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;
  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 }
  43
  44 #[derive(Copy, Clone)]
  45 struct CheckLoopVisitor<'a, 'hir: 'a> {
  46     sess: &'a Session,
  47     hir_map: &'a Map<'hir>,
  48     cx: Context,
  49 }
  50
  51 pub fn check_crate(sess: &Session, map: &Map) {
  52     let krate = map.krate();
  53     krate.visit_all_item_likes(&mut CheckLoopVisitor {
  54         sess: sess,
  55         hir_map: map,
  56         cx: Normal,
  57     }.as_deep_visitor());
  58 }
  59
  60 impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
  61     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'hir> {
  62         NestedVisitorMap::OnlyBodies(&self.hir_map)
  63     }
  64
  65     fn visit_item(&mut self, i: &'hir hir::Item) {
  66         self.with_context(Normal, |v| intravisit::walk_item(v, i));
  67     }
  68
  69     fn visit_impl_item(&mut self, i: &'hir hir::ImplItem) {
  70         self.with_context(Normal, |v| intravisit::walk_impl_item(v, i));
  71     }
  72
  73     fn visit_expr(&mut self, e: &'hir hir::Expr) {
  74         match e.node {
  75             hir::ExprWhile(ref e, ref b, _) => {
  76                 self.with_context(Loop(LoopKind::WhileLoop), |v| {
  77                     v.visit_expr(&e);
  78                     v.visit_block(&b);
  79                 });
  80             }
  81             hir::ExprLoop(ref b, _, source) => {
  82                 self.with_context(Loop(LoopKind::Loop(source)), |v| v.visit_block(&b));
  83             }
  84             hir::ExprClosure(.., b, _) => {
  85                 self.with_context(Closure, |v| v.visit_nested_body(b));
  86             }
  87             hir::ExprBreak(label, ref opt_expr) => {
  88                 let loop_id = match label.target_id {
  89                     hir::ScopeTarget::Block(_) => return,
  90                     hir::ScopeTarget::Loop(loop_res) => {
  91                         match loop_res.into() {
  92                             Ok(loop_id) => loop_id,
  93                             Err(hir::LoopIdError::OutsideLoopScope) => ast::DUMMY_NODE_ID,
  94                             Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
  95                                 self.emit_unlabled_cf_in_while_condition(e.span, "break");
  96                                 ast::DUMMY_NODE_ID
  97                             },
  98                             Err(hir::LoopIdError::UnresolvedLabel) => ast::DUMMY_NODE_ID,
  99                         }
 100                     }
 101                 };
 102
 103                 if opt_expr.is_some() {
 104                     let loop_kind = if loop_id == ast::DUMMY_NODE_ID {
 105                         None
 106                     } else {
 107                         Some(match self.hir_map.expect_expr(loop_id).node {
 108                             hir::ExprWhile(..) => LoopKind::WhileLoop,
 109                             hir::ExprLoop(_, _, source) => LoopKind::Loop(source),
 110                             ref r => span_bug!(e.span,
 111                                                "break label resolved to a non-loop: {:?}", r),
 112                         })
 113                     };
 114                     match loop_kind {
 115                         None | Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
 116                         Some(kind) => {
 117                             struct_span_err!(self.sess, e.span, E0571,
 118                                              "`break` with value from a `{}` loop",
 119                                              kind.name())
 120                                 .span_label(e.span,
 121                                             "can only break with a value inside `loop`")
 122                                 .emit();
 123                         }
 124                     }
 125                 }
 126
 127                 self.require_loop("break", e.span);
 128             }
 129             hir::ExprAgain(label) => {
 130                 if let hir::ScopeTarget::Loop(
 131                     hir::LoopIdResult::Err(
 132                         hir::LoopIdError::UnlabeledCfInWhileCondition)) = label.target_id {
 133                     self.emit_unlabled_cf_in_while_condition(e.span, "continue");
 134                 }
 135                 self.require_loop("continue", e.span)
 136             },
 137             _ => intravisit::walk_expr(self, e),
 138         }
 139     }
 140 }
 141
 142 impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
 143     fn with_context<F>(&mut self, cx: Context, f: F)
 144         where F: FnOnce(&mut CheckLoopVisitor<'a, 'hir>)
 145     {
 146         let old_cx = self.cx;
 147         self.cx = cx;
 148         f(self);
 149         self.cx = old_cx;
 150     }
 151
 152     fn require_loop(&self, name: &str, span: Span) {
 153         match self.cx {
 154             Loop(_) => {}
 155             Closure => {
 156                 struct_span_err!(self.sess, span, E0267, "`{}` inside of a closure", name)
 157                 .span_label(span, "cannot break inside of a closure")
 158                 .emit();
 159             }
 160             Normal => {
 161                 struct_span_err!(self.sess, span, E0268, "`{}` outside of loop", name)
 162                 .span_label(span, "cannot break outside of a loop")
 163                 .emit();
 164             }
 165         }
 166     }
 167
 168     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
 169         struct_span_err!(self.sess, span, E0590,
 170                          "`break` or `continue` with no label in the condition of a `while` loop")
 171             .span_label(span,
 172                         format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
 173             .emit();
 174     }
 175 }