compiler/rustc_passes/src/loops.rs

   1 use Context::*;
   2
   3 use rustc_errors::{struct_span_err, Applicability};
   4 use rustc_hir as hir;
   5 use rustc_hir::def_id::LocalDefId;
   6 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
   7 use rustc_hir::{Destination, Movability, Node};
   8 use rustc_middle::hir::map::Map;
   9 use rustc_middle::ty::query::Providers;
  10 use rustc_middle::ty::TyCtxt;
  11 use rustc_session::Session;
  12 use rustc_span::hygiene::DesugaringKind;
  13 use rustc_span::Span;
  14
  15 #[derive(Clone, Copy, Debug, PartialEq)]
  16 enum Context {
  17     Normal,
  18     Loop(hir::LoopSource),
  19     Closure(Span),
  20     AsyncClosure(Span),
  21     LabeledBlock,
  22     AnonConst,
  23 }
  24
  25 #[derive(Copy, Clone)]
  26 struct CheckLoopVisitor<'a, 'hir> {
  27     sess: &'a Session,
  28     hir_map: Map<'hir>,
  29     cx: Context,
  30 }
  31
  32 fn check_mod_loops(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
  33     tcx.hir().visit_item_likes_in_module(
  34         module_def_id,
  35         &mut CheckLoopVisitor { sess: &tcx.sess, hir_map: tcx.hir(), cx: Normal }.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(break_label, ref opt_expr) => {
  72                 if let Some(e) = opt_expr {
  73                     self.visit_expr(e);
  74                 }
  75
  76                 if self.require_label_in_labeled_block(e.span, &break_label, "break") {
  77                     // If we emitted an error about an unlabeled break in a labeled
  78                     // block, we don't need any further checking for this break any more
  79                     return;
  80                 }
  81
  82                 let loop_id = match break_label.target_id {
  83                     Ok(loop_id) => Some(loop_id),
  84                     Err(hir::LoopIdError::OutsideLoopScope) => None,
  85                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
  86                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
  87                         None
  88                     }
  89                     Err(hir::LoopIdError::UnresolvedLabel) => None,
  90                 };
  91
  92                 if let Some(Node::Block(_)) = loop_id.and_then(|id| self.hir_map.find(id)) {
  93                     return;
  94                 }
  95
  96                 if let Some(break_expr) = opt_expr {
  97                     let (head, loop_label, loop_kind) = if let Some(loop_id) = loop_id {
  98                         match self.hir_map.expect_expr(loop_id).kind {
  99                             hir::ExprKind::Loop(_, label, source, sp) => {
 100                                 (Some(sp), label, Some(source))
 101                             }
 102                             ref r => {
 103                                 span_bug!(e.span, "break label resolved to a non-loop: {:?}", r)
 104                             }
 105                         }
 106                     } else {
 107                         (None, None, None)
 108                     };
 109                     match loop_kind {
 110                         None | Some(hir::LoopSource::Loop) => (),
 111                         Some(kind) => {
 112                             let mut err = struct_span_err!(
 113                                 self.sess,
 114                                 e.span,
 115                                 E0571,
 116                                 "`break` with value from a `{}` loop",
 117                                 kind.name()
 118                             );
 119                             err.span_label(
 120                                 e.span,
 121                                 "can only break with a value inside `loop` or breakable block",
 122                             );
 123                             if let Some(head) = head {
 124                                 err.span_label(
 125                                     head,
 126                                     &format!(
 127                                         "you can't `break` with a value in a `{}` loop",
 128                                         kind.name()
 129                                     ),
 130                                 );
 131                             }
 132                             err.span_suggestion(
 133                                 e.span,
 134                                 &format!(
 135                                     "use `break` on its own without a value inside this `{}` loop",
 136                                     kind.name(),
 137                                 ),
 138                                 format!(
 139                                     "break{}",
 140                                     break_label
 141                                         .label
 142                                         .map_or_else(String::new, |l| format!(" {}", l.ident))
 143                                 ),
 144                                 Applicability::MaybeIncorrect,
 145                             );
 146                             if let (Some(label), None) = (loop_label, break_label.label) {
 147                                 match break_expr.kind {
 148                                     hir::ExprKind::Path(hir::QPath::Resolved(
 149                                         None,
 150                                         hir::Path {
 151                                             segments: [segment],
 152                                             res: hir::def::Res::Err,
 153                                             ..
