collect.rs

// Copyright 2012-2014 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.

/*

# Collect phase

The collect phase of type check has the job of visiting all items,
determining their type, and writing that type into the `tcx.tcache`
table.  Despite its name, this table does not really operate as a
*cache*, at least not for the types of items defined within the
current crate: we assume that after the collect phase, the types of
all local items will be present in the table.

Unlike most of the types that are present in Rust, the types computed
for each item are in fact polytypes.  In "layman's terms", this means
that they are generic types that may have type parameters (more
mathematically phrased, they are universally quantified over a set of
type parameters).  Polytypes are represented by an instance of
`ty::Polytype`.  This combines the core type along with a list of the
bounds for each parameter.  Type parameters themselves are represented
as `ty_param()` instances.

*/


use metadata::csearch;
use middle::def;
use middle::lang_items::SizedTraitLangItem;
use middle::resolve_lifetime;
use middle::subst;
use middle::subst::{Substs};
use middle::ty::{ImplContainer, ImplOrTraitItemContainer, TraitContainer};
use middle::ty::{Polytype};
use middle::ty;
use middle::ty_fold::TypeFolder;
use middle::typeck::astconv::{AstConv, ty_of_arg};
use middle::typeck::astconv::{ast_ty_to_ty};
use middle::typeck::astconv;
use middle::typeck::infer;
use middle::typeck::rscope::*;
use middle::typeck::{CrateCtxt, lookup_def_tcx, no_params, write_ty_to_tcx};
use middle::typeck;
use util::ppaux;
use util::ppaux::Repr;

use std::collections::{HashMap, HashSet};
use std::rc::Rc;
use std::gc::Gc;

use syntax::abi;
use syntax::ast::{StaticRegionTyParamBound, OtherRegionTyParamBound};
use syntax::ast::{TraitTyParamBound, UnboxedFnTyParamBound};
use syntax::ast;
use syntax::ast_map;
use syntax::ast_util::{local_def, split_trait_methods, PostExpansionMethod};
use syntax::codemap::Span;
use syntax::codemap;
use syntax::owned_slice::OwnedSlice;
use syntax::parse::token::special_idents;
use syntax::parse::token;
use syntax::print::pprust::{path_to_string};
use syntax::visit;

struct CollectItemTypesVisitor<'a> {
    ccx: &'a CrateCtxt<'a>
}

impl<'a> visit::Visitor<()> for CollectItemTypesVisitor<'a> {
    fn visit_item(&mut self, i: &ast::Item, _: ()) {
        convert(self.ccx, i);
        visit::walk_item(self, i, ());
    }
    fn visit_foreign_item(&mut self, i: &ast::ForeignItem, _: ()) {
        convert_foreign(self.ccx, i);
        visit::walk_foreign_item(self, i, ());
    }
}

pub fn collect_item_types(ccx: &CrateCtxt, krate: &ast::Crate) {
    fn collect_intrinsic_type(ccx: &CrateCtxt,
                              lang_item: ast::DefId) {
        let ty::Polytype { ty: ty, .. } =
            ccx.get_item_ty(lang_item);
        ccx.tcx.intrinsic_defs.borrow_mut().insert(lang_item, ty);
    }

    match ccx.tcx.lang_items.ty_desc() {
        Some(id) => { collect_intrinsic_type(ccx, id); } None => {}
    }
    match ccx.tcx.lang_items.opaque() {
        Some(id) => { collect_intrinsic_type(ccx, id); } None => {}
    }

    let mut visitor = CollectItemTypesVisitor{ ccx: ccx };
    visit::walk_crate(&mut visitor, krate, ());
}

pub trait ToTy {
    fn to_ty<RS:RegionScope>(&self, rs: &RS, ast_ty: &ast::Ty) -> ty::t;
}

impl<'a> ToTy for CrateCtxt<'a> {
    fn to_ty<RS:RegionScope>(&self, rs: &RS, ast_ty: &ast::Ty) -> ty::t {
        ast_ty_to_ty(self, rs, ast_ty)
    }
}

impl<'a> AstConv for CrateCtxt<'a> {
    fn tcx<'a>(&'a self) -> &'a ty::ctxt { self.tcx }

    fn get_item_ty(&self, id: ast::DefId) -> ty::Polytype {
        if id.krate != ast::LOCAL_CRATE {
            return csearch::get_type(self.tcx, id)
        }

        match self.tcx.map.find(id.node) {
            Some(ast_map::NodeItem(item)) => ty_of_item(self, &*item),
            Some(ast_map::NodeForeignItem(foreign_item)) => {
                let abi = self.tcx.map.get_foreign_abi(id.node);
                ty_of_foreign_item(self, &*foreign_item, abi)
            }
            x => {
                self.tcx.sess.bug(format!("unexpected sort of node \
                                           in get_item_ty(): {:?}",
                                          x).as_slice());
            }
        }
    }

    fn get_trait_def(&self, id: ast::DefId) -> Rc<ty::TraitDef> {
        get_trait_def(self, id)
    }

    fn ty_infer(&self, span: Span) -> ty::t {
        span_err!(self.tcx.sess, span, E0121,
                  "the type placeholder `_` is not allowed within types on item signatures.");
        ty::mk_err()
    }
}

pub fn get_enum_variant_types(ccx: &CrateCtxt,
                              enum_ty: ty::t,
                              variants: &[ast::P<ast::Variant>],
                              generics: &ast::Generics) {
    let tcx = ccx.tcx;

