Revert "deposit: Remove 'parent' deposit"

This reverts commit f6905cdf.

That commit was a first step toward making loaders write releases
instead of revisions.

Unfortunately, we will still write revisions for a non-negligeable time,
so I prefer to defer the removal of parent deposit revisions to the
moment we actually make that switch, so we don't end up with inconsistent
revisions.

swh/loader/package/deposit/loader.py

@@ -57,6 +57,9 @@ class DepositPackageInfo(BasePackageInfo):
     """The collection in the deposit; see SWORD specification."""
     author = attr.ib(type=Person)
     committer = attr.ib(type=Person)
+    revision_parents = attr.ib(type=Tuple[Sha1Git, ...])
+    """Revisions created from previous deposits, that will be used as parents of the
+    revision created for this deposit."""
 
     @classmethod
     def from_metadata(
@@ -87,6 +90,7 @@ class DepositPackageInfo(BasePackageInfo):
             collection=depo["collection"],
             author=parse_author(depo["author"]),
             committer=parse_author(depo["committer"]),
+            revision_parents=tuple(hash_to_bytes(p) for p in depo["revision_parents"]),
             raw_info=raw_info,
             directory_extrinsic_metadata=[
                 RawExtrinsicMetadataCore(
@@ -202,6 +206,7 @@ class DepositLoader(PackageLoader[DepositPackageInfo]):
             date=TimestampWithTimezone.from_dict(p_info.author_date),
             committer=p_info.committer,
             committer_date=TimestampWithTimezone.from_dict(p_info.commit_date),
+            parents=p_info.revision_parents,
             directory=directory,
             synthetic=True,
         )

swh/loader/package/deposit/tests/test_deposit.py

@@ -19,15 +19,10 @@ from swh.model.model import (
     MetadataAuthorityType,
     MetadataFetcher,
     Origin,
-    Person,
     RawExtrinsicMetadata,
-    Revision,
-    RevisionType,
     Snapshot,
     SnapshotBranch,
     TargetType,
-    Timestamp,
-    TimestampWithTimezone,
 )
 from swh.model.swhids import CoreSWHID, ExtendedObjectType, ExtendedSWHID, ObjectType
 
@@ -205,30 +200,7 @@ def test_deposit_loading_ok(swh_storage, deposit_client, requests_mock_datadir):
     check_snapshot(expected_snapshot, storage=loader.storage)
 
     revision = loader.storage.revision_get([revision_id])[0]
-    date = TimestampWithTimezone(
-        timestamp=Timestamp(seconds=1507389428, microseconds=0),
-        offset=0,
-        negative_utc=False,
-    )
-    person = Person(
-        fullname=b"Software Heritage",
-        name=b"Software Heritage",
-        email=b"robot@softwareheritage.org",
-    )
-    assert revision == Revision(
-        id=revision_id,
-        message=b"hal: Deposit 666 in collection hal",
-        author=person,
-        committer=person,
-        date=date,
-        committer_date=date,
-        type=RevisionType.TAR,
-        directory=b"\xfd-\xf1-\xc5SL\x1d\xa1\xe9\x18\x0b\x91Q\x02\xfbo`\x1d\x19",
-        synthetic=True,
-        metadata=None,
-        parents=(),
-        extra_headers=(),
-    )
+    assert revision is not None
 
     # check metadata