[webkit-changes] [WebKit/WebKit] e75a5c: [Multicolumn] Margins incorrectly accounted for be...

[Ahmad Saleem]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: e75a5cd7e299cc3e318f0f720ff991856c201155
      https://github.com/WebKit/WebKit/commit/e75a5cd7e299cc3e318f0f720ff991856c201155
  Author: Ahmad Saleem <ahmad.saleem792+github at gmail.com>
  Date:   2023-02-18 (Sat, 18 Feb 2023)

  Changed paths:
    A LayoutTests/fast/multicol/margin-bottom-and-break-after-expected.txt
    A LayoutTests/fast/multicol/margin-bottom-and-break-after.html
    M Source/WebCore/rendering/RenderBlockFlow.cpp

  Log Message:
  -----------
  [Multicolumn] Margins incorrectly accounted for before forced breaks

https://bugs.webkit.org/show_bug.cgi?id=252507

Reviewed by Alan Baradlay.

This patch is to align WebKit with Gecko / Firefox and Blink / Chromium.

Merge - https://src.chromium.org/viewvc/blink?view=revision&revision=188456

The spec [1] basically says that margins should be ignored at column boundaries,
although it's explicitly ambiguous about what should happen to top margins
after a forced break. This CL is solely about margins before a break, though,
and they should all be set to 0, so that contents that follow start at the top
of the next column, instead of leaving one column blank and skipping to the
next one after that.

[1] https://www.w3.org/TR/CSS2/page.html#allowed-page-breaks

* Source/WebCore/rendering/RenderBlockFlow.cpp:
(RenderBlockFlow::applyAfterBreak): Remove "marginOffset" usecase
* LayoutTests/fast/multicol/margin-bottom-and-break-after.html: Add Test Case
* LayoutTests/fast/multicol/margin-bottom-and-break-after-expected.txt: Add Test Case Expectation

Canonical link: https://commits.webkit.org/260510@main