src/librustc_passes/loops.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10 use self::Context::*;
  11
  12 use rustc::session::Session;
  13
  14 use rustc::hir::map::Map;
  15 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  16 use rustc::hir::{self, Node, Destination};
  17 use syntax::ast;
  18 use syntax_pos::Span;
  19 use errors::Applicability;
  20
  21 #[derive(Clone, Copy, Debug, PartialEq)]
  22 enum LoopKind {
  23     Loop(hir::LoopSource),
  24     WhileLoop,
  25 }
  26
  27 impl LoopKind {
  28     fn name(self) -> &'static str {
  29         match self {
  30             LoopKind::Loop(hir::LoopSource::Loop) => "loop",
  31             LoopKind::Loop(hir::LoopSource::WhileLet) => "while let",
  32             LoopKind::Loop(hir::LoopSource::ForLoop) => "for",
  33             LoopKind::WhileLoop => "while",
  34         }
  35     }
  36 }
  37
  38 #[derive(Clone, Copy, Debug, PartialEq)]
  39 enum Context {
  40     Normal,
  41     Loop(LoopKind),
  42     Closure,
  43     LabeledBlock,
  44     AnonConst,
  45 }
  46
  47 #[derive(Copy, Clone)]
  48 struct CheckLoopVisitor<'a, 'hir: 'a> {
  49     sess: &'a Session,
  50     hir_map: &'a Map<'hir>,
  51     cx: Context,
  52 }
  53
  54 pub fn check_crate(sess: &Session, map: &Map) {
  55     let krate = map.krate();
  56     krate.visit_all_item_likes(&mut CheckLoopVisitor {
  57         sess,
  58         hir_map: map,
  59         cx: Normal,
  60     }.as_deep_visitor());
  61 }
  62
  63 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  64     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  65         NestedVisitorMap::OnlyBodies(&self.hir_map)
  66     }
  67
  68     fn visit_item(&mut self, i: &'hir hir::Item) {
  69         self.with_context(Normal, |v| intravisit::walk_item(v, i));
  70     }
  71
  72     fn visit_impl_item(&mut self, i: &'hir hir::ImplItem) {
  73         self.with_context(Normal, |v| intravisit::walk_impl_item(v, i));
  74     }
  75
  76     fn visit_anon_const(&mut self, c: &'hir hir::AnonConst) {
  77         self.with_context(AnonConst, |v| intravisit::walk_anon_const(v, c));
  78     }
  79
  80     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  81         match e.node {
  82             hir::ExprKind::While(ref e, ref b, _) => {
  83                 self.with_context(Loop(LoopKind::WhileLoop), |v| {
  84                     v.visit_expr(&e);
  85                     v.visit_block(&b);
  86                 });
  87             }
  88             hir::ExprKind::Loop(ref b, _, source) => {
  89                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
  90             }
  91             hir::ExprKind::Closure(_, ref function_decl, b, _, _) => {
  92                 self.visit_fn_decl(&function_decl);
  93                 self.with_context(Closure, |v| v.visit_nested_body(b));
  94             }
  95             hir::ExprKind::Block(ref b, Some(_label)) => {
  96                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  97             }
  98             hir::ExprKind::Break(label, ref opt_expr) => {
  99                 opt_expr.as_ref().map(|e| self.visit_expr(e));
 100
 101                 if self.require_label_in_labeled_block(e.span, &label, "break") {
 102                     // If we emitted an error about an unlabeled break in a labeled
 103                     // block, we don't need any further checking for this break any more
 104                     return;
 105                 }
 106
 107                 let loop_id = match label.target_id.into() {
 108                     Ok(loop_id) => loop_id,
 109                     Err(hir::LoopIdError::OutsideLoopScope) => ast::DUMMY_NODE_ID,
 110                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 111                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
 112                         ast::DUMMY_NODE_ID
 113                     },
 114                     Err(hir::LoopIdError::UnresolvedLabel) => ast::DUMMY_NODE_ID,
 115                 };
 116
 117                 if loop_id != ast::DUMMY_NODE_ID {
 118                     if let Node::Block(_) = self.hir_map.find(loop_id).unwrap() {
 119                         return
 120                     }
 121                 }
 122
 123                 if opt_expr.is_some() {
 124                     let loop_kind = if loop_id == ast::DUMMY_NODE_ID {
 125                         None
 126                     } else {
 127                         Some(match self.hir_map.expect_expr(loop_id).node {
 128                             hir::ExprKind::While(..) => LoopKind::WhileLoop,
 129                             hir::ExprKind::Loop(_, _, source) => LoopKind::Loop(source),
 130                             ref r => span_bug!(e.span,
 131                                                "break label resolved to a non-loop: {:?}", r),
