fix(overlay): clear last calculated position when new set of positions is provided

src/cdk/overlay/position/connected-position-strategy.ts

@@ -31,7 +31,7 @@ import {FlexibleConnectedPositionStrategy} from './flexible-connected-position-s
  * a point on the origin element that is connected to a point on the overlay element. For example,
  * a basic dropdown is connecting the bottom-left corner of the origin to the top-left corner
  * of the overlay.
- * @deprecated
+ * @deprecated Use `FlexibleConnectedPositionStrategy` instead.
  * @deletion-target 7.0.0
  */
 export class ConnectedPositionStrategy implements PositionStrategy {

src/cdk/overlay/position/flexible-connected-position-strategy.spec.ts

@@ -633,6 +633,45 @@ describe('FlexibleConnectedPositionStrategy', () => {
       expect(recalcSpy).toHaveBeenCalled();
     });
 
+    it('should not retain the last preferred position when overriding the positions', () => {
+      originElement.style.top = '100px';
+      originElement.style.left = '100px';
+
+      const originRect = originElement.getBoundingClientRect();
+
+      positionStrategy.withPositions([{
+        originX: 'start',
+        originY: 'top',
+        overlayX: 'start',
+        overlayY: 'top',
+        offsetX: 10,
+        offsetY: 20
+      }]);
+
+      attachOverlay({positionStrategy});
+
+      let overlayRect = overlayRef.overlayElement.getBoundingClientRect();
+
+      expect(Math.floor(overlayRect.top)).toBe(Math.floor(originRect.top) + 20);
+      expect(Math.floor(overlayRect.left)).toBe(Math.floor(originRect.left) + 10);
+
+      positionStrategy.withPositions([{
+        originX: 'start',
+        originY: 'top',
+        overlayX: 'start',
+        overlayY: 'top',
+        offsetX: 20,
+        offsetY: 40
+      }]);
+
+      positionStrategy.reapplyLastPosition();
+
+      overlayRect = overlayRef.overlayElement.getBoundingClientRect();
+
+      expect(Math.floor(overlayRect.top)).toBe(Math.floor(originRect.top) + 40);
+      expect(Math.floor(overlayRect.left)).toBe(Math.floor(originRect.left) + 20);
+    });
+
     /**
      * Run all tests for connecting the overlay to the origin such that first preferred
      * position does not go off-screen. We do this because there are several cases where we

src/cdk/overlay/position/flexible-connected-position-strategy.ts

@@ -95,7 +95,7 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
   private _boundingBox: HTMLElement | null;
 
   /** The last position to have been calculated as the best fit position. */
-  private _lastPosition: ConnectedPosition;
+  private _lastPosition: ConnectedPosition | null;
 
   /** Subject that emits whenever the position changes. */
   private _positionChanges = new Subject<ConnectedOverlayPositionChange>();
@@ -305,6 +305,13 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
    */
   withPositions(positions: ConnectedPosition[]): this {
     this._preferredPositions = positions;
+
+    // If the last calculated position object isn't part of the positions anymore, clear
+    // it in order to avoid it being picked up if the consumer tries to re-apply.
+    if (positions.indexOf(this._lastPosition!) === -1) {
+      this._lastPosition = null;
+    }
+
     return this;
   }
 

src/cdk/overlay/position/overlay-position-builder.ts

@@ -34,6 +34,8 @@ export class OverlayPositionBuilder {
    * @param elementRef
    * @param originPos
    * @param overlayPos
+   * @deprecated Use `flexibleConnectedTo` instead.
+   * @deletion-target 7.0.0
    */
   connectedTo(
       elementRef: ElementRef,

src/lib/select/select.html

@@ -15,11 +15,10 @@
   <div class="mat-select-arrow-wrapper"><div class="mat-select-arrow"></div></div>
 </div>
 
-<!-- TODO(crisbeto): re-enable locked position after flexible positioning gets in. -->
 <ng-template
   cdk-connected-overlay
-  cdkConnectedOverlayHasBackdrop
   cdkConnectedOverlayLockPosition
+  cdkConnectedOverlayHasBackdrop
   cdkConnectedOverlayBackdropClass="cdk-overlay-transparent-backdrop"
   [cdkConnectedOverlayScrollStrategy]="_scrollStrategy"
   [cdkConnectedOverlayOrigin]="origin"