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
  20 #[derive(Clone, Copy, Debug, PartialEq)]
  21 enum LoopKind {
  22     Loop(hir::LoopSource),
  23     WhileLoop,
  24 }
  25
  26 impl LoopKind {
  27     fn name(self) -> &'static str {
  28         match self {
  29             LoopKind::Loop(hir::LoopSource::Loop) => "loop",
  30             LoopKind::Loop(hir::LoopSource::WhileLet) => "while let",
  31             LoopKind::Loop(hir::LoopSource::ForLoop) => "for",
  32             LoopKind::WhileLoop => "while",
  33         }
  34     }
  35 }
  36
  37 #[derive(Clone, Copy, Debug, PartialEq)]
  38 enum Context {
  39     Normal,
  40     Loop(LoopKind),
  41     Closure,
  42     LabeledBlock,
  43     AnonConst,
  44 }
  45
  46 #[derive(Copy, Clone)]
  47 struct CheckLoopVisitor<'a, 'hir: 'a> {
  48     sess: &'a Session,
  49     hir_map: &'a Map<'hir>,
  50     cx: Context,
  51 }
  52
  53 pub fn check_crate(sess: &Session, map: &Map) {
  54     let krate = map.krate();
  55     krate.visit_all_item_likes(&mut CheckLoopVisitor {
  56         sess,
  57         hir_map: map,
  58         cx: Normal,
  59     }.as_deep_visitor());
  60 }
  61
  62 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  63     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  64         NestedVisitorMap::OnlyBodies(&self.hir_map)
  65     }
  66
  67     fn visit_item(&mut self, i: &'hir hir::Item) {
  68         self.with_context(Normal, |v| intravisit::walk_item(v, i));
  69     }
  70
  71     fn visit_impl_item(&mut self, i: &'hir hir::ImplItem) {
  72         self.with_context(Normal, |v| intravisit::walk_impl_item(v, i));
  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(e.span,
 144                                                  &format!("instead, use `break` on its own \
 145                                                            without a value inside this `{}` loop",
 146                                                           kind.name()),
 147                                                  "break".to_string())
 148                                 .emit();
 149                         }
 150                     }
 151                 }
 152
 153                 self.require_break_cx("break", e.span);
 154             }
 155             hir::ExprKind::Continue(destination) => {
 156                 self.require_label_in_labeled_block(e.span, &destination, "continue");
 157
 158                 match destination.target_id {
 159                     Ok(loop_id) => {
 160                         if let Node::Block(block) = self.hir_map.find(loop_id).unwrap() {
 161                             struct_span_err!(self.sess, e.span, E0696,
 162                                             "`continue` pointing to a labeled block")
 163                                 .span_label(e.span,
 164                                             "labeled blocks cannot be `continue`'d")
 165                                 .span_note(block.span,
 166                                             "labeled block the continue points to")
 167                                 .emit();
 168                         }
 169                     }
 170                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 171                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 172                     }
 173                     Err(_) => {}
 174                 }
 175                 self.require_break_cx("continue", e.span)
 176             },
 177             _ => intravisit::walk_expr(self, e),
 178         }
 179     }
 180 }
 181
 182 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 183     fn with_context<F>(&mut self, cx: Context, f: F)
 184         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 185     {
 186         let old_cx = self.cx;
 187         self.cx = cx;
 188         f(self);
 189         self.cx = old_cx;
 190     }
 191
 192     fn require_break_cx(&self, name: &str, span: Span) {
 193         match self.cx {
 194             LabeledBlock | Loop(_) => {}
 195             Closure => {
 196                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 197                 .span_label(span, "cannot break inside of a closure")
 198                 .emit();
 199             }
 200             Normal | AnonConst => {
 201                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 202                 .span_label(span, "cannot break outside of a loop")
 203                 .emit();
 204             }
 205         }
 206     }
 207
 208     fn require_label_in_labeled_block(&mut self, span: Span, label: &Destination, cf_type: &str)
 209         -> bool
 210     {
 211         if self.cx == LabeledBlock {
 212             if label.label.is_none() {
 213                 struct_span_err!(self.sess, span, E0695,
 214                                 "unlabeled `{}` inside of a labeled block", cf_type)
 215                     .span_label(span,
 216                                 format!("`{}` statements that would diverge to or through \
 217                                 a labeled block need to bear a label", cf_type))
 218                     .emit();
 219                 return true;
 220             }
 221         }
 222         return false;
 223     }
 224     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 225         struct_span_err!(self.sess, span, E0590,
 226                          "`break` or `continue` with no label in the condition of a `while` loop")
 227             .span_label(span,
 228                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 229             .emit();
 230     }
 231 }