feat: add PlacementController to Gen2

2nd-gen/packages/core/controllers/index.ts

@@ -25,3 +25,12 @@ export {
   LanguageResolutionController,
   languageResolverUpdatedSymbol,
 } from './language-resolution.js';
+export {
+  ALL_PLACEMENTS,
+  fromFloatingPlacement,
+  PlacementController,
+  toFloatingPlacement,
+  type Placement,
+  type PlacementOptions,
+  type VirtualTrigger,
+} from './placement-controller/index.js';

2nd-gen/packages/core/controllers/placement-controller/index.ts

@@ -0,0 +1,21 @@
+/**
+ * Copyright 2026 Adobe. All rights reserved.
+ * This file is licensed to you under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License. You may obtain a copy
+ * of the License at http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
+ * OF ANY KIND, either express or implied. See the License for the specific language
+ * governing permissions and limitations under the License.
+ */
+
+export {
+  ALL_PLACEMENTS,
+  fromFloatingPlacement,
+  PlacementController,
+  toFloatingPlacement,
+  type Placement,
+  type PlacementOptions,
+  type VirtualTrigger,
+} from './src/placement-controller.js';

2nd-gen/packages/core/controllers/placement-controller/src/fallback-placements.ts

@@ -0,0 +1,41 @@
+/**
+ * Copyright 2026 Adobe. All rights reserved.
+ * This file is licensed to you under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License. You may obtain a copy
+ * of the License at http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
+ * OF ANY KIND, either express or implied. See the License for the specific language
+ * governing permissions and limitations under the License.
+ */
+
+import type { Placement as FloatingPlacement } from '@floating-ui/dom';
+
+const FALLBACKS: Record<FloatingPlacement, FloatingPlacement[]> = {
+  left: ['right', 'bottom', 'top'],
+  'left-start': ['right-start', 'bottom', 'top'],
+  'left-end': ['right-end', 'bottom', 'top'],
+  right: ['left', 'bottom', 'top'],
+  'right-start': ['left-start', 'bottom', 'top'],
+  'right-end': ['left-end', 'bottom', 'top'],
+  top: ['bottom', 'left', 'right'],
+  'top-start': ['bottom-start', 'left', 'right'],
+  'top-end': ['bottom-end', 'left', 'right'],
+  bottom: ['top', 'left', 'right'],
+  'bottom-start': ['top-start', 'left', 'right'],
+  'bottom-end': ['top-end', 'left', 'right'],
+};
+
+/**
+ * Look up the fallback placement order for Floating UI's `flip` middleware
+ * when the anchor is a `VirtualTrigger`.
+ *
+ * @param placement - Normalized Floating UI placement for the current side.
+ * @returns Ordered list of placements to try when the primary side does not fit.
+ */
+export function getFallbackPlacements(
+  placement: FloatingPlacement
+): FloatingPlacement[] {
+  return FALLBACKS[placement] ?? [placement];
+}