[Webkit-unassigned] [Bug 244232] New: overscroll-behavior: none doesn't prevent overscroll when page is too small to scroll

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=244232

            Bug ID: 244232
           Summary: overscroll-behavior: none doesn't prevent overscroll
                    when page is too small to scroll
           Product: WebKit
           Version: Other
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Scrolling
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: krevis at figma.com
                CC: simon.fraser at apple.com

When a document has overscroll-behavior: none, but the page's height is too small to be scrollable, the page can still be overscrolled using a touch (iOS) or trackpad scroll (iOS, Mac).

Steps:
1. Load attached html file in Safari Technical Preview 151 on macOS 12, or Safari on iOS/iPadOS 16 beta, or Safari in macOS 13 beta
2. On Mac, scroll up and down using two-finger scroll gesture on trackpad.
3. On iPhone, scroll up and down with touch.
4. On iPad, scroll up and down with touch, or with two-finger scroll gesture on trackpad, or with mouse wheel.

Expected: Since the html and body elements have `overscroll-behavior: none`, overscroll aka "bouncing" should not happen.
Actual: Overscroll aka "bouncing" does happen. If you click on the element that increases the body height, so scrolling is possible, then overscroll stops working.

Notes:

Both Chrome and Firefox behave as expected. (Chrome 104.0.5112.101 and Firefox 103.0.2 on macOS 12.5.1.)

The Overscroll Behavior spec says, about overscroll-behavior: none, that "this element must also not perform local boundary default actions such as showing any overscroll affordances". 
https://drafts.csswg.org/css-overscroll/#valdef-overscroll-behavior-none

Also, "If a scroll container has no potential to scroll, because it does not overflow in the direction of the scroll, the element is always considered to be at the scroll boundary."
https://drafts.csswg.org/css-overscroll/#scroll-boundary

Nothing in the spec appears to say that the overscroll-behavior should be ignored in this case. 

There's an existing bug with a similar complaint:  https://bugs.webkit.org/show_bug.cgi?id=243452
but this case is simpler, with no nested scroll views, just a simple document.

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