From fa8752df6a2c9cdec3d9108614bf2bf9b713626b Mon Sep 17 00:00:00 2001
From: Oriol Brufau <obrufau@igalia.com>
Date: Fri, 13 Sep 2024 18:56:14 +0200
Subject: [PATCH] Fix precision issue with line heights (#33438)

When computing the ascent and descent in an inline formatting context,
we weren't taking into account that app units have precision limitations.
Therefore, in some cases we were getting a line height that was slightly
taller than the value specified in `line-height`.

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>
---
 components/layout_2020/flow/inline/mod.rs                   | 6 +++++-
 .../meta/css/CSS2/tables/fixed-table-layout-003b01.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b02.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b03.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b04.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b05.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b06.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b07.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b08.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b09.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b10.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b11.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003b12.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003c01.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003c02.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003c03.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003c04.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003c05.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003c06.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003c07.xht.ini  | 2 --
 .../meta/css/CSS2/tables/fixed-table-layout-003c08.xht.ini  | 2 --
 21 files changed, 5 insertions(+), 41 deletions(-)
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b01.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b02.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b03.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b04.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b05.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b06.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b07.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b08.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b09.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b10.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b11.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b12.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c01.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c02.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c03.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c04.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c05.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c06.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c07.xht.ini
 delete mode 100644 tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c08.xht.ini

diff --git a/components/layout_2020/flow/inline/mod.rs b/components/layout_2020/flow/inline/mod.rs
index 9e93644f094..19d8980f926 100644
--- a/components/layout_2020/flow/inline/mod.rs
+++ b/components/layout_2020/flow/inline/mod.rs
@@ -1815,8 +1815,12 @@ impl InlineContainerState {
             ascent = font_metrics_of_first_font.ascent;
             descent = font_metrics_of_first_font.descent;
             let half_leading = (line_height - (ascent + descent)).scale_by(0.5);
+            // We want the sum of `ascent` and `descent` to equal `line_height`.
+            // If we just add `half_leading` to both, then we may not get `line_height`
+            // due to precision limitations of `Au`. Instead, we set `descent` to
+            // the value that will guarantee the correct sum.
             ascent += half_leading;
-            descent += half_leading;
+            descent = line_height - ascent;
         }
 
         LineBlockSizes {
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b01.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b01.xht.ini
deleted file mode 100644
index a2eb9d76325..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b01.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b01.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b02.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b02.xht.ini
deleted file mode 100644
index 1ffc770f94a..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b02.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b02.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b03.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b03.xht.ini
deleted file mode 100644
index 89bf3660b25..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b03.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b03.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b04.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b04.xht.ini
deleted file mode 100644
index 5d74d444b47..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b04.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b04.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b05.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b05.xht.ini
deleted file mode 100644
index f6daa39f735..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b05.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b05.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b06.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b06.xht.ini
deleted file mode 100644
index ff9c943aabc..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b06.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b06.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b07.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b07.xht.ini
deleted file mode 100644
index 8d064f14feb..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b07.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b07.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b08.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b08.xht.ini
deleted file mode 100644
index 1ac28e11028..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b08.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b08.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b09.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b09.xht.ini
deleted file mode 100644
index 0c94c573916..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b09.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b09.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b10.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b10.xht.ini
deleted file mode 100644
index 5216a678904..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b10.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b10.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b11.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b11.xht.ini
deleted file mode 100644
index 44bd69aaa5d..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b11.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b11.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b12.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b12.xht.ini
deleted file mode 100644
index 9bf7c48d5e6..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003b12.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003b12.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c01.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c01.xht.ini
deleted file mode 100644
index 7997b2df600..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c01.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003c01.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c02.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c02.xht.ini
deleted file mode 100644
index f45a17492f2..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c02.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003c02.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c03.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c03.xht.ini
deleted file mode 100644
index bc7bdd43de7..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c03.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003c03.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c04.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c04.xht.ini
deleted file mode 100644
index 9f21980c160..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c04.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003c04.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c05.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c05.xht.ini
deleted file mode 100644
index d9e02340a21..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c05.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003c05.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c06.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c06.xht.ini
deleted file mode 100644
index e6a1cd91f1e..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c06.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003c06.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c07.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c07.xht.ini
deleted file mode 100644
index 32abd51caf4..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c07.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003c07.xht]
-  expected: FAIL
diff --git a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c08.xht.ini b/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c08.xht.ini
deleted file mode 100644
index 6a59c294df0..00000000000
--- a/tests/wpt/meta/css/CSS2/tables/fixed-table-layout-003c08.xht.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[fixed-table-layout-003c08.xht]
-  expected: FAIL