Add a match_ignore_ascii_case! macro that does not allocate.

It should replace `match foo.to_ascii_lower().as_slice() { ...}`

@Manishearth I changed map.get to map.find in the lint to work around an ICE:

    task 'rustc' panicked at 'couldn't find node id 0 in the AST map'

Does this look OK?

components/plugins/lib.rs

@@ -65,11 +65,10 @@ macro_rules! define_css_keyword_enum {
 
         impl $name {
             pub fn parse(component_value: &::cssparser::ast::ComponentValue) -> Result<$name, ()> {
-                use std::ascii::AsciiExt;
                 match component_value {
                     &::cssparser::ast::Ident(ref value) => {
-                        match value.to_ascii_lower().as_slice() {
-                            $( concat!($css) => Ok($name::$variant), )+
+                        match_ignore_ascii_case! { value:
+                            $( $css => Ok($name::$variant) ),+
                             _ => Err(())
                         }
                     }
@@ -96,3 +95,23 @@ macro_rules! define_css_keyword_enum {
         }
     }
 }
+
+
+#[macro_export]
+macro_rules! match_ignore_ascii_case {
+    ( $value: expr: $( $string: expr => $result: expr ),+ _ => $fallback: expr, ) => {
+        match_ignore_ascii_case! { $value:
+            $( $string => $result ),+
+            _ => $fallback
+        }
+    };
+    ( $value: expr: $( $string: expr => $result: expr ),+ _ => $fallback: expr ) => {
+        {
+            use std::ascii::AsciiExt;
+            match $value.as_slice() {
+                $( s if s.eq_ignore_ascii_case($string) => $result, )+
+                _ => $fallback
+            }
+        }
+    };
+}

components/plugins/lints.rs

@@ -104,8 +104,8 @@ fn lint_unrooted_ty(cx: &Context, ty: &ast::Ty, warning: &str) {
 // Determines if a block is in an unsafe context so that an unhelpful
 // lint can be aborted.
 fn unsafe_context(map: &ast_map::Map, id: ast::NodeId) -> bool {
-    match map.get(map.get_parent(id)) {
-        ast_map::NodeImplItem(itm) => {
+    match map.find(map.get_parent(id)) {
+        Some(ast_map::NodeImplItem(itm)) => {
             match *itm {
                 ast::MethodImplItem(ref meth) => match meth.node {
                     ast::MethDecl(_, _, _, _, style, _, _, _) => match style {
@@ -117,7 +117,7 @@ fn unsafe_context(map: &ast_map::Map, id: ast::NodeId) -> bool {
                 _ => false,
             }
         },
-        ast_map::NodeItem(itm) => {
+        Some(ast_map::NodeItem(itm)) => {
             match itm.node {
                 ast::ItemFn(_, style, _, _, _) => match style {
                     ast::UnsafeFn => true,

components/util/Cargo.toml

@@ -7,6 +7,9 @@ authors = ["The Servo Project Developers"]
 name = "util"
 path = "lib.rs"
 
+[dependencies.plugins]
+path = "../plugins"
+
 [dependencies.cssparser]
 git = "https://github.com/servo/rust-cssparser"
 

components/util/cursor.rs

@@ -19,8 +19,8 @@ macro_rules! define_cursor {
 
         impl Cursor {
             pub fn from_css_keyword(keyword: &str) -> Result<Cursor, ()> {
-                match keyword.to_ascii_lower().as_slice() {
-                    $( concat!($css) => Ok(Cursor::$variant), )+
+                match_ignore_ascii_case! { keyword:
+                    $( concat!($css) => Ok(Cursor::$variant) ),+
                     _ => Err(())
                 }
             }

components/util/lib.rs

@@ -31,10 +31,9 @@ extern crate string_cache;
 extern crate unicode;
 extern crate url;
 
-#[phase(plugin)]
-extern crate string_cache_macros;
-#[phase(plugin)]
-extern crate lazy_static;
+#[phase(plugin)] extern crate plugins;
+#[phase(plugin)] extern crate string_cache_macros;
+#[phase(plugin)] extern crate lazy_static;
 
 use std::sync::Arc;