feat(datatypes): allow trailing comma in struct string shorthands (#10393)

Co-authored-by: Phillip Cloud <[email protected]>

Author: NickCrews

ibis/expr/datatypes/parse.py

@@ -195,7 +195,14 @@ def geotype_parser(typ: type[dt.DataType]) -> dt.DataType:
     struct = (
         spaceless_string("struct")
         .then(LANGLE)
-        .then(parsy.seq(spaceless(FIELD).skip(COLON), ty).sep_by(COMMA))
+        .then(
+            parsy.alt(
+                parsy.seq(spaceless(FIELD).skip(COLON), ty)
+                .sep_by(COMMA, min=1)
+                .skip(COMMA.optional()),
+                parsy.seq(),
+            )
+        )
         .skip(RANGLE)
         .map(dt.Struct.from_tuples)
     )

ibis/expr/datatypes/tests/test_parse.py

@@ -6,6 +6,7 @@
 import hypothesis.strategies as st
 import parsy
 import pytest
+from pytest import param
 
 import ibis.expr.datatypes as dt
 import ibis.tests.strategies as its
@@ -159,6 +160,34 @@ def test_struct_with_string_types():
     )
 
 
+@pytest.mark.parametrize(
+    ("type_string", "expected_dtype"),
+    [
+        ("struct<a: int32,>", {"a": dt.int32}),
+        ("struct<a: int32, b: string  , >", {"a": dt.int32, "b": dt.string}),
+    ],
+    ids=["single_field", "multiple_fields"],
+)
+def test_struct_trailing_comma(type_string, expected_dtype):
+    result = dt.dtype(type_string)
+    assert result == dt.Struct(expected_dtype)
+
+
+@pytest.mark.parametrize(
+    "invalid_type_string",
+    [
+        param("struct<,>", id="missing_key"),
+        param("struct<a,>", id="missing_colon"),
+        param("struct<b: ,>", id="missing_value"),
+        param("struct<c:in,>", id="invalid_type"),
+        param("struct<a:int,b:int64,,>", id="double_comma"),
+    ],
+)
+def test_struct_trailing_comma_invalid(invalid_type_string):
+    with pytest.raises(parsy.ParseError):
+        dt.dtype(invalid_type_string)
+
+
 def test_array_with_string_value_types():
     assert dt.Array("int32") == dt.Array(dt.int32)
     assert dt.Array(dt.Array("array<map<string, double>>")) == (
@@ -293,3 +322,7 @@ def test_parse_null():
 @h.given(roundtrippable_dtypes)
 def test_parse_dtype_roundtrip(dtype):
     assert dt.dtype(str(dtype)) == dtype
+
+
+def test_parse_empty_struct():
+    assert dt.dtype("struct<>") == dt.Struct({})