src/librustc_passes/loops.rs

   1 use Context::*;
   2
   3 use rustc::session::Session;
   4
   5 use rustc::ty::query::Providers;
   6 use rustc::ty::TyCtxt;
   7 use rustc::hir::def_id::DefId;
   8 use rustc::hir::map::Map;
   9 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  10 use rustc::hir::{self, Node, Destination};
  11 use syntax::struct_span_err;
  12 use syntax_pos::Span;
  13 use errors::Applicability;
  14
  15 #[derive(Clone, Copy, Debug, PartialEq)]
  16 enum LoopKind {
  17     Loop(hir::LoopSource),
  18     WhileLoop,
  19 }
  20
  21 impl LoopKind {
  22     fn name(self) -> &'static str {
  23         match self {
  24             LoopKind::Loop(hir::LoopSource::Loop) => "loop",
  25             LoopKind::Loop(hir::LoopSource::WhileLet) => "while let",
  26             LoopKind::Loop(hir::LoopSource::ForLoop) => "for",
  27             LoopKind::WhileLoop => "while",
  28         }
  29     }
  30 }
  31
  32 #[derive(Clone, Copy, Debug, PartialEq)]
  33 enum Context {
  34     Normal,
  35     Loop(LoopKind),
  36     Closure,
  37     LabeledBlock,
  38     AnonConst,
  39 }
  40
  41 #[derive(Copy, Clone)]
  42 struct CheckLoopVisitor<'a, 'hir: 'a> {
  43     sess: &'a Session,
  44     hir_map: &'a Map<'hir>,
  45     cx: Context,
  46 }
  47
  48 fn check_mod_loops<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>, module_def_id: DefId) {
  49     tcx.hir().visit_item_likes_in_module(module_def_id, &mut CheckLoopVisitor {
  50         sess: &tcx.sess,
  51         hir_map: &tcx.hir(),
  52         cx: Normal,
  53     }.as_deep_visitor());
  54 }
  55
  56 pub(crate) fn provide(providers: &mut Providers<'_>) {
  57     *providers = Providers {
  58         check_mod_loops,
  59         ..*providers
  60     };
  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_anon_const(&mut self, c: &'hir hir::AnonConst) {
  69         self.with_context(AnonConst, |v| intravisit::walk_anon_const(v, c));
  70     }
  71
  72     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  73         match e.node {
  74             hir::ExprKind::While(ref e, ref b, _) => {
  75                 self.with_context(Loop(LoopKind::WhileLoop), |v| {
  76                     v.visit_expr(&e);
  77                     v.visit_block(&b);
  78                 });
  79             }
  80             hir::ExprKind::Loop(ref b, _, source) => {
  81                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
  82             }
  83             hir::ExprKind::Closure(_, ref function_decl, b, _, _) => {
  84                 self.visit_fn_decl(&function_decl);
  85                 self.with_context(Closure, |v| v.visit_nested_body(b));
  86             }
  87             hir::ExprKind::Block(ref b, Some(_label)) => {
  88                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  89             }
  90             hir::ExprKind::Break(label, ref opt_expr) => {
  91                 opt_expr.as_ref().map(|e| self.visit_expr(e));
  92
  93                 if self.require_label_in_labeled_block(e.span, &label, "break") {
  94                     // If we emitted an error about an unlabeled break in a labeled
  95                     // block, we don't need any further checking for this break any more
  96                     return;
  97                 }
  98
  99                 let loop_id = match label.target_id.into() {
 100                     Ok(loop_id) => loop_id,
 101                     Err(hir::LoopIdError::OutsideLoopScope) => hir::DUMMY_HIR_ID,
 102                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 103                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
 104                         hir::DUMMY_HIR_ID
 105                     },
 106                     Err(hir::LoopIdError::UnresolvedLabel) => hir::DUMMY_HIR_ID,
 107                 };
 108
 109                 if loop_id != hir::DUMMY_HIR_ID {
 110                     if let Node::Block(_) = self.hir_map.find_by_hir_id(loop_id).unwrap() {
 111                         return
 112                     }
 113                 }
 114
 115                 if opt_expr.is_some() {
 116                     let loop_kind = if loop_id == hir::DUMMY_HIR_ID {
 117                         None
 118                     } else {
 119                         Some(match self.hir_map.expect_expr_by_hir_id(loop_id).node {
 120                             hir::ExprKind::While(..) => LoopKind::WhileLoop,
 121                             hir::ExprKind::Loop(_, _, source) => LoopKind::Loop(source),
 122                             ref r => span_bug!(e.span,
 123                                                "break label resolved to a non-loop: {:?}", r),
 124                         })
 125                     };
