package loader: Discuss revision metadata normalization

Auditing the state of the revision's metadata field, we use the field metadata to convey multiple meanings. It'd be great we have a look at how we want to set that.

Understanding that this should not be there (but it is for now).

current reimplementation for gnu/pypi/npm (T1389)

            'metadata': {
              'intrinsic_metadata': intrinsic_metadata,  # raw metadata parsed out of internal file (PKG-INFO, package.json)
              'original_artifact': a_metadata,             # extrinsic artifact metadata, raw data from api/provider
              'hashes_artifact': a_c_metadata,          # extra artifact metadata computed by us
            },

in-production pypi

            'metadata': {
              'original_artifact': artifact,  # extrinsic metadata about the release artifact to download
              'project': project_info,  # extrinsic metadata about the project
            },

in-production npm

            'metadata': {
                'package_source': package_source_data,
                'package': package_metadata,
            },

mercurial

all intrinsic metadata:

           'node': hash_to_hex(header['node']),  # -> this probably should be in extra headers, must check if it is or not (unsure)
           'extra_headers': [
               ['time_offset_seconds',
                str(commit['time_offset_seconds']).encode('utf-8')],
           ] + extra_meta

git

           ret['metadata'] = {
               'extra_headers': git_metadata,  # intrinsic metadata
           }

svn

all intrinsic metadata

          'extra_headers': [
              ['svn_repo_uuid', repo_uuid],
              ['svn_revision', str(rev).encode('utf-8')]
          ]

tar

Those are computations and extrinsic metadata:

          'metadata': {
            'original_artifact': {
              'name': filename
              'archive_type': 'zip' || 'tar'
              **hashes
            }
          }

debian

  'metadata': {
    'original_artifact': [{
      name,
      **hashes,
    }],           # <- built from intrinsic metadata parsed out of *.dsc
    package_info: # <- built from intrinsic metadata parsed out of debian/changelog
  }

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Migrated from T2017 (view on Phabricator)