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