1 files changed, 36 insertions, 32 deletions

diff --git a/layout/style/ServoStyleConstsInlines.h b/layout/style/ServoStyleConstsInlines.h
index b6a574037a..1985e8fbeb 100644
--- a/layout/style/ServoStyleConstsInlines.h
+++ b/layout/style/ServoStyleConstsInlines.h
@@ -507,20 +507,15 @@ StyleCSSPixelLength StyleCSSPixelLength::ScaledBy(float aScale) const {
   return FromPixels(ToCSSPixels() * aScale);
 }
 
-nscoord StyleCSSPixelLength::ToAppUnits() const {
-  // We want to resolve the length part of the calc() expression rounding 0.5
-  // away from zero, instead of the default behavior of
-  // NSToCoordRound{,WithClamp} which do floor(x + 0.5).
-  //
-  // This is what the rust code in the app_units crate does, and not doing this
-  // would regress bug 1323735, for example.
-  //
-  // FIXME(emilio, bug 1528114): Probably we should do something smarter.
-  if (IsZero()) {
-    // Avoid the expensive FP math below.
-    return 0;
-  }
-  float length = _0 * float(mozilla::AppUnitsPerCSSPixel());
+namespace detail {
+static inline nscoord DefaultPercentLengthToAppUnits(float aPixelLength) {
+  return NSToCoordTruncClamped(aPixelLength);
+}
+
+static inline nscoord DefaultLengthToAppUnits(float aPixelLength) {
+  // We want to round lengths rounding 0.5 away from zero, instead of the
+  // default behavior of NSToCoordRound{,WithClamp} which do floor(x + 0.5).
+  float length = aPixelLength * float(mozilla::AppUnitsPerCSSPixel());
   if (length >= float(nscoord_MAX)) {
     return nscoord_MAX;
   }
@@ -529,6 +524,15 @@ nscoord StyleCSSPixelLength::ToAppUnits() const {
   }
   return NSToIntRound(length);
 }
+}  // namespace detail
+
+nscoord StyleCSSPixelLength::ToAppUnits() const {
+  if (IsZero()) {
+    // Avoid the expensive FP math below.
+    return 0;
+  }
+  return detail::DefaultLengthToAppUnits(_0);
+}
 
 bool LengthPercentage::IsLength() const { return Tag() == TAG_LENGTH; }
 
@@ -693,6 +697,11 @@ CSSCoord StyleCalcLengthPercentage::ResolveToCSSPixels(CSSCoord aBasis) const {
   return Servo_ResolveCalcLengthPercentage(this, aBasis);
 }
 
+nscoord StyleCalcLengthPercentage::Resolve(nscoord aBasis) const {
+  return detail::DefaultLengthToAppUnits(
+      ResolveToCSSPixels(CSSPixel::FromAppUnits(aBasis)));
+}
+
 template <>
 void StyleCalcNode::ScaleLengthsBy(float);
 
@@ -708,20 +717,18 @@ CSSCoord LengthPercentage::ResolveToCSSPixels(CSSCoord aPercentageBasis) const {
 
 template <typename T>
 CSSCoord LengthPercentage::ResolveToCSSPixelsWith(T aPercentageGetter) const {
-  static_assert(std::is_same<decltype(aPercentageGetter()), CSSCoord>::value,
-                "Should return CSS pixels");
+  static_assert(std::is_same_v<decltype(aPercentageGetter()), CSSCoord>);
   if (ConvertsToLength()) {
     return ToLengthInCSSPixels();
   }
   return ResolveToCSSPixels(aPercentageGetter());
 }
 
-template <typename T, typename U>
-nscoord LengthPercentage::Resolve(T aPercentageGetter, U aRounder) const {
-  static_assert(std::is_same<decltype(aPercentageGetter()), nscoord>::value,
-                "Should return app units");
-  static_assert(std::is_same<decltype(aRounder(1.0f)), nscoord>::value,
-                "Should return app units");
+template <typename T, typename PercentRounder>
+nscoord LengthPercentage::Resolve(T aPercentageGetter,
+                                  PercentRounder aPercentRounder) const {
+  static_assert(std::is_same_v<decltype(aPercentageGetter()), nscoord>);
+  static_assert(std::is_same_v<decltype(aPercentRounder(1.0f)), nscoord>);
   if (ConvertsToLength()) {
     return ToLength();
   }
@@ -730,29 +737,26 @@ nscoord LengthPercentage::Resolve(T aPercentageGetter, U aRounder) const {
   }
   nscoord basis = aPercentageGetter();
   if (IsPercentage()) {
-    return aRounder(basis * AsPercentage()._0);
+    return aPercentRounder(basis * AsPercentage()._0);
   }
-  return AsCalc().Resolve(basis, aRounder);
+  return AsCalc().Resolve(basis);
 }
 
-// Note: the static_cast<> wrappers below are needed to disambiguate between
-// the versions of NSToCoordTruncClamped that take float vs. double as the arg.
 nscoord LengthPercentage::Resolve(nscoord aPercentageBasis) const {
   return Resolve([=] { return aPercentageBasis; },
-                 static_cast<nscoord (*)(float)>(NSToCoordTruncClamped));
+                 detail::DefaultPercentLengthToAppUnits);
 }
 
 template <typename T>
 nscoord LengthPercentage::Resolve(T aPercentageGetter) const {
-  return Resolve(aPercentageGetter,
-                 static_cast<nscoord (*)(float)>(NSToCoordTruncClamped));
+  return Resolve(aPercentageGetter, detail::DefaultPercentLengthToAppUnits);
 }
 
-template <typename T>
+template <typename PercentRounder>
 nscoord LengthPercentage::Resolve(nscoord aPercentageBasis,
-                                  T aPercentageRounder) const {
+                                  PercentRounder aPercentRounder) const {
   return Resolve([aPercentageBasis] { return aPercentageBasis; },
-                 aPercentageRounder);
+                 aPercentRounder);
 }
 
 void LengthPercentage::ScaleLengthsBy(float aScale) {