src/librustc/middle/effect.rs

   1 // Copyright 2012-2013 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
  11 //! Enforces the Rust effect system. Currently there is just one effect,
  12 //! `unsafe`.
  13 use self::RootUnsafeContext::*;
  14
  15 use ty::{self, Ty, TyCtxt};
  16 use ty::MethodCall;
  17 use lint;
  18
  19 use syntax::ast;
  20 use syntax_pos::Span;
  21 use hir::{self, PatKind};
  22 use hir::def::Def;
  23 use hir::intravisit::{self, FnKind, Visitor, NestedVisitorMap};
  24
  25 #[derive(Copy, Clone)]
  26 struct UnsafeContext {
  27     push_unsafe_count: usize,
  28     root: RootUnsafeContext,
  29 }
  30
  31 impl UnsafeContext {
  32     fn new(root: RootUnsafeContext) -> UnsafeContext {
  33         UnsafeContext { root: root, push_unsafe_count: 0 }
  34     }
  35 }
  36
  37 #[derive(Copy, Clone, PartialEq)]
  38 enum RootUnsafeContext {
  39     SafeContext,
  40     UnsafeFn,
  41     UnsafeBlock(ast::NodeId),
  42 }
  43
  44 fn type_is_unsafe_function(ty: Ty) -> bool {
  45     match ty.sty {
  46         ty::TyFnDef(.., f) |
  47         ty::TyFnPtr(f) => f.unsafety() == hir::Unsafety::Unsafe,
  48         _ => false,
  49     }
  50 }
  51
  52 struct EffectCheckVisitor<'a, 'tcx: 'a> {
  53     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  54     tables: &'a ty::TypeckTables<'tcx>,
  55     body_id: hir::BodyId,
  56
  57     /// Whether we're in an unsafe context.
  58     unsafe_context: UnsafeContext,
  59 }
  60
  61 impl<'a, 'tcx> EffectCheckVisitor<'a, 'tcx> {
  62     fn require_unsafe_ext(&mut self, node_id: ast::NodeId, span: Span,
  63                           description: &str, is_lint: bool) {
  64         if self.unsafe_context.push_unsafe_count > 0 { return; }
  65         match self.unsafe_context.root {
  66             SafeContext => {
  67                 if is_lint {
  68                     self.tcx.sess.add_lint(lint::builtin::SAFE_EXTERN_STATICS,
  69                                            node_id,
  70                                            span,
  71                                            format!("{} requires unsafe function or \
  72                                                     block (error E0133)", description));
  73                 } else {
  74                     // Report an error.
  75                     struct_span_err!(
  76                         self.tcx.sess, span, E0133,
  77                         "{} requires unsafe function or block", description)
  78                         .span_label(span, description)
  79                         .emit();
  80                 }
  81             }
  82             UnsafeBlock(block_id) => {
  83                 // OK, but record this.
  84                 debug!("effect: recording unsafe block as used: {}", block_id);
  85                 self.tcx.used_unsafe.borrow_mut().insert(block_id);
  86             }
  87             UnsafeFn => {}
  88         }
  89     }
  90
  91     fn require_unsafe(&mut self, span: Span, description: &str) {
  92         self.require_unsafe_ext(ast::DUMMY_NODE_ID, span, description, false)
  93     }
  94 }
  95
  96 impl<'a, 'tcx> Visitor<'tcx> for EffectCheckVisitor<'a, 'tcx> {
  97     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  98         NestedVisitorMap::None
  99     }
 100
 101     fn visit_nested_body(&mut self, body: hir::BodyId) {
 102         let old_tables = self.tables;
 103         let old_body_id = self.body_id;
 104         self.tables = self.tcx.body_tables(body);
 105         self.body_id = body;
 106         let body = self.tcx.hir.body(body);
 107         self.visit_body(body);
 108         self.tables = old_tables;
 109         self.body_id = old_body_id;
 110     }
 111
 112     fn visit_fn(&mut self, fn_kind: FnKind<'tcx>, fn_decl: &'tcx hir::FnDecl,
 113                 body_id: hir::BodyId, span: Span, id: ast::NodeId) {
 114
 115         let (is_item_fn, is_unsafe_fn) = match fn_kind {
 116             FnKind::ItemFn(_, _, unsafety, ..) =>
 117                 (true, unsafety == hir::Unsafety::Unsafe),
 118             FnKind::Method(_, sig, ..) =>
 119                 (true, sig.unsafety == hir::Unsafety::Unsafe),
 120             _ => (false, false),
 121         };
 122
 123         let old_unsafe_context = self.unsafe_context;
 124         if is_unsafe_fn {
 125             self.unsafe_context = UnsafeContext::new(UnsafeFn)
 126         } else if is_item_fn {
 127             self.unsafe_context = UnsafeContext::new(SafeContext)
 128         }
 129
 130         intravisit::walk_fn(self, fn_kind, fn_decl, body_id, span, id);
 131
 132         self.unsafe_context = old_unsafe_context
 133     }
 134
 135     fn visit_block(&mut self, block: &'tcx hir::Block) {
 136         let old_unsafe_context = self.unsafe_context;
 137         match block.rules {
 138             hir::UnsafeBlock(source) => {
 139                 // By default only the outermost `unsafe` block is
 140                 // "used" and so nested unsafe blocks are pointless
 141                 // (the inner ones are unnecessary and we actually
 142                 // warn about them). As such, there are two cases when
 143                 // we need to create a new context, when we're
 144                 // - outside `unsafe` and found a `unsafe` block
 145                 //   (normal case)
 146                 // - inside `unsafe`, found an `unsafe` block
 147                 //   created internally to the compiler
 148                 //
 149                 // The second case is necessary to ensure that the
 150                 // compiler `unsafe` blocks don't accidentally "use"
 151                 // external blocks (e.g. `unsafe { println("") }`,
 152                 // expands to `unsafe { ... unsafe { ... } }` where
 153                 // the inner one is compiler generated).
