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                 let loop_id = match label.target_id {
  91                     hir::ScopeTarget::Block(_) => return,
  92                     hir::ScopeTarget::Loop(loop_res) => {
  93                         match loop_res.into() {
  94                             Ok(loop_id) => loop_id,
  95                             Err(hir::LoopIdError::OutsideLoopScope) => ast::DUMMY_NODE_ID,
  96                             Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
  97                                 self.emit_unlabled_cf_in_while_condition(e.span, "break");
  98                                 ast::DUMMY_NODE_ID
  99                             },
 100                             Err(hir::LoopIdError::UnresolvedLabel) => ast::DUMMY_NODE_ID,
 101                         }
 102                     }
 103                 };
 104
 105                 if opt_expr.is_some() {
 106                     let loop_kind = if loop_id == ast::DUMMY_NODE_ID {
 107                         None
 108                     } else {
 109                         Some(match self.hir_map.expect_expr(loop_id).node {
 110                             hir::ExprWhile(..) => LoopKind::WhileLoop,
 111                             hir::ExprLoop(_, _, source) => LoopKind::Loop(source),
 112                             ref r => span_bug!(e.span,
 113                                                "break label resolved to a non-loop: {:?}", r),
 114                         })
 115                     };
 116                     match loop_kind {
 117                         None | Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
 118                         Some(kind) => {
 119                             struct_span_err!(self.sess, e.span, E0571,
 120                                              "`break` with value from a `{}` loop",
 121                                              kind.name())
 122                                 .span_label(e.span,
 123                                             &format!("can only break with a value inside `loop`"))
 124                                 .emit();
 125                         }
 126                     }
 127                 }
 128
 129                 self.require_loop("break", e.span);
 130             }
 131             hir::ExprAgain(label) => {
 132                 if let hir::ScopeTarget::Loop(
 133                     hir::LoopIdResult::Err(
 134                         hir::LoopIdError::UnlabeledCfInWhileCondition)) = label.target_id {
 135                     self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 136                 }
 137                 self.require_loop("continue", e.span)
 138             },
 139             _ => intravisit::walk_expr(self, e),
 140         }
 141     }
 142 }
 143
 144 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 145     fn with_context<F>(&mut self, cx: Context, f: F)
 146         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 147     {
 148         let old_cx = self.cx;
 149         self.cx = cx;
 150         f(self);
 151         self.cx = old_cx;
 152     }
 153
 154     fn require_loop(&self, name: &str, span: Span) {
 155         match self.cx {
 156             Loop(_) => {}
 157             Closure => {
 158                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 159                 .span_label(span, &format!("cannot break inside of a closure"))
 160                 .emit();
 161             }
 162             Normal => {
 163                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 164                 .span_label(span, &format!("cannot break outside of a loop"))
 165                 .emit();
 166             }
 167         }
 168     }
 169
 170     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 171         struct_span_err!(self.sess, span, E0590,
 172                          "`break` or `continue` with no label in the condition of a `while` loop")
 173             .span_label(span,
 174                         &format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 175             .emit();
 176     }
 177 }