fix: introduce a reproduction case for List casting with polars

See #3063

Signed-off-by: R. Tyler Croy <[email protected]>

python/Makefile

@@ -8,7 +8,7 @@ DAT_VERSION := 0.0.2
 .PHONY: setup
 setup: ## Setup the requirements
 	$(info --- Setup dependencies ---)
-	uv sync --extra devel --extra pandas
+	uv sync --extra devel --extra pandas --extra polars
 
 .PHONY: setup-dat
 setup-dat: ## Download DAT test files
@@ -28,21 +28,21 @@ build: setup ## Build Python binding of delta-rs
 .PHONY: develop
 develop: setup ## Install Python binding of delta-rs
 	$(info --- Develop with Python binding ---)
-	uvx --from 'maturin[zig]' maturin develop --extras=devel,pandas $(MATURIN_EXTRA_ARGS)
+	uvx --from 'maturin[zig]' maturin develop --extras=devel,pandas,polars $(MATURIN_EXTRA_ARGS)
 
 .PHONY: install
 install: build ## Install Python binding of delta-rs
 	$(info --- Uninstall Python binding ---)
 	uv pip uninstall deltalake
 	$(info --- Install Python binding ---)
 	$(eval TARGET_WHEEL := $(shell ls ../target/wheels/deltalake-${PACKAGE_VERSION}-*.whl))
-	uv pip install $(TARGET_WHEEL)[devel,pandas]
+	uv pip install $(TARGET_WHEEL)[devel,pandas,polars]
 
 .PHONY: develop-pyspark
 develop-pyspark:
 	uv sync --all-extras
 	$(info --- Develop with Python binding ---)
-	uvx --from 'maturin[zig]' maturin develop --extras=devel,pandas,pyspark $(MATURIN_EXTRA_ARGS)
+	uvx --from 'maturin[zig]' maturin develop --extras=devel,pandas,polars,pyspark $(MATURIN_EXTRA_ARGS)
 
 .PHONY: format
 format: ## Format the code

python/pyproject.toml

@@ -38,6 +38,7 @@ devel = [
     "mypy==1.10.1",
     "ruff==0.5.2",
 ]
+polars = ["polars==1.17.1"]
 pyspark = [
     "pyspark",
     "delta-spark",
@@ -93,6 +94,7 @@ markers = [
     "s3: marks tests as integration tests with S3 (deselect with '-m \"not s3\"')",
     "azure: marks tests as integration tests with Azure Blob Store",
     "pandas: marks tests that require pandas",
+    "polars: marks tests that require polars",
     "pyspark: marks tests that require pyspark",
 ]
 

python/tests/test_writer.py

@@ -2025,3 +2025,42 @@ def test_write_transactions(tmp_path: pathlib.Path, sample_data: pa.Table):
     assert transaction_2.app_id == "app_2"
     assert transaction_2.version == 2
     assert transaction_2.last_updated == 123456
+
+
+# <https://github.com/delta-io/delta-rs/issues/3063>
+@pytest.mark.polars
+def test_write_structs(tmp_path: pathlib.Path):
+    import polars as pl
+    dt = DeltaTable.create(
+        tmp_path,
+        schema=pa.schema(
+            [
+                ("a", pa.int32()),
+                ("b", pa.string()),
+                ("c", pa.struct({"d": pa.int16(), "e": pa.int16()})),
+            ]
+        ),
+    )
+
+    df = pl.DataFrame(
+        {
+            "a": [0, 1],
+            "b": ["x", "y"],
+            "c": [
+                {"d": -55, "e": -32},
+                {"d": 0, "e": 0},
+            ],
+        }
+    )
+
+    dt.merge(
+        source=df.to_arrow(),
+        predicate=" AND ".join([f"target.{x} = source.{x}" for x in ["a"]]),
+        source_alias="source",
+        target_alias="target",
+        large_dtypes=False,
+    ).when_not_matched_insert_all().execute()
+
+    arrow_dt = dt.to_pyarrow_dataset()
+    new_df = pl.scan_pyarrow_dataset(arrow_dt)
+    new_df.collect()