From 1563c1e3a851d13982c2e9a0c2eabb8287823b35 Mon Sep 17 00:00:00 2001
From: Andreu Botella <abotella@igalia.com>
Date: Fri, 4 Oct 2024 16:39:40 -0700
Subject: [PATCH] [line-clamp] Always clamp immediately after a line box

In our initial implementation of `line-clamp: auto`, we allowed
clamping after lineless boxes, in order to better match the behavior
of `line-clamp` as it follows from the spec's `continue: discard`
model, even though our implementation uses a different model which is
not yet in the specification (see
https://github.com/w3c/csswg-drafts/issues/7708).

However, in hallway conversations in TPAC 2024, we agreed that it
would be better for this model to instead only allow clamping
immediately after a line. If the first line does not fit, we calmp at
the first line even if that overflows the clamp height. If there are
no lines, we do not clamp. This patch implements this.

Additionally, a previous patch (https://crrev.com/c/5868971) had
increased the memory size of `LineClampData` from 8 to 20 bytes,
causing a memory regression. This patch shrinks it to 12 bytes, since
`LineClampData` no longer needs to keep track of how many block boxes
there are between the last line and the clmap point, and now OOFs
after the clamped line behave the same when clamping by a number of
lines or by a height, so there is no need for a flag to distinguish
these behaviors. This patch also adds a size assertion for
`LineClampData`.

This patch also changes or removes some WPT tests that were written
assuming the previous behavior.

Bug: 40336192, 368114054
Change-Id: I8c8afebb5dc566de92112cee2fcf24a2e60b42c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5904459
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Andreu Botella <abotella@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1364495}
---
 .../line-clamp-auto-011.tentative.html        |  2 +-
 .../line-clamp-auto-025.tentative.html        |  7 +--
 .../line-clamp-auto-026.tentative.html        | 40 ---------------
 .../line-clamp-auto-032.tentative.html        | 50 -------------------
 .../line-clamp-auto-034.tentative.html        | 11 ++--
 .../line-clamp-auto-037.tentative.html        |  2 +-
 .../reference/line-clamp-auto-011-ref.html    |  5 +-
 .../reference/line-clamp-auto-025-ref.html    | 27 ----------
 .../reference/line-clamp-auto-026-ref.html    | 32 ------------
 .../reference/line-clamp-auto-032-ref.html    | 34 -------------
 .../reference/line-clamp-auto-034-ref.html    | 23 ---------
 .../reference/line-clamp-auto-037-ref.html    | 15 ++++++
 12 files changed, 30 insertions(+), 218 deletions(-)
 delete mode 100644 css/css-overflow/line-clamp/line-clamp-auto-026.tentative.html
 delete mode 100644 css/css-overflow/line-clamp/line-clamp-auto-032.tentative.html
 delete mode 100644 css/css-overflow/line-clamp/reference/line-clamp-auto-025-ref.html
 delete mode 100644 css/css-overflow/line-clamp/reference/line-clamp-auto-026-ref.html
 delete mode 100644 css/css-overflow/line-clamp/reference/line-clamp-auto-032-ref.html
 delete mode 100644 css/css-overflow/line-clamp/reference/line-clamp-auto-034-ref.html
 create mode 100644 css/css-overflow/line-clamp/reference/line-clamp-auto-037-ref.html

diff --git a/css/css-overflow/line-clamp/line-clamp-auto-011.tentative.html b/css/css-overflow/line-clamp/line-clamp-auto-011.tentative.html
index 00076a5336e890..50513516cc9daa 100644
--- a/css/css-overflow/line-clamp/line-clamp-auto-011.tentative.html
+++ b/css/css-overflow/line-clamp/line-clamp-auto-011.tentative.html
@@ -4,7 +4,7 @@
 <link rel="author" title="Andreu Botella" href="mailto:abotella@igalia.com">
 <link rel="help" href="https://drafts.csswg.org/css-overflow-4/#line-clamp">
 <link rel="match" href="reference/line-clamp-auto-011-ref.html">
-<meta name="assert" content="When line-clamp: auto is used with max-height: 0, it should not show any lines and its content box's intrinsic size should be zero">
+<meta name="assert" content="When line-clamp: auto is used with max-height: 0, it should still show the first line">
 <style>
 .clamp {
   line-clamp: auto;
diff --git a/css/css-overflow/line-clamp/line-clamp-auto-025.tentative.html b/css/css-overflow/line-clamp/line-clamp-auto-025.tentative.html
index ee394b2a76d12a..ab741d3df4d9ba 100644
--- a/css/css-overflow/line-clamp/line-clamp-auto-025.tentative.html
+++ b/css/css-overflow/line-clamp/line-clamp-auto-025.tentative.html
@@ -1,15 +1,16 @@
 <!DOCTYPE html>
 <meta charset="utf-8">
-<title>CSS Overflow: abspos exactly at the clamp point is visible</title>
+<title>CSS Overflow: abspos exactly at the clamp point is hidden</title>
 <link rel="author" title="Andreu Botella" href="mailto:abotella@igalia.com">
 <link rel="help" href="https://drafts.csswg.org/css-overflow-4/#line-clamp">
-<link rel="match" href="reference/line-clamp-auto-025-ref.html">
-<meta name="assert" content="The chosen clamp point with line-clamp: auto is the last one where the box size doesn't overflow. Since non-inline abspos have a clamp point after them, and they don't take up any space in the container, an abspos right at the boundary should be visible.">
+<link rel="match" href="reference/webkit-line-clamp-005-ref.html">
+<meta name="assert" content="The chosen clamp point with line-clamp: auto is at the last line where the box size doesn't overflow. An immediately following box, even if it's an abspos that takes up no block size, should still be hidden.">
 <style>
 .clamp {
   line-clamp: auto;
   max-height: 4lh;
   font: 16px / 32px serif;
+  padding: 0 4px;
   background-color: yellow;
 }
 .inner {
diff --git a/css/css-overflow/line-clamp/line-clamp-auto-026.tentative.html b/css/css-overflow/line-clamp/line-clamp-auto-026.tentative.html
deleted file mode 100644
index f616cbed028a82..00000000000000
--- a/css/css-overflow/line-clamp/line-clamp-auto-026.tentative.html
+++ /dev/null
@@ -1,40 +0,0 @@
-<!DOCTYPE html>
-<meta charset="utf-8">
-<title>CSS Overflow: abspos exactly at the clamp point is visible</title>
-<link rel="author" title="Andreu Botella" href="mailto:abotella@igalia.com">
-<link rel="help" href="https://drafts.csswg.org/css-overflow-4/#line-clamp">
-<link rel="match" href="reference/line-clamp-auto-026-ref.html">
-<meta name="assert" content="The chosen clamp point with line-clamp: auto is the last one where the box size doesn't overflow. Since non-inline abspos have a clamp point after them, and they don't take up any space in the container, an abspos right at the boundary should be visible. If there's bottom padding in a container box, that counts as effectively shrinking the boundary.">
-<style>
-.clamp {
-  line-clamp: auto;
-  max-height: calc(4lh + 2 * 2px);
-  font: 16px / 32px serif;
-  background-color: yellow;
-}
-.padding {
-  padding: 2px;
-}
-.inner {
-  white-space: pre-wrap;
-}
-.abspos {
-  position: absolute;
-  width: 100px;
-  height: 100px;
-  background-color: skyblue;
-}
-</style>
-
-<div class="clamp">
-<div class="padding">
-<div class="inner">Line 1
-Line 2
-Line 3
-Line 4
-</div>
-<div class="abspos"></div>
-<div class="inner">Line 5
-Line 6</div>
-</div>
-</div>
diff --git a/css/css-overflow/line-clamp/line-clamp-auto-032.tentative.html b/css/css-overflow/line-clamp/line-clamp-auto-032.tentative.html
deleted file mode 100644
index 17c6981ae33f11..00000000000000
--- a/css/css-overflow/line-clamp/line-clamp-auto-032.tentative.html
+++ /dev/null
@@ -1,50 +0,0 @@
-<!DOCTYPE html>
-<meta charset="utf-8">
-<title>CSS Overflow: `line-clamp: auto` margin collapsing accounts for self-collapsing boxes</title>
-<link rel="author" title="Andreu Botella" href="mailto:abotella@igalia.com">
-<link rel="help" href="https://drafts.csswg.org/css-overflow-4/#line-clamp">
-<link rel="match" href="reference/line-clamp-auto-032-ref.html">
-<meta name="assert" content="With `line-clamp: auto`, if a clamp point might fall inside a box, its margins are accounted for correctly. This is the case even for self-collapsing boxes before the clamp point.">
-<style>
-.clamp {
-  line-clamp: auto;
-  max-height: calc(4lh + 2 * 5px);
-  font: 16px / 32px serif;
-  background-color: orange;
-}
-.inner {
-  white-space: pre;
-  margin: 5px;
-  background-color: yellow;
-}
-.collapse-through {
-  margin: 5px;
-}
-.abspos {
-  position: absolute;
-  right: 0;
-  height: 100px;
-  width: 100px;
-  background-color: skyblue;
-}
-</style>
-
-<!--
-  The bottom margins of both the first `.inner` and of `.collapse-through` end
-  at the clamp boundary, since the bottom margin of `.inner` collapses through
-  `.collapse-through`. This also puts the static position of `.abspos` at the
-  clamp boundary, which means it will be visible.
--->
-
-<div class="clamp">
-<div class="inner">Line 1
-Line 2
-Line 3
-Line 4</div>
-<div class="collapse-through"></div>
-<div class="abspos"></div>
-<div class="inner">Line 5
-Line 6
-Line 7
-Line 8</div>
-</div>
diff --git a/css/css-overflow/line-clamp/line-clamp-auto-034.tentative.html b/css/css-overflow/line-clamp/line-clamp-auto-034.tentative.html
index ebb676dfd8e0fa..96fe675d1b10c7 100644
--- a/css/css-overflow/line-clamp/line-clamp-auto-034.tentative.html
+++ b/css/css-overflow/line-clamp/line-clamp-auto-034.tentative.html
@@ -1,10 +1,10 @@
 <!DOCTYPE html>
 <meta charset="utf-8">
-<title>CSS Overflow: `line-clamp: auto` clamp between IFCs</title>
+<title>CSS Overflow: `line-clamp: auto` clamp height after IFC</title>
 <link rel="author" title="Andreu Botella" href="mailto:abotella@igalia.com">
 <link rel="help" href="https://drafts.csswg.org/css-overflow-4/#line-clamp">
-<link rel="match" href="reference/line-clamp-auto-034-ref.html">
-<meta name="assert" content="With `line-clamp: auto`, there can be a clamp point between two IFCs. In that case, no line will have an ellipsis.">
+<link rel="match" href="reference/webkit-line-clamp-005-ref.html">
+<meta name="assert" content="With `line-clamp: auto`, if the clamp height is after an IFC, the clamp point will be set after the last line before that.">
 <style>
 .clamp {
   line-clamp: auto;
@@ -28,6 +28,5 @@
 Line 2
 Line 3
 Line 4
-<div class="ifc">Line 5
-Line 6</div><div class="ifc red">Line 7
-Line 8</div>Line 9</div>
+<div class="ifc red">Line 5
+Line 6</div>Line 7</div>
diff --git a/css/css-overflow/line-clamp/line-clamp-auto-037.tentative.html b/css/css-overflow/line-clamp/line-clamp-auto-037.tentative.html
index 4a2fc3c82064e1..37b366660241f9 100644
--- a/css/css-overflow/line-clamp/line-clamp-auto-037.tentative.html
+++ b/css/css-overflow/line-clamp/line-clamp-auto-037.tentative.html
@@ -3,7 +3,7 @@
 <title>CSS Overflow: `line-clamp: auto` with non-zero max-height that doesn't fit any content</title>
 <link rel="author" title="Andreu Botella" href="mailto:abotella@igalia.com">
 <link rel="help" href="https://drafts.csswg.org/css-overflow-4/#line-clamp">
-<link rel="match" href="reference/line-clamp-auto-011-ref.html">
+<link rel="match" href="reference/line-clamp-auto-037-ref.html">
 <meta name="assert" content="When line-clamp: auto is used with a max-height that isn't enough for any contained boxes or line boxes, then it should not show any content and its content box's intrinsic size should be zero">
 <style>
 .clamp {
diff --git a/css/css-overflow/line-clamp/reference/line-clamp-auto-011-ref.html b/css/css-overflow/line-clamp/reference/line-clamp-auto-011-ref.html
index 5f7120ee39a201..27a2e7b2bc07ba 100644
--- a/css/css-overflow/line-clamp/reference/line-clamp-auto-011-ref.html
+++ b/css/css-overflow/line-clamp/reference/line-clamp-auto-011-ref.html
@@ -3,10 +3,13 @@
 <title>CSS Reference</title>
 <style>
 .clamp {
+  height: 0;
+  font: 16px / 32px serif;
+  white-space: pre;
   background-color: yellow;
   border: 1px solid black;
   padding: 4px;
 }
 </style>
-<div class="clamp"></div>
+<div class="clamp">Line 1…</div>
 <p>Following content.</p>
diff --git a/css/css-overflow/line-clamp/reference/line-clamp-auto-025-ref.html b/css/css-overflow/line-clamp/reference/line-clamp-auto-025-ref.html
deleted file mode 100644
index a76468d6d546e1..00000000000000
--- a/css/css-overflow/line-clamp/reference/line-clamp-auto-025-ref.html
+++ /dev/null
@@ -1,27 +0,0 @@
-<!DOCTYPE html>
-<meta charset="utf-8">
-<title>CSS Reference</title>
-<style>
-.clamp {
-  font: 16px / 32px serif;
-  background-color: yellow;
-}
-.inner {
-  white-space: pre-wrap;
-}
-.abspos {
-  position: absolute;
-  width: 100px;
-  height: 100px;
-  background-color: skyblue;
-}
-</style>
-
-<div class="clamp">
-<div class="inner">Line 1
-Line 2
-Line 3
-Line 4…
-</div>
-<div class="abspos"></div>
-</div>
diff --git a/css/css-overflow/line-clamp/reference/line-clamp-auto-026-ref.html b/css/css-overflow/line-clamp/reference/line-clamp-auto-026-ref.html
deleted file mode 100644
index 44d503a05220fd..00000000000000
--- a/css/css-overflow/line-clamp/reference/line-clamp-auto-026-ref.html
+++ /dev/null
@@ -1,32 +0,0 @@
-<!DOCTYPE html>
-<meta charset="utf-8">
-<title>CSS Reference</title>
-<style>
-.clamp {
-  font: 16px / 32px serif;
-  background-color: yellow;
-}
-.padding {
-  padding: 2px;
-}
-.inner {
-  white-space: pre-wrap;
-}
-.abspos {
-  position: absolute;
-  width: 100px;
-  height: 100px;
-  background-color: skyblue;
-}
-</style>
-
-<div class="clamp">
-<div class="padding">
-<div class="inner">Line 1
-Line 2
-Line 3
-Line 4…
-</div>
-<div class="abspos"></div>
-</div>
-</div>
diff --git a/css/css-overflow/line-clamp/reference/line-clamp-auto-032-ref.html b/css/css-overflow/line-clamp/reference/line-clamp-auto-032-ref.html
deleted file mode 100644
index 4768c77ddabc93..00000000000000
--- a/css/css-overflow/line-clamp/reference/line-clamp-auto-032-ref.html
+++ /dev/null
@@ -1,34 +0,0 @@
-<!DOCTYPE html>
-<meta charset="utf-8">
-<title>CSS Reference</title>
-<style>
-.clamp {
-  display: flow-root;
-  font: 16px / 32px serif;
-  background-color: orange;
-}
-.inner {
-  white-space: pre;
-  margin: 5px;
-  background-color: yellow;
-}
-.collapse-through {
-  margin: 5px;
-}
-.abspos {
-  position: absolute;
-  right: 0;
-  height: 100px;
-  width: 100px;
-  background-color: skyblue;
-}
-</style>
-
-<div class="clamp">
-<div class="inner">Line 1
-Line 2
-Line 3
-Line 4</div>
-<div class="collapse-through"></div>
-<div class="abspos"></div>
-</div>
diff --git a/css/css-overflow/line-clamp/reference/line-clamp-auto-034-ref.html b/css/css-overflow/line-clamp/reference/line-clamp-auto-034-ref.html
deleted file mode 100644
index 8fae3b278c124d..00000000000000
--- a/css/css-overflow/line-clamp/reference/line-clamp-auto-034-ref.html
+++ /dev/null
@@ -1,23 +0,0 @@
-<!DOCTYPE html>
-<meta charset="utf-8">
-<title>CSS Reference</title>
-<style>
-.clamp {
-  display: flow-root;
-  font: 16px / 32px serif;
-  white-space: pre;
-  padding: 0 4px;
-  background-color: yellow;
-}
-.ifc {
-  display: flow-root;
-  background-color: orange;
-}
-</style>
-
-<div class="clamp">Line 1
-Line 2
-Line 3
-Line 4
-<div class="ifc">Line 5
-Line 6</div></div>
diff --git a/css/css-overflow/line-clamp/reference/line-clamp-auto-037-ref.html b/css/css-overflow/line-clamp/reference/line-clamp-auto-037-ref.html
new file mode 100644
index 00000000000000..eeb9543554d996
--- /dev/null
+++ b/css/css-overflow/line-clamp/reference/line-clamp-auto-037-ref.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>CSS Reference</title>
+<style>
+.clamp {
+  height: 0.5lh;
+  font: 16px / 32px serif;
+  white-space: pre;
+  background-color: yellow;
+  border: 1px solid black;
+  padding: 4px;
+}
+</style>
+<div class="clamp">Line 1…</div>
+<p>Following content.</p>