Auto merge of #15237 - samuknet:negative-letter-spacing-word-spacing, r=emilio

Allow negative values for letter-spacing and word-spacing.  Inline Le…

<!-- Please describe your changes on the following line: -->
Allow negative values when parsing `letter-spacing` and `word-spacing`.  Inline `parse_non_negative` in `Length`.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #15204 (github issue number if applicable).

<!-- Either: -->
- [x] There are tests for these changes

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

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components/style/properties/longhand/inherited_text.mako.rs

@@ -335,11 +335,11 @@ ${helpers.single_keyword("text-align-last",
         }
     }
 
-    pub fn parse(_context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
+    pub fn parse(context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
         if input.try(|input| input.expect_ident_matching("normal")).is_ok() {
             Ok(SpecifiedValue::Normal)
         } else {
-            specified::Length::parse_non_negative(input).map(SpecifiedValue::Specified)
+            specified::Length::parse(context, input).map(SpecifiedValue::Specified)
         }
     }
 </%helpers:longhand>
@@ -416,11 +416,11 @@ ${helpers.single_keyword("text-align-last",
         }
     }
 
-    pub fn parse(_context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
+    pub fn parse(context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
         if input.try(|input| input.expect_ident_matching("normal")).is_ok() {
             Ok(SpecifiedValue::Normal)
         } else {
-            specified::LengthOrPercentage::parse_non_negative(input)
+            specified::LengthOrPercentage::parse(context, input)
                                           .map(SpecifiedValue::Specified)
         }
     }

components/style/values/specified/length.rs

@@ -463,6 +463,7 @@ impl Length {
     }
 
     /// Parse a non-negative length
+    #[inline]
     pub fn parse_non_negative(input: &mut Parser) -> Result<Length, ()> {
         Length::parse_internal(input, AllowedNumericType::NonNegative)
     }

tests/unit/style/parsing/inherited_text.rs

@@ -7,6 +7,29 @@ use media_queries::CSSErrorReporterTest;
 use style::parser::ParserContext;
 use style::stylesheets::Origin;
 
+#[test]
+fn negative_letter_spacing_should_parse_properly() {
+    use style::properties::longhands::letter_spacing;
+    use style::properties::longhands::letter_spacing::SpecifiedValue;
+    use style::values::specified::length::{Length, NoCalcLength, FontRelativeLength};
+
+    let negative_value = parse_longhand!(letter_spacing, "-0.5em");
+    let expected = SpecifiedValue::Specified(Length::NoCalc(NoCalcLength::FontRelative(FontRelativeLength::Em(-0.5))));
+    assert_eq!(negative_value, expected);
+}
+
+#[test]
+fn negative_word_spacing_should_parse_properly() {
+    use style::properties::longhands::word_spacing;
+    use style::properties::longhands::word_spacing::SpecifiedValue;
+    use style::values::specified::length::{NoCalcLength, LengthOrPercentage, FontRelativeLength};
+
+    let negative_value = parse_longhand!(word_spacing, "-0.5em");
+    let expected = SpecifiedValue::Specified(LengthOrPercentage::Length(NoCalcLength::FontRelative(
+                                             FontRelativeLength::Em(-0.5))));
+    assert_eq!(negative_value, expected);
+}
+
 #[test]
 fn text_emphasis_style_longhand_should_parse_properly() {
     use style::properties::longhands::text_emphasis_style;
@@ -79,7 +102,6 @@ fn test_text_emphasis_position() {
     assert_eq!(left_under, SpecifiedValue(HorizontalWritingModeValue::Under, VerticalWritingModeValue::Left));
 }
 
-
 #[test]
 fn webkit_text_stroke_shorthand_should_parse_properly() {
     use media_queries::CSSErrorReporterTest;

tests/wpt/metadata-css/css-text-3_dev/html/text-word-spacing-001.htm.ini

@@ -1,3 +0,0 @@
-[text-word-spacing-001.htm]
-  type: reftest
-  expected: FAIL

tests/wpt/metadata-css/css21_dev/html4/c542-letter-sp-001.htm.ini

@@ -1,3 +0,0 @@
-[c542-letter-sp-001.htm]
-  type: reftest
-  expected: FAIL