From 2e713d436636ce8ef49937f61c00206153caefee Mon Sep 17 00:00:00 2001
From: CanadaHonk <oj@oojmed.com>
Date: Mon, 1 May 2023 14:50:32 +0000
Subject: [PATCH] style: Serialize NaN and infinity percentages correctly

NaN and infinity percentages are now serialized as expected.

Also added some new WPT tests as percentages were previously untested
and added some spec comments to previous NaN/inf serialization code.

Differential Revision: https://phabricator.services.mozilla.com/D176726
---
 components/style/values/computed/percentage.rs  |  4 ++--
 components/style/values/mod.rs                  | 15 ++++++++++++++-
 components/style/values/specified/percentage.rs |  4 ++--
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/components/style/values/computed/percentage.rs b/components/style/values/computed/percentage.rs
index 30ef5ab0f0d..994c01594a3 100644
--- a/components/style/values/computed/percentage.rs
+++ b/components/style/values/computed/percentage.rs
@@ -7,7 +7,7 @@
 use crate::values::animated::ToAnimatedValue;
 use crate::values::generics::NonNegative;
 use crate::values::specified::percentage::ToPercentage;
-use crate::values::{serialize_percentage, CSSFloat};
+use crate::values::{serialize_normalized_percentage, CSSFloat};
 use crate::Zero;
 use std::fmt;
 use style_traits::{CssWriter, ToCss};
@@ -106,7 +106,7 @@ impl ToCss for Percentage {
     where
         W: fmt::Write,
     {
-        serialize_percentage(self.0, dest)
+        serialize_normalized_percentage(self.0, dest)
     }
 }
 
diff --git a/components/style/values/mod.rs b/components/style/values/mod.rs
index 64950166ecd..ce0d9fc42f3 100644
--- a/components/style/values/mod.rs
+++ b/components/style/values/mod.rs
@@ -109,6 +109,11 @@ where
     }
 
     if !v.is_finite() && nan_inf_enabled() {
+        // https://drafts.csswg.org/css-values/#calc-error-constants:
+        // "While not technically numbers, these keywords act as numeric values,
+        // similar to e and pi. Thus to get an infinite length, for example,
+        // requires an expression like calc(infinity * 1px)."
+
         if v.is_nan() {
             dest.write_str("NaN * 1")?;
         } else if v == f32::INFINITY {
@@ -398,8 +403,16 @@ impl std::borrow::Borrow<crate::gecko_string_cache::WeakAtom> for AtomIdent {
     }
 }
 
-/// Serialize a normalized value into percentage.
+/// Serialize a value into percentage.
 pub fn serialize_percentage<W>(value: CSSFloat, dest: &mut CssWriter<W>) -> fmt::Result
+where
+    W: Write,
+{
+    serialize_specified_dimension(value * 100., "%", /* was_calc = */ false, dest)
+}
+
+/// Serialize a value into normalized (no NaN/inf serialization) percentage.
+pub fn serialize_normalized_percentage<W>(value: CSSFloat, dest: &mut CssWriter<W>) -> fmt::Result
 where
     W: Write,
 {
diff --git a/components/style/values/specified/percentage.rs b/components/style/values/specified/percentage.rs
index 6e6869d8700..c44a2781a8a 100644
--- a/components/style/values/specified/percentage.rs
+++ b/components/style/values/specified/percentage.rs
@@ -10,7 +10,7 @@ use crate::values::computed::{Context, ToComputedValue};
 use crate::values::generics::NonNegative;
 use crate::values::specified::calc::CalcNode;
 use crate::values::specified::Number;
-use crate::values::{serialize_percentage, CSSFloat};
+use crate::values::{serialize_percentage, normalize, CSSFloat};
 use cssparser::{Parser, Token};
 use std::fmt::{self, Write};
 use style_traits::values::specified::AllowedNumericType;
@@ -172,7 +172,7 @@ impl ToComputedValue for Percentage {
 
     #[inline]
     fn to_computed_value(&self, _: &Context) -> Self::ComputedValue {
-        ComputedPercentage(self.get())
+        ComputedPercentage(normalize(self.get()))
     }
 
     #[inline]