    // Create a set of parameter types shared among all the variants.
    for variant in variants.iter() {
        // Nullary enum constructors get turned into constants; n-ary enum
        // constructors get turned into functions.
        let scope = variant.node.id;
        let result_ty = match variant.node.kind {
            ast::TupleVariantKind(ref args) if args.len() > 0 => {
                let rs = ExplicitRscope;
                let input_tys: Vec<_> = args.iter().map(|va| ccx.to_ty(&rs, &*va.ty)).collect();
                ty::mk_ctor_fn(tcx, scope, input_tys.as_slice(), enum_ty)
            }

            ast::TupleVariantKind(_) => {
                enum_ty
            }

            ast::StructVariantKind(struct_def) => {
                let pty = Polytype {
                    generics: ty_generics_for_type(ccx, generics),
                    ty: enum_ty
                };

                convert_struct(ccx, &*struct_def, pty, variant.node.id);

                let input_tys: Vec<_> = struct_def.fields.iter().map(
                    |f| ty::node_id_to_type(ccx.tcx, f.node.id)).collect();
                ty::mk_ctor_fn(tcx, scope, input_tys.as_slice(), enum_ty)
            }
        };

        let pty = Polytype {
            generics: ty_generics_for_type(ccx, generics),
            ty: result_ty
        };

        tcx.tcache.borrow_mut().insert(local_def(variant.node.id), pty);

        write_ty_to_tcx(tcx, variant.node.id, result_ty);
    }
}

pub fn ensure_trait_methods(ccx: &CrateCtxt,
                            trait_id: ast::NodeId,
                            trait_def: &ty::TraitDef) {
    let tcx = ccx.tcx;
    match tcx.map.get(trait_id) {
        ast_map::NodeItem(item) => {
            match item.node {
                ast::ItemTrait(_, _, _, ref trait_items) => {
                    // For each method, construct a suitable ty::Method and
                    // store it into the `tcx.impl_or_trait_items` table:
                    for trait_item in trait_items.iter() {
                        match *trait_item {
                            ast::RequiredMethod(_) |
                            ast::ProvidedMethod(_) => {
                                let ty_method = Rc::new(match *trait_item {
                                    ast::RequiredMethod(ref m) => {
                                        ty_method_of_trait_method(
                                            ccx,
                                            trait_id,
                                            &trait_def.generics,
                                            &m.id,
                                            &m.ident,
                                            &m.explicit_self,
                                            m.abi,
                                            &m.generics,
                                            &m.fn_style,
                                            &*m.decl)
                                    }
                                    ast::ProvidedMethod(ref m) => {
                                        ty_method_of_trait_method(
                                            ccx,
                                            trait_id,
                                            &trait_def.generics,
                                            &m.id,
                                            &m.pe_ident(),
                                            m.pe_explicit_self(),
                                            m.pe_abi(),
                                            m.pe_generics(),
                                            &m.pe_fn_style(),
                                            &*m.pe_fn_decl())
                                    }
                                });

                                if ty_method.explicit_self ==
                                        ty::StaticExplicitSelfCategory {
                                    make_static_method_ty(ccx, &*ty_method);
                                }

                                tcx.impl_or_trait_items
                                   .borrow_mut()
                                   .insert(ty_method.def_id,
                                           ty::MethodTraitItem(ty_method));
                            }
                        }
                    }

                    // Add an entry mapping
                    let trait_item_def_ids =
                        Rc::new(trait_items.iter()
                                           .map(|ti| {
                            match *ti {
                                ast::RequiredMethod(ref ty_method) => {
                                    ty::MethodTraitItemId(local_def(
                                            ty_method.id))
                                }
                                ast::ProvidedMethod(ref method) => {
                                    ty::MethodTraitItemId(local_def(
                                            method.id))
                                }
                            }
                        }).collect());

                    let trait_def_id = local_def(trait_id);
                    tcx.trait_item_def_ids.borrow_mut()
                        .insert(trait_def_id, trait_item_def_ids);
                }
                _ => {} // Ignore things that aren't traits.
            }
        }
        _ => { /* Ignore things that aren't traits */ }
    }

    fn make_static_method_ty(ccx: &CrateCtxt, m: &ty::Method) {
        ccx.tcx.tcache.borrow_mut().insert(
            m.def_id,
            Polytype {
                generics: m.generics.clone(),
                ty: ty::mk_bare_fn(ccx.tcx, m.fty.clone()) });
    }

