From 6a3c3ee29119c3f5b1de4f3f92c7797a455ccab5 Mon Sep 17 00:00:00 2001
From: Jelle Raaijmakers <jelle@gmta.nl>
Date: Tue, 25 Mar 2025 18:58:08 +0000
Subject: [PATCH] LibWeb: Coerce NaNs to 0 when escaping top-level calculations

---
 .../LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp | 13 ++++++++++---
 .../expected/css/getComputedStyle-transform.txt     |  1 +
 .../Text/input/css/getComputedStyle-transform.html  |  1 +
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp b/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
index bba0585c244..757559217a4 100644
--- a/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
+++ b/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
@@ -2716,9 +2716,16 @@ Optional<Time> CalculatedStyleValue::resolve_time(CalculationResolutionContext c
 Optional<double> CalculatedStyleValue::resolve_number(CalculationResolutionContext const& context) const
 {
     auto result = m_calculation->resolve(context);
-    if (result.type().has_value() && result.type()->matches_number(m_context.percentages_resolve_as))
-        return result.value();
-    return {};
+    if (!result.type().has_value() || !result.type()->matches_number(m_context.percentages_resolve_as))
+        return {};
+
+    // https://drafts.csswg.org/css-values/#calc-ieee
+    // NaN does not escape a top-level calculation; it’s censored into a zero value.
+    auto value = result.value();
+    if (isnan(value))
+        return 0.;
+
+    return value;
 }
 
 Optional<i64> CalculatedStyleValue::resolve_integer(CalculationResolutionContext const& context) const
diff --git a/Tests/LibWeb/Text/expected/css/getComputedStyle-transform.txt b/Tests/LibWeb/Text/expected/css/getComputedStyle-transform.txt
index 1226aeb465d..b1035db7929 100644
--- a/Tests/LibWeb/Text/expected/css/getComputedStyle-transform.txt
+++ b/Tests/LibWeb/Text/expected/css/getComputedStyle-transform.txt
@@ -12,6 +12,7 @@ scale(1, 2) => matrix(1, 0, 0, 2, 0, 0)
 scale(100%, 200%) => matrix(1, 0, 0, 2, 0, 0)
 scale(calc(1 / 2)) => matrix(0.5, 0, 0, 0.5, 0, 0)
 scale(calc(50% + 25%)) => matrix(0.75, 0, 0, 0.75, 0, 0)
+scale(calc(NaN)) => matrix(0, 0, 0, 0, 0, 0)
 scaleX(2) => matrix(2, 0, 0, 1, 0, 0)
 scaleX(200%) => matrix(2, 0, 0, 1, 0, 0)
 scaleY(2.5) => matrix(1, 0, 0, 2.5, 0, 0)
diff --git a/Tests/LibWeb/Text/input/css/getComputedStyle-transform.html b/Tests/LibWeb/Text/input/css/getComputedStyle-transform.html
index 0cfda9ddc8a..b537b2a1d47 100644
--- a/Tests/LibWeb/Text/input/css/getComputedStyle-transform.html
+++ b/Tests/LibWeb/Text/input/css/getComputedStyle-transform.html
@@ -25,6 +25,7 @@
             "scale(100%, 200%)",
             "scale(calc(1 / 2))",
             "scale(calc(50% + 25%))",
+            "scale(calc(NaN))",
             "scaleX(2)",
             "scaleX(200%)",
             "scaleY(2.5)",