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, GeneratorMovability};
  11 use syntax::struct_span_err;
  12 use syntax_pos::Span;
  13 use errors::Applicability;
  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: &'a Map<'hir>,
  29     cx: Context,
  30 }
  31
  32 fn check_mod_loops(tcx: TyCtxt<'_>, module_def_id: DefId) {
  33     tcx.hir().visit_item_likes_in_module(module_def_id, &mut CheckLoopVisitor {
  34         sess: &tcx.sess,
  35         hir_map: &tcx.hir(),
  36         cx: Normal,
  37     }.as_deep_visitor());
  38 }
  39
  40 pub(crate) fn provide(providers: &mut Providers<'_>) {
  41     *providers = Providers {
  42         check_mod_loops,
  43         ..*providers
  44     };
  45 }
  46
  47 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  48     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  49         NestedVisitorMap::OnlyBodies(&self.hir_map)
  50     }
  51
  52     fn visit_anon_const(&mut self, c: &'hir hir::AnonConst) {
  53         self.with_context(AnonConst, |v| intravisit::walk_anon_const(v, c));
  54     }
  55
  56     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  57         match e.kind {
  58             hir::ExprKind::Loop(ref b, _, source) => {
  59                 self.with_context(Loop(source), |v| v.visit_block(&b));
  60             }
  61             hir::ExprKind::Closure(_, ref function_decl, b, span, movability) => {
  62                 let cx = if let Some(GeneratorMovability::Static) = movability {
  63                     AsyncClosure(span)
  64                 } else {
  65                     Closure(span)
  66                 };
  67                 self.visit_fn_decl(&function_decl);
  68                 self.with_context(cx, |v| v.visit_nested_body(b));
  69             }
  70             hir::ExprKind::Block(ref b, Some(_label)) => {
  71                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  72             }
  73             hir::ExprKind::Break(label, ref opt_expr) => {
  74                 opt_expr.as_ref().map(|e| self.visit_expr(e));
  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.into() {
  83                     Ok(loop_id) => loop_id,
  84                     Err(hir::LoopIdError::OutsideLoopScope) => hir::DUMMY_HIR_ID,
  85                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
  86                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
  87                         hir::DUMMY_HIR_ID
  88                     },
  89                     Err(hir::LoopIdError::UnresolvedLabel) => hir::DUMMY_HIR_ID,
  90                 };
  91
  92                 if loop_id != hir::DUMMY_HIR_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 loop_id == hir::DUMMY_HIR_ID {
 100                         None
 101                     } else {
 102                         Some(match self.hir_map.expect_expr(loop_id).kind {
 103                             hir::ExprKind::Loop(_, _, source) => source,
 104                             ref r => span_bug!(e.span,
 105                                                "break label resolved to a non-loop: {:?}", r),
 106                         })
 107                     };
 108                     match loop_kind {
 109                         None |
 110                         Some(hir::LoopSource::Loop) => (),
 111                         Some(kind) => {
 112                             struct_span_err!(self.sess, e.span, E0571,
 113                                              "`break` with value from a `{}` loop",
 114                                              kind.name())
 115                                 .span_label(e.span,
 116                                             "can only break with a value inside \
 117                                             `loop` or breakable block")
 118                                 .span_suggestion(
 119                                     e.span,
 120                                     &format!(
 121                                         "instead, use `break` on its own \
 122                                         without a value inside this `{}` loop",
 123                                         kind.name()
 124                                     ),
 125                                     "break".to_string(),
 126                                     Applicability::MaybeIncorrect,
 127                                 )
 128                                 .emit();
 129                         }
 130                     }
 131                 }
 132
 133                 self.require_break_cx("break", e.span);
 134             }
 135             hir::ExprKind::Continue(destination) => {
 136                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 137
 138                 match destination.target_id {
 139                     Ok(loop_id) => {
 140                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 141                             struct_span_err!(self.sess, e.span, E0696,
 142                                             "`continue` pointing to a labeled block")
 143                                 .span_label(e.span,
 144                                             "labeled blocks cannot be `continue`'d")
 145                                 .span_note(block.span,
 146                                             "labeled block the continue points to")
 147                                 .emit();
 148                         }
 149                     }
 150                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 151                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 152                     }
 153                     Err(_) => {}
 154                 }
 155                 self.require_break_cx("continue", e.span)
 156             },
 157             _ => intravisit::walk_expr(self, e),
 158         }
 159     }
 160 }
 161
 162 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 163     fn with_context<F>(&mut self, cx: Context, f: F)
 164         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 165     {
 166         let old_cx = self.cx;
 167         self.cx = cx;
 168         f(self);
 169         self.cx = old_cx;
 170     }
 171
 172     fn require_break_cx(&self, name: &str, span: Span) {
 173         let err_inside_of = |article, ty, closure_span| {
 174             struct_span_err!(self.sess, span, E0267, "`{}` inside of {} {}", name, article, ty)
 175                 .span_label(span, format!("cannot `{}` inside of {} {}", name, article, ty))
 176                 .span_label(closure_span, &format!("enclosing {}", ty))
 177                 .emit();
 178         };
 179
 180         match self.cx {
 181             LabeledBlock | Loop(_) => {},
 182             Closure(closure_span) => err_inside_of("a", "closure", closure_span),
 183             AsyncClosure(closure_span) => err_inside_of("an", "`async` block", closure_span),
 184             Normal | AnonConst => {
 185                 struct_span_err!(self.sess, span, E0268, "`{}` outside of a loop", name)
 186                 .span_label(span, format!("cannot `{}` outside of a loop", name))
 187                 .emit();
 188             },
 189         }
 190     }
 191
 192     fn require_label_in_labeled_block(&mut self, span: Span, label: &Destination, cf_type: &str)
 193         -> bool
 194     {
 195         if self.cx == LabeledBlock {
 196             if label.label.is_none() {
 197                 struct_span_err!(self.sess, span, E0695,
 198                                 "unlabeled `{}` inside of a labeled block", cf_type)
 199                     .span_label(span,
 200                                 format!("`{}` statements that would diverge to or through \
 201                                 a labeled block need to bear a label", cf_type))
 202                     .emit();
 203                 return true;
 204             }
 205         }
 206         return false;
 207     }
 208     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 209         struct_span_err!(self.sess, span, E0590,
 210                          "`break` or `continue` with no label in the condition of a `while` loop")
 211             .span_label(span,
 212                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 213             .emit();
 214     }
 215 }