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 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  49     for &module in tcx.hir().krate().modules.keys() {
  50         tcx.ensure().check_mod_loops(tcx.hir().local_def_id(module));
  51     }
  52 }
  53
  54 fn check_mod_loops<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>, module_def_id: DefId) {
  55     tcx.hir().visit_item_likes_in_module(module_def_id, &mut CheckLoopVisitor {
  56         sess: &tcx.sess,
  57         hir_map: &tcx.hir(),
  58         cx: Normal,
  59     }.as_deep_visitor());
  60 }
  61
  62 pub(crate) fn provide(providers: &mut Providers<'_>) {
  63     *providers = Providers {
  64         check_mod_loops,
  65         ..*providers
  66     };
  67 }
  68
  69 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  70     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  71         NestedVisitorMap::OnlyBodies(&self.hir_map)
  72     }
  73
  74     fn visit_anon_const(&mut self, c: &'hir hir::AnonConst) {
  75         self.with_context(AnonConst, |v| intravisit::walk_anon_const(v, c));
  76     }
  77
  78     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  79         match e.node {
  80             hir::ExprKind::While(ref e, ref b, _) => {
  81                 self.with_context(Loop(LoopKind::WhileLoop), |v| {
  82                     v.visit_expr(&e);
  83                     v.visit_block(&b);
  84                 });
  85             }
  86             hir::ExprKind::Loop(ref b, _, source) => {
  87                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
  88             }
  89             hir::ExprKind::Closure(_, ref function_decl, b, _, _) => {
  90                 self.visit_fn_decl(&function_decl);
  91                 self.with_context(Closure, |v| v.visit_nested_body(b));
  92             }
  93             hir::ExprKind::Block(ref b, Some(_label)) => {
  94                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  95             }
  96             hir::ExprKind::Break(label, ref opt_expr) => {
  97                 opt_expr.as_ref().map(|e| self.visit_expr(e));
  98
  99                 if self.require_label_in_labeled_block(e.span, &label, "break") {
 100                     // If we emitted an error about an unlabeled break in a labeled
 101                     // block, we don't need any further checking for this break any more
 102                     return;
 103                 }
 104
 105                 let loop_id = match label.target_id.into() {
 106                     Ok(loop_id) => loop_id,
 107                     Err(hir::LoopIdError::OutsideLoopScope) => hir::DUMMY_HIR_ID,
 108                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 109                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
 110                         hir::DUMMY_HIR_ID
 111                     },
 112                     Err(hir::LoopIdError::UnresolvedLabel) => hir::DUMMY_HIR_ID,
 113                 };
 114
 115                 if loop_id != hir::DUMMY_HIR_ID {
 116                     if let Node::Block(_) = self.hir_map.find_by_hir_id(loop_id).unwrap() {
 117                         return
 118                     }
 119                 }
 120
 121                 if opt_expr.is_some() {
 122                     let loop_kind = if loop_id == hir::DUMMY_HIR_ID {
 123                         None
 124                     } else {
 125                         Some(match self.hir_map.expect_expr_by_hir_id(loop_id).node {
 126                             hir::ExprKind::While(..) => LoopKind::WhileLoop,
 127                             hir::ExprKind::Loop(_, _, source) => LoopKind::Loop(source),
 128                             ref r => span_bug!(e.span,
 129                                                "break label resolved to a non-loop: {:?}", r),
 130                         })
 131                     };
 132                     match loop_kind {
 133                         None |
 134                         Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
 135                         Some(kind) => {
 136                             struct_span_err!(self.sess, e.span, E0571,
 137                                              "`break` with value from a `{}` loop",
 138                                              kind.name())
 139                                 .span_label(e.span,
 140                                             "can only break with a value inside \
 141                                             `loop` or breakable block")
 142                                 .span_suggestion(
 143                                     e.span,
 144                                     &format!(
 145                                         "instead, use `break` on its own \
 146                                         without a value inside this `{}` loop",
 147                                         kind.name()
 148                                     ),
 149                                     "break".to_string(),
 150                                     Applicability::MaybeIncorrect,
 151                                 )
 152                                 .emit();
 153                         }
 154                     }
 155                 }
 156
 157                 self.require_break_cx("break", e.span);
 158             }
 159             hir::ExprKind::Continue(destination) => {
 160                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 161
 162                 match destination.target_id {
 163                     Ok(loop_id) => {
 164                         if let Node::Block(block) = self.hir_map.find_by_hir_id(loop_id).unwrap() {
 165                             struct_span_err!(self.sess, e.span, E0696,
 166                                             "`continue` pointing to a labeled block")
 167                                 .span_label(e.span,
 168                                             "labeled blocks cannot be `continue`'d")
 169                                 .span_note(block.span,
 170                                             "labeled block the continue points to")
 171                                 .emit();
 172                         }
 173                     }
 174                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 175                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 176                     }
 177                     Err(_) => {}
 178                 }
 179                 self.require_break_cx("continue", e.span)
 180             },
 181             _ => intravisit::walk_expr(self, e),
 182         }
 183     }
 184 }
 185
 186 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 187     fn with_context<F>(&mut self, cx: Context, f: F)
 188         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 189     {
 190         let old_cx = self.cx;
 191         self.cx = cx;
 192         f(self);
 193         self.cx = old_cx;
 194     }
 195
 196     fn require_break_cx(&self, name: &str, span: Span) {
 197         match self.cx {
 198             LabeledBlock | Loop(_) => {}
 199             Closure => {
 200                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 201                 .span_label(span, "cannot break inside of a closure")
 202                 .emit();
 203             }
 204             Normal | AnonConst => {
 205                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 206                 .span_label(span, "cannot break outside of a loop")
 207                 .emit();
 208             }
 209         }
 210     }
 211
 212     fn require_label_in_labeled_block(&mut self, span: Span, label: &Destination, cf_type: &str)
 213         -> bool
 214     {
 215         if self.cx == LabeledBlock {
 216             if label.label.is_none() {
 217                 struct_span_err!(self.sess, span, E0695,
 218                                 "unlabeled `{}` inside of a labeled block", cf_type)
 219                     .span_label(span,
 220                                 format!("`{}` statements that would diverge to or through \
 221                                 a labeled block need to bear a label", cf_type))
 222                     .emit();
 223                 return true;
 224             }
 225         }
 226         return false;
 227     }
 228     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 229         struct_span_err!(self.sess, span, E0590,
 230                          "`break` or `continue` with no label in the condition of a `while` loop")
 231             .span_label(span,
 232                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 233             .emit();
 234     }
 235 }