Auto merge of #15662 - canaltinova:column, r=Manishearth

Fix parsing methods of column-{gap,width}

<!-- Please describe your changes on the following line: -->
They weren't accepting {normal, auto} keywords. Fixed parsing methods of these properties.

---
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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 #15088 (github issue number if applicable).

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- [X] There are tests for these changes

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tests/unit/style/parsing/column.rs

@@ -0,0 +1,42 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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 servo_url::ServoUrl;
+use style::parser::ParserContext;
+use style::stylesheets::Origin;
+use style_traits::ToCss;
+
+#[test]
+fn test_column_width() {
+    use style::properties::longhands::column_width;
+
+    assert_roundtrip_with_context!(column_width::parse, "auto");
+    assert_roundtrip_with_context!(column_width::parse, "6px");
+    assert_roundtrip_with_context!(column_width::parse, "2.5em");
+    assert_roundtrip_with_context!(column_width::parse, "0.3vw");
+
+    let url = ServoUrl::parse("http://localhost").unwrap();
+    let context = ParserContext::new(Origin::Author, &url, Box::new(CSSErrorReporterTest));
+
+    let mut negative = Parser::new("-6px");
+    assert!(column_width::parse(&context, &mut negative).is_err());
+}
+
+#[test]
+fn test_column_gap() {
+    use style::properties::longhands::column_gap;
+
+    assert_roundtrip_with_context!(column_gap::parse, "normal");
+    assert_roundtrip_with_context!(column_gap::parse, "6px");
+    assert_roundtrip_with_context!(column_gap::parse, "2.5em");
+    assert_roundtrip_with_context!(column_gap::parse, "0.3vw");
+
+    let url = ServoUrl::parse("http://localhost").unwrap();
+    let context = ParserContext::new(Origin::Author, &url, Box::new(CSSErrorReporterTest));
+
+    let mut negative = Parser::new("-6px");
+    assert!(column_gap::parse(&context, &mut negative).is_err());
+}

tests/unit/style/parsing/mod.rs

@@ -70,6 +70,7 @@ mod animation;
 mod background;
 mod basic_shape;
 mod border;
+mod column;
 mod font;
 mod image;
 mod inherited_box;