Extracted shorthands to separate files.

I've deliberately tried to keep things similarly structured as in the longhand files. I.e. if a given property is in e.g. longhand/box.mako.rs, the shorthand stuff that relates to the same property is in shorthand/box.mako.rs and so forth.

components/style/properties/shorthand/list.mako.rs

@@ -0,0 +1,92 @@
+/* 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/. */
+
+<%namespace name="helpers" file="/helpers.mako.rs" />
+
+<%helpers:shorthand name="list-style"
+                    sub_properties="list-style-image list-style-position list-style-type">
+    use properties::longhands::{list_style_image, list_style_position, list_style_type};
+
+    // `none` is ambiguous until we've finished parsing the shorthands, so we count the number
+    // of times we see it.
+    let mut nones = 0u8;
+    let (mut image, mut position, mut list_style_type, mut any) = (None, None, None, false);
+    loop {
+        if input.try(|input| input.expect_ident_matching("none")).is_ok() {
+            nones = nones + 1;
+            if nones > 2 {
+                return Err(())
+            }
+            any = true;
+            continue
+        }
+
+        if list_style_type.is_none() {
+            if let Ok(value) = input.try(|input| list_style_type::parse(context, input)) {
+                list_style_type = Some(value);
+                any = true;
+                continue
+            }
+        }
+
+        if image.is_none() {
+            if let Ok(value) = input.try(|input| list_style_image::parse(context, input)) {
+                image = Some(value);
+                any = true;
+                continue
+            }
+        }
+
+        if position.is_none() {
+            if let Ok(value) = input.try(|input| list_style_position::parse(context, input)) {
+                position = Some(value);
+                any = true;
+                continue
+            }
+        }
+        break
+    }
+
+    // If there are two `none`s, then we can't have a type or image; if there is one `none`,
+    // then we can't have both a type *and* an image; if there is no `none` then we're fine as
+    // long as we parsed something.
+    match (any, nones, list_style_type, image) {
+        (true, 2, None, None) => {
+            Ok(Longhands {
+                list_style_position: position,
+                list_style_image: Some(list_style_image::SpecifiedValue::None),
+                list_style_type: Some(list_style_type::SpecifiedValue::none),
+            })
+        }
+        (true, 1, None, Some(image)) => {
+            Ok(Longhands {
+                list_style_position: position,
+                list_style_image: Some(image),
+                list_style_type: Some(list_style_type::SpecifiedValue::none),
+            })
+        }
+        (true, 1, Some(list_style_type), None) => {
+            Ok(Longhands {
+                list_style_position: position,
+                list_style_image: Some(list_style_image::SpecifiedValue::None),
+                list_style_type: Some(list_style_type),
+            })
+        }
+        (true, 1, None, None) => {
+            Ok(Longhands {
+                list_style_position: position,
+                list_style_image: Some(list_style_image::SpecifiedValue::None),
+                list_style_type: Some(list_style_type::SpecifiedValue::none),
+            })
+        }
+        (true, 0, list_style_type, image) => {
+            Ok(Longhands {
+                list_style_position: position,
+                list_style_image: image,
+                list_style_type: list_style_type,
+            })
+        }
+        _ => Err(()),
+    }
+</%helpers:shorthand>