librustc: Stop desugaring for expressions and translate them directly.

This makes edge cases in which the `Iterator` trait was not in scope
and/or `Option` or its variants were not in scope work properly.

This breaks code that looks like:

    struct MyStruct { ... }

    impl MyStruct {
        fn next(&mut self) -> Option<int> { ... }
    }

    for x in MyStruct { ... } { ... }

Change ad-hoc `next` methods like the above to implementations of the
`Iterator` trait. For example:

    impl Iterator<int> for MyStruct {
        fn next(&mut self) -> Option<int> { ... }
    }

Closes #15392.

[breaking-change]

src/test/bench/shootout-meteor.rs

@@ -297,10 +297,10 @@ fn search(
     // for every unused piece
     for id in range(0u, 10).filter(|id| board & (1 << (id + 50)) == 0) {
         // for each mask that fits on the board
-        for &m in masks_at.get(id).iter().filter(|&m| board & *m == 0) {
+        for m in masks_at.get(id).iter().filter(|&m| board & *m == 0) {
             // This check is too costy.
             //if is_board_unfeasible(board | m, masks) {continue;}
-            search(masks, board | m, i + 1, Cons(m, &cur), data);
+            search(masks, board | *m, i + 1, Cons(*m, &cur), data);
         }
     }
 }
@@ -311,9 +311,10 @@ fn par_search(masks: Vec<Vec<Vec<u64>>>) -> Data {
 
     // launching the search in parallel on every masks at minimum
     // coordinate (0,0)
-    for &m in masks.get(0).iter().flat_map(|masks_pos| masks_pos.iter()) {
+    for m in masks.get(0).iter().flat_map(|masks_pos| masks_pos.iter()) {
         let masks = masks.clone();
         let tx = tx.clone();
+        let m = *m;
         spawn(proc() {
             let mut data = Data::new();
             search(&*masks, m, 1, Cons(m, &Nil), &mut data);

src/test/compile-fail/for-loop-bogosity.rs

@@ -0,0 +1,31 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct MyStruct {
+    x: int,
+    y: int,
+}
+
+impl MyStruct {
+    fn next(&mut self) -> Option<int> {
+        Some(self.x)
+    }
+}
+
+pub fn main() {
+    let mut bogus = MyStruct {
+        x: 1,
+        y: 2,
+    };
+    for x in bogus {    //~ ERROR does not implement the `Iterator` trait
+        drop(x);
+    }
+}
+

src/test/compile-fail/issue-15167.rs

@@ -9,13 +9,18 @@
 // except according to those terms.
 
 // macro f should not be able to inject a reference to 'n'.
+//
+// Ignored because `for` loops are not hygienic yet; they will require special
+// handling since they introduce a new pattern binding position.
+
+// ignore-test
 
 #![feature(macro_rules)]
 
 macro_rules! f(() => (n))
 
 fn main() -> (){
-    for n in range(0, 1) {
+    for n in range(0i, 1) {
         println!("{}", f!()); //~ ERROR unresolved name `n`
     }
 }

src/test/compile-fail/vec-mut-iter-borrow.rs

@@ -9,9 +9,9 @@
 // except according to those terms.
 
 fn main() {
-    let mut xs = vec!(1i, 2, 3, 4);
+    let mut xs: Vec<int> = vec!();
 
     for x in xs.mut_iter() {
-        xs.push(1) //~ ERROR cannot borrow `xs`
+        xs.push(1i) //~ ERROR cannot borrow `xs`
     }
 }

src/test/debuginfo/lexical-scope-in-for-loop.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 // ignore-android: FIXME(#10381)
+// ignore-test: Not sure what is going on here --pcwalton
 
 // compile-flags:-g
 

src/test/run-pass/for-loop-goofiness.rs

@@ -0,0 +1,24 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+enum BogusOption<T> {
+    None,
+    Some(T),
+}
+
+type Iterator = int;
+
+pub fn main() {
+    let x = [ 3i, 3, 3 ];
+    for i in x.iter() {
+        assert_eq!(*i, 3);
+    }
+}
+