lib: implement node:logger

[jasnell]

A simpler attempt to add a structured logging API.

Uses a provider model similar to VFS.

This implements two providers out of the box,
ConsoleProvider and ReadableProvider. ConsoleProvider is the default and uses Utf8Stream to emit to either stdout or stderr.

const { create } = require('node:logger');
const logger = create(); // default logger to console
logger.info('foo');

// ...
const als = new AsyncLocalStorage();
const logger2 = create(new ConsoleProvider({ pid: true }), {
  name: 'foo',
  bindings: {
    'abc': 'included in every log line',
    'xyz': als,  // current als.getStore() included in
                 // every log line
  }
});
logger2.info('foo', { baz: 1 });

The Logger keeps things as simple as possible, leaving actual handling of the log events to the providers, which can be fully customized. Easy to adapt to other loggers like pino or extend capabilities without directly touching the facade.

The current json output produced by the ConsoleProvider is:

{"attributes":{},"bindings":{},"level":{"name":"info","value":30},"message":"test","name":"foo","timestamp":1788677600214,"pid":670179}

We should bikeshed the format a bit before this lands.

[nodejs-github-bot]

Review requested:

• @nodejs/loaders
• @nodejs/startup

[TheOneTheOnlyJJ]

@mertcanaltin, your experience from #60468 may be valuable here.

[codecov]

Codecov Report

❌ Patch coverage is 96.82152% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.19%. Comparing base (7aba44d) to head (f04ec12).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/logger.js	96.81%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65840      +/-   ##
==========================================
- Coverage   90.20%   90.19%   -0.01%     
==========================================
  Files         771      772       +1     
  Lines      264622   265031     +409     
  Branches    50228    50304      +76     
==========================================
+ Hits       238704   239051     +347     
- Misses      16907    16971      +64     
+ Partials     9011     9009       -2     

Files with missing lines	Coverage Δ
lib/internal/bootstrap/realm.js	96.98% <100.00%> (+<0.01%)	⬆️
lib/logger.js	96.81% <96.81%> (ø)

... and 32 files with indirect coverage changes

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[mertcanaltin]

The Logger keeps things as simple as possible, leaving actual handling of the log events to the providers, which can be fully customized. Easy to adapt to other loggers like pino or extend capabilities without directly touching the facade.

I think this step is very good for review. We started with a big step before, but it was very costly for reviewers.

I want to share some topics we had in #60468. I hope they help this PR.

Do custom levels need to be part of the public contract in the first version? I'm not sure. Level names and numeric ordering are a long-term cost for both users and providers.

My suggestion is to limit the first version to the built-in levels, so the API stays smaller. Providers can do their own mapping internally when necessary.

This comment is not a blocker for this PR.

[jasnell]

Do custom levels need to be part of the public contract in the first version

I think they ought to be, yes, at least to an extent. I absolutely don't think we should do the automatic custom level method installation like what pino does (e.g. logger.foo(...)) but the generic logger.log(level, ... gives enough coverage to minimally meet the need.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77087/