Auto merge of #18131 - emilio:calc-serialization, r=canaltinova

style: Multiple calc serialization fixes.

This puts us in line with the spec as written, except for caveat in w3c/csswg-drafts#1731.

Need to fix computed calc() too, I'm less confident that we won't need to change test expectations.

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components/style/values/computed/length.rs

@@ -194,6 +194,18 @@ impl From<LengthOrPercentageOrNone> for Option<CalcLengthOrPercentage> {
 
 impl ToCss for CalcLengthOrPercentage {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        // FIXME(emilio): This should be consistent with specified calc().
+        //
+        // Also, serialisation here is kinda weird with negative percentages,
+        // for example, as of right now:
+        //
+        //  calc(10px - 5%)
+        //
+        // would serialize as:
+        //
+        //  calc(10px + -5%)
+        //
+        // Need to update and run through try.
         match (self.length, self.percentage) {
             (l, Some(p)) if l == Au(0) => p.to_css(dest),
             (l, Some(p)) => write!(dest, "calc({}px + {}%)", Au::to_px(l), p.0 * 100.),

components/style/values/computed/percentage.rs

@@ -11,7 +11,7 @@ use values::CSSFloat;
 use values::animated::ToAnimatedZero;
 
 /// A computed percentage.
-#[derive(Clone, ComputeSquaredDistance, Copy, Debug, Default, HasViewportPercentage, PartialEq)]
+#[derive(Clone, ComputeSquaredDistance, Copy, Debug, Default, HasViewportPercentage, PartialEq, PartialOrd)]
 #[cfg_attr(feature = "servo", derive(Deserialize, HeapSizeOf, Serialize))]
 pub struct Percentage(pub CSSFloat);
 
@@ -27,6 +27,12 @@ impl Percentage {
     pub fn hundred() -> Self {
         Percentage(1.)
     }
+
+    /// Returns the absolute value for this percentage.
+    #[inline]
+    pub fn abs(&self) -> Self {
+        Percentage(self.0.abs())
+    }
 }
 
 /// https://drafts.csswg.org/css-transitions/#animtype-percentage

components/style/values/specified/calc.rs

@@ -90,25 +90,33 @@ impl HasViewportPercentage for CalcLengthOrPercentage {
 }
 
 impl ToCss for CalcLengthOrPercentage {
+    /// https://drafts.csswg.org/css-values/#calc-serialize
     #[allow(unused_assignments)]
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        use num_traits::Zero;
+
         let mut first_value = true;
         macro_rules! first_value_check {
-            () => {
+            ($val:expr) => {
                 if !first_value {
-                    dest.write_str(" + ")?;
-                } else {
-                    first_value = false;
+                    dest.write_str(if $val < Zero::zero() {
+                        " - "
+                    } else {
+                        " + "
+                    })?;
+                } else if $val < Zero::zero() {
+                    dest.write_str("-")?;
                 }
+                first_value = false;
             };
         }
 
         macro_rules! serialize {
             ( $( $val:ident ),* ) => {
                 $(
                     if let Some(val) = self.$val {
-                        first_value_check!();
-                        val.to_css(dest)?;
+                        first_value_check!(val);
+                        val.abs().to_css(dest)?;
                         dest.write_str(stringify!($val))?;
                     }
                 )*
@@ -117,24 +125,32 @@ impl ToCss for CalcLengthOrPercentage {
 
         dest.write_str("calc(")?;
 
-        serialize!(ch, em, ex, rem, vh, vmax, vmin, vw);
+        // NOTE(emilio): Percentages first because of web-compat problems, see:
+        // https://github.com/w3c/csswg-drafts/issues/1731
+        if let Some(val) = self.percentage {
+            first_value_check!(val.0);
+            val.abs().to_css(dest)?;
+        }
+
+        // NOTE(emilio): The order here it's very intentional, and alphabetic
+        // per the spec linked above.
+        serialize!(ch, em, ex);
 
         #[cfg(feature = "gecko")]
         {
             serialize!(mozmm);
         }
 
         if let Some(val) = self.absolute {
-            first_value_check!();
-            val.to_css(dest)?;
+            first_value_check!(val);
+            // FIXME(emilio): Au::abs() would be nice.
+            let abs = if val < Zero::zero() { -val } else { val };
+            abs.to_css(dest)?;
         }
 
-        if let Some(val) = self.percentage {
-            first_value_check!();
-            val.to_css(dest)?;
-        }
+        serialize!(rem, vh, vmax, vmin, vw);
 
-        write!(dest, ")")
+        dest.write_str(")")
     }
 }
 

tests/wpt/mozilla/meta/MANIFEST.json

@@ -13512,6 +13512,12 @@
      {}
     ]
    ],
+   "css/calc-serialization.html": [
+    [
+     "/_mozilla/css/calc-serialization.html",
+     {}
+    ]
+   ],
    "css/empty-keyframes.html": [
     [
      "/_mozilla/css/empty-keyframes.html",
@@ -22847,6 +22853,10 @@
    "b9e77c824d0c96e51d51fb8f1e923d3ab67be027",
    "testharness"
   ],
+  "css/calc-serialization.html": [
+   "628597eb36bf21a1ec982c7f6935ee7949c62044",
+   "testharness"
+  ],
   "css/canvas_as_block_element_a.html": [
    "668d93da2dab9722998cc7c5785c20e2ab9a1ced",
    "reftest"

tests/wpt/mozilla/tests/css/calc-serialization.html

@@ -0,0 +1,34 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>CSS Values and Units: calc() serialization.</title>
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@mozilla.com">
+<link rel="help" href="https://drafts.csswg.org/css-values/#calc-serialize">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<!-- FIXME(emilio): Upstream when spec stops being under discussion -->
+<div id="content"></div>
+<script>
+
+// NOTE(emilio): This intentionally doesn't test for order of percentages
+// because of:
+//
+// https://github.com/w3c/csswg-drafts/issues/1731
+
+test(function() {
+  // specified -> expected
+  var values = {
+    "calc(10px + 1vmin)": "calc(10px + 1vmin)",
+    "calc(10px + 1em)": "calc(1em + 10px)",
+    "calc(1vmin - 10px)": "calc(-10px + 1vmin)",
+    "calc(-10px + 1em)": "calc(1em - 10px)",
+    "calc(-10px)": "calc(-10px)",
+  };
+
+  var content = document.getElementById("content");
+
+  for (var prop in values) {
+    content.style.width = prop;
+    assert_equals(content.style.width, values[prop], "Serialization of " + prop);
+  }
+}, "calc() serialization")
+</script>