From 3dc3fb9412d23769ab05e0cdb13f2f11b1fe1f70 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Sat, 27 May 2023 06:05:52 +0200
Subject: [PATCH] style: Plumb layer order through ApplicableDeclarationBlock,
 and make it have an effect

Same, I want to land this separately to see if it affects
micro-benchmarks. If so, we might want to pack the layer order
_somewhere_ (though in this case I'm not sure where, tbh).

With this, layer rules should have an effect on the page. There are
a few things missing before being able to enable them:

 * Fix nested layer order in some cases (when parent layers are declared
   out of order, see the previous commit mentioning this).
 * Some kind of OM representation, perhaps.
 * Tests of course, which are coming in bug 1728722 and bug 1727276.

But this should be enough to allow playing with them.

Depends on D124337

Differential Revision: https://phabricator.services.mozilla.com/D124338
---
 components/style/applicable_declarations.rs | 10 +++++++---
 components/style/rule_collector.rs          |  2 +-
 components/style/stylist.rs                 |  3 ++-
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/components/style/applicable_declarations.rs b/components/style/applicable_declarations.rs
index 6353fb4c5e5..168aae643cd 100644
--- a/components/style/applicable_declarations.rs
+++ b/components/style/applicable_declarations.rs
@@ -69,8 +69,10 @@ pub struct ApplicableDeclarationBlock {
     /// The bits containing the source order, cascade level, and shadow cascade
     /// order.
     bits: ApplicableDeclarationBits,
-    /// The specificity of the selector this block is represented by.
+    /// The specificity of the selector.
     pub specificity: u32,
+    /// The layer order of the selector.
+    pub layer_order: u32,
 }
 
 impl ApplicableDeclarationBlock {
@@ -85,16 +87,18 @@ impl ApplicableDeclarationBlock {
             source: StyleSource::from_declarations(declarations),
             bits: ApplicableDeclarationBits::new(0, level),
             specificity: 0,
+            layer_order: 0,
         }
     }
 
     /// Constructs an applicable declaration block from the given components
     #[inline]
-    pub fn new(source: StyleSource, order: u32, level: CascadeLevel, specificity: u32) -> Self {
+    pub fn new(source: StyleSource, source_order: u32, level: CascadeLevel, specificity: u32, layer_order: u32) -> Self {
         ApplicableDeclarationBlock {
             source,
-            bits: ApplicableDeclarationBits::new(order, level),
+            bits: ApplicableDeclarationBits::new(source_order, level),
             specificity,
+            layer_order,
         }
     }
 
diff --git a/components/style/rule_collector.rs b/components/style/rule_collector.rs
index 86293e5c785..bb34396f9aa 100644
--- a/components/style/rule_collector.rs
+++ b/components/style/rule_collector.rs
@@ -148,7 +148,7 @@ where
         f(self);
         if start != self.rules.len() {
             self.rules[start..]
-                .sort_unstable_by_key(|block| (block.specificity, block.source_order()));
+                .sort_unstable_by_key(|block| (block.layer_order, block.specificity, block.source_order()));
         }
         self.context.current_host = old_host;
         self.in_sort_scope = false;
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 7298e0d2fc9..0a87da95bc8 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -2176,6 +2176,7 @@ impl CascadeData {
                                         self.rules_source_order,
                                         CascadeLevel::UANormal,
                                         selector.specificity(),
+                                        current_layer_order,
                                     ));
                                 continue;
                             }
@@ -2678,7 +2679,7 @@ impl Rule {
         level: CascadeLevel,
     ) -> ApplicableDeclarationBlock {
         let source = StyleSource::from_rule(self.style_rule.clone());
-        ApplicableDeclarationBlock::new(source, self.source_order, level, self.specificity())
+        ApplicableDeclarationBlock::new(source, self.source_order, level, self.specificity(), self.layer_order)
     }
 
     /// Creates a new Rule.