fix: log full error object in logerror (fixes #6462)

[myselfsiddharth]

Summary

Changes logerror in lib/application.js to use console.error(err) instead of console.error(err.stack || err.toString()), so Node's built-in error inspection preserves Error.cause, custom enumerable properties (e.g. Sequelize parent/original), and AggregateError details.

This matches the approach in #6464 (approved in review; vestigial err.stack workaround from pre-Node-18 when console.error(err) did not print stacks). Express 5 already requires Node >= 18.

This PR is rebased on current master and adds regression test coverage (test/app.logerror.js) for the default error handler logging path.

Fixes #6462

Related PRs

• Improve error logging by logging full error object #6464 — same one-line fix; happy to close this in favor of Improve error logging by logging full error object #6464 if maintainers prefer, as long as the test lands (here or there).

Test plan

• npm test -- test/app.logerror.js
• Full suite: npm test (1250 passing)

Behavior note

Only affects stderr when the default error handler runs and env !== 'test'. HTTP responses are unchanged.

[myselfsiddharth]

cc @Nitin-Mohapatra — happy to help rebase #6464 or fold this test into that PR if maintainers prefer a single PR.

[Ap-0007]

This is a very clean and necessary improvement! Passing the raw error object directly to console.error leverages Node's built-in error inspection (especially with standard Error.cause support since Node 18).

One minor suggestion to make the added test more robust:
In test/app.logerror.js, console.error is mocked inline inside the test case and restored inside the async callbacks:

    var logged
    var original = console.error
    console.error = function (err) {
      logged = err
    }
    ...

If the HTTP request or test times out, or if an unexpected exception occurs before the callbacks are executed, console.error might not be restored, potentially leaking the mock to other tests in the runner.

To ensure global state is always restored, we can use Mocha's standard beforeEach/afterEach hooks:

describe('logerror', function () {
  var original

  beforeEach(function () {
    original = console.error
  })

  afterEach(function () {
    if (original) {
      console.error = original
    }
  })

  it('should log the full error object', function (done) {
    var app = express()
    app.set('env', 'development')

    var logged
    console.error = function (err) {
      logged = err
    }

    app.use(function (req, res, next) {
      var inner = new Error('inner')
      next(new Error('outer', { cause: inner }))
    })

    request(app)
      .get('/')
      .expect(500, function (err) {
        if (err) return done(err)
        setImmediate(function () {
          assert.ok(logged instanceof Error)
          assert.strictEqual(logged.message, 'outer')
          assert.ok(logged.cause instanceof Error)
          assert.strictEqual(logged.cause.message, 'inner')
          done()
        })
      })
  })
})

This guarantees cleanup regardless of whether the assertions pass or the test times out.

[myselfsiddharth]

Good catch, @Ap-0007
Thanks! You're right. if the request times out the mock could leak. I'll move the save/restore into beforeEach / afterEach hooks and push an update shortly.