layout: Implement computation of table column widths (#31165)

* layout: Implement computation of table column widths

This change implements the various steps of table column width
computation, ignoring features that don't exist yet (such as separated
borders, column elements, and colgroups).

Co-authored-by: Oriol Brufau <obrufau@igalia.com>

* Fix an issue with the assignment of column percent width

* Respond to review comments

---------

Co-authored-by: Oriol Brufau <obrufau@igalia.com>

components/layout_2020/flow/mod.rs

@@ -308,7 +308,8 @@ fn calculate_inline_content_size_for_block_level_boxes(
 
     impl AccumulatedData {
         fn max_size_including_uncleared_floats(&self) -> ContentSizes {
-            self.max_size.max(self.left_floats.add(&self.right_floats))
+            self.max_size
+                .max(self.left_floats.union(&self.right_floats))
         }
         fn clear_floats(&mut self, clear: Clear) {
             match clear {
@@ -333,12 +334,12 @@ fn calculate_inline_content_size_for_block_level_boxes(
     let accumulate = |mut data: AccumulatedData, (size, float, clear)| {
         data.clear_floats(clear);
         match float {
-            Float::Left => data.left_floats = data.left_floats.add(&size),
-            Float::Right => data.right_floats = data.right_floats.add(&size),
+            Float::Left => data.left_floats = data.left_floats.union(&size),
+            Float::Right => data.right_floats = data.right_floats.union(&size),
             Float::None => {
                 data.max_size = data
                     .max_size
-                    .max(data.left_floats.add(&data.right_floats).add(&size));
+                    .max(data.left_floats.union(&data.right_floats).union(&size));
                 data.left_floats = ContentSizes::zero();
                 data.right_floats = ContentSizes::zero();
             },

components/layout_2020/sizing.rs

@@ -4,6 +4,8 @@
 
 //! <https://drafts.csswg.org/css-sizing/>
 
+use std::ops::{Add, AddAssign};
+
 use app_units::Au;
 use serde::Serialize;
 use style::logical_geometry::WritingMode;
@@ -14,7 +16,7 @@ use style::Zero;
 
 use crate::style_ext::{Clamp, ComputedValuesExt};
 
-#[derive(Clone, Debug, Serialize)]
+#[derive(Clone, Copy, Debug, Serialize)]
 pub(crate) struct ContentSizes {
     pub min_content: Au,
     pub max_content: Au,
@@ -43,14 +45,35 @@ impl ContentSizes {
         }
     }
 
-    pub fn add(&self, other: &Self) -> Self {
+    pub fn max_assign(&mut self, other: Self) {
+        *self = self.max(other);
+    }
+
+    pub fn union(&self, other: &Self) -> Self {
         Self {
             min_content: self.min_content.max(other.min_content),
             max_content: self.max_content + other.max_content,
         }
     }
 }
 
+impl Add for ContentSizes {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self {
+        Self {
+            min_content: self.min_content + rhs.min_content,
+            max_content: self.max_content + rhs.max_content,
+        }
+    }
+}
+
+impl AddAssign for ContentSizes {
+    fn add_assign(&mut self, rhs: Self) {
+        *self = self.add(rhs)
+    }
+}
+
 impl ContentSizes {
     /// <https://drafts.csswg.org/css2/visudet.html#shrink-to-fit-float>
     pub fn shrink_to_fit(&self, available_size: Au) -> Au {