 154                                         },
 155                                     )) if label.ident.to_string()
 156                                         == format!("'{}", segment.ident) =>
 157                                     {
 158                                         // This error is redundant, we will have already emitted a
 159                                         // suggestion to use the label when `segment` wasn't found
 160                                         // (hence the `Res::Err` check).
 161                                         err.delay_as_bug();
 162                                     }
 163                                     _ => {
 164                                         err.span_suggestion(
 165                                             break_expr.span,
 166                                             "alternatively, you might have meant to use the \
 167                                              available loop label",
 168                                             label.ident.to_string(),
 169                                             Applicability::MaybeIncorrect,
 170                                         );
 171                                     }
 172                                 }
 173                             }
 174                             err.emit();
 175                         }
 176                     }
 177                 }
 178
 179                 self.require_break_cx("break", e.span);
 180             }
 181             hir::ExprKind::Continue(destination) => {
 182                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 183
 184                 match destination.target_id {
 185                     Ok(loop_id) => {
 186                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 187                             struct_span_err!(
 188                                 self.sess,
 189                                 e.span,
 190                                 E0696,
 191                                 "`continue` pointing to a labeled block"
 192                             )
 193                             .span_label(e.span, "labeled blocks cannot be `continue`'d")
 194                             .span_label(block.span, "labeled block the `continue` points to")
 195                             .emit();
 196                         }
 197                     }
 198                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 199                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 200                     }
 201                     Err(_) => {}
 202                 }
 203                 self.require_break_cx("continue", e.span)
 204             }
 205             _ => intravisit::walk_expr(self, e),
 206         }
 207     }
 208 }
 209
 210 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 211     fn with_context<F>(&mut self, cx: Context, f: F)
 212     where
 213         F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>),
 214     {
 215         let old_cx = self.cx;
 216         self.cx = cx;
 217         f(self);
 218         self.cx = old_cx;
 219     }
 220
 221     fn require_break_cx(&self, name: &str, span: Span) {
 222         let err_inside_of = |article, ty, closure_span| {
 223             struct_span_err!(self.sess, span, E0267, "`{}` inside of {} {}", name, article, ty)
 224                 .span_label(span, format!("cannot `{}` inside of {} {}", name, article, ty))
 225                 .span_label(closure_span, &format!("enclosing {}", ty))
 226                 .emit();
 227         };
 228
 229         match self.cx {
 230             LabeledBlock | Loop(_) => {}
 231             Closure(closure_span) => err_inside_of("a", "closure", closure_span),
 232             AsyncClosure(closure_span) => err_inside_of("an", "`async` block", closure_span),
 233             Normal | AnonConst => {
 234                 struct_span_err!(self.sess, span, E0268, "`{}` outside of a loop", name)
 235                     .span_label(span, format!("cannot `{}` outside of a loop", name))
 236                     .emit();
 237             }
 238         }
 239     }
 240
 241     fn require_label_in_labeled_block(
 242         &mut self,
 243         span: Span,
 244         label: &Destination,
 245         cf_type: &str,
 246     ) -> bool {
 247         if !span.is_desugaring(DesugaringKind::QuestionMark) && self.cx == LabeledBlock {
 248             if label.label.is_none() {
 249                 struct_span_err!(
 250                     self.sess,
 251                     span,
 252                     E0695,
 253                     "unlabeled `{}` inside of a labeled block",
 254                     cf_type
 255                 )
 256                 .span_label(
 257                     span,
 258                     format!(
 259                         "`{}` statements that would diverge to or through \
 260                                 a labeled block need to bear a label",
 261                         cf_type
 262                     ),
 263                 )
 264                 .emit();
 265                 return true;
 266             }
 267         }
 268         false
 269     }
 270     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 271         struct_span_err!(
 272             self.sess,
 273             span,
 274             E0590,
 275             "`break` or `continue` with no label in the condition of a `while` loop"
 276         )
 277         .span_label(span, format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 278         .emit();
 279     }
 280 }