KinematicBody2D: odd move_and_slide behaviour when exactly on tile edge

[snoopdouglas]

Godot version:
3.2.3-official

OS/device including version:
Ubuntu Linux 20.04

Issue description:
Possibly related to #33833.

When using KinematicBody2D's move_and_slide or move_and_slide_with_snap to enact gravity, I've noticed that when a body is exactly on the diagonal edge of a tile:

• is_on_floor() returns false
• is_on_wall() returns true
• The body can't travel any further, but keeps gaining velocity (when setting it from the result of move_and_slide)

So we essentially end up with a Mario 64 speedrunner's dream:

Interestingly, the value of y tends to fluctuate, and sometimes (seemingly non-deterministically) the body unhooks itself and so goes flying downwards.

Steps to reproduce:

• Position a KinematicBody2D on the edge of a tile
• Apply gravity to it
• Note the weird behaviour of its position and velocity

Minimal reproduction project:
floor-wall-test.zip

[madmiraal]

Related to #43012 and #43014.

[snoopdouglas]

I've reproduced this in 3.2.4-rc1.

Edit: still reproducible in 3.3.4

[pouleyKetchoupp]

Confirmed still present in 3.4 beta 6 and master (6877ccc).

[MaxMarauder]

I can confirm that the issue is still reproducible in v3.5.3.stable.official.

Here's a workaround I used:

    if is_on_wall() && is_equal_approx(position.x, round(position.x)):
        position.x += 0.001