dumb: Add support for tree and blob refs

Previously the dumb git loader was only considering refs targeting
commits and tags but those can also occasionally target blobs and
trees, so ensure to support such refs.

Fixes #4756.

swh/loader/git/dumb.py

@@ -128,11 +128,9 @@ class GitObjectsFetcher:
         commit_objects = []
         for ref in wants:
             ref_object = self._get_git_object(ref)
-            if ref_object.type_num == Commit.type_num:
+            self.objects[ref_object.type_name].add(ref)
+            if ref_object.type_name == Commit.type_name:
                 commit_objects.append(cast(Commit, ref_object))
-                self.objects[b"commit"].add(ref)
-            else:
-                self.objects[b"tag"].add(ref)
 
         # perform DFS on commits graph
         while commit_objects:

swh/loader/git/tests/test_loader.py

@@ -34,6 +34,7 @@ from swh.loader.tests import (
     get_stats,
     prepare_repository_from_archive,
 )
+from swh.model.hashutil import hash_to_bytes
 from swh.model.model import (
     MetadataAuthority,
     MetadataAuthorityType,
@@ -43,6 +44,8 @@ from swh.model.model import (
     OriginVisitStatus,
     RawExtrinsicMetadata,
     Snapshot,
+    SnapshotBranch,
+    SnapshotTargetType,
 )
 
 
@@ -974,6 +977,42 @@ class DumbGitLoaderTestBase(FullGitLoaderTests):
         assert b"HEAD" in self.loader.snapshot.branches
         assert self.loader.snapshot.branches[b"HEAD"].target == b"refs/heads/master"
 
+    def test_load_refs_targeting_tree_or_blob(self, mocker):
+        known_tree = "fbf70528223d263661b5ad4b80f26caf3860eb8e"
+        known_blob = "534d61ecee4f6da4d6ca6ddd8abf258208d2d1bc"
+        tree_ref = "refs/tree"
+        blob_ref = "refs/blob"
+
+        class GitObjectsFetcherTreeAndBlobRefs(dumb.GitObjectsFetcher):
+            def _http_get(self, path: str) -> SpooledTemporaryFile:
+                buffer = super()._http_get(path)
+                if path == "info/refs":
+                    # Add two refs targeting blob and tree in the refs list
+                    refs = buffer.read().decode("utf-8")
+                    buffer.seek(0)
+                    buffer.write(
+                        (
+                            f"{known_tree}\t{tree_ref}\n"
+                            f"{known_blob}\t{blob_ref}\n" + refs
+                        ).encode()
+                    )
+                    buffer.flush()
+                    buffer.seek(0)
+                return buffer
+
+        mocker.patch.object(dumb, "GitObjectsFetcher", GitObjectsFetcherTreeAndBlobRefs)
+
+        res = self.loader.load()
+        assert res == {"status": "eventful"}
+
+        assert self.loader.snapshot.branches[tree_ref.encode()] == SnapshotBranch(
+            target=hash_to_bytes(known_tree), target_type=SnapshotTargetType.DIRECTORY
+        )
+
+        assert self.loader.snapshot.branches[blob_ref.encode()] == SnapshotBranch(
+            target=hash_to_bytes(known_blob), target_type=SnapshotTargetType.CONTENT
+        )
+
 
 class TestDumbGitLoaderWithPack(DumbGitLoaderTestBase):
     @classmethod