 132                         })
 133                     };
 134                     match loop_kind {
 135                         None |
 136                         Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
 137                         Some(kind) => {
 138                             struct_span_err!(self.sess, e.span, E0571,
 139                                              "`break` with value from a `{}` loop",
 140                                              kind.name())
 141                                 .span_label(e.span,
 142                                             "can only break with a value inside \
 143                                             `loop` or breakable block")
 144                                 .span_suggestion_with_applicability(
 145                                     e.span,
 146                                     &format!(
 147                                         "instead, use `break` on its own \
 148                                         without a value inside this `{}` loop",
 149                                         kind.name()
 150                                     ),
 151                                     "break".to_string(),
 152                                     Applicability::MaybeIncorrect,
 153                                 )
 154                                 .emit();
 155                         }
 156                     }
 157                 }
 158
 159                 self.require_break_cx("break", e.span);
 160             }
 161             hir::ExprKind::Continue(destination) => {
 162                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 163
 164                 match destination.target_id {
 165                     Ok(loop_id) => {
 166                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 167                             struct_span_err!(self.sess, e.span, E0696,
 168                                             "`continue` pointing to a labeled block")
 169                                 .span_label(e.span,
 170                                             "labeled blocks cannot be `continue`'d")
 171                                 .span_note(block.span,
 172                                             "labeled block the continue points to")
 173                                 .emit();
 174                         }
 175                     }
 176                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 177                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 178                     }
 179                     Err(_) => {}
 180                 }
 181                 self.require_break_cx("continue", e.span)
 182             },
 183             _ => intravisit::walk_expr(self, e),
 184         }
 185     }
 186 }
 187
 188 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 189     fn with_context<F>(&mut self, cx: Context, f: F)
 190         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 191     {
 192         let old_cx = self.cx;
 193         self.cx = cx;
 194         f(self);
 195         self.cx = old_cx;
 196     }
 197
 198     fn require_break_cx(&self, name: &str, span: Span) {
 199         match self.cx {
 200             LabeledBlock | Loop(_) => {}
 201             Closure => {
 202                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 203                 .span_label(span, "cannot break inside of a closure")
 204                 .emit();
 205             }
 206             Normal | AnonConst => {
 207                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 208                 .span_label(span, "cannot break outside of a loop")
 209                 .emit();
 210             }
 211         }
 212     }
 213
 214     fn require_label_in_labeled_block(&mut self, span: Span, label: &Destination, cf_type: &str)
 215         -> bool
 216     {
 217         if self.cx == LabeledBlock {
 218             if label.label.is_none() {
 219                 struct_span_err!(self.sess, span, E0695,
 220                                 "unlabeled `{}` inside of a labeled block", cf_type)
 221                     .span_label(span,
 222                                 format!("`{}` statements that would diverge to or through \
 223                                 a labeled block need to bear a label", cf_type))
 224                     .emit();
 225                 return true;
 226             }
 227         }
 228         return false;
 229     }
 230     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 231         struct_span_err!(self.sess, span, E0590,
 232                          "`break` or `continue` with no label in the condition of a `while` loop")
 233             .span_label(span,
 234                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 235             .emit();
 236     }
 237 }