From 6e80a34d09e8bb22bdac5feeff4cf30b571987ff Mon Sep 17 00:00:00 2001
From: Oriol Brufau <obrufau@igalia.com>
Date: Fri, 13 Sep 2024 09:31:23 +0200
Subject: [PATCH] Simplify table logic in effective_overflow() (#33431)

On tables, we need to treat an overflow value of `scroll` or `auto` as
`visible`. Both `scroll` or `auto` are scrollable, which implies that
the other axis must also have a scrollable value.

Therefore, when we make the value behave as the non-scrollable `visible`,
we need to adjust the other axis too.

The previous logic was checking `is_scrollable()` but that wasn't
necessary, since computed values must have the same scrollability.

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
---
 components/layout_2020/style_ext.rs | 55 ++++++++++++-----------------
 1 file changed, 22 insertions(+), 33 deletions(-)

diff --git a/components/layout_2020/style_ext.rs b/components/layout_2020/style_ext.rs
index f9aa9650c53..53bf9e6df33 100644
--- a/components/layout_2020/style_ext.rs
+++ b/components/layout_2020/style_ext.rs
@@ -622,49 +622,38 @@ impl ComputedValuesExt for ComputedValues {
     /// <https://www.w3.org/TR/css-overflow-3/#overflow-control>
     fn effective_overflow(&self) -> PhysicalVec<Overflow> {
         let style_box = self.get_box();
-        let mut overflow_x = style_box.overflow_x;
-        let mut overflow_y = style_box.overflow_y;
-        // According to <https://drafts.csswg.org/css-tables/#global-style-overrides>,
-        // overflow applies to table-wrapper boxes and not to table grid boxes.
-        // That's what Blink and WebKit do, however Firefox matches a CSSWG resolution that says
-        // the opposite: <https://lists.w3.org/Archives/Public/www-style/2012Aug/0298.html>
-        // Due to the way that we implement table-wrapper boxes, it's easier to align with Firefox.
-        match style_box.display.inside() {
-            stylo::DisplayInside::Table
-                if matches!(self.pseudo(), Some(PseudoElement::ServoTableGrid)) =>
-            {
-                // <https://drafts.csswg.org/css-tables/#global-style-overrides>
-                // Tables ignore overflow values different than visible, clip and hidden.
-                // We also need to make sure that both axes have the same scrollability.
-                if matches!(overflow_x, Overflow::Auto | Overflow::Scroll) {
-                    overflow_x = Overflow::Visible;
-                    if overflow_y.is_scrollable() {
-                        overflow_y = Overflow::Visible;
-                    }
-                }
-                if matches!(overflow_y, Overflow::Auto | Overflow::Scroll) {
-                    overflow_y = Overflow::Visible;
-                    if overflow_x.is_scrollable() {
-                        overflow_x = Overflow::Visible;
-                    }
-                }
+        let overflow_x = style_box.overflow_x;
+        let overflow_y = style_box.overflow_y;
+        let ignores_overflow = match style_box.display.inside() {
+            stylo::DisplayInside::Table => {
+                // According to <https://drafts.csswg.org/css-tables/#global-style-overrides>,
+                // - overflow applies to table-wrapper boxes and not to table grid boxes.
+                //   That's what Blink and WebKit do, however Firefox matches a CSSWG resolution that says
+                //   the opposite: <https://lists.w3.org/Archives/Public/www-style/2012Aug/0298.html>
+                //   Due to the way that we implement table-wrapper boxes, it's easier to align with Firefox.
+                // - Tables ignore overflow values different than visible, clip and hidden.
+                //   This affects both axes, to ensure they have the same scrollability.
+                !matches!(self.pseudo(), Some(PseudoElement::ServoTableGrid)) ||
+                    matches!(overflow_x, Overflow::Auto | Overflow::Scroll) ||
+                    matches!(overflow_y, Overflow::Auto | Overflow::Scroll)
             },
             stylo::DisplayInside::TableColumn |
             stylo::DisplayInside::TableColumnGroup |
             stylo::DisplayInside::TableRow |
             stylo::DisplayInside::TableRowGroup |
             stylo::DisplayInside::TableHeaderGroup |
-            stylo::DisplayInside::TableFooterGroup |
-            stylo::DisplayInside::Table => {
+            stylo::DisplayInside::TableFooterGroup => {
                 // <https://drafts.csswg.org/css-tables/#global-style-overrides>
                 // Table-track and table-track-group boxes ignore overflow.
-                // We also ignore it on table-wrapper boxes (see above).
-                overflow_x = Overflow::Visible;
-                overflow_y = Overflow::Visible;
+                true
             },
-            _ => {},
+            _ => false,
+        };
+        if ignores_overflow {
+            PhysicalVec::new(Overflow::Visible, Overflow::Visible)
+        } else {
+            PhysicalVec::new(overflow_x, overflow_y)
         }
-        PhysicalVec::new(overflow_x, overflow_y)
     }
 
     /// Return true if this style is a normal block and establishes