Chart builder: SelectControl pickers, channel chooser, per-type aggregates

src/core/chart-builder.test.ts

@@ -6,6 +6,7 @@ import {
   isChannelTypeAllowed,
   isColumnAllowedOnChannel,
   supportsAggregate,
+  validAggregateOps,
   supportsBin,
   supportsTimeUnit,
   supportsSort,
@@ -840,12 +841,96 @@ describe('transforms — aggregate / bin / timeUnit', () => {
 
   it('exposes the transform-applicability predicates by field type', () => {
     expect(supportsAggregate('quantitative')).toBe(true);
-    expect(supportsAggregate('nominal')).toBe(false);
+    // Every type now takes at least one aggregate (`distinct` applies to anything).
+    expect(supportsAggregate('nominal')).toBe(true);
     expect(supportsBin('quantitative')).toBe(true);
     expect(supportsBin('temporal')).toBe(false);
     expect(supportsTimeUnit('temporal')).toBe(true);
     expect(supportsTimeUnit('quantitative')).toBe(false);
   });
+
+  it('offers per-type aggregate menus: arithmetic needs numbers, min/max an ordering, distinct anything', () => {
+    expect(validAggregateOps('quantitative')).toEqual([
+      'sum',
+      'mean',
+      'median',
+      'min',
+      'max',
+      'distinct',
+    ]);
+    expect(validAggregateOps('temporal')).toEqual(['min', 'max', 'distinct']);
+    expect(validAggregateOps('ordinal')).toEqual(['min', 'max', 'distinct']);
+    expect(validAggregateOps('nominal')).toEqual(['distinct']);
+  });
+
+  it('emits a distinct-count of a categorical field as a quantitative measure', () => {
+    const spec = buildChartSpec({
+      datasetName: 'D',
+      mark: 'bar',
+      encodings: {
+        x: { field: 'region', type: 'nominal' },
+        y: { field: 'customer', type: 'nominal', aggregate: 'distinct' },
+      },
+    });
+    const enc = spec.encoding as Record<string, Record<string, unknown>>;
+    // The carried (nominal) type is for round-tripping; the emitted type is the
+    // effective one — a count of unique values reads as a quantitative measure.
+    expect(enc.y).toEqual({ field: 'customer', type: 'quantitative', aggregate: 'distinct' });
+  });
+
+  it('keeps the field type on order-preserving aggregates (a temporal min is still temporal)', () => {
+    const spec = buildChartSpec({
+      datasetName: 'D',
+      mark: 'point',
+      encodings: {
+        x: { field: 'region', type: 'nominal' },
+        y: { field: 'orderDate', type: 'temporal', aggregate: 'min' },
+      },
+    });
+    const enc = spec.encoding as Record<string, Record<string, unknown>>;
+    expect(enc.y).toEqual({ field: 'orderDate', type: 'temporal', aggregate: 'min' });
+  });
+
+  it('emits title as a bare string, the object form with a subtitle, nothing without a title', () => {
+    const base: BuilderConfig = {
+      datasetName: 'D',
+      mark: 'bar',
+      encodings: { x: { field: 'region', type: 'nominal' } },
+    };
+    expect(buildChartSpec({ ...base, title: 'Sales by region' }).title).toBe('Sales by region');
+    expect(buildChartSpec({ ...base, title: 'Sales', subtitle: 'FY26' }).title).toEqual({
+      text: 'Sales',
+      subtitle: 'FY26',
+    });
+    // A subtitle alone is not emitted (VL has no standalone subtitle), nor is a
+    // whitespace-only title.
+    expect(buildChartSpec({ ...base, subtitle: 'orphan' }).title).toBeUndefined();
+    expect(buildChartSpec({ ...base, title: '   ' }).title).toBeUndefined();
+  });
+
+  it('prefers a user-written title as the generated snippet name', () => {
+    expect(
+      generateChartName({
+        datasetName: 'D',
+        mark: 'bar',
+        title: 'Quarterly revenue',
+        encodings: { x: { field: 'region', type: 'nominal' } },
+      }),
+    ).toBe('Quarterly revenue');
+  });
+
+  it('names a distinct-count chart with a "unique" phrase', () => {
+    expect(
+      generateChartName({
+        datasetName: 'D',
+        mark: 'bar',
+        encodings: {
+          x: { field: 'region', type: 'nominal' },
+          y: { field: 'customer', type: 'nominal', aggregate: 'distinct' },
+        },
+      }),
+    ).toBe('Bar chart of unique customer by region');
+  });
 });
 
 describe('sort (ranking)', () => {