src/librustc_passes/loops.rs

   1 use Context::*;
   2
   3 use rustc::session::Session;
   4
   5 use rustc::hir::map::Map;
   6 use rustc::ty::query::Providers;
   7 use rustc::ty::TyCtxt;
   8 use rustc_errors::{struct_span_err, Applicability};
   9 use rustc_hir as hir;
  10 use rustc_hir::def_id::DefId;
  11 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  12 use rustc_hir::{Destination, Movability, Node};
  13 use rustc_span::Span;
  14
  15 use rustc_error_codes::*;
  16
  17 #[derive(Clone, Copy, Debug, PartialEq)]
  18 enum Context {
  19     Normal,
  20     Loop(hir::LoopSource),
  21     Closure(Span),
  22     AsyncClosure(Span),
  23     LabeledBlock,
  24     AnonConst,
  25 }
  26
  27 #[derive(Copy, Clone)]
  28 struct CheckLoopVisitor<'a, 'hir> {
  29     sess: &'a Session,
  30     hir_map: &'a Map<'hir>,
  31     cx: Context,
  32 }
  33
  34 fn check_mod_loops(tcx: TyCtxt<'_>, module_def_id: DefId) {
  35     tcx.hir().visit_item_likes_in_module(
  36         module_def_id,
  37         &mut CheckLoopVisitor { sess: &tcx.sess, hir_map: &tcx.hir(), cx: Normal }
  38             .as_deep_visitor(),
  39     );
  40 }
  41
  42 pub(crate) fn provide(providers: &mut Providers<'_>) {
  43     *providers = Providers { check_mod_loops, ..*providers };
  44 }
  45
  46 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  47     type Map = Map<'hir>;
  48
  49     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
  50         NestedVisitorMap::OnlyBodies(&self.hir_map)
  51     }
  52
  53     fn visit_anon_const(&mut self, c: &'hir hir::AnonConst) {
  54         self.with_context(AnonConst, |v| intravisit::walk_anon_const(v, c));
  55     }
  56
  57     fn visit_expr(&mut self, e: &'hir hir::Expr<'hir>) {
  58         match e.kind {
  59             hir::ExprKind::Loop(ref b, _, source) => {
  60                 self.with_context(Loop(source), |v| v.visit_block(&b));
  61             }
  62             hir::ExprKind::Closure(_, ref function_decl, b, span, movability) => {
  63                 let cx = if let Some(Movability::Static) = movability {
  64                     AsyncClosure(span)
  65                 } else {
  66                     Closure(span)
  67                 };
  68                 self.visit_fn_decl(&function_decl);
  69                 self.with_context(cx, |v| v.visit_nested_body(b));
  70             }
  71             hir::ExprKind::Block(ref b, Some(_label)) => {
  72                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  73             }
  74             hir::ExprKind::Break(label, ref opt_expr) => {
  75                 opt_expr.as_ref().map(|e| self.visit_expr(e));
  76
  77                 if self.require_label_in_labeled_block(e.span, &label, "break") {
  78                     // If we emitted an error about an unlabeled break in a labeled
  79                     // block, we don't need any further checking for this break any more
  80                     return;
  81                 }
  82
  83                 let loop_id = match label.target_id.into() {
  84                     Ok(loop_id) => loop_id,
  85                     Err(hir::LoopIdError::OutsideLoopScope) => hir::DUMMY_HIR_ID,
  86                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
  87                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
  88                         hir::DUMMY_HIR_ID
  89                     }
  90                     Err(hir::LoopIdError::UnresolvedLabel) => hir::DUMMY_HIR_ID,
  91                 };
  92
  93                 if loop_id != hir::DUMMY_HIR_ID {
  94                     if let Node::Block(_) = self.hir_map.find(loop_id).unwrap() {
  95                         return;
  96                     }
  97                 }
  98
  99                 if opt_expr.is_some() {
 100                     let loop_kind = if loop_id == hir::DUMMY_HIR_ID {
 101                         None
 102                     } else {
 103                         Some(match self.hir_map.expect_expr(loop_id).kind {
 104                             hir::ExprKind::Loop(_, _, source) => source,
 105                             ref r => {
 106                                 span_bug!(e.span, "break label resolved to a non-loop: {:?}", r)
 107                             }
 108                         })
 109                     };
 110                     match loop_kind {
 111                         None | Some(hir::LoopSource::Loop) => (),
 112                         Some(kind) => {
 113                             struct_span_err!(
 114                                 self.sess,
 115                                 e.span,
 116                                 E0571,
 117                                 "`break` with value from a `{}` loop",
 118                                 kind.name()
 119                             )
 120                             .span_label(
 121                                 e.span,
