From b2ec60c7d5b8ab1ded9edfae217285f4059aa28d Mon Sep 17 00:00:00 2001
From: Alan Baradlay <zalan@apple.com>
Date: Sat, 16 Mar 2024 16:47:10 -0700
Subject: [PATCH] [IFC][Intrinsic width] Incorrect shrink-to-fit box logical
 width when negative text-indent is present
 https://bugs.webkit.org/show_bug.cgi?id=271113 <rdar://problem/124784190>

Reviewed by Antti Koivisto.

Negative text-indent value could confuse the min/max inline size computation as running layout with 0 constraint
may produce wider content than running layout with infinite constraint.

Consider the following case:

<div style="text-indent: -100px;">some content</div>

With infinite constraint this content produce only one line with the line box width of 0 (assume the measured content width of "some content" is < 100px)
It simply means that [some content] visually overflows on the left due to this implicit negative content margin.
              _
some content |_|

However when computing the minimum content size we have to take into account all the possible soft wrap opportunities with the constraint value of 0.
Now we end up constructing 2 lines where the second line has 0px used text-indent.
              _
some         |_|
              ________
             |content |
              --------
which clearly computes a content value > 0px.

Let's fix this by making sure minimum width is never larger than maximum width. This behavior also seems to match with other rendering engines.

* LayoutTests/fast/text/min-max-content-negative-text-indent-expected.html: Added.
* LayoutTests/fast/text/min-max-content-negative-text-indent.html: Added.
* Source/WebCore/layout/formattingContexts/inline/InlineFormattingContext.cpp:
(WebCore::Layout::InlineFormattingContext::minimumMaximumContentSize):
(WebCore::Layout::InlineFormattingContext::minimumContentSize):

Canonical link: https://commits.webkit.org/276246@main
---
 ...content-negative-text-indent-expected.html | 19 +++++++++++++++
 .../min-max-content-negative-text-indent.html | 19 +++++++++++++++
 .../inline/InlineFormattingContext.cpp        | 23 +++++++++++++++++++
 3 files changed, 61 insertions(+)
 create mode 100644 LayoutTests/fast/text/min-max-content-negative-text-indent-expected.html
 create mode 100644 LayoutTests/fast/text/min-max-content-negative-text-indent.html

diff --git a/LayoutTests/fast/text/min-max-content-negative-text-indent-expected.html b/LayoutTests/fast/text/min-max-content-negative-text-indent-expected.html
new file mode 100644
index 000000000000..db5adac10189
--- /dev/null
+++ b/LayoutTests/fast/text/min-max-content-negative-text-indent-expected.html
@@ -0,0 +1,19 @@
+<style>
+div {
+ width: min-content;
+ height: 50px;
+ background-color: green;
+ color: transparent;
+ font-family: Ahem;
+ font-size: 20px;
+}
+</style>
+<div>X</div>
+<div>XX</div>
+<div>XXX</div>
+<div>XXXX</div>
+<div>XXXXX</div>
+<div>XXXXX</div>
+<div>XXXXX</div>
+<div>XXXXX</div>
+<div>XXXXXXX</div>
\ No newline at end of file
diff --git a/LayoutTests/fast/text/min-max-content-negative-text-indent.html b/LayoutTests/fast/text/min-max-content-negative-text-indent.html
new file mode 100644
index 000000000000..fb2dc3389080
--- /dev/null
+++ b/LayoutTests/fast/text/min-max-content-negative-text-indent.html
@@ -0,0 +1,19 @@
+<style>
+div {
+ width: min-content; 
+ height: 50px;
+ background-color: green;
+ color: transparent;
+ font-family: Ahem;
+ font-size: 20px;
+}
+</style>
+<div style="text-indent: -180px;">XXXX XXXXX</div>
+<div style="text-indent: -160px;">XXXX XXXXX</div>
+<div style="text-indent: -140px;">XXXX XXXXX</div>
+<div style="text-indent: -120px;">XXXX XXXXX</div>
+<div style="text-indent: -100px;">XXXX XXXXX</div>
+<div style="text-indent: -80px;">XXXX XXXXX</div>
+<div style="text-indent: -60px;">XXXX XXXXX</div>
+<div style="text-indent: 0px;">XXXX XXXXX</div>
+<div style="text-indent: 60px;">XXXX XXXXX</div>
diff --git a/Source/WebCore/layout/formattingContexts/inline/InlineFormattingContext.cpp b/Source/WebCore/layout/formattingContexts/inline/InlineFormattingContext.cpp
index 75b4447857d1..d0fe4ec458fe 100644
--- a/Source/WebCore/layout/formattingContexts/inline/InlineFormattingContext.cpp
+++ b/Source/WebCore/layout/formattingContexts/inline/InlineFormattingContext.cpp
@@ -44,6 +44,7 @@
 #include "IntrinsicWidthHandler.h"
 #include "LayoutBox.h"
 #include "LayoutContext.h"
+#include "LayoutDescendantIterator.h"
 #include "LayoutElementBox.h"
 #include "LayoutInitialContainingBlock.h"
 #include "LayoutInlineTextBox.h"
@@ -180,6 +181,28 @@ std::pair<LayoutUnit, LayoutUnit> InlineFormattingContext::minimumMaximumContent
         minimumContentSize = minimumContentSize.value_or(0.f);
         maximumContentSize = maximumContentSize.value_or(0.f);
     }
+#ifndef NDEBUG
+    // FIXME: "Nominally, the smallest size a box could take that doesn’t lead to overflow that could be avoided by choosing a larger size.
+    // Formally, the size of the box when sized under a min-content constraint"
+    // 'nominally' seems to overrule 'formally' when inline content has negative text indent.
+    // This also undermines the idea of computing min/max values independently.
+    if (*minimumContentSize > *maximumContentSize) {
+        auto hasNegativeImplicitMargin = [](auto& style) {
+            return (style.textIndent().isFixed() && style.textIndent().value() < 0) || style.wordSpacing() < 0 || style.letterSpacing() < 0;
+        };
+        auto contentHasNegativeImplicitMargin = hasNegativeImplicitMargin(root().style());
+        if (!contentHasNegativeImplicitMargin) {
+            for (auto& layoutBox : descendantsOfType<Box>(root())) {
+                contentHasNegativeImplicitMargin = hasNegativeImplicitMargin(layoutBox.style());
+                if (contentHasNegativeImplicitMargin)
+                    break;
+            }
+        }
+        ASSERT(contentHasNegativeImplicitMargin);
+    }
+#endif
+    minimumContentSize = std::min(*minimumContentSize, *maximumContentSize);
+
     inlineContentCache.setMinimumContentSize(*minimumContentSize);
     inlineContentCache.setMaximumContentSize(*maximumContentSize);
     return { ceiledLayoutUnit(*minimumContentSize), ceiledLayoutUnit(*maximumContentSize) };