Chart builder: discoverable entry points — Build Chart door, dataset picker, no-datasets state

src/core/chart-builder.test.ts

@@ -28,6 +28,7 @@ import {
   calculatedFieldNames,
   effectiveColumns,
   pruneEncodings,
+  rebaseBuilderConfig,
   type BuilderCalculate,
   type BuilderColumns,
   type BuilderConfig,
@@ -1290,3 +1291,91 @@ describe('pruneEncodings', () => {
     expect(pruneEncodings(config, columns)).toBe(config);
   });
 });
+
+describe('rebaseBuilderConfig (dataset switch)', () => {
+  // The new dataset shares `category` but lacks `value`/`when`/`flag`.
+  const newColumns: BuilderColumns = {
+    columns: ['category', 'profit'],
+    columnTypes: [
+      { name: 'category', type: 'string' },
+      { name: 'profit', type: 'number' },
+    ],
+  };
+
+  it('keeps chart-level intent and same-name bindings, re-pointing the dataset', () => {
+    const config: BuilderConfig = {
+      datasetName: 'Old',
+      mark: 'bar',
+      title: 'Revenue by region',
+      subtitle: 'FY26',
+      width: 400,
+      height: 200,
+      sort: 'descending',
+      stack: 'normalize',
+      encodings: { x: { field: 'category', type: 'nominal' } },
+    };
+    const out = rebaseBuilderConfig(config, 'New', newColumns);
+    expect(out.datasetName).toBe('New');
+    expect(out.mark).toBe('bar');
+    expect(out.title).toBe('Revenue by region');
+    expect(out.subtitle).toBe('FY26');
+    expect(out.width).toBe(400);
+    expect(out.height).toBe(200);
+    expect(out.sort).toBe('descending');
+    expect(out.stack).toBe('normalize');
+    expect(out.encodings.x).toEqual({ field: 'category', type: 'nominal' });
+  });
+
+  it('sheds encodings and predicate filters bound to columns the new dataset lacks', () => {
+    const config: BuilderConfig = {
+      datasetName: 'Old',
+      mark: 'bar',
+      encodings: {
+        x: { field: 'category', type: 'nominal' },
+        y: { field: 'value', type: 'quantitative' },
+      },
+      filters: [
+        filter({ id: 'f1', field: 'value', fieldType: 'quantitative', op: 'gt', value: '0' }),
+        filter({ id: 'f2', field: 'category', fieldType: 'nominal', op: 'equal', value: 'A' }),
+      ],
+    };
+    const out = rebaseBuilderConfig(config, 'New', newColumns);
+    expect(out.encodings.x).toEqual({ field: 'category', type: 'nominal' });
+    expect(out.encodings.y).toBeNull();
+    expect(out.filters?.map((f) => f.id)).toEqual(['f2']);
+  });
+
+  it('keeps expression filters, constants, count mappings, and calculated-field bindings', () => {
+    const config: BuilderConfig = {
+      datasetName: 'Old',
+      mark: 'bar',
+      encodings: {
+        x: { field: 'ratio', type: 'quantitative' }, // a calculated field travels along
+        y: { type: 'quantitative', aggregate: 'count' }, // field-less count
+        color: { value: '#ff0000', type: 'nominal' }, // constant — no column binding
+      },
+      calculates: [calc({ as: 'ratio', expr: 'datum.profit * 2' })],
+      filters: [filter({ id: 'fx', mode: 'expression', expr: 'datum.value > 0' })],
+    };
+    const out = rebaseBuilderConfig(config, 'New', newColumns);
+    expect(out.encodings.x).toEqual({ field: 'ratio', type: 'quantitative' });
+    expect(out.encodings.y).toEqual({ type: 'quantitative', aggregate: 'count' });
+    expect(out.encodings.color).toEqual({ value: '#ff0000', type: 'nominal' });
+    expect(out.calculates).toEqual(config.calculates);
+    expect(out.filters).toEqual(config.filters);
+  });
+
+  it('a same-schema dataset keeps the whole config (only the name changes)', () => {
+    const config: BuilderConfig = {
+      datasetName: 'Old',
+      mark: 'line',
+      encodings: {
+        x: { field: 'when', type: 'temporal' },
+        y: { field: 'value', type: 'quantitative', aggregate: 'sum' },
+      },
+      filters: [filter({ field: 'category', fieldType: 'nominal', op: 'equal', value: 'A' })],
+    };
+    const out = rebaseBuilderConfig(config, 'New', columns);
+    expect(out).toEqual({ ...config, datasetName: 'New' });
+  });
+});