src/librustc_passes/loops.rs

   1 use self::Context::*;
   2
   3 use rustc::session::Session;
   4
   5 use rustc::hir::map::Map;
   6 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
   7 use rustc::hir::{self, Node, Destination};
   8 use syntax::ast;
   9 use syntax_pos::Span;
  10 use errors::Applicability;
  11
  12 #[derive(Clone, Copy, Debug, PartialEq)]
  13 enum LoopKind {
  14     Loop(hir::LoopSource),
  15     WhileLoop,
  16 }
  17
  18 impl LoopKind {
  19     fn name(self) -> &'static str {
  20         match self {
  21             LoopKind::Loop(hir::LoopSource::Loop) => "loop",
  22             LoopKind::Loop(hir::LoopSource::WhileLet) => "while let",
  23             LoopKind::Loop(hir::LoopSource::ForLoop) => "for",
  24             LoopKind::WhileLoop => "while",
  25         }
  26     }
  27 }
  28
  29 #[derive(Clone, Copy, Debug, PartialEq)]
  30 enum Context {
  31     Normal,
  32     Loop(LoopKind),
  33     Closure,
  34     LabeledBlock,
  35     AnonConst,
  36 }
  37
  38 #[derive(Copy, Clone)]
  39 struct CheckLoopVisitor<'a, 'hir: 'a> {
  40     sess: &'a Session,
  41     hir_map: &'a Map<'hir>,
  42     cx: Context,
  43 }
  44
  45 pub fn check_crate(sess: &Session, map: &Map) {
  46     let krate = map.krate();
  47     krate.visit_all_item_likes(&mut CheckLoopVisitor {
  48         sess,
  49         hir_map: map,
  50         cx: Normal,
  51     }.as_deep_visitor());
  52 }
  53
  54 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  55     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  56         NestedVisitorMap::OnlyBodies(&self.hir_map)
  57     }
  58
  59     fn visit_item(&mut self, i: &'hir hir::Item) {
  60         self.with_context(Normal, |v| intravisit::walk_item(v, i));
  61     }
  62
  63     fn visit_impl_item(&mut self, i: &'hir hir::ImplItem) {
  64         self.with_context(Normal, |v| intravisit::walk_impl_item(v, i));
  65     }
  66
  67     fn visit_anon_const(&mut self, c: &'hir hir::AnonConst) {
  68         self.with_context(AnonConst, |v| intravisit::walk_anon_const(v, c));
  69     }
  70
  71     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  72         match e.node {
  73             hir::ExprKind::While(ref e, ref b, _) => {
  74                 self.with_context(Loop(LoopKind::WhileLoop), |v| {
  75                     v.visit_expr(&e);
  76                     v.visit_block(&b);
  77                 });
  78             }
  79             hir::ExprKind::Loop(ref b, _, source) => {
  80                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
  81             }
  82             hir::ExprKind::Closure(_, ref function_decl, b, _, _) => {
  83                 self.visit_fn_decl(&function_decl);
  84                 self.with_context(Closure, |v| v.visit_nested_body(b));
  85             }
  86             hir::ExprKind::Block(ref b, Some(_label)) => {
  87                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  88             }
  89             hir::ExprKind::Break(label, ref opt_expr) => {
  90                 opt_expr.as_ref().map(|e| self.visit_expr(e));
  91
  92                 if self.require_label_in_labeled_block(e.span, &label, "break") {
  93                     // If we emitted an error about an unlabeled break in a labeled
  94                     // block, we don't need any further checking for this break any more
  95                     return;
  96                 }
  97
  98                 let loop_id = match label.target_id.into() {
  99                     Ok(loop_id) => loop_id,
 100                     Err(hir::LoopIdError::OutsideLoopScope) => ast::DUMMY_NODE_ID,
 101                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 102                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
 103                         ast::DUMMY_NODE_ID
 104                     },
 105                     Err(hir::LoopIdError::UnresolvedLabel) => ast::DUMMY_NODE_ID,
 106                 };
 107
 108                 if loop_id != ast::DUMMY_NODE_ID {
 109                     if let Node::Block(_) = self.hir_map.find(loop_id).unwrap() {
 110                         return
 111                     }
 112                 }
 113
 114                 if opt_expr.is_some() {
 115                     let loop_kind = if loop_id == ast::DUMMY_NODE_ID {
 116                         None
 117                     } else {
 118                         Some(match self.hir_map.expect_expr(loop_id).node {
 119                             hir::ExprKind::While(..) => LoopKind::WhileLoop,
 120                             hir::ExprKind::Loop(_, _, source) => LoopKind::Loop(source),
 121                             ref r => span_bug!(e.span,
 122                                                "break label resolved to a non-loop: {:?}", r),
