Resolve incosistency in directory option in JS vs CLI usage

[webketje]

There is an inconsistency in the metalsmith CLI vs JS approach: in the CLI Metalsmith.directory is defaulted to process.cwd(). In the JS approach there is no default and __dirname needs to be passed explicitly. Solution:A) force specifying a directory option in metalsmith.json (breaking) or B) Make __dirname also the default for the JS solution (backwards-compatible)

[webketje]

To resolve the inconsistency, path.dirname(path) of the metalsmith.json config path must be used as the metalsmith.directory. This would allow the CLI to properly execute metalsmith from a subfolder of a project/package, as the JS approach already does

[webketje]

See https://replit.com/@webketje/Metalsmith-CLI-dirpath-tests which does multiple CLI tests from different $PWD paths. Below is a test run. The tests that start with "Next - " use a modified path resolution for local plugins & loading the config that is a candidate for Metalsmith 2.4+

[
  {
    chdir: '/home/runner/Metalsmith-CLI-dirpath-tests',
    name: 'Repo root (default)',
    success: true
  },
  {
    chdir: '/home/runner/Metalsmith-CLI-dirpath-tests',
    name: 'Next - Repo root (default)',
    success: true
  },
  {
    chdir: '/home/runner/Metalsmith-CLI-dirpath-tests',
    name: 'Repo root (absolute config path)',
    success: true
  },
  {
    chdir: '/home/runner/Metalsmith-CLI-dirpath-tests',
    name: 'Next - Repo root (absolute config path)',
    success: true
  },
  {
    chdir: '/home/runner/Metalsmith-CLI-dirpath-tests/src',
    name: 'Repo subdir',
    error: 'Command failed: node ../bin/metalsmith -c ../metalsmith.json'
  },
  {
    chdir: '/home/runner/Metalsmith-CLI-dirpath-tests/src',
    name: 'Next - Repo subdir',
    success: true
  },
  {
    chdir: '/home/runner/Metalsmith-CLI-dirpath-tests',
    name: 'Repo subdir (absolute config path)',
    success: true
  },
  {
    chdir: '/home/runner/Metalsmith-CLI-dirpath-tests',
    name: 'Next - Repo subdir (absolute config path)',
    success: true
  },
  {
    chdir: '/home/runner',
    name: 'Outside repo',
    error: 'Command failed: node ./Metalsmith-CLI-dirpath-tests/bin/metalsmith -c ./Metalsmith-CLI-dirpath-tests/metalsmith.json'
  },
  { chdir: '/home/runner', name: 'Next - Outside repo', success: true }
]

As you can see with Metalsmith 2.3, running the metalsmith bin from a path other than the repo root fails. It fails because it resolves local plugins and Metalsmith.directory to process.cwd()

[webketje]

It looks interesting to do some default path resolution in both the CLI as the JS API, especially given the unavailability of __dirname in ES modules, see https://techsparx.com/nodejs/esnext/dirname-es-modules.html