feat: enable spatial support in the Vega-Lite writer

Add the crate's spatial feature so DRAW spatial map layers render
through VegaLiteWriter instead of raising "Spatial visualization
requires the 'spatial' feature to be enabled". Geometry columns (WKB)
and the built-in ggsql:world dataset work out of the box with the
default projection; named map projections (e.g. PROJECT TO mercator)
and ST_* SQL functions additionally require the DuckDB spatial
extension.

Binary size impact is negligible (+~134 KB, 0.22%): the feature only
pulls in the pure-Rust geozero crate (wkb/wkt/geojson), no native
dependencies.

Author: cpsievert

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## UNRELEASED
+
+### Added
+
+- Enabled the crate's `spatial` feature, so `DRAW spatial` map layers now render through the Vega-Lite writer instead of raising "Spatial visualization requires the 'spatial' feature to be enabled". Geometry columns (WKB) and the built-in `ggsql:world` dataset work out of the box with the default projection. Named map projections (e.g. `PROJECT TO mercator`) and `ST_*` SQL functions additionally require the DuckDB `spatial` extension (`INSTALL spatial; LOAD spatial;`).
+
 ## 0.5.2
 
 ### Added

Cargo.lock

@@ -16,7 +16,7 @@ crate-type = ["cdylib"]
 [dependencies]
 pyo3 = { version = "0.26", features = ["extension-module", "abi3-py310"] }
 arrow = { version = "58", default-features = false, features = ["ipc"] }
-ggsql = { version = "0.5.2", default-features = false, features = ["duckdb", "vegalite", "builtin-data", "svg", "pdf", "hep"] }
+ggsql = { version = "0.5.2", default-features = false, features = ["duckdb", "vegalite", "builtin-data", "svg", "pdf", "hep", "spatial"] }
 
 [features]
 default = []

Cargo.toml

@@ -217,6 +217,44 @@ def test_render_multi_layer(self):
         assert "layer" in spec_dict
 
 
+class TestSpatial:
+    """Tests for spatial (map) layers via the VegaLiteWriter."""
+
+    def test_render_spatial_builtin_world(self):
+        reader = ggsql.DuckDBReader("duckdb://memory")
+        spec = reader.execute("VISUALISE FROM ggsql:world DRAW spatial")
+        writer = ggsql.VegaLiteWriter()
+
+        result = writer.render(spec)
+        spec_dict = json.loads(result)
+        marks = [
+            layer["mark"]["type"] if isinstance(layer["mark"], dict) else layer["mark"]
+            for layer in spec_dict["layer"]
+        ]
+        assert "geoshape" in marks
+
+    def test_render_spatial_choropleth(self):
+        reader = ggsql.DuckDBReader("duckdb://memory")
+        spec = reader.execute(
+            "VISUALISE FROM ggsql:world DRAW spatial MAPPING population AS fill"
+        )
+        writer = ggsql.VegaLiteWriter()
+
+        result = writer.render(spec)
+        assert "geoshape" in result
+
+    def test_render_chart_spatial(self):
+        reader = ggsql.DuckDBReader("duckdb://memory")
+        spec = reader.execute("VISUALISE FROM ggsql:world DRAW spatial")
+        writer = ggsql.VegaLiteWriter()
+
+        chart = writer.render_chart(spec)
+        assert isinstance(chart, altair.TopLevelMixin)
+        # The chart survives Altair-level round-tripping (this is how the
+        # spec reaches the browser widget)
+        assert "projection" in chart.to_dict()
+
+
 class TestRenderAltairDataFrameConversion:
     """Tests for DataFrame handling in render_altair()."""