Read an out-array as callee-allocated only where the callee can allocate it

.github/workflows/pytest.yml

@@ -96,7 +96,7 @@ jobs:
       # carries, or a change to them is not exercised until after it merges.
       # Consumers use the action; this repository owns the rules.
       - name: Refuse a skip, and a suite that shrank
-        run: tools/check-test-outcome.py "$RUNNER_TEMP/pytest.log" --min-tests 314
+        run: tools/check-test-outcome.py "$RUNNER_TEMP/pytest.log" --min-tests 315
 
       # The rules earn their place by refusing a log that carries what they
       # name. Both fixtures are written here rather than tracked, and the

parser/shapeinfer.py

@@ -49,10 +49,26 @@ def _out_count_param(func: dict) -> str | None:
 
 
 def _is_written_back_array(p: dict) -> bool:
-    """A non-const double (or higher) pointer parameter the callee allocates
-    and writes back, i.e. a parallel output array."""
+    """A non-const pointer parameter the callee ALLOCATES and writes back, i.e.
+    a parallel output array.
+
+    The callee writes ``*p = <the array>``, and an array of ``E`` is spelled
+    ``E *``, so such a parameter is spelled ``E **`` — one pointer level for the
+    array and one for the write-back.  Stripping both leaves ``E``, and ``E`` is
+    what says whether the callee can have allocated the array at all: a binding
+    reads an array of by-value scalars (``TimestampTz **bins`` -> ``TimestampTz``)
+    or an array of pointers (``SpanSet ***result`` -> ``SpanSet *``), and nothing
+    else.  A MEOS value type left bare — ``Jsonb **values`` -> ``Jsonb`` — is
+    neither: MEOS holds such a value by reference, never by value in an array,
+    so that parameter is an array the CALLER allocates and the callee only
+    fills.  Reading it as callee-allocated makes every binding hand the callee
+    one element's worth of storage and take the first element it writes for the
+    address of the array."""
     ct = p.get("cType", "")
-    return "**" in ct and not ct.lstrip().startswith("const")
+    if "**" not in ct or ct.lstrip().startswith("const"):
+        return False
+    element = _strip_one_ptr(_strip_one_ptr(ct))
+    return element.endswith("*") or _bare(element) in _ELEMENT_SCALARS
 
 
 def _strip_one_ptr(ctype: str) -> str:

tests/test_shapeinfer.py

@@ -163,17 +163,37 @@ def test_a_value_beside_a_number_is_not_an_array(self):
             self.assertNotIn("inputArrays", f.get("shape", {}))
 
     def test_an_out_array_is_not_read_as_an_input_one(self):
-        # `jsonb_each(jb, Jsonb **values, int *count)` writes `values` back, and
-        # its length being BY POINTER is what says so.
+        # `temporal_time_split(temp, ..., TimestampTz **bins, int *count)` writes
+        # `bins` back, and its length being BY POINTER is what says so.
         idl = {"functions": [_fn(
-            "jsonb_each", "text **",
-            [("jb", "const Jsonb *"), ("values", "Jsonb **"),
+            "temporal_time_split", "Temporal **",
+            [("temp", "const Temporal *"), ("bins", "TimestampTz **"),
              ("count", "int *")])]}
         idl, stats = infer_shapes(idl)
         shape = idl["functions"][0]["shape"]
         self.assertEqual(stats["inputArrays"], 0)
         self.assertNotIn("inputArrays", shape)
-        self.assertEqual(shape["outputArrays"], [{"param": "values"}])
+        self.assertEqual(shape["outputArrays"], [{"param": "bins"}])
+
+    def test_an_array_of_bare_meos_values_is_not_callee_allocated(self):
+        # `jsonb_each(jb, Jsonb **values, int *count)` fills an array the CALLER
+        # allocates: stripping the write-back and the array levels leaves `Jsonb`,
+        # a value MEOS holds by reference, so `values` cannot be the address of an
+        # array MEOS made.  Its callee-allocated sibling spells the same element
+        # `SpanSet ***periods`.  A binding reading this one as callee-allocated
+        # hands MEOS one element's worth of storage for `count` of them.
+        idl = {"functions": [_fn(
+            "jsonb_each", "text **",
+            [("jb", "const Jsonb *"), ("values", "Jsonb **"),
+             ("count", "int *")]),
+            _fn("tdwithin_tgeoarr_tgeoarr", "int *",
+                [("arr1", "const Temporal **"), ("count1", "int"),
+                 ("periods", "SpanSet ***"), ("count", "int *")])]}
+        idl, stats = infer_shapes(idl)
+        self.assertNotIn("outputArrays", idl["functions"][0]["shape"])
+        self.assertEqual(idl["functions"][1]["shape"]["outputArrays"],
+                         [{"param": "periods"}])
+        self.assertEqual(stats["outputArrays"], 1)
 
 
 if __name__ == "__main__":