fix: support Altair 6+ Vega-Lite MIME types in FigureAltair

maartenbreddels · SAKSHI-DOT693 · claude · maartenbreddels · commit 724c01c83cec · 2026-01-21T10:09:24.000+01:00
Altair 6 introduces a new MIME type format (application/vnd.vegalite.v6.json) that differs from v4/v5 (+json suffix). Update the MIME type detection to find any vegalite MIME type instead of hardcoding specific versions. Based on the issue identified in #1135. Co-Authored-By: SAKSHI-DOT693 <SAKSHI-DOT693@users.noreply.github.com> Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
diff --git a/solara/components/figure_altair.py b/solara/components/figure_altair.py
@@ -25,11 +25,15 @@ def FigureAltair(
 
     with alt.renderers.enable("mimetype"):
         bundle = chart._repr_mimebundle_()[0]
-        key4 = "application/vnd.vegalite.v4+json"
-        key5 = "application/vnd.vegalite.v5+json"
-        if key4 not in bundle and key5 not in bundle:
-            raise KeyError(f"{key4} and {key5} not in mimebundle:\n\n{bundle}")
-        spec = bundle.get(key5, bundle.get(key4))
+        # Find the Vega-Lite spec from the bundle (supports v4, v5, v6+)
+        # MIME type format varies: v4/v5 use "+json" suffix, v6 uses ".json"
+        spec = None
+        for key in bundle:
+            if key.startswith("application/vnd.vegalite.v"):
+                spec = bundle[key]
+                break
+        if spec is None:
+            raise KeyError(f"No Vega-Lite MIME type found in mimebundle: {list(bundle.keys())}")
         return solara.widgets.VegaLite.element(
             spec=spec, on_click=on_click, listen_to_click=on_click is not None, on_hover=on_hover, listen_to_hover=on_hover is not None
         )
diff --git a/tests/unit/figure_altair_test.py b/tests/unit/figure_altair_test.py
@@ -0,0 +1,75 @@
+import unittest.mock
+
+import pytest
+
+import solara
+import solara.widgets
+
+
+class MockChart:
+    """Mock Altair chart that returns a configurable mimebundle."""
+
+    def __init__(self, bundle):
+        self._bundle = bundle
+
+    def _repr_mimebundle_(self):
+        return (self._bundle, {})
+
+
+@pytest.fixture
+def mock_altair_renderers():
+    """Mock altair.renderers.enable to be a no-op context manager."""
+    import contextlib
+
+    import altair as alt
+
+    @contextlib.contextmanager
+    def mock_enable(renderer):
+        yield
+
+    with unittest.mock.patch.object(alt.renderers, "enable", mock_enable):
+        yield
+
+
+def test_figure_altair_v4(mock_altair_renderers):
+    spec = {"$schema": "https://vega.github.io/schema/vega-lite/v4.json", "data": {"values": []}}
+    chart = MockChart({"application/vnd.vegalite.v4+json": spec})
+
+    el = solara.FigureAltair(chart)
+    _, rc = solara.render(el, handle_error=False)
+    widget = rc.find(solara.widgets.VegaLite).widget
+    assert widget.spec == spec
+    rc.close()
+
+
+def test_figure_altair_v5(mock_altair_renderers):
+    spec = {"$schema": "https://vega.github.io/schema/vega-lite/v5.json", "data": {"values": []}}
+    chart = MockChart({"application/vnd.vegalite.v5+json": spec})
+
+    el = solara.FigureAltair(chart)
+    _, rc = solara.render(el, handle_error=False)
+    widget = rc.find(solara.widgets.VegaLite).widget
+    assert widget.spec == spec
+    rc.close()
+
+
+def test_figure_altair_v6(mock_altair_renderers):
+    """Test that Altair 6+ with v6 MIME type works (uses .json suffix instead of +json)."""
+    spec = {"$schema": "https://vega.github.io/schema/vega-lite/v6.json", "data": {"values": []}}
+    # Altair 6 uses ".json" suffix instead of "+json"
+    chart = MockChart({"application/vnd.vegalite.v6.json": spec})
+
+    el = solara.FigureAltair(chart)
+    _, rc = solara.render(el, handle_error=False)
+    widget = rc.find(solara.widgets.VegaLite).widget
+    assert widget.spec == spec
+    rc.close()
+
+
+def test_figure_altair_no_vegalite_mime(mock_altair_renderers):
+    """Test that a KeyError is raised when no Vega-Lite MIME type is found."""
+    chart = MockChart({"text/plain": "some text"})
+
+    el = solara.FigureAltair(chart)
+    with pytest.raises(KeyError, match="No Vega-Lite MIME type found"):
+        solara.render(el, handle_error=False)
