fix(duckdb): udfs builtins taking zero args

chore: add test_builtin_scalr_noargs to test/expr/test_udf.py

ibis/backends/duckdb/tests/test_udf.py

@@ -57,6 +57,19 @@ def test_builtin_scalar(con, func):
     assert con.execute(expr) == expected
 
 
+def test_builtin_scalar_noargs(con):
+    @udf.scalar.builtin
+    def version() -> str:
+        ...
+
+    expr = version()
+
+    with con.begin() as c:
+        expected = c.exec_driver_sql("SELECT version()").scalar()
+
+    assert con.execute(expr) == expected
+
+
 @udf.agg.builtin
 def product(x, where: bool = True) -> float:
     ...

ibis/expr/operations/udf.py

@@ -10,11 +10,12 @@
 from public import public
 
 import ibis.common.exceptions as exc
+import ibis.expr.datashape as ds
 import ibis.expr.datatypes as dt
 import ibis.expr.operations as ops
 import ibis.expr.rules as rlz
 from ibis import util
-from ibis.common.annotations import Argument
+from ibis.common.annotations import Argument, attribute
 from ibis.common.collections import FrozenDict
 from ibis.common.deferred import deferrable
 
@@ -35,7 +36,16 @@ class InputType(enum.Enum):
 
 @public
 class ScalarUDF(ops.Value):
-    shape = rlz.shape_like("args")
+    @attribute
+    def shape(self):
+        if not (args := getattr(self, "args")):  # noqa: B009
+            # if a udf builtin takes no args then the shape check will fail
+            # because there are no arguments to grab the shape of. In that case
+            # default to a scalar shape
+            return ds.scalar
+        else:
+            args = args if util.is_iterable(args) else [args]
+            return rlz.highest_precedence_shape(args)
 
 
 @public
@@ -95,6 +105,7 @@ def _make_node(
                 )
                 for arg_name, param in inspect.signature(fn).parameters.items()
             }
+
         else:
             arg_types, return_annotation = signature
             arg_names = list(inspect.signature(fn).parameters)

ibis/tests/expr/test_udf.py

@@ -146,3 +146,13 @@ def myfunc(x: int) -> int:
     assert isinstance(expr, Deferred)
     assert repr(expr) == "myfunc(_.a)"
     assert expr.resolve(table).equals(myfunc(table.a))
+
+
+def test_builtin_scalar_noargs():
+    @ibis.udf.scalar.builtin
+    def version() -> str:
+        ...
+
+    expr = version()
+    assert expr.type().is_string()
+    assert type(expr.op().shape) is ibis.expr.datashape.Scalar