Set baseURL to support "data/movies.json" style URLs (#100)

vl-convert-rs/src/converter.rs

@@ -200,7 +200,9 @@ import('{url}').then((sg) => {{
             let function_str = r#"
 function vegaToSvg(vgSpec) {
     let runtime = vega.parse(vgSpec);
-    let view = new vega.View(runtime, {renderer: 'none'});
+    const baseURL = 'https://vega.github.io/vega-datasets/';
+    const loader = vega.loader({ mode: 'http', baseURL });
+    let view = new vega.View(runtime, {renderer: 'none', loader});
     let svgPromise = view.toSVG();
     return svgPromise
 }

vl-convert-rs/tests/test_specs.rs

@@ -270,6 +270,7 @@ mod test_svg {
     fn test(
         #[values(
             "circle_binned",
+            "circle_binned_base_url",
             "stacked_bar_h",
             "bar_chart_trellis_compact",
             "line_with_log_scale",
@@ -314,6 +315,7 @@ mod test_png_no_theme {
 
     #[rstest(name, scale,
         case("circle_binned", 1.0),
+        case("circle_binned_base_url", 1.0),
         case("stacked_bar_h", 2.0),
         case("bar_chart_trellis_compact", 2.0),
         case("line_with_log_scale", 2.0),

vl-convert-rs/tests/vl-specs/circle_binned_base_url.vl.json

@@ -0,0 +1,16 @@
+{
+  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
+  "data": {"url": "data/movies.json"},
+  "mark": "circle",
+  "encoding": {
+    "x": {
+      "bin": {"maxbins": 10},
+      "field": "IMDB Rating"
+    },
+    "y": {
+      "bin": {"maxbins": 10},
+      "field": "Rotten Tomatoes Rating"
+    },
+    "size": {"aggregate": "count"}
+  }
+}