Add GridLine type for grids

components/style/values/specified/grid.rs

@@ -0,0 +1,96 @@
+/* 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 parser::{Parse, ParserContext};
+use std::fmt;
+use style_traits::ToCss;
+use values::NoViewportPercentage;
+use values::computed::ComputedValueAsSpecified;
+
+// https://drafts.csswg.org/css-grid/#typedef-grid-row-start-grid-line
+#[derive(PartialEq, Clone, Debug)]
+#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+pub struct GridLine {
+    pub is_span: bool,
+    pub ident: Option<String>,
+    pub integer: Option<i32>,
+}
+
+impl Default for GridLine {
+    fn default() -> Self {
+        GridLine {
+            is_span: false,
+            ident: None,
+            integer: None,
+        }
+    }
+}
+
+impl ToCss for GridLine {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        if !self.is_span && self.ident.is_none() && self.integer.is_none() {
+            return dest.write_str("auto")
+        }
+
+        if self.is_span {
+            try!(dest.write_str("span"));
+        }
+
+        if let Some(i) = self.integer {
+            try!(write!(dest, " {}", i));
+        }
+
+        if let Some(ref s) = self.ident {
+            try!(write!(dest, " {}", s));
+        }
+
+        Ok(())
+    }
+}
+
+impl Parse for GridLine {
+    fn parse(_context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
+        let mut grid_line = Default::default();
+        if input.try(|i| i.expect_ident_matching("auto")).is_ok() {
+            return Ok(grid_line)
+        }
+
+        for _ in 0..3 {     // Maximum possible entities for <grid-line>
+            if input.try(|i| i.expect_ident_matching("span")).is_ok() {
+                if grid_line.is_span {
+                    return Err(())
+                }
+                grid_line.is_span = true;
+            } else if let Ok(i) = input.try(|i| i.expect_integer()) {
+                if i == 0 || grid_line.integer.is_some() {
+                    return Err(())
+                }
+                grid_line.integer = Some(i);
+            } else if let Ok(name) = input.try(|i| i.expect_ident()) {
+                if grid_line.ident.is_some() {
+                    return Err(())
+                }
+                grid_line.ident = Some(name.into_owned());
+            } else {
+                break
+            }
+        }
+
+        if grid_line.is_span {
+            if let Some(i) = grid_line.integer {
+                if i < 0 {      // disallow negative integers for grid spans
+                    return Err(())
+                }
+            } else {
+                grid_line.integer = Some(1);
+            }
+        }
+
+        Ok(grid_line)
+    }
+}
+
+impl ComputedValueAsSpecified for GridLine {}
+impl NoViewportPercentage for GridLine {}