rust/src/librustc/middle/check_loop.rs

// Copyright 2012 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.

use syntax::ast::*;
use syntax::visit;

type ctx = {in_loop: bool, can_ret: bool};

fn check_crate(tcx: ty::ctxt, crate: @crate) {
    visit::visit_crate(*crate,
                       {in_loop: false, can_ret: true},
                       visit::mk_vt(@{
        visit_item: |i, _cx, v| {
            visit::visit_item(i, {in_loop: false, can_ret: true}, v);
        },
        visit_expr: |e: @expr, cx: ctx, v: visit::vt<ctx>| {
            match e.node {
              expr_while(e, ref b) => {
                (v.visit_expr)(e, cx, v);
                (v.visit_block)((*b), {in_loop: true,.. cx}, v);
              }
              expr_loop(ref b, _) => {
                (v.visit_block)((*b), {in_loop: true,.. cx}, v);
              }
              expr_fn(_, _, _, _) => {
                visit::visit_expr(e, {in_loop: false, can_ret: true}, v);
              }
              expr_fn_block(_, ref b, _) => {
                (v.visit_block)((*b), {in_loop: false, can_ret: false}, v);
              }
              expr_loop_body(@{node: expr_fn_block(_, ref b, _), _}) => {
                let proto = ty::ty_fn_proto(ty::expr_ty(tcx, e));
                let blk = (proto == ProtoBorrowed);
                (v.visit_block)((*b), {in_loop: true, can_ret: blk}, v);
              }
              expr_break(_) => {
                if !cx.in_loop {
                    tcx.sess.span_err(e.span, ~"`break` outside of loop");
                }
              }
              expr_again(_) => {
                if !cx.in_loop {
                    tcx.sess.span_err(e.span, ~"`again` outside of loop");
                }
              }
              expr_ret(oe) => {
                if !cx.can_ret {
                    tcx.sess.span_err(e.span, ~"`return` in block function");
                }
                visit::visit_expr_opt(oe, cx, v);
              }
              _ => visit::visit_expr(e, cx, v)
            }
        },
        .. *visit::default_visitor()
    }));
}