 122                                 "can only break with a value inside \
 123                                             `loop` or breakable block",
 124                             )
 125                             .span_suggestion(
 126                                 e.span,
 127                                 &format!(
 128                                     "instead, use `break` on its own \
 129                                         without a value inside this `{}` loop",
 130                                     kind.name()
 131                                 ),
 132                                 "break".to_string(),
 133                                 Applicability::MaybeIncorrect,
 134                             )
 135                             .emit();
 136                         }
 137                     }
 138                 }
 139
 140                 self.require_break_cx("break", e.span);
 141             }
 142             hir::ExprKind::Continue(destination) => {
 143                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 144
 145                 match destination.target_id {
 146                     Ok(loop_id) => {
 147                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 148                             struct_span_err!(
 149                                 self.sess,
 150                                 e.span,
 151                                 E0696,
 152                                 "`continue` pointing to a labeled block"
 153                             )
 154                             .span_label(e.span, "labeled blocks cannot be `continue`'d")
 155                             .span_label(block.span, "labeled block the `continue` points to")
 156                             .emit();
 157                         }
 158                     }
 159                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 160                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 161                     }
 162                     Err(_) => {}
 163                 }
 164                 self.require_break_cx("continue", e.span)
 165             }
 166             _ => intravisit::walk_expr(self, e),
 167         }
 168     }
 169 }
 170
 171 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 172     fn with_context<F>(&mut self, cx: Context, f: F)
 173     where
 174         F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>),
 175     {
 176         let old_cx = self.cx;
 177         self.cx = cx;
 178         f(self);
 179         self.cx = old_cx;
 180     }
 181
 182     fn require_break_cx(&self, name: &str, span: Span) {
 183         let err_inside_of = |article, ty, closure_span| {
 184             struct_span_err!(self.sess, span, E0267, "`{}` inside of {} {}", name, article, ty)
 185                 .span_label(span, format!("cannot `{}` inside of {} {}", name, article, ty))
 186                 .span_label(closure_span, &format!("enclosing {}", ty))
 187                 .emit();
 188         };
 189
 190         match self.cx {
 191             LabeledBlock | Loop(_) => {}
 192             Closure(closure_span) => err_inside_of("a", "closure", closure_span),
 193             AsyncClosure(closure_span) => err_inside_of("an", "`async` block", closure_span),
 194             Normal | AnonConst => {
 195                 struct_span_err!(self.sess, span, E0268, "`{}` outside of a loop", name)
 196                     .span_label(span, format!("cannot `{}` outside of a loop", name))
 197                     .emit();
 198             }
 199         }
 200     }
 201
 202     fn require_label_in_labeled_block(
 203         &mut self,
 204         span: Span,
 205         label: &Destination,
 206         cf_type: &str,
 207     ) -> bool {
 208         if self.cx == LabeledBlock {
 209             if label.label.is_none() {
 210                 struct_span_err!(
 211                     self.sess,
 212                     span,
 213                     E0695,
 214                     "unlabeled `{}` inside of a labeled block",
 215                     cf_type
 216                 )
 217                 .span_label(
 218                     span,
 219                     format!(
 220                         "`{}` statements that would diverge to or through \
 221                                 a labeled block need to bear a label",
 222                         cf_type
 223                     ),
 224                 )
 225                 .emit();
 226                 return true;
 227             }
 228         }
 229         return false;
 230     }
 231     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 232         struct_span_err!(
 233             self.sess,
 234             span,
 235             E0590,
 236             "`break` or `continue` with no label in the condition of a `while` loop"
 237         )
 238         .span_label(span, format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 239         .emit();
 240     }
 241 }