src/librustc_passes/loops.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10 use self::Context::*;
  11
  12 use rustc::session::Session;
  13
  14 use rustc::dep_graph::DepNode;
  15 use rustc::hir::map::Map;
  16 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  17 use rustc::hir;
  18 use syntax::ast;
  19 use syntax_pos::Span;
  20
  21 #[derive(Clone, Copy, PartialEq)]
  22 enum LoopKind {
  23     Loop(hir::LoopSource),
  24     WhileLoop,
  25 }
  26
  27 impl LoopKind {
  28     fn name(self) -> &'static str {
  29         match self {
  30             LoopKind::Loop(hir::LoopSource::Loop) => "loop",
  31             LoopKind::Loop(hir::LoopSource::WhileLet) => "while let",
  32             LoopKind::Loop(hir::LoopSource::ForLoop) => "for",
  33             LoopKind::WhileLoop => "while",
  34         }
  35     }
  36 }
  37
  38 #[derive(Clone, Copy, PartialEq)]
  39 enum Context {
  40     Normal,
  41     Loop(LoopKind),
  42     Closure,
  43 }
  44
  45 #[derive(Copy, Clone)]
  46 struct CheckLoopVisitor<'a, 'hir: 'a> {
  47     sess: &'a Session,
  48     hir_map: &'a Map<'hir>,
  49     cx: Context,
  50 }
  51
  52 pub fn check_crate(sess: &Session, map: &Map) {
  53     let _task = map.dep_graph.in_task(DepNode::CheckLoops);
  54     let krate = map.krate();
  55     krate.visit_all_item_likes(&mut CheckLoopVisitor {
  56         sess: sess,
  57         hir_map: map,
  58         cx: Normal,
  59     }.as_deep_visitor());
  60 }
  61
  62 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  63     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  64         NestedVisitorMap::OnlyBodies(&self.hir_map)
  65     }
  66
  67     fn visit_item(&mut self, i: &'hir hir::Item) {
  68         self.with_context(Normal, |v| intravisit::walk_item(v, i));
  69     }
  70
  71     fn visit_impl_item(&mut self, i: &'hir hir::ImplItem) {
  72         self.with_context(Normal, |v| intravisit::walk_impl_item(v, i));
  73     }
  74
  75     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  76         match e.node {
  77             hir::ExprWhile(ref e, ref b, _) => {
  78                 self.with_context(Loop(LoopKind::WhileLoop), |v| {
  79                     v.visit_expr(&e);
  80                     v.visit_block(&b);
  81                 });
  82             }
  83             hir::ExprLoop(ref b, _, source) => {
  84                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
  85             }
  86             hir::ExprClosure(.., b, _) => {
  87                 self.with_context(Closure, |v| v.visit_nested_body(b));
  88             }
  89             hir::ExprBreak(label, ref opt_expr) => {
  90                 if opt_expr.is_some() {
  91                     let loop_kind = if let Some(label) = label {
  92                         if label.loop_id == ast::DUMMY_NODE_ID {
  93                             None
  94                         } else {
  95                             Some(match self.hir_map.expect_expr(label.loop_id).node {
  96                                 hir::ExprWhile(..) => LoopKind::WhileLoop,
  97                                 hir::ExprLoop(_, _, source) => LoopKind::Loop(source),
  98                                 ref r => span_bug!(e.span,
  99                                                    "break label resolved to a non-loop: {:?}", r),
 100                             })
 101                         }
 102                     } else if let Loop(kind) = self.cx {
 103                         Some(kind)
 104                     } else {
 105                         // `break` outside a loop - caught below
 106                         None
 107                     };
 108                     match loop_kind {
 109                         None | Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
 110                         Some(kind) => {
 111                             struct_span_err!(self.sess, e.span, E0571,
 112                                              "`break` with value from a `{}` loop",
 113                                              kind.name())
 114                                 .span_label(e.span,
 115                                             &format!("can only break with a value inside `loop`"))
 116                                 .emit();
 117                         }
 118                     }
 119                 }
 120                 self.require_loop("break", e.span);
 121             }
 122             hir::ExprAgain(_) => self.require_loop("continue", e.span),
 123             _ => intravisit::walk_expr(self, e),
 124         }
 125     }
 126 }
 127
 128 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 129     fn with_context<F>(&mut self, cx: Context, f: F)
 130         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 131     {
 132         let old_cx = self.cx;
 133         self.cx = cx;
 134         f(self);
 135         self.cx = old_cx;
 136     }
 137
 138     fn require_loop(&self, name: &str, span: Span) {
 139         match self.cx {
 140             Loop(_) => {}
 141             Closure => {
 142                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 143                 .span_label(span, &format!("cannot break inside of a closure"))
 144                 .emit();
 145             }
 146             Normal => {
 147                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 148                 .span_label(span, &format!("cannot break outside of a loop"))
 149                 .emit();
 150             }
 151         }
 152     }
 153 }