Add syntax support for attributes on expressions and all syntax

nodes in statement position.

Extended #[cfg] folder to allow removal of statements, and
of expressions in optional positions like expression lists and trailing
block expressions.

Extended lint checker to recognize lint levels on expressions and
locals.

src/libsyntax/fold.rs

@@ -134,6 +134,14 @@ pub trait Folder : Sized {
         e.map(|e| noop_fold_expr(e, self))
     }
 
+    fn fold_opt_expr(&mut self, e: P<Expr>) -> Option<P<Expr>> {
+        noop_fold_opt_expr(e, self)
+    }
+
+    fn fold_exprs(&mut self, es: Vec<P<Expr>>) -> Vec<P<Expr>> {
+        noop_fold_exprs(es, self)
+    }
+
     fn fold_ty(&mut self, t: P<Ty>) -> P<Ty> {
         noop_fold_ty(t, self)
     }
@@ -508,12 +516,13 @@ pub fn noop_fold_parenthesized_parameter_data<T: Folder>(data: ParenthesizedPara
 }
 
 pub fn noop_fold_local<T: Folder>(l: P<Local>, fld: &mut T) -> P<Local> {
-    l.map(|Local {id, pat, ty, init, span}| Local {
+    l.map(|Local {id, pat, ty, init, span, attrs}| Local {
         id: fld.new_id(id),
         ty: ty.map(|t| fld.fold_ty(t)),
         pat: fld.fold_pat(pat),
         init: init.map(|e| fld.fold_expr(e)),
-        span: fld.new_span(span)
+        span: fld.new_span(span),
+        attrs: attrs.map_opt_attrs(|v| fold_attrs(v, fld)),
     })
 }
 
@@ -891,7 +900,7 @@ pub fn noop_fold_block<T: Folder>(b: P<Block>, folder: &mut T) -> P<Block> {
     b.map(|Block {id, stmts, expr, rules, span}| Block {
         id: folder.new_id(id),
         stmts: stmts.into_iter().flat_map(|s| folder.fold_stmt(s).into_iter()).collect(),
-        expr: expr.map(|x| folder.fold_expr(x)),
+        expr: expr.and_then(|x| folder.fold_opt_expr(x)),
         rules: rules,
         span: folder.new_span(span),
     })
@@ -1171,7 +1180,7 @@ pub fn noop_fold_pat<T: Folder>(p: P<Pat>, folder: &mut T) -> P<Pat> {
     })
 }
 
-pub fn noop_fold_expr<T: Folder>(Expr {id, node, span}: Expr, folder: &mut T) -> Expr {
+pub fn noop_fold_expr<T: Folder>(Expr {id, node, span, attrs}: Expr, folder: &mut T) -> Expr {
     Expr {
         id: folder.new_id(id),
         node: match node {
@@ -1182,21 +1191,21 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span}: Expr, folder: &mut T) ->
                 ExprInPlace(folder.fold_expr(p), folder.fold_expr(e))
             }
             ExprVec(exprs) => {
-                ExprVec(exprs.move_map(|x| folder.fold_expr(x)))
+                ExprVec(folder.fold_exprs(exprs))
             }
             ExprRepeat(expr, count) => {
                 ExprRepeat(folder.fold_expr(expr), folder.fold_expr(count))
             }
-            ExprTup(elts) => ExprTup(elts.move_map(|x| folder.fold_expr(x))),
+            ExprTup(exprs) => ExprTup(folder.fold_exprs(exprs)),
             ExprCall(f, args) => {
                 ExprCall(folder.fold_expr(f),
-                         args.move_map(|x| folder.fold_expr(x)))
+                         folder.fold_exprs(args))
             }
             ExprMethodCall(i, tps, args) => {
                 ExprMethodCall(
                     respan(folder.new_span(i.span), folder.fold_ident(i.node)),
                     tps.move_map(|x| folder.fold_ty(x)),
-                    args.move_map(|x| folder.fold_expr(x)))
+                    folder.fold_exprs(args))
             }
             ExprBinary(binop, lhs, rhs) => {
                 ExprBinary(binop,
@@ -1329,10 +1338,20 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span}: Expr, folder: &mut T) ->
             },
             ExprParen(ex) => ExprParen(folder.fold_expr(ex))
         },
-        span: folder.new_span(span)
+        span: folder.new_span(span),
+        attrs: attrs.map_opt_attrs(|v| fold_attrs(v, folder)),
     }
 }
 
+pub fn noop_fold_opt_expr<T: Folder>(e: P<Expr>, folder: &mut T) -> Option<P<Expr>> {
+    Some(folder.fold_expr(e))
+}
+
+pub fn noop_fold_exprs<T: Folder>(es: Vec<P<Expr>>, folder: &mut T) -> Vec<P<Expr>> {
+    // FIXME: Needs a efficient in-place flat_map
+    es.into_iter().flat_map(|e| folder.fold_opt_expr(e)).collect()
+}
+
 pub fn noop_fold_stmt<T: Folder>(Spanned {node, span}: Stmt, folder: &mut T)
                                  -> SmallVector<P<Stmt>> {
     let span = folder.new_span(span);
@@ -1346,20 +1365,30 @@ pub fn noop_fold_stmt<T: Folder>(Spanned {node, span}: Stmt, folder: &mut T)
         }
         StmtExpr(e, id) => {
             let id = folder.new_id(id);
-            SmallVector::one(P(Spanned {
-                node: StmtExpr(folder.fold_expr(e), id),
-                span: span
-            }))
+            if let Some(e) = folder.fold_opt_expr(e) {
+                SmallVector::one(P(Spanned {
+                    node: StmtExpr(e, id),
+                    span: span
+                }))
+            } else {
+                SmallVector::zero()
+            }
         }
         StmtSemi(e, id) => {
             let id = folder.new_id(id);
-            SmallVector::one(P(Spanned {
-                node: StmtSemi(folder.fold_expr(e), id),
-                span: span
-            }))
+            if let Some(e) = folder.fold_opt_expr(e) {
+                SmallVector::one(P(Spanned {
+                    node: StmtSemi(e, id),
+                    span: span
+                }))
+            } else {
+                SmallVector::zero()
+            }
         }
-        StmtMac(mac, semi) => SmallVector::one(P(Spanned {
-            node: StmtMac(mac.map(|m| folder.fold_mac(m)), semi),
+        StmtMac(mac, semi, attrs) => SmallVector::one(P(Spanned {
+            node: StmtMac(mac.map(|m| folder.fold_mac(m)),
+                          semi,
+                          attrs.map_opt_attrs(|v| fold_attrs(v, folder))),
             span: span
         }))
     }