Compact singleton arrays in the crate

docs/api/crate.md

@@ -25,7 +25,10 @@ Source: `src/lightcone/engine/crate.py` (converged by
   never-materialized project) and must override rocrate's
   construction-time default. Entities build in sorted order,
   serialization is `sort_keys` — render-twice-identical is the one
-  byte-level claim, and it is what makes convergence sound.
+  byte-level claim, and it is what makes convergence sound. The
+  serialization also compacts every one-element array to its value,
+  as RO-Crate 1.1 recommends: which properties hold one value depends
+  on the project, so the rule lives in one place, not in each builder.
 - **Maintenance is derived, never configured.** RO-Crate requires a
   license; materialize must not refuse to run science over a missing
   key, and inventing one asserts terms over someone's data. Absent ⇒

pyproject.toml

@@ -39,7 +39,7 @@ dev = [
     "ruff",
     "mypy",
     "datalad",
-    "roc-validator>=0.11.3",
+    "roc-validator>=0.11.4",
 ]
 docs = [
     "zensical>=0.0.33",

src/lightcone/engine/crate.py

@@ -173,9 +173,18 @@ def document(self) -> str:
             self._control(key, self._action(key, manifest))
         self._runs(workflow)
         self._root()
-        text: str = json.dumps(
-            self.crate.metadata.generate(), indent=1, sort_keys=True, ensure_ascii=False
-        )
+        document = self.crate.metadata.generate()
+        # Compacted JSON-LD: a property with one value is that value, not
+        # a one-element array. Applied here rather than at each builder
+        # because the arrays come from three places — rocrate's
+        # `append_to`, and two literal lists — and which of them hold one
+        # element depends on the project (one output, one author). The
+        # same rule rocrate itself applies to `@context`.
+        for entity in document["@graph"]:
+            for name, value in entity.items():
+                if isinstance(value, list) and len(value) == 1:
+                    entity[name] = value[0]
+        text: str = json.dumps(document, indent=1, sort_keys=True, ensure_ascii=False)
         return text + "\n"
 
     # ----- the workflow and its structure -----

tests/test_crate.py

@@ -140,6 +140,22 @@ def test_rendering_twice_at_the_same_state_is_byte_identical(project: Path) -> N
     assert first == second
 
 
+def test_a_single_value_is_never_a_singleton_array(project: Path) -> None:
+    """Compacted JSON-LD: one author, one parameter, one result are plain
+    values — RO-Crate 1.1's recommendation, and what its validator checks.
+    The arrays come from three builders, so this pins the serialization."""
+    _made(project, "baseline", "first", git_sha="aaa111")
+    rendered = crate.render(
+        project, _graph(project), license="MIT", dsid=_DSID, writer=_writer, keys={}
+    )
+    document = json.loads(rendered)
+    for entity in document["@graph"]:
+        for name, value in entity.items():
+            assert not (isinstance(value, list) and len(value) == 1), (entity["@id"], name)
+    entities = _entities(document)
+    assert entities["./"]["author"] == {"@id": "mailto:ada@example.org"}
+
+
 def test_the_clock_never_enters_the_document(project: Path) -> None:
     """`datePublished` is the newest recorded instant — rocrate's own
     default stamps the current time, and this pins the override."""
@@ -230,7 +246,7 @@ def test_an_action_chains_its_inputs_and_its_environment(project: Path) -> None:
     first_objects = {ref["@id"] for ref in first["object"]}
     assert {"uv.lock", ".python-version", "pyproject.toml", "data/catalog.csv"} <= first_objects
     assert "results/baseline/first.txt" in {ref["@id"] for ref in second["object"]}
-    assert second["result"] == [{"@id": "results/baseline/second.txt"}]
+    assert second["result"] == {"@id": "results/baseline/second.txt"}
     assert second["description"] == "make second"
     assert entities["results/baseline/second.txt"]["version"] == "sha256:baseline-second"
 
@@ -280,7 +296,7 @@ def test_the_person_is_the_saving_commits_author(project: Path) -> None:
     assert person["name"] == "Ada Lovelace"
     action = next(e for e in entities.values() if e["@type"] == "CreateAction")
     assert action["agent"] == {"@id": "mailto:ada@example.org"}
-    assert {"@id": "mailto:ada@example.org"} in entities["./"]["author"]
+    assert {"@id": "mailto:ada@example.org"} in _as_list(entities["./"]["author"])
 
 
 def test_decision_values_point_back_at_their_parameter(project: Path) -> None:

tests/test_crate_smoke.py

@@ -41,8 +41,8 @@
     "process-run-crate-0.5_13.2",
     # lc knows no publishing organization and no author affiliation
     "ro-crate-1.1_22.3",
-    "ro-crate-1.1_29.2",
-    "ro-crate-1.1_29.3",
+    "ro-crate-1.1_30.2",
+    "ro-crate-1.1_30.3",
 }
 
 _SPEC = """