From 0dfd45ba2153bda841a32a48938ecadfeb3f1999 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Wed, 7 Sep 2022 23:57:18 +0000
Subject: [PATCH] style: Make -webkit-line-clamp create a block container in
 the appropriate situations

This is a hack, sorta, similar to Chromium's:

  https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/layout/layout_object.cc;l=356;drc=312b74e385e6aba98ab31fd911238c0dc16b396c

except at computed-value rather than used-value time, because it's both
simpler to reason about and prevents lying in the computed style.

This fixes the relevant test-case, and matches closer what Chromium does,
by not creating anonymous flex items for all elements inside the
line-clamp context.

The behavior change is covered by the test changes. I had to also fix a
couple pre-existing bugs that were caught by tests, now that the
line-clamped block is the -webkit-box-styled element rather than an anonymous
flex item (and thus now had padding).

Depends on D155180

Differential Revision: https://phabricator.services.mozilla.com/D155181
---
 components/style/style_adjuster.rs | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/components/style/style_adjuster.rs b/components/style/style_adjuster.rs
index b855b937dfb..09bdb2a6522 100644
--- a/components/style/style_adjuster.rs
+++ b/components/style/style_adjuster.rs
@@ -150,6 +150,35 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
         }
     }
 
+    /// -webkit-box with line-clamp and vertical orientation gets turned into
+    /// flow-root at computed-value time.
+    ///
+    /// This makes the element not be a flex container, with all that it
+    /// implies, but it should be safe. It matches blink, see
+    /// https://bugzilla.mozilla.org/show_bug.cgi?id=1786147#c10
+    fn adjust_for_webkit_line_clamp(&mut self) {
+        use crate::properties::longhands::_moz_box_orient::computed_value::T as BoxOrient;
+        use crate::values::specified::box_::{DisplayOutside, DisplayInside};
+        let box_style= self.style.get_box();
+        if box_style.clone__webkit_line_clamp().is_none() {
+            return;
+        }
+        let disp = box_style.clone_display();
+        if disp.inside() != DisplayInside::WebkitBox {
+            return;
+        }
+        if self.style.get_xul().clone__moz_box_orient() != BoxOrient::Vertical {
+            return;
+        }
+        let new_display = if disp.outside() == DisplayOutside::Block {
+            Display::FlowRoot
+        } else {
+            debug_assert_eq!(disp.outside(), DisplayOutside::Inline);
+            Display::InlineBlock
+        };
+        self.style.mutate_box().set_adjusted_display(new_display, false);
+    }
+
     /// CSS 2.1 section 9.7:
     ///
     ///    If 'position' has the value 'absolute' or 'fixed', [...] the computed
@@ -856,6 +885,7 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
         }
         self.adjust_for_top_layer();
         self.blockify_if_necessary(layout_parent_style, element);
+        self.adjust_for_webkit_line_clamp();
         self.adjust_for_position();
         self.adjust_for_overflow();
         #[cfg(feature = "gecko")]