fix!: use local git command to resolve existing commits instead of GitHub API

[mauriziovitale]

Fix: Replace the API call with git merge-base --is-ancestor, which is local, O(1), and has no depth limit.

Fixes #144

[meeroslav]

Hi @mauriziovitale,

Thank you for the PR. The proposed change looks solid.
Please also include the following changes:

• bump version in package.json to 6.0.0
• update README.md to reference v6
• build code and include compiled .js file

Thank you!

[JamesHenry]

I think it would be worth failing fast on shallow clones here. This change you are making fully relies on local history being complete enough for git merge-base --is-ancestor to be meaningful, and with a shallow checkout the action can otherwise fall through into “no previous successful workflow” behavior instead of surfacing the real configuration problem.

Something along these lines would make the failure mode much clearer:

  const isShallow = spawnSync('git', ['rev-parse', '--is-shallow-repository'], {
    encoding: 'utf-8',
  });

  if (isShallow.stdout?.trim() === 'true') {
    core.setFailed(
      'Shallow clone detected. nx-set-shas requires fetch-depth: 0 to work correctly. ' +
        'We also recommend filter: tree:0 to reduce checkout size. ' +
        'See https://github.com/nrwl/nx-set-shas for the recommended checkout configuration.',
    );
    return;
  }

[JamesHenry]

NOTE: This is in addition to @meeroslav review notes above, those are also needed