tree 76cae94f76cbe7252067f7a821c881885e74a4db
parent 629833fd0d6f68454180b1f3fc3c53703fe29184
author Ting-Yu Lin <tlin@mozilla.com> 1646526767 +0000
committer moz-wptsync-bot <wptsync@mozilla.com> 1646560526 +0000

Include child frame's overflow area locating at its normal position into parent's overflow.

When a position:sticky element "sticks" in the scroll container's scrollport, we
compute its containing block's overflow areas by including its overflow areas
located at its relative position. This makes the element's normal position
unreachable because its overflow areas located at its "normal position" might
not be within its containing block's overflow areas. Block frame doesn't have
this problem because `nsLineBox` always includes the element's normal position
rect in its own rect.

Therefore, when including a sticky child frame's overflow area into its parent's
overflow area, the overflow areas located at its normal position should be
included as well. This behavior is consistent with a relatively positioned child
frame. (A position:relative frame's normal position is always reachable when
scrolling, at least in both axes that grow positively.)

Differential Revision: https://phabricator.services.mozilla.com/D140373

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1377072
gecko-commit: 159e0423f98738a9d68b22d41420bb67df391ad5
gecko-reviewers: dholbert