src/librustc_passes/loops.rs

   1 use Context::*;
   2
   3 use rustc::hir::map::Map;
   4 use rustc::ty::query::Providers;
   5 use rustc::ty::TyCtxt;
   6 use rustc_errors::{struct_span_err, Applicability};
   7 use rustc_hir as hir;
   8 use rustc_hir::def_id::DefId;
   9 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  10 use rustc_hir::{Destination, Movability, Node};
  11 use rustc_session::Session;
  12 use rustc_span::Span;
  13
  14 #[derive(Clone, Copy, Debug, PartialEq)]
  15 enum Context {
  16     Normal,
  17     Loop(hir::LoopSource),
  18     Closure(Span),
  19     AsyncClosure(Span),
  20     LabeledBlock,
  21     AnonConst,
  22 }
  23
  24 #[derive(Copy, Clone)]
  25 struct CheckLoopVisitor<'a, 'hir> {
  26     sess: &'a Session,
  27     hir_map: &'a Map<'hir>,
  28     cx: Context,
  29 }
  30
  31 fn check_mod_loops(tcx: TyCtxt<'_>, module_def_id: DefId) {
  32     tcx.hir().visit_item_likes_in_module(
  33         module_def_id,
  34         &mut CheckLoopVisitor { sess: &tcx.sess, hir_map: &tcx.hir(), cx: Normal }
  35             .as_deep_visitor(),
  36     );
  37 }
  38
  39 pub(crate) fn provide(providers: &mut Providers<'_>) {
  40     *providers = Providers { check_mod_loops, ..*providers };
  41 }
  42
  43 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  44     type Map = Map<'hir>;
  45
  46     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
  47         NestedVisitorMap::OnlyBodies(&self.hir_map)
  48     }
  49
  50     fn visit_anon_const(&mut self, c: &'hir hir::AnonConst) {
  51         self.with_context(AnonConst, |v| intravisit::walk_anon_const(v, c));
  52     }
  53
  54     fn visit_expr(&mut self, e: &'hir hir::Expr<'hir>) {
  55         match e.kind {
  56             hir::ExprKind::Loop(ref b, _, source) => {
  57                 self.with_context(Loop(source), |v| v.visit_block(&b));
  58             }
  59             hir::ExprKind::Closure(_, ref function_decl, b, span, movability) => {
  60                 let cx = if let Some(Movability::Static) = movability {
  61                     AsyncClosure(span)
  62                 } else {
  63                     Closure(span)
  64                 };
  65                 self.visit_fn_decl(&function_decl);
  66                 self.with_context(cx, |v| v.visit_nested_body(b));
  67             }
  68             hir::ExprKind::Block(ref b, Some(_label)) => {
  69                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  70             }
  71             hir::ExprKind::Break(label, ref opt_expr) => {
  72                 opt_expr.as_ref().map(|e| self.visit_expr(e));
  73
  74                 if self.require_label_in_labeled_block(e.span, &label, "break") {
  75                     // If we emitted an error about an unlabeled break in a labeled
  76                     // block, we don't need any further checking for this break any more
  77                     return;
  78                 }
  79
  80                 let loop_id = match label.target_id.into() {
  81                     Ok(loop_id) => loop_id,
  82                     Err(hir::LoopIdError::OutsideLoopScope) => hir::DUMMY_HIR_ID,
  83                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
  84                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
  85                         hir::DUMMY_HIR_ID
  86                     }
  87                     Err(hir::LoopIdError::UnresolvedLabel) => hir::DUMMY_HIR_ID,
  88                 };
  89
  90                 if loop_id != hir::DUMMY_HIR_ID {
  91                     if let Node::Block(_) = self.hir_map.find(loop_id).unwrap() {
  92                         return;
  93                     }
  94                 }
  95
  96                 if opt_expr.is_some() {
  97                     let loop_kind = if loop_id == hir::DUMMY_HIR_ID {
  98                         None
  99                     } else {
 100                         Some(match self.hir_map.expect_expr(loop_id).kind {
 101                             hir::ExprKind::Loop(_, _, source) => source,
 102                             ref r => {
 103                                 span_bug!(e.span, "break label resolved to a non-loop: {:?}", r)
 104                             }
 105                         })
 106                     };
 107                     match loop_kind {
 108                         None | Some(hir::LoopSource::Loop) => (),
 109                         Some(kind) => {
 110                             struct_span_err!(
 111                                 self.sess,
 112                                 e.span,
 113                                 E0571,
 114                                 "`break` with value from a `{}` loop",
 115                                 kind.name()