    fn ty_method_of_trait_method(this: &CrateCtxt,
                                 trait_id: ast::NodeId,
                                 trait_generics: &ty::Generics,
                                 m_id: &ast::NodeId,
                                 m_ident: &ast::Ident,
                                 m_explicit_self: &ast::ExplicitSelf,
                                 m_abi: abi::Abi,
                                 m_generics: &ast::Generics,
                                 m_fn_style: &ast::FnStyle,
                                 m_decl: &ast::FnDecl)
                                 -> ty::Method {
        let trait_self_ty = ty::mk_self_type(this.tcx, local_def(trait_id));

        let (fty, explicit_self_category) =
            astconv::ty_of_method(this,
                                  *m_id,
                                  *m_fn_style,
                                  trait_self_ty,
                                  *m_explicit_self,
                                  m_decl,
                                  m_abi);
        let ty_generics =
            ty_generics_for_fn_or_method(this,
                                         m_generics,
                                         (*trait_generics).clone());
        ty::Method::new(
            *m_ident,
            ty_generics,
            fty,
            explicit_self_category,
            // assume public, because this is only invoked on trait methods
            ast::Public,
            local_def(*m_id),
            TraitContainer(local_def(trait_id)),
            None
        )
    }
}

pub fn convert_field(ccx: &CrateCtxt,
                     struct_generics: &ty::Generics,
                     v: &ast::StructField,
                     origin: ast::DefId) -> ty::field_ty {
    let tt = ccx.to_ty(&ExplicitRscope, &*v.node.ty);
    write_ty_to_tcx(ccx.tcx, v.node.id, tt);
    /* add the field to the tcache */
    ccx.tcx.tcache.borrow_mut().insert(local_def(v.node.id),
                                       ty::Polytype {
                                           generics: struct_generics.clone(),
                                           ty: tt
                                       });

    match v.node.kind {
        ast::NamedField(ident, visibility) => {
            ty::field_ty {
                name: ident.name,
                id: local_def(v.node.id),
                vis: visibility,
                origin: origin,
            }
        }
        ast::UnnamedField(visibility) => {
            ty::field_ty {
                name: special_idents::unnamed_field.name,
                id: local_def(v.node.id),
                vis: visibility,
                origin: origin,
            }
        }
    }
}

fn convert_methods(ccx: &CrateCtxt,
                   container: ImplOrTraitItemContainer,
                   ms: &[Gc<ast::Method>],
                   untransformed_rcvr_ty: ty::t,
                   rcvr_ty_generics: &ty::Generics,
                   rcvr_visibility: ast::Visibility) {
    let tcx = ccx.tcx;
    let mut seen_methods = HashSet::new();
    for m in ms.iter() {
        if !seen_methods.insert(m.pe_ident().repr(ccx.tcx)) {
            tcx.sess.span_err(m.span, "duplicate method in trait impl");
        }

        let mty = Rc::new(ty_of_method(ccx,
                                       container,
                                       &**m,
                                       untransformed_rcvr_ty,
                                       rcvr_ty_generics,
                                       rcvr_visibility));
        let fty = ty::mk_bare_fn(tcx, mty.fty.clone());
        debug!("method {} (id {}) has type {}",
                m.pe_ident().repr(ccx.tcx),
                m.id,
                fty.repr(ccx.tcx));
        tcx.tcache.borrow_mut().insert(
            local_def(m.id),
            Polytype {
                generics: mty.generics.clone(),
                ty: fty
            });

        write_ty_to_tcx(tcx, m.id, fty);

        tcx.impl_or_trait_items
           .borrow_mut()
           .insert(mty.def_id, ty::MethodTraitItem(mty));
    }

    fn ty_of_method(ccx: &CrateCtxt,
                    container: ImplOrTraitItemContainer,
                    m: &ast::Method,
                    untransformed_rcvr_ty: ty::t,
                    rcvr_ty_generics: &ty::Generics,
                    rcvr_visibility: ast::Visibility)
                    -> ty::Method {
        // FIXME(pcwalton): Hack until we have syntax in stage0 for snapshots.
        let real_abi = match container {
            ty::TraitContainer(trait_id) => {
                if ccx.tcx.lang_items.fn_trait() == Some(trait_id) ||
                        ccx.tcx.lang_items.fn_mut_trait() == Some(trait_id) ||
                        ccx.tcx.lang_items.fn_once_trait() == Some(trait_id) {
                    abi::RustCall
                } else {
                    m.pe_abi()
                }
            }
            _ => m.pe_abi(),
        };

        let (fty, explicit_self_category) =
            astconv::ty_of_method(ccx,
                                  m.id,
                                  m.pe_fn_style(),
                                  untransformed_rcvr_ty,
                                  *m.pe_explicit_self(),
                                  &*m.pe_fn_decl(),
                                  real_abi);

        // if the method specifies a visibility, use that, otherwise
        // inherit the visibility from the impl (so `foo` in `pub impl
        // { fn foo(); }` is public, but private in `priv impl { fn
        // foo(); }`).
        let method_vