[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

[codecov]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.92%. Comparing base (87696d5) to head (2e71d62).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/cli/options.mjs	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5986      +/-   ##
==========================================
- Coverage   78.12%   77.92%   -0.21%     
==========================================
  Files          63       63              
  Lines        4590     4602      +12     
  Branches      997      984      -13     
==========================================
  Hits         3586     3586              
- Misses       1004     1016      +12     

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[mark-wiemer]

Test failure is known issue #6036

[JoshuaKGoldberg]

Thanks for the contribution! And sorry it took so long to review. But:

• We've since refactored this area of logic in Mocha significantly. See #6164 & co.
• This was clearly authored with AI in a way that runs counter to the AI-Generated Code section of our contributing guidelines

For just one of those I'd request changes, but for both I'm going to go ahead and close this out. Feel free to send another PR if you'd like though - I left a couple of thoughts on this one. Cheers!

[JoshuaKGoldberg]

[Comments] This // comment conflicts with the existing JSDoc for the function. This should add to the JSDoc instead.

[JoshuaKGoldberg]

[Refactor] This is quite a lot of complexity for a pretty small area of bug. And, we actually refactored away yargs & yargs-parser on main in the meantime. The mergeConfigObjects we added on main would be a good place for this kind of thing.