librustc: Prefer Option::map/etc over match where applicable

Author: Wallacoloo

src/librustc/traits/on_unimplemented.rs

@@ -190,11 +190,10 @@ impl<'a, 'gcx, 'tcx> OnUnimplementedDirective {
         for command in self.subcommands.iter().chain(Some(self)).rev() {
             if let Some(ref condition) = command.condition {
                 if !attr::eval_condition(condition, &tcx.sess.parse_sess, &mut |c| {
-                    options.contains(&(c.name().as_str().to_string(),
-                                      match c.value_str().map(|s| s.as_str().to_string()) {
-                                          Some(s) => Some(s),
-                                          None => None
-                                      }))
+                    options.contains(&(
+                        c.name().as_str().to_string(),
+                        c.value_str().map(|s| s.as_str().to_string())
+                    ))
                 }) {
                     debug!("evaluate: skipping {:?} due to condition", command);
                     continue

src/librustc/ty/mod.rs

@@ -2697,15 +2697,12 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             self.opt_associated_item(def_id)
         };
 
-        match item {
-            Some(trait_item) => {
-                match trait_item.container {
-                    TraitContainer(_) => None,
-                    ImplContainer(def_id) => Some(def_id),
-                }
+        item.and_then(|trait_item|
+            match trait_item.container {
+                TraitContainer(_) => None,
+                ImplContainer(def_id) => Some(def_id),
             }
-            None => None
-        }
+        )
     }
 
     /// Looks up the span of `impl_did` if the impl is local; otherwise returns `Err`

src/librustc_metadata/locator.rs

@@ -824,17 +824,14 @@ impl<'a> Context<'a> {
         if rlib.is_none() && rmeta.is_none() && dylib.is_none() {
             return None;
         }
-        match slot {
-            Some((_, metadata)) => {
-                Some(Library {
-                    dylib,
-                    rlib,
-                    rmeta,
-                    metadata,
-                })
+        slot.map(|(_, metadata)|
+            Library {
+                dylib,
+                rlib,
+                rmeta,
+                metadata,
             }
-            None => None,
-        }
+        )
     }
 }