Implement fit-mode rendering contract with container sizing and pane re-fit

src/core/rendering.test.ts

@@ -14,19 +14,84 @@ describe('prepareSpecForRender', () => {
     const spec = {
       data: { values: [{ a: 1 }] },
       mark: 'bar',
+      width: 200,
+      height: 100,
       encoding: { x: { field: 'a', type: 'quantitative' } },
     };
     const before = structuredClone(spec);
-    const out = prepareSpecForRender(spec, { fitMode: 'width' });
-
-    // Mutating the output must not touch the input.
-    (out as { mark: string }).mark = 'point';
+    // A mode that both sets and removes sizing — the most invasive transform.
+    prepareSpecForRender(spec, { fitMode: 'width' });
     expect(spec).toEqual(before);
   });
 
-  test('M1 is a faithful pass-through of the spec content', () => {
+  test('Original (default) leaves sizing untouched', () => {
     const spec = { $schema: 'x', mark: 'line', width: 200, height: 100 };
     expect(prepareSpecForRender(spec)).toEqual(spec);
+    expect(prepareSpecForRender(spec, { fitMode: 'default' })).toEqual(spec);
+  });
+});
+
+describe('prepareSpecForRender — fit modes (spec §04 Rendering Contract step 2)', () => {
+  const base = { mark: 'bar', width: 200, height: 100 };
+
+  test('Width: width→container, height removed', () => {
+    const out = prepareSpecForRender(base, { fitMode: 'width' }) as Record<string, unknown>;
+    expect(out.width).toBe('container');
+    expect('height' in out).toBe(false);
+  });
+
+  test('Height: height→container, width removed', () => {
+    const out = prepareSpecForRender(base, { fitMode: 'height' }) as Record<string, unknown>;
+    expect(out.height).toBe('container');
+    expect('width' in out).toBe(false);
+  });
+
+  test('Full: both dimensions→container', () => {
+    const out = prepareSpecForRender(base, { fitMode: 'full' }) as Record<string, unknown>;
+    expect(out.width).toBe('container');
+    expect(out.height).toBe('container');
+  });
+
+  test('adds container sizing even when the spec declares no width/height', () => {
+    const out = prepareSpecForRender({ mark: 'point' }, { fitMode: 'full' }) as Record<
+      string,
+      unknown
+    >;
+    expect(out).toEqual({ mark: 'point', width: 'container', height: 'container' });
+  });
+
+  test('recurses into layered sub-specs', () => {
+    const spec = {
+      layer: [
+        { mark: 'bar', width: 50, height: 50 },
+        { mark: 'line', height: 50 },
+      ],
+    };
+    const out = prepareSpecForRender(spec, { fitMode: 'full' }) as unknown as {
+      width: string;
+      height: string;
+      layer: Array<Record<string, unknown>>;
+    };
+    expect(out.width).toBe('container');
+    expect(out.height).toBe('container');
+    expect(out.layer[0]).toMatchObject({ width: 'container', height: 'container' });
+    expect(out.layer[1]).toMatchObject({ width: 'container', height: 'container' });
+  });
+
+  test('recurses into concat arrays and a child spec (facet/repeat)', () => {
+    const spec = {
+      facet: { field: 'g', type: 'nominal' },
+      spec: {
+        hconcat: [{ mark: 'bar', height: 80 }, { mark: 'point' }],
+      },
+    };
+    const out = prepareSpecForRender(spec, { fitMode: 'width' }) as unknown as {
+      spec: { hconcat: Array<Record<string, unknown>> };
+    };
+    for (const child of out.spec.hconcat) {
+      expect(child.width).toBe('container');
+      expect('height' in child).toBe(false);
+    }
   });
 });