rust/src/rustc/middle/check_loop.rs

import syntax::ast::*;
import syntax::visit;
import driver::session::session;

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>|
            alt e.node {
              expr_for(_, e, b) | expr_while(e, b) | expr_do_while(b, e) {
                v.visit_expr(e, cx, v);
                v.visit_block(b, {in_loop: true with cx}, v);
              }
              expr_loop(b) {
                v.visit_block(b, {in_loop: true with cx}, v);
              }
              expr_fn(_, _, _, _) {
                visit::visit_expr(e, {in_loop: false, can_ret: true}, v);
              }
              expr_fn_block(_, b) {
                v.visit_block(b, {in_loop: false, can_ret: false}, v);
              }
              expr_loop_body(@{node: expr_fn_block(_, b), _}) {
                v.visit_block(b, {in_loop: true, can_ret: false}, v);
              }
              expr_break {
                if !cx.in_loop {
                    tcx.sess.span_err(e.span, "`break` outside of loop");
                }
              }
              expr_cont {
                if !cx.in_loop {
                    tcx.sess.span_err(e.span, "`cont` outside of loop");
                }
              }
              expr_ret(oe) {
                if !cx.can_ret {
                    tcx.sess.span_err(e.span, "`ret` in block function");
                }
                visit::visit_expr_opt(oe, cx, v);
              }
              expr_be(re) {
                if !cx.can_ret {
                    tcx.sess.span_err(e.span, "`be` in block function");
                }
                v.visit_expr(re, cx, v);
              }
              _ { visit::visit_expr(e, cx, v); }
            }
        }
        with *visit::default_visitor()
    }));
}