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, Destination};
  17 use syntax::ast;
  18 use syntax_pos::Span;
  19
  20 #[derive(Clone, Copy, 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, PartialEq)]
  38 enum Context {
  39     Normal,
  40     Loop(LoopKind),
  41     Closure,
  42     LabeledBlock,
  43 }
  44
  45 #[derive(Copy, Clone)]
  46 struct CheckLoopVisitor<'a, 'hir: 'a> {
  47     sess: &'a Session,
  48     hir_map: &'a Map<'hir>,
  49     cx: Context,
  50 }
  51
  52 pub fn check_crate(sess: &Session, map: &Map) {
  53     let krate = map.krate();
  54     krate.visit_all_item_likes(&mut CheckLoopVisitor {
  55         sess,
  56         hir_map: map,
  57         cx: Normal,
  58     }.as_deep_visitor());
  59 }
  60
  61 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  62     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  63         NestedVisitorMap::OnlyBodies(&self.hir_map)
  64     }
  65
  66     fn visit_item(&mut self, i: &'hir hir::Item) {
  67         self.with_context(Normal, |v| intravisit::walk_item(v, i));
  68     }
  69
  70     fn visit_impl_item(&mut self, i: &'hir hir::ImplItem) {
  71         self.with_context(Normal, |v| intravisit::walk_impl_item(v, i));
  72     }
  73
  74     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  75         match e.node {
  76             hir::ExprWhile(ref e, ref b, _) => {
  77                 self.with_context(Loop(LoopKind::WhileLoop), |v| {
  78                     v.visit_expr(&e);
  79                     v.visit_block(&b);
  80                 });
  81             }
  82             hir::ExprLoop(ref b, _, source) => {
  83                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
  84             }
  85             hir::ExprClosure(_, ref function_decl, b, _, _) => {
  86                 self.visit_fn_decl(&function_decl);
  87                 self.with_context(Closure, |v| v.visit_nested_body(b));
  88             }
  89             hir::ExprBlock(ref b, Some(_label)) => {
  90                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
  91             }
  92             hir::ExprBreak(label, ref opt_expr) => {
  93                 opt_expr.as_ref().map(|e| self.visit_expr(e));
  94
  95                 if self.require_label_in_labeled_block(e.span, &label, "break") {
  96                     // If we emitted an error about an unlabeled break in a labeled
  97                     // block, we don't need any further checking for this break any more
  98                     return;
  99                 }
 100
 101                 let loop_id = match label.target_id.into() {
 102                     Ok(loop_id) => loop_id,
 103                     Err(hir::LoopIdError::OutsideLoopScope) => ast::DUMMY_NODE_ID,
 104                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 105                         self.emit_unlabled_cf_in_while_condition(e.span, "break");
 106                         ast::DUMMY_NODE_ID
 107                     },
 108                     Err(hir::LoopIdError::UnresolvedLabel) => ast::DUMMY_NODE_ID,
 109                 };
 110
 111                 if loop_id != ast::DUMMY_NODE_ID {
 112                     match self.hir_map.find(loop_id).unwrap() {
 113                         hir::map::NodeBlock(_) => return,
 114                         _=> (),
 115                     }
 116                 }
 117
 118                 if opt_expr.is_some() {
 119                     let loop_kind = if loop_id == ast::DUMMY_NODE_ID {
 120                         None
 121                     } else {
 122                         Some(match self.hir_map.expect_expr(loop_id).node {
 123                             hir::ExprWhile(..) => LoopKind::WhileLoop,
 124                             hir::ExprLoop(_, _, source) => LoopKind::Loop(source),
 125                             ref r => span_bug!(e.span,
 126                                                "break label resolved to a non-loop: {:?}", r),
 127                         })
 128                     };
 129                     match loop_kind {
 130                         None |
 131                         Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
 132                         Some(kind) => {
 133                             struct_span_err!(self.sess, e.span, E0571,
 134                                              "`break` with value from a `{}` loop",
 135                                              kind.name())
 136                                 .span_label(e.span,
 137                                             "can only break with a value inside \
 138                                             `loop` or breakable block")
 139                                 .span_suggestion(e.span,
 140                                                  &format!("instead, use `break` on its own \
 141                                                            without a value inside this `{}` loop",
 142                                                           kind.name()),
 143                                                  "break".to_string())
 144                                 .emit();
 145                         }
 146                     }
 147                 }
 148
 149                 self.require_break_cx("break", e.span);
 150             }
 151             hir::ExprAgain(label) => {
 152                 self.require_label_in_labeled_block(e.span, &label, "continue");
 153
 154                 match label.target_id {
 155                     Ok(loop_id) => {
 156                         if let hir::map::NodeBlock(block) = self.hir_map.find(loop_id).unwrap() {
 157                             struct_span_err!(self.sess, e.span, E0696,
 158                                             "`continue` pointing to a labeled block")
 159                                 .span_label(e.span,
 160                                             "labeled blocks cannot be `continue`'d")
 161                                 .span_note(block.span,
 162                                             "labeled block the continue points to")
 163                                 .emit();
 164                         }
 165                     }
 166                     Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
 167                         self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 168                     }
 169                     _ => {}
 170                 }
 171                 self.require_break_cx("continue", e.span)
 172             },
 173             _ => intravisit::walk_expr(self, e),
 174         }
 175     }
 176 }
 177
 178 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 179     fn with_context<F>(&mut self, cx: Context, f: F)
 180         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 181     {
 182         let old_cx = self.cx;
 183         self.cx = cx;
 184         f(self);
 185         self.cx = old_cx;
 186     }
 187
 188     fn require_break_cx(&self, name: &str, span: Span) {
 189         match self.cx {
 190             LabeledBlock |
 191             Loop(_) => {}
 192             Closure => {
 193                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 194                 .span_label(span, "cannot break inside of a closure")
 195                 .emit();
 196             }
 197             Normal => {
 198                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 199                 .span_label(span, "cannot break outside of a loop")
 200                 .emit();
 201             }
 202         }
 203     }
 204
 205     fn require_label_in_labeled_block(&mut self, span: Span, label: &Destination, cf_type: &str)
 206         -> bool
 207     {
 208         if self.cx == LabeledBlock {
 209             if label.label.is_none() {
 210                 struct_span_err!(self.sess, span, E0695,
 211                                 "unlabeled `{}` inside of a labeled block", cf_type)
 212                     .span_label(span,
 213                                 format!("`{}` statements that would diverge to or through \
 214                                 a labeled block need to bear a label", cf_type))
 215                     .emit();
 216                 return true;
 217             }
 218         }
 219         return false;
 220     }
 221     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 222         struct_span_err!(self.sess, span, E0590,
 223                          "`break` or `continue` with no label in the condition of a `while` loop")
 224             .span_label(span,
 225                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 226             .emit();
 227     }
 228 }