Preserve parenthesization in the AST

for better pretty-printing, as per #1458

Author: catamorphism

src/libsyntax/ast.rs

@@ -744,7 +744,10 @@ enum expr_ {
     expr_struct(@path, ~[field], Option<@expr>),
 
     // A vector literal constructed from one repeated element.
-    expr_repeat(@expr /* element */, @expr /* count */, mutability)
+    expr_repeat(@expr /* element */, @expr /* count */, mutability),
+
+    // No-op: used solely so we can pretty-print faithfully
+    expr_paren(@expr)
 }
 
 #[auto_serialize]

src/libsyntax/fold.rs

@@ -494,7 +494,8 @@ fn noop_fold_expr(e: expr_, fld: ast_fold) -> expr_ {
             expr_struct(fld.fold_path(path),
                         vec::map(fields, |x| fold_field(*x)),
                         option::map(&maybe_expr, |x| fld.fold_expr(*x)))
-          }
+          },
+          expr_paren(ex) => expr_paren(fld.fold_expr(ex))
         }
 }
 

src/libsyntax/parse/classify.rs

@@ -36,39 +36,3 @@ fn stmt_ends_with_semi(stmt: ast::stmt) -> bool {
       }
     }
 }
-
-fn need_parens(expr: @ast::expr, outer_prec: uint) -> bool {
-    match expr.node {
-      ast::expr_binary(op, _, _) => operator_prec(op) < outer_prec,
-      ast::expr_cast(_, _) => parse::prec::as_prec < outer_prec,
-      // This may be too conservative in some cases
-      ast::expr_assign(_, _) => true,
-      ast::expr_swap(_, _) => true,
-      ast::expr_assign_op(_, _, _) => true,
-      ast::expr_ret(_) => true,
-      ast::expr_assert(_) => true,
-      ast::expr_log(_, _, _) => true,
-      _ => !parse::classify::expr_requires_semi_to_be_stmt(expr)
-    }
-}
-
-fn ends_in_lit_int(ex: @ast::expr) -> bool {
-    match ex.node {
-      ast::expr_lit(node) => match node {
-        @{node: ast::lit_int(_, ast::ty_i), _}
-        | @{node: ast::lit_int_unsuffixed(_), _} => true,
-        _ => false
-      },
-      ast::expr_binary(_, _, sub) | ast::expr_unary(_, sub) |
-      ast::expr_copy(sub) | ast::expr_assign(_, sub) |
-      ast::expr_assign_op(_, _, sub) | ast::expr_swap(_, sub) |
-      ast::expr_log(_, _, sub) | ast::expr_assert(sub) => {
-        ends_in_lit_int(sub)
-      }
-      ast::expr_fail(osub) | ast::expr_ret(osub) => match osub {
-        Some(ex) => ends_in_lit_int(ex),
-        _ => false
-      },
-      _ => false
-    }
-}