction now yields the correct result: CLI overrides env overrides rc overrides pkg. Per-key merge semantics are preserved — CLI overrides only the clashing keys; non-clashing keys from the config still flow through.

A small helper (readReporterOption) reads the value under any of the supported source-side aliases (reporter-option, reporter-options, reporterOption, reporterOptions, O) so config files written with either casing/spelling are respected.

Behavior matrix (verified locally)

Scenario	Result
CLI output=cli.xml, config output=config.xml	CLI wins → cli.xml
CLI output=cli.xml, config output=config.xml, suiteName=FromConfig	{output: 'cli.xml', suiteName: 'FromConfig'}
CLI repeats foo=bar foo=baz, no config	{foo: 'baz'} (last wins, unchanged)
Env foo=fromEnv, config foo=fromConfig	Env wins

Tests

• New integration test in test/integration/options/reporter-option.spec.js: "should allow the CLI to override clashing keys from the config", driving Mocha via --config <fixture-yaml> + --reporter-option foo=fromCli and asserting the custom reporter prints {"foo":"fromCli","extra":"keepMe"}.
• New fixture: test/integration/fixtures/options/reporter-option-mocharc.yml.

Validation

• npm run format:check, npm run tsc — clean
• npm run test-smoke — 1/1 passing
• npm run -s test-node-run -- "test/integration/options/reporter-option.spec.js" — 4/4 passing (3 pre-existing + 1 new)
• npm run -s test-node-run -- "test/integration/options/*.spec.js" — 158/158 passing
• npm run test-node:unit — 1008 passing, 3 pending

Closes #5532