Use FromIterator<_> for TokenStream

Also remove conservative_impl_trait feature flag, as this is now a
stable feature.

Refs lambda-fairy#121

maud/tests/control_structures.rs

@@ -1,4 +1,3 @@
-#![feature(conservative_impl_trait)]
 #![feature(plugin)]
 #![feature(proc_macro)]
 

maud_macros/src/build.rs

@@ -34,15 +34,7 @@ impl Builder {
     /// Reifies the `Builder` into a raw list of statements.
     pub fn build(mut self) -> TokenStream {
         let Builder { stmts, .. } = { self.flush(); self };
-
-        // use a Group here?
-        let mut tts: Vec<TokenTree> = Vec::new();
-        for s in stmts.into_iter() {
-            let i = s.into_iter();
-            tts.extend(i);
-        }
-
-        tts.into_iter().collect()
+        stmts.into_iter().collect()
     }
 
     /// Pushes a statement, flushing the tail buffer in the process.

maud_macros/src/parse.rs

@@ -10,6 +10,7 @@ use proc_macro::{
 };
 
 use proc_macro::token_stream;
+use std::iter;
 use std::mem;
 
 use literalext::LiteralExt;
@@ -302,14 +303,14 @@ impl Parser {
     }
 
     fn match_arms(&mut self) -> ParseResult<TokenStream> {
-        let mut arms: Vec<TokenTree> = Vec::new();
+        let mut arms = Vec::new();
         while let Some(arm) = self.match_arm()? {
-            arms.extend(arm);
+            arms.push(arm);
         }
         Ok(arms.into_iter().collect())
     }
 
-    fn match_arm(&mut self) -> ParseResult<Option<Vec<TokenTree>>> {
+    fn match_arm(&mut self) -> ParseResult<Option<TokenStream>> {
         let mut pat: Vec<TokenTree> = Vec::new();
         loop {
             match self.peek2() {
@@ -364,8 +365,7 @@ impl Parser {
             },
             None => return self.error("unexpected end of @match arm"),
         };
-        pat.push(body);
-        Ok(Some(pat))
+        Ok(Some(pat.into_iter().chain(iter::once(body)).collect()))
     }
 
     /// Parses and renders a `@let` expression.