 116                             )
 117                             .span_label(
 118                                 e.span,
 119                                 "can only break with a value inside \
 120                                             `loop` or breakable block",
 121                             )
 122                             .span_suggestion(
 123                                 e.span,
 124                                 &format!(
 125                                     "instead, use `break` on its own \
 126                                         without a value inside this `{}` loop",
 127                                     kind.name()
 128                                 ),
 129                                 "break".to_string(),
 130                                 Applicability::MaybeIncorrect,
 131                             )
 132                             .emit();
 133                         }
 134                     }
 135                 }
 136
 137                 self.require_break_cx("break", e.span);
 138             }
 139             hir::ExprKind::Continue(destination) => {
 140                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 141
 142                 match destination.target_id {
 143                     Ok(loop_id) => {
 144                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 145                             struct_span_err!(
 146                                 self.sess,
 147                                 e.span,
 148                                 E0696,
 149                                 "`continue` pointing to a labeled block"
 150                             )
 151                             .span_label(e.span, "labeled blocks cannot be `continue`'d")
 152                             .span_label(block.span, "labeled block the `continue` points to")
 153                             .emit();
 154                         }
 155                     }
 156                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 157                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 158                     }
 159                     Err(_) => {}
 160                 }
 161                 self.require_break_cx("continue", e.span)
 162             }
 163             _ => intravisit::walk_expr(self, e),
 164         }
 165     }
 166 }
 167
 168 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 169     fn with_context<F>(&mut self, cx: Context, f: F)
 170     where
 171         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         let err_inside_of = |article, ty, closure_span| {
 181             struct_span_err!(self.sess, span, E0267, "`{}` inside of {} {}", name, article, ty)
 182                 .span_label(span, format!("cannot `{}` inside of {} {}", name, article, ty))
 183                 .span_label(closure_span, &format!("enclosing {}", ty))
 184                 .emit();
 185         };
 186
 187         match self.cx {
 188             LabeledBlock | Loop(_) => {}
 189             Closure(closure_span) => err_inside_of("a", "closure", closure_span),
 190             AsyncClosure(closure_span) => err_inside_of("an", "`async` block", closure_span),
 191             Normal | AnonConst => {
 192                 struct_span_err!(self.sess, span, E0268, "`{}` outside of a loop", name)
 193                     .span_label(span, format!("cannot `{}` outside of a loop", name))
 194                     .emit();
 195             }
 196         }
 197     }
 198
 199     fn require_label_in_labeled_block(
 200         &mut self,
 201         span: Span,
 202         label: &Destination,
 203         cf_type: &str,
 204     ) -> bool {
 205         if self.cx == LabeledBlock {
 206             if label.label.is_none() {
 207                 struct_span_err!(
 208                     self.sess,
 209                     span,
 210                     E0695,
 211                     "unlabeled `{}` inside of a labeled block",
 212                     cf_type
 213                 )
 214                 .span_label(
 215                     span,
 216                     format!(
 217                         "`{}` statements that would diverge to or through \
 218                                 a labeled block need to bear a label",
 219                         cf_type
 220                     ),
 221                 )
 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!(
 230             self.sess,
 231             span,
 232             E0590,
 233             "`break` or `continue` with no label in the condition of a `while` loop"
 234         )
 235         .span_label(span, format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 236         .emit();
 237     }
 238 }