bug(cdk/drag-drop): Wrong direction of drop placeholder when moving between two different horizontal drop lists

[fmancuso]

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

Video: https://github.com/angular/components/assets/75433150/224b9a5c-cb45-44d4-8a94-04cae935fe65

As per the attached video and reproducible in the stackblitz, when you drag from one horizontal drop list to another, the direction reverses. For example, if you drag from a first row to a second row starting from the right and moving down to the left, once you get to the second row, the drop placeholder will show up on the right regardless of where the cursor was when you entered the second row. From here on, the directions will be reversed. If you drag to the right the drop placeholder will be seen on the left and vice versa.
Am I doing something wrong?

Edit: It seems that the problem occurs only when I change the width of the placeholder and when passing from the first droplist to the second droplist. In this case I do not land on the space intended for the drop placeholder but on another list item. The problem seems to be in the "_getItemIndexFromPointerPosition" method, where, analyzing the conditions, the case of not landing on the placeholder is not allowed. In fact, everything works fine when landing on the placeholder and then moving to the other list item since the condition "drag == this._previousSwap.drag" will result false and will allow the placeholder to be recalculated. While having a custom width of the placeholder and landing directly on the element make the previous condition to will always be true.

Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-aotvtz
Steps to reproduce:

1. Drag the "component2" div and go to the bottom left from the first row to the second row
2. Keep dragging and start moving to the left/right

Expected Behavior

I expect the placeholder to show up based on where the cursor is when entering the drop list and that the direction is not reversed, like it does when dragging the "component2" div going from right to bottom right.

Actual Behavior

The placeholder appears regardless of the cursor position when entering the droplist and the direction is reversed

Environment

• Angular: 17.3.5
• CDK/Material: 17.3.5
• Browser(s): Chrome
• Operating System (e.g. Windows, macOS, Ubuntu): macOs