Don't serialize unitless zero inside calc() expressions

Author: devongovett

src/lib.rs

@@ -2532,6 +2532,8 @@ mod tests {
     minify_test(".foo { top: calc(1 * clamp(1.75rem, 8vw, 4rem)) }", ".foo{top:calc(clamp(1.75rem,8vw,4rem))}");
     minify_test(".foo { top: calc(2 * clamp(1.75rem, 8vw, 4rem) / 2) }", ".foo{top:calc(clamp(1.75rem,8vw,4rem))}");
 
+    minify_test(".foo { width: max(0px, 1vw) }", ".foo{width:max(0px,1vw)}");
+
     prefix_test(
       ".foo { border-width: clamp(1em, 2px, 4vh) }",
       indoc! { r#"

src/printer.rs

@@ -14,7 +14,8 @@ pub struct Printer<'a, W> {
   pub targets: Option<Browsers>,
   /// Vendor prefix override. When non-empty, it overrides 
   /// the vendor prefix of whatever is being printed.
-  pub vendor_prefix: VendorPrefix
+  pub vendor_prefix: VendorPrefix,
+  pub in_calc: bool
 }
 
 impl<'a, W: Write + Sized> Printer<'a, W> {
@@ -32,7 +33,8 @@ impl<'a, W: Write + Sized> Printer<'a, W> {
       col: 0,
       minify,
       targets,
-      vendor_prefix: VendorPrefix::empty()
+      vendor_prefix: VendorPrefix::empty(),
+      in_calc: false
     }
   }
 

src/values/calc.rs

@@ -373,7 +373,10 @@ impl<V: std::cmp::PartialOrd<f32>> std::cmp::PartialOrd<f32> for Calc<V> {
 
 impl<V: ToCss + std::cmp::PartialOrd<f32> + std::ops::Mul<f32, Output = V> + Clone + std::fmt::Debug> ToCss for Calc<V> {
   fn to_css<W>(&self, dest: &mut Printer<W>) -> std::fmt::Result where W: std::fmt::Write {
-    match self {
+    let was_in_calc = dest.in_calc;
+    dest.in_calc = true;
+    
+    let res = match self {
       Calc::Value(v) => v.to_css(dest),
       Calc::Number(n) => serialize_number(*n, dest),
       Calc::Sum(a, b) => {
@@ -383,12 +386,11 @@ impl<V: ToCss + std::cmp::PartialOrd<f32> + std::ops::Mul<f32, Output = V> + Clo
         if *b < 0.0 {
           dest.write_str(" - ")?;
           let b = b.clone() * -1.0;
-          b.to_css(dest)?;
+          b.to_css(dest)
         } else {
           dest.write_str(" + ")?;
-          b.to_css(dest)?;
+          b.to_css(dest)
         }
-        Ok(())
       }
       Calc::Product(num, calc) => {
         if num.abs() < 1.0 {
@@ -403,6 +405,9 @@ impl<V: ToCss + std::cmp::PartialOrd<f32> + std::ops::Mul<f32, Output = V> + Clo
         }
       }
       Calc::Function(f) => f.to_css(dest)
-    }
+    };
+
+    dest.in_calc = was_in_calc;
+    res
   }
 }

src/values/length.rs

@@ -112,7 +112,10 @@ impl Parse for LengthValue {
 impl ToCss for LengthValue {
   fn to_css<W>(&self, dest: &mut Printer<W>) -> std::fmt::Result where W: std::fmt::Write {
     let (value, unit) = self.to_unit_value();
-    if value == 0.0 {
+
+    // The unit can be omitted if the value is zero, except inside calc()
+    // expressions, where unitless numbers won't be parsed as dimensions.
+    if !dest.in_calc && value == 0.0 {
       return dest.write_char('0')
     }