 123                         })
 124                     };
 125                     match loop_kind {
 126                         None |
 127                         Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
 128                         Some(kind) => {
 129                             struct_span_err!(self.sess, e.span, E0571,
 130                                              "`break` with value from a `{}` loop",
 131                                              kind.name())
 132                                 .span_label(e.span,
 133                                             "can only break with a value inside \
 134                                             `loop` or breakable block")
 135                                 .span_suggestion_with_applicability(
 136                                     e.span,
 137                                     &format!(
 138                                         "instead, use `break` on its own \
 139                                         without a value inside this `{}` loop",
 140                                         kind.name()
 141                                     ),
 142                                     "break".to_string(),
 143                                     Applicability::MaybeIncorrect,
 144                                 )
 145                                 .emit();
 146                         }
 147                     }
 148                 }
 149
 150                 self.require_break_cx("break", e.span);
 151             }
 152             hir::ExprKind::Continue(destination) => {
 153                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 154
 155                 match destination.target_id {
 156                     Ok(loop_id) => {
 157                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 158                             struct_span_err!(self.sess, e.span, E0696,
 159                                             "`continue` pointing to a labeled block")
 160                                 .span_label(e.span,
 161                                             "labeled blocks cannot be `continue`'d")
 162                                 .span_note(block.span,
 163                                             "labeled block the continue points to")
 164                                 .emit();
 165                         }
 166                     }
 167                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 168                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 169                     }
 170                     Err(_) => {}
 171                 }
 172                 self.require_break_cx("continue", e.span)
 173             },
 174             _ => intravisit::walk_expr(self, e),
 175         }
 176     }
 177 }
 178
 179 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 180     fn with_context<F>(&mut self, cx: Context, f: F)
 181         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 182     {
 183         let old_cx = self.cx;
 184         self.cx = cx;
 185         f(self);
 186         self.cx = old_cx;
 187     }
 188
 189     fn require_break_cx(&self, name: &str, span: Span) {
 190         match self.cx {
 191             LabeledBlock | Loop(_) => {}
 192             Closure => {
 193                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 194                 .span_label(span, "cannot break inside of a closure")
 195                 .emit();
 196             }
 197             Normal | AnonConst => {
 198                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 199                 .span_label(span, "cannot break outside of a loop")
 200                 .emit();
 201             }
 202         }
 203     }
 204
 205     fn require_label_in_labeled_block(&mut self, span: Span, label: &Destination, cf_type: &str)
 206         -> bool
 207     {
 208         if self.cx == LabeledBlock {
 209             if label.label.is_none() {
 210                 struct_span_err!(self.sess, span, E0695,
 211                                 "unlabeled `{}` inside of a labeled block", cf_type)
 212                     .span_label(span,
 213                                 format!("`{}` statements that would diverge to or through \
 214                                 a labeled block need to bear a label", cf_type))
 215                     .emit();
 216                 return true;
 217             }
 218         }
 219         return false;
 220     }
 221     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 222         struct_span_err!(self.sess, span, E0590,
 223                          "`break` or `continue` with no label in the condition of a `while` loop")
 224             .span_label(span,
 225                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 226             .emit();
 227     }
 228 }