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