Auto merge of #16229 - tomhoule:fix-lengths, r=emilio

style: Do not immediately convert absolute specified lengths

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This PR aims to solve issue #15729. I tried to follow the recommendations there as much as possible.

This is my first attempt at contributing to Servo, so this will probably need a lot of input, although I'm eager to make it as polished as possible.

- The base inaccuracy issue seems solved, as can be easily verified with the `console.log` based example in the issue.
- Very basic unit tests were added.

I have doubts mainly about the right way to represent these new enum variants for the various length units:

1. With new enum variants in `NoCalcLength` *and* newtypes (current solution)
2. With a `NoCalcLength::Absolute` variant that contains a new `AbsoluteLength` enum, but without newtypes
3. Same as solution 2 but with newtypes

- I mostly cared about unit tests until now but will investigate other types of tests
- Tests to check the clamping
- Write a proper commit message

Thanks for your time and feedback :)

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #15729.

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- [X] There are tests for these changes

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tests/unit/style/parsing/length.rs

@@ -2,9 +2,13 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cssparser::Parser;
+use media_queries::CSSErrorReporterTest;
 use parsing::parse;
-use style::parser::Parse;
+use style::parser::{Parse, ParserContext};
+use style::stylesheets::Origin;
 use style::values::specified::length::Length;
+use style_traits::ToCss;
 
 #[test]
 fn test_calc() {
@@ -13,3 +17,14 @@ fn test_calc() {
     assert!(parse(Length::parse, "calc(1px + 2px )").is_ok());
     assert!(parse(Length::parse, "calc( 1px + 2px)").is_ok());
 }
+
+#[test]
+fn test_length_literals() {
+    assert_roundtrip_with_context!(Length::parse, "0.33px", "0.33px");
+    assert_roundtrip_with_context!(Length::parse, "0.33in", "0.33in");
+    assert_roundtrip_with_context!(Length::parse, "0.33cm", "0.33cm");
+    assert_roundtrip_with_context!(Length::parse, "0.33mm", "0.33mm");
+    assert_roundtrip_with_context!(Length::parse, "0.33q", "0.33q");
+    assert_roundtrip_with_context!(Length::parse, "0.33pt", "0.33pt");
+    assert_roundtrip_with_context!(Length::parse, "0.33pc", "0.33pc");
+}

tests/unit/style/properties/viewport.rs

@@ -6,7 +6,7 @@ use app_units::Au;
 use style::properties::PropertyDeclaration;
 use style::properties::longhands::border_top_width;
 use style::values::HasViewportPercentage;
-use style::values::specified::{Length, NoCalcLength, ViewportPercentageLength};
+use style::values::specified::{AbsoluteLength, Length, NoCalcLength, ViewportPercentageLength};
 
 #[test]
 fn has_viewport_percentage_for_specified_value() {
@@ -20,7 +20,7 @@ fn has_viewport_percentage_for_specified_value() {
 
     let pabs = PropertyDeclaration::BorderTopWidth(Box::new(
         border_top_width::SpecifiedValue::from_length(
-            Length::NoCalc(NoCalcLength::Absolute(Au(100)))
+            Length::NoCalc(NoCalcLength::Absolute(AbsoluteLength::Px(Au(100).to_f32_px())))
         )
     ));
     assert!(!pabs.has_viewport_percentage());

tests/unit/style/value.rs

@@ -5,14 +5,14 @@
 use app_units::Au;
 use cssparser::Parser;
 use style::values::HasViewportPercentage;
-use style::values::specified::{ViewportPercentageLength, NoCalcLength};
+use style::values::specified::{AbsoluteLength, ViewportPercentageLength, NoCalcLength};
 use style::values::specified::length::{CalcLengthOrPercentage, CalcUnit};
 
 #[test]
 fn length_has_viewport_percentage() {
     let l = NoCalcLength::ViewportPercentage(ViewportPercentageLength::Vw(100.));
     assert!(l.has_viewport_percentage());
-    let l = NoCalcLength::Absolute(Au(100));
+    let l = NoCalcLength::Absolute(AbsoluteLength::Px(Au(100).to_f32_px()));
     assert!(!l.has_viewport_percentage());
 }