 126                     match loop_kind {
 127                         None |
 128                         Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
 129                         Some(kind) => {
 130                             struct_span_err!(self.sess, e.span, E0571,
 131                                              "`break` with value from a `{}` loop",
 132                                              kind.name())
 133                                 .span_label(e.span,
 134                                             "can only break with a value inside \
 135                                             `loop` or breakable block")
 136                                 .span_suggestion(
 137                                     e.span,
 138                                     &format!(
 139                                         "instead, use `break` on its own \
 140                                         without a value inside this `{}` loop",
 141                                         kind.name()
 142                                     ),
 143                                     "break".to_string(),
 144                                     Applicability::MaybeIncorrect,
 145                                 )
 146                                 .emit();
 147                         }
 148                     }
 149                 }
 150
 151                 self.require_break_cx("break", e.span);
 152             }
 153             hir::ExprKind::Continue(destination) => {
 154                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 155
 156                 match destination.target_id {
 157                     Ok(loop_id) => {
 158                         if let Node::Block(block) = self.hir_map.find_by_hir_id(loop_id).unwrap() {
 159                             struct_span_err!(self.sess, e.span, E0696,
 160                                             "`continue` pointing to a labeled block")
 161                                 .span_label(e.span,
 162                                             "labeled blocks cannot be `continue`'d")
 163                                 .span_note(block.span,
 164                                             "labeled block the continue points to")
 165                                 .emit();
 166                         }
 167                     }
 168                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 169                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 170                     }
 171                     Err(_) => {}
 172                 }
 173                 self.require_break_cx("continue", e.span)
 174             },
 175             _ => intravisit::walk_expr(self, e),
 176         }
 177     }
 178 }
 179
 180 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 181     fn with_context<F>(&mut self, cx: Context, f: F)
 182         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 183     {
 184         let old_cx = self.cx;
 185         self.cx = cx;
 186         f(self);
 187         self.cx = old_cx;
 188     }
 189
 190     fn require_break_cx(&self, name: &str, span: Span) {
 191         match self.cx {
 192             LabeledBlock | Loop(_) => {}
 193             Closure => {
 194                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 195                 .span_label(span, "cannot break inside of a closure")
 196                 .emit();
 197             }
 198             Normal | AnonConst => {
 199                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 200                 .span_label(span, "cannot break outside of a loop")
 201                 .emit();
 202             }
 203         }
 204     }
 205
 206     fn require_label_in_labeled_block(&mut self, span: Span, label: &Destination, cf_type: &str)
 207         -> bool
 208     {
 209         if self.cx == LabeledBlock {
 210             if label.label.is_none() {
 211                 struct_span_err!(self.sess, span, E0695,
 212                                 "unlabeled `{}` inside of a labeled block", cf_type)
 213                     .span_label(span,
 214                                 format!("`{}` statements that would diverge to or through \
 215                                 a labeled block need to bear a label", cf_type))
 216                     .emit();
 217                 return true;
 218             }
 219         }
 220         return false;
 221     }
 222     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 223         struct_span_err!(self.sess, span, E0590,
 224                          "`break` or `continue` with no label in the condition of a `while` loop")
 225             .span_label(span,
 226                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 227             .emit();
 228     }
 229 }