src/librustc/middle/check_const.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
  12 use middle::def::*;
  13 use middle::ty;
  14 use util::ppaux;
  15
  16 use syntax::ast;
  17 use syntax::visit::{self, Visitor};
  18
  19 struct CheckCrateVisitor<'a, 'tcx: 'a> {
  20     tcx: &'a ty::ctxt<'tcx>,
  21     in_const: bool
  22 }
  23
  24 impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
  25     fn with_const<F>(&mut self, in_const: bool, f: F) where
  26         F: FnOnce(&mut CheckCrateVisitor<'a, 'tcx>),
  27     {
  28         let was_const = self.in_const;
  29         self.in_const = in_const;
  30         f(self);
  31         self.in_const = was_const;
  32     }
  33     fn inside_const<F>(&mut self, f: F) where
  34         F: FnOnce(&mut CheckCrateVisitor<'a, 'tcx>),
  35     {
  36         self.with_const(true, f);
  37     }
  38 }
  39
  40 impl<'a, 'tcx, 'v> Visitor<'v> for CheckCrateVisitor<'a, 'tcx> {
  41     fn visit_item(&mut self, i: &ast::Item) {
  42         match i.node {
  43             ast::ItemStatic(_, _, ref ex) |
  44             ast::ItemConst(_, ref ex) => {
  45                 self.inside_const(|v| v.visit_expr(&**ex));
  46             }
  47             ast::ItemEnum(ref enum_definition, _) => {
  48                 self.inside_const(|v| {
  49                     for var in enum_definition.variants.iter() {
  50                         if let Some(ref ex) = var.node.disr_expr {
  51                             v.visit_expr(&**ex);
  52                         }
  53                     }
  54                 });
  55             }
  56             _ => self.with_const(false, |v| visit::walk_item(v, i))
  57         }
  58     }
  59     fn visit_pat(&mut self, p: &ast::Pat) {
  60         let is_const = match p.node {
  61             ast::PatLit(_) | ast::PatRange(..) => true,
  62             _ => false
  63         };
  64         self.with_const(is_const, |v| visit::walk_pat(v, p))
  65     }
  66     fn visit_expr(&mut self, ex: &ast::Expr) {
  67         if self.in_const {
  68             check_expr(self, ex);
  69         }
  70         visit::walk_expr(self, ex);
  71     }
  72 }
  73
  74 pub fn check_crate(tcx: &ty::ctxt) {
  75     visit::walk_crate(&mut CheckCrateVisitor { tcx: tcx, in_const: false },
  76                       tcx.map.krate());
  77     tcx.sess.abort_if_errors();
  78 }
  79
  80 fn check_expr(v: &mut CheckCrateVisitor, e: &ast::Expr) {
  81     match e.node {
  82         ast::ExprUnary(ast::UnDeref, _) => {}
  83         ast::ExprUnary(ast::UnUniq, _) => {
  84             span_err!(v.tcx.sess, e.span, E0010,
  85                       "cannot do allocations in constant expressions");
  86         }
  87         ast::ExprBinary(..) | ast::ExprUnary(..) => {
  88             let method_call = ty::MethodCall::expr(e.id);
  89             if v.tcx.method_map.borrow().contains_key(&method_call) {
  90                 span_err!(v.tcx.sess, e.span, E0011,
  91                           "user-defined operators are not allowed in constant \
  92                            expressions");
  93             }
  94         }
  95         ast::ExprLit(_) => {}
  96         ast::ExprCast(ref from, _) => {
  97             let toty = ty::expr_ty(v.tcx, e);
  98             let fromty = ty::expr_ty(v.tcx, &**from);
  99             let is_legal_cast =
 100                 ty::type_is_numeric(toty) ||
 101                 ty::type_is_unsafe_ptr(toty) ||
 102                 (ty::type_is_bare_fn(toty) && ty::type_is_bare_fn_item(fromty));
 103             if !is_legal_cast {
 104                 span_err!(v.tcx.sess, e.span, E0012,
 105                           "can not cast to `{}` in a constant expression",
 106                           ppaux::ty_to_string(v.tcx, toty));
 107             }
 108             if ty::type_is_unsafe_ptr(fromty) && ty::type_is_numeric(toty) {
 109                 span_err!(v.tcx.sess, e.span, E0018,
 110                           "can not cast a pointer to an integer in a constant \
 111                            expression");
 112             }
 113         }
 114         ast::ExprPath(_) => {
 115             match v.tcx.def_map.borrow()[e.id] {
 116                 DefStatic(..) | DefConst(..) |
 117                 DefFn(..) | DefStaticMethod(..) | DefMethod(..) |
 118                 DefStruct(_) | DefVariant(_, _, _) => {}
 119
 120                 def => {
 121                     debug!("(checking const) found bad def: {:?}", def);
 122                     span_err!(v.tcx.sess, e.span, E0014,
 123                               "paths in constants may only refer to constants \
 124                                or functions");
 125                 }
 126             }
 127         }
 128         ast::ExprCall(ref callee, _) => {
 129             match v.tcx.def_map.borrow()[callee.id] {
 130                 DefStruct(..) | DefVariant(..) => {}    // OK.
 131                 _ => {
 132                     span_err!(v.tcx.sess, e.span, E0015,
 133                               "function calls in constants are limited to \
 134                                struct and enum constructors");
 135                 }
 136             }
 137         }
 138         ast::ExprBlock(ref block) => {
 139             // Check all statements in the block
 140             for stmt in block.stmts.iter() {
 141                 let block_span_err = |&: span|
 142                     span_err!(v.tcx.sess, span, E0016,
 143                               "blocks in constants are limited to items and \
 144                                tail expressions");
 145                 match stmt.node {
 146                     ast::StmtDecl(ref decl, _) => {
 147                         match decl.node {
 148                             ast::DeclLocal(_) => block_span_err(decl.span),
 149
 150                             // Item statements are allowed
 151                             ast::DeclItem(_) => {}
 152                         }
 153                     }
 154                     ast::StmtExpr(ref expr, _) => block_span_err(expr.span),
 155                     ast::StmtSemi(ref semi, _) => block_span_err(semi.span),
 156                     ast::StmtMac(..) => {
 157                         v.tcx.sess.span_bug(e.span, "unexpanded statement \
 158                                                      macro in const?!")
 159                     }
 160                 }
 161             }
 162         }
 163         ast::ExprVec(_) |
 164         ast::ExprAddrOf(ast::MutImmutable, _) |
 165         ast::ExprParen(..) |
 166         ast::ExprField(..) |
 167         ast::ExprTupField(..) |
 168         ast::ExprIndex(..) |
 169         ast::ExprTup(..) |
 170         ast::ExprRepeat(..) |
 171         ast::ExprStruct(..) => {}
 172
 173         ast::ExprAddrOf(_, ref inner) => {
 174             match inner.node {
 175                 // Mutable slices are allowed.
 176                 ast::ExprVec(_) => {}
 177                 _ => span_err!(v.tcx.sess, e.span, E0017,
 178                                "references in constants may only refer \
 179                                 to immutable values")
 180
 181             }
 182         }
 183
 184         _ => span_err!(v.tcx.sess, e.span, E0019,
 185                        "constant contains unimplemented expression type")
 186     }
 187 }