src/librustc_passes/loops.rs

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