rust/src/librustc/middle/check_const.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use syntax::ast::*;
use syntax::{visit, ast_util, ast_map};
use driver::session::Session;
use std::map::HashMap;
use dvec::DVec;

fn check_crate(sess: Session, crate: @crate, ast_map: ast_map::map,
               def_map: resolve::DefMap,
                method_map: typeck::method_map, tcx: ty::ctxt) {
    visit::visit_crate(*crate, false, visit::mk_vt(@{
        visit_item: |a,b,c| check_item(sess, ast_map, def_map, a, b, c),
        visit_pat: check_pat,
        visit_expr: |a,b,c|
            check_expr(sess, def_map, method_map, tcx, a, b, c),
        .. *visit::default_visitor()
    }));
    sess.abort_if_errors();
}

fn check_item(sess: Session, ast_map: ast_map::map,
              def_map: resolve::DefMap,
              it: @item, &&_is_const: bool, v: visit::vt<bool>) {
    match it.node {
      item_const(_, ex) => {
        (v.visit_expr)(ex, true, v);
        check_item_recursion(sess, ast_map, def_map, it);
      }
      item_enum(ref enum_definition, _) => {
        for (*enum_definition).variants.each |var| {
            do option::iter(&var.node.disr_expr) |ex| {
                (v.visit_expr)(*ex, true, v);
            }
        }
      }
      _ => visit::visit_item(it, false, v)
    }
}

fn check_pat(p: @pat, &&_is_const: bool, v: visit::vt<bool>) {
    fn is_str(e: @expr) -> bool {
        match e.node {
          expr_vstore(@{node: expr_lit(@{node: lit_str(_), _}), _},
                      expr_vstore_uniq) => true,
          _ => false
        }
    }
    match p.node {
      // Let through plain ~-string literals here
      pat_lit(a) => if !is_str(a) { (v.visit_expr)(a, true, v); },
      pat_range(a, b) => {
        if !is_str(a) { (v.visit_expr)(a, true, v); }
        if !is_str(b) { (v.visit_expr)(b, true, v); }
      }
      _ => visit::visit_pat(p, false, v)
    }
}

fn check_expr(sess: Session, def_map: resolve::DefMap,
              method_map: typeck::method_map, tcx: ty::ctxt,
              e: @expr, &&is_const: bool, v: visit::vt<bool>) {
    if is_const {
        match e.node {
          expr_unary(box(_), _) | expr_unary(uniq(_), _) |
          expr_unary(deref, _) => {
            sess.span_err(e.span,
                          ~"disallowed operator in constant expression");
            return;
          }
          expr_lit(@{node: lit_str(_), _}) => { }
          expr_binary(_, _, _) | expr_unary(_, _) => {
            if method_map.contains_key(e.id) {
                sess.span_err(e.span, ~"user-defined operators are not \
                                       allowed in constant expressions");
            }
          }
          expr_lit(_) => (),
          expr_cast(_, _) => {
            let ety = ty::expr_ty(tcx, e);
            if !ty::type_is_numeric(ety) {
                sess.span_err(e.span, ~"can not cast to `" +
                              util::ppaux::ty_to_str(tcx, ety) +
                              ~"` in a constant expression");
            }
          }
          expr_path(pth) => {
            // NB: In the future you might wish to relax this slightly
            // to handle on-demand instantiation of functions via
            // foo::<bar> in a const. Currently that is only done on
            // a path in trans::callee that only works in block contexts.
            if pth.types.len() != 0 {
                sess.span_err(
                    e.span, ~"paths in constants may only refer to \
                              items without type parameters");
            }
            match def_map.find(e.id) {
              Some(def_const(def_id)) |
                Some(def_fn(def_id, _)) |
                Some(def_variant(_, def_id)) |
                Some(def_struct(def_id)) => {
                if !ast_util::is_local(def_id) {
                    sess.span_err(
                        e.span, ~"paths in constants may only refer to \
                                 crate-local constants, functions, or \
                                 structs");
                }
              }
              Some(def) => {
                debug!("(checking const) found bad def: %?", def);
                sess.span_err(
                    e.span,
                    fmt!("paths in constants may only refer to \
                          constants or functions"));
              }
              None => {
                sess.span_bug(e.span, ~"unbound path in const?!");
              }
            }
          }
          expr_call(callee, _, false) => {
            match def_map.find(callee.id) {
                Some(def_struct(*)) => {}    // OK.
                _ => {
                    sess.span_err(
                        e.span,
                        ~"function calls in constants are limited to \
                          structure constructors");
                }
            }
          }
          expr_paren(e) => { check_expr(sess, def_map, method_map,
                                         tcx, e, is_const, v); }
          expr_vstore(_, expr_vstore_slice) |
          expr_vstore(_, expr_vstore_fixed(_)) |
          expr_vec(_, m_imm) |
          expr_addr_of(m_imm, _) |
          expr_field(*) |
          expr_index(*) |
          expr_tup(*) |
          expr_struct(*) |
          expr_rec(*) => { }
          expr_addr_of(*) => {
                sess.span_err(
                    e.span,
                    ~"borrowed pointers in constants may only refer to \
                      immutable values");
          }
          _ => {
            sess.span_err(e.span,
                          ~"constant contains unimplemented expression type");
            return;
          }
        }
    }
    match e.node {
      expr_lit(@{node: lit_int(v, t), _}) => {
        if t != ty_char {
            if (v as u64) > ast_util::int_ty_max(
                if t == ty_i { sess.targ_cfg.int_type } else { t }) {
                sess.span_err(e.span, ~"literal out of range for its type");
            }
        }
      }
      expr_lit(@{node: lit_uint(v, t), _}) => {
        if v > ast_util::uint_ty_max(
            if t == ty_u { sess.targ_cfg.uint_type } else { t }) {
            sess.span_err(e.span, ~"literal out of range for its type");
        }
      }
      _ => ()
    }
    visit::visit_expr(e, is_const, v);
}

// Make sure a const item doesn't recursively refer to itself
// FIXME: Should use the dependency graph when it's available (#1356)
fn check_item_recursion(sess: Session, ast_map: ast_map::map,
                        def_map: resolve::DefMap, it: @item) {

    type env = {
        root_it: @item,
        sess: Session,
        ast_map: ast_map::map,
        def_map: resolve::DefMap,
        idstack: @DVec<node_id>,
    };

    let env = {
        root_it: it,
        sess: sess,
        ast_map: ast_map,
        def_map: def_map,
        idstack: @DVec()
    };

    let visitor = visit::mk_vt(@{
        visit_item: visit_item,
        visit_expr: visit_expr,
        .. *visit::default_visitor()
    });
    (visitor.visit_item)(it, env, visitor);

    fn visit_item(it: @item, &&env: env, v: visit::vt<env>) {
        if (*env.idstack).contains(&(it.id)) {
            env.sess.span_fatal(env.root_it.span, ~"recursive constant");
        }
        (*env.idstack).push(it.id);
        visit::visit_item(it, env, v);
        (*env.idstack).pop();
    }

    fn visit_expr(e: @expr, &&env: env, v: visit::vt<env>) {
        match e.node {
          expr_path(*) => {
            match env.def_map.find(e.id) {
              Some(def_const(def_id)) => {
                match env.ast_map.get(def_id.node) {
                  ast_map::node_item(it, _) => {
                    (v.visit_item)(it, env, v);
                  }
                  _ => fail ~"const not bound to an item"
                }
              }
              _ => ()
            }
          }
          _ => ()
        }
        visit::visit_expr(e, env, v);
    }
}

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