 154                 if self.unsafe_context.root == SafeContext || source == hir::CompilerGenerated {
 155                     self.unsafe_context.root = UnsafeBlock(block.id)
 156                 }
 157             }
 158             hir::PushUnsafeBlock(..) => {
 159                 self.unsafe_context.push_unsafe_count =
 160                     self.unsafe_context.push_unsafe_count.checked_add(1).unwrap();
 161             }
 162             hir::PopUnsafeBlock(..) => {
 163                 self.unsafe_context.push_unsafe_count =
 164                     self.unsafe_context.push_unsafe_count.checked_sub(1).unwrap();
 165             }
 166             hir::DefaultBlock => {}
 167         }
 168
 169         intravisit::walk_block(self, block);
 170
 171         self.unsafe_context = old_unsafe_context
 172     }
 173
 174     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 175         match expr.node {
 176             hir::ExprMethodCall(..) => {
 177                 let method_call = MethodCall::expr(expr.id);
 178                 let base_type = self.tables.method_map[&method_call].ty;
 179                 debug!("effect: method call case, base type is {:?}",
 180                         base_type);
 181                 if type_is_unsafe_function(base_type) {
 182                     self.require_unsafe(expr.span,
 183                                         "invocation of unsafe method")
 184                 }
 185             }
 186             hir::ExprCall(ref base, _) => {
 187                 let base_type = self.tables.expr_ty_adjusted(base);
 188                 debug!("effect: call case, base type is {:?}",
 189                         base_type);
 190                 if type_is_unsafe_function(base_type) {
 191                     self.require_unsafe(expr.span, "call to unsafe function")
 192                 }
 193             }
 194             hir::ExprUnary(hir::UnDeref, ref base) => {
 195                 let base_type = self.tables.expr_ty_adjusted(base);
 196                 debug!("effect: unary case, base type is {:?}",
 197                         base_type);
 198                 if let ty::TyRawPtr(_) = base_type.sty {
 199                     self.require_unsafe(expr.span, "dereference of raw pointer")
 200                 }
 201             }
 202             hir::ExprInlineAsm(..) => {
 203                 self.require_unsafe(expr.span, "use of inline assembly");
 204             }
 205             hir::ExprPath(hir::QPath::Resolved(_, ref path)) => {
 206                 if let Def::Static(def_id, mutbl) = path.def {
 207                     if mutbl {
 208                         self.require_unsafe(expr.span, "use of mutable static");
 209                     } else if match self.tcx.hir.get_if_local(def_id) {
 210                         Some(hir::map::NodeForeignItem(..)) => true,
 211                         Some(..) => false,
 212                         None => self.tcx.is_foreign_item(def_id),
 213                     } {
 214                         self.require_unsafe_ext(expr.id, expr.span, "use of extern static", true);
 215                     }
 216                 }
 217             }
 218             hir::ExprField(ref base_expr, field) => {
 219                 if let ty::TyAdt(adt, ..) = self.tables.expr_ty_adjusted(base_expr).sty {
 220                     if adt.is_union() {
 221                         self.require_unsafe(field.span, "access to union field");
 222                     }
 223                 }
 224             }
 225             hir::ExprAssign(ref lhs, ref rhs) => {
 226                 if let hir::ExprField(ref base_expr, field) = lhs.node {
 227                     if let ty::TyAdt(adt, ..) = self.tables.expr_ty_adjusted(base_expr).sty {
 228                         if adt.is_union() {
 229                             let field_ty = self.tables.expr_ty_adjusted(lhs);
 230                             let owner_def_id = self.tcx.hir.body_owner_def_id(self.body_id);
 231                             let param_env = self.tcx.param_env(owner_def_id);
 232                             if field_ty.moves_by_default(self.tcx, param_env, field.span) {
 233                                 self.require_unsafe(field.span,
 234                                                     "assignment to non-`Copy` union field");
 235                             }
 236                             // Do not walk the field expr again.
 237                             intravisit::walk_expr(self, base_expr);
 238                             intravisit::walk_expr(self, rhs);
 239                             return
 240                         }
 241                     }
 242                 }
 243             }
 244             _ => {}
 245         }
 246
 247         intravisit::walk_expr(self, expr);
 248     }
 249
 250     fn visit_pat(&mut self, pat: &'tcx hir::Pat) {
 251         if let PatKind::Struct(_, ref fields, _) = pat.node {
 252             if let ty::TyAdt(adt, ..) = self.tables.pat_ty(pat).sty {
 253                 if adt.is_union() {
 254                     for field in fields {
 255                         self.require_unsafe(field.span, "matching on union field");
 256                     }
 257                 }
 258             }
 259         }
 260
 261         intravisit::walk_pat(self, pat);
 262     }
 263 }
 264
 265 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
 266     let mut visitor = EffectCheckVisitor {
 267         tcx: tcx,
 268         tables: &ty::TypeckTables::empty(),
 269         body_id: hir::BodyId { node_id: ast::CRATE_NODE_ID },
 270         unsafe_context: UnsafeContext::new(SafeContext),
 271     };
 272
 273     tcx.hir.krate().visit_all_item_likes(&mut visitor.as_deep_visitor());
 274 }