src/librustc_passes/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(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, &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 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(loop_id) = loop_id {
  93                     if let Node::Block(_) = self.hir_map.find(loop_id).unwrap() {
  94                         return;
  95                     }
  96                 }
  97
  98                 if opt_expr.is_some() {
  99                     let loop_kind = if let Some(loop_id) = loop_id {
 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                     } else {
 107                         None
 108                     };
 109                     match loop_kind {
 110                         None | Some(hir::LoopSource::Loop) => (),
 111                         Some(kind) => {
 112                             struct_span_err!(
 113                                 self.sess,
 114                                 e.span,
 115                                 E0571,
 116                                 "`break` with value from a `{}` loop",
 117                                 kind.name()
 118                             )
 119                             .span_label(
 120                                 e.span,
 121                                 "can only break with a value inside \
 122                                             `loop` or breakable block",
 123                             )
 124                             .span_suggestion(
 125                                 e.span,
 126                                 &format!(
 127                                     "instead, use `break` on its own \
 128                                         without a value inside this `{}` loop",
 129                                     kind.name()
 130                                 ),
 131                                 "break".to_string(),
 132                                 Applicability::MaybeIncorrect,
 133                             )
 134                             .emit();
 135                         }
 136                     }
 137                 }
 138
 139                 self.require_break_cx("break", e.span);
 140             }
 141             hir::ExprKind::Continue(destination) => {
 142                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 143
 144                 match destination.target_id {
 145                     Ok(loop_id) => {
 146                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 147                             struct_span_err!(
 148                                 self.sess,
 149                                 e.span,
 150                                 E0696,
 151                                 "`continue` pointing to a labeled block"
 152                             )
 153                             .span_label(e.span, "labeled blocks cannot be `continue`'d")
 154                             .span_label(block.span, "labeled block the `continue` points to")
 155                             .emit();
 156                         }
 157                     }
 158                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 159                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 160                     }
 161                     Err(_) => {}
 162                 }
 163                 self.require_break_cx("continue", e.span)
 164             }
 165             _ => intravisit::walk_expr(self, e),
 166         }
 167     }
 168 }
 169
 170 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 171     fn with_context<F>(&mut self, cx: Context, f: F)
 172     where
 173         F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>),
 174     {
 175         let old_cx = self.cx;
 176         self.cx = cx;
 177         f(self);
 178         self.cx = old_cx;
 179     }
 180
 181     fn require_break_cx(&self, name: &str, span: Span) {
 182         let err_inside_of = |article, ty, closure_span| {
 183             struct_span_err!(self.sess, span, E0267, "`{}` inside of {} {}", name, article, ty)
 184                 .span_label(span, format!("cannot `{}` inside of {} {}", name, article, ty))
 185                 .span_label(closure_span, &format!("enclosing {}", ty))
 186                 .emit();
 187         };
 188
 189         match self.cx {
 190             LabeledBlock | Loop(_) => {}
 191             Closure(closure_span) => err_inside_of("a", "closure", closure_span),
 192             AsyncClosure(closure_span) => err_inside_of("an", "`async` block", closure_span),
 193             Normal | AnonConst => {
 194                 struct_span_err!(self.sess, span, E0268, "`{}` outside of a loop", name)
 195                     .span_label(span, format!("cannot `{}` outside of a loop", name))
 196                     .emit();
 197             }
 198         }
 199     }
 200
 201     fn require_label_in_labeled_block(
 202         &mut self,
 203         span: Span,
 204         label: &Destination,
 205         cf_type: &str,
 206     ) -> bool {
 207         if !span.is_desugaring(DesugaringKind::QuestionMark) && self.cx == LabeledBlock {
 208             if label.label.is_none() {
 209                 struct_span_err!(
 210                     self.sess,
 211                     span,
 212                     E0695,
 213                     "unlabeled `{}` inside of a labeled block",
 214                     cf_type
 215                 )
 216                 .span_label(
 217                     span,
 218                     format!(
 219                         "`{}` statements that would diverge to or through \
 220                                 a labeled block need to bear a label",
 221                         cf_type
 222                     ),
 223                 )
 224                 .emit();
 225                 return true;
 226             }
 227         }
 228         false
 229     }
 230     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 231         struct_span_err!(
 232             self.sess,
 233             span,
 234             E0590,
 235             "`break` or `continue` with no label in the condition of a `while` loop"
 236         )
 237         .span_label(span, format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 238         .emit();
 239     }
 240 }