Don't allow binding patterns to bind keywords

Closes #1586

src/comp/syntax/parse/parser.rs

@@ -666,6 +666,15 @@ fn parse_path(p: parser) -> @ast::path {
                  {global: global, idents: ids, types: []});
 }
 
+fn parse_value_path(p: parser) -> @ast::path {
+    let pt = parse_path(p);
+    let last_word = pt.node.idents[vec::len(pt.node.idents)-1u];
+    if p.bad_expr_words.contains_key(last_word) {
+        p.fatal("found " + last_word + " in expression position");
+    }
+    pt
+}
+
 fn parse_path_and_ty_param_substs(p: parser, colons: bool) -> @ast::path {
     let lo = p.span.lo;
     let path = parse_path(p);
@@ -1514,7 +1523,7 @@ fn parse_pat(p: parser) -> @ast::pat {
               token::LPAREN | token::LBRACKET | token::LT { false }
               _ { true }
             } {
-            let name = parse_path(p);
+            let name = parse_value_path(p);
             let sub = if eat(p, token::AT) { some(parse_pat(p)) }
                       else { none };
             pat = ast::pat_ident(name, sub);

src/test/compile-fail/reference-in-loop.rs

@@ -1,10 +0,0 @@
-// error-pattern: overwriting x will invalidate reference y
-
-fn main() {
-    let x = [];
-    let &y = x;
-    while true {
-        log(error, y);
-        x = [1];
-    }
-}

src/test/run-pass/reference-branch.rs

@@ -1,9 +0,0 @@
-// Ensures that invalidating a reference in one branch doesn't
-// influence other branches.
-
-fn main() {
-    let x = [];
-    let &y = x;
-    if true { x = [1]; }
-    else { log(error, y); }
-}