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::hir::map::Map;
  15 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  16 use rustc::hir;
  17 use syntax::ast;
  18 use syntax_pos::Span;
  19
  20 #[derive(Clone, Copy, PartialEq)]
  21 enum LoopKind {
  22     Loop(hir::LoopSource),
  23     WhileLoop,
  24     Block,
  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             LoopKind::Block => "block",
  35         }
  36     }
  37 }
  38
  39 #[derive(Clone, Copy, PartialEq)]
  40 enum Context {
  41     Normal,
  42     Loop(LoopKind),
  43     Closure,
  44     LabeledBlock,
  45 }
  46
  47 #[derive(Copy, Clone)]
  48 struct CheckLoopVisitor<'a, 'hir: 'a> {
  49     sess: &'a Session,
  50     hir_map: &'a Map<'hir>,
  51     cx: Context,
  52 }
  53
  54 pub fn check_crate(sess: &Session, map: &Map) {
  55     let krate = map.krate();
  56     krate.visit_all_item_likes(&mut CheckLoopVisitor {
  57         sess,
  58         hir_map: map,
  59         cx: Normal,
  60     }.as_deep_visitor());
  61 }
  62
  63 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  64     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  65         NestedVisitorMap::OnlyBodies(&self.hir_map)
  66     }
  67
  68     fn visit_item(&mut self, i: &'hir hir::Item) {
  69         self.with_context(Normal, |v| intravisit::walk_item(v, i));
  70     }
  71
  72     fn visit_impl_item(&mut self, i: &'hir hir::ImplItem) {
  73         self.with_context(Normal, |v| intravisit::walk_impl_item(v, i));
  74     }
  75
  76     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  77         match e.node {
  78             hir::ExprWhile(ref e, ref b, _) => {
  79                 self.with_context(Loop(LoopKind::WhileLoop), |v| {
  80                     v.visit_expr(&e);
  81                     v.visit_block(&b);
  82                 });
  83             }
  84             hir::ExprLoop(ref b, _, source) => {
  85                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
  86             }
  87             hir::ExprClosure(.., b, _, _) => {
  88                 self.with_context(Closure, |v| v.visit_nested_body(b));
  89             }
  90             hir::ExprBlock(ref b, Some(_label)) => {
  91                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  92             }
  93             hir::ExprBreak(label, ref opt_expr) => {
  94                 let loop_id = match label.target_id.into() {
  95                     Ok(loop_id) => loop_id,
  96                     Err(hir::LoopIdError::OutsideLoopScope) => ast::DUMMY_NODE_ID,
  97                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
  98                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
  99                         ast::DUMMY_NODE_ID
 100                     },
 101                     Err(hir::LoopIdError::UnresolvedLabel) => ast::DUMMY_NODE_ID,
 102                 };
 103
 104                 if loop_id != ast::DUMMY_NODE_ID {
 105                     match self.hir_map.find(loop_id).unwrap() {
 106                         hir::map::NodeBlock(_) => return,
 107                         _=> (),
 108                     }
 109                 }
 110
 111                 if self.cx == LabeledBlock {
 112                     if label.label.is_none() {
 113                         struct_span_err!(self.sess, e.span, E0695,
 114                                         "unlabeled `break` inside of a labeled block")
 115                             .span_label(e.span,
 116                                         "`break` statements that would diverge to or through \
 117                                         a labeled block need to bear a label")
 118                             .emit();
 119                     }
 120                     return;
 121                 }
 122
 123                 if opt_expr.is_some() {
 124                     let loop_kind = if loop_id == ast::DUMMY_NODE_ID {
 125                         None
 126                     } else {
 127                         Some(match self.hir_map.expect_expr(loop_id).node {
 128                             hir::ExprWhile(..) => LoopKind::WhileLoop,
 129                             hir::ExprLoop(_, _, source) => LoopKind::Loop(source),
 130                             hir::ExprBlock(..) => LoopKind::Block,
 131                             ref r => span_bug!(e.span,
 132                                                "break label resolved to a non-loop: {:?}", r),
 133                         })
 134                     };
 135                     match loop_kind {
 136                         None |
 137                         Some(LoopKind::Loop(hir::LoopSource::Loop)) |
 138                         Some(LoopKind::Block) => (),
 139                         Some(kind) => {
 140                             struct_span_err!(self.sess, e.span, E0571,
 141                                              "`break` with value from a `{}` loop",
 142                                              kind.name())
 143                                 .span_label(e.span,
 144                                             "can only break with a value inside \
 145                                             `loop` or breakable block")
 146                                 .span_suggestion(e.span,
 147                                                  &format!("instead, use `break` on its own \
 148                                                            without a value inside this `{}` loop",
 149                                                           kind.name()),
 150                                                  "break".to_string())
 151                                 .emit();
 152                         }
 153                     }
 154                 }
 155
 156                 self.require_break_cx("break", e.span);
 157             }
 158             hir::ExprAgain(label) => {
 159                 if let Err(hir::LoopIdError::UnlabeledCfInWhileCondition) = label.target_id {
 160                     self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 161                 }
 162                 self.require_break_cx("continue", e.span)
 163             },
 164             _ => intravisit::walk_expr(self, e),
 165         }
 166     }
 167 }
 168
 169 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 170     fn with_context<F>(&mut self, cx: Context, f: F)
 171         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 172     {
 173         let old_cx = self.cx;
 174         self.cx = cx;
 175         f(self);
 176         self.cx = old_cx;
 177     }
 178
 179     fn require_break_cx(&self, name: &str, span: Span) {
 180         match self.cx {
 181             LabeledBlock |
 182             Loop(_) => {}
 183             Closure => {
 184                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 185                 .span_label(span, "cannot break inside of a closure")
 186                 .emit();
 187             }
 188             Normal => {
 189                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 190                 .span_label(span, "cannot break outside of a loop")
 191                 .emit();
 192             }
 193         }
 194     }
 195
 196     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 197         struct_span_err!(self.sess, span, E0590,
 198                          "`break` or `continue` with no label in the condition of a `while` loop")
 199             .span_label(span,
 200                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 201             .emit();
 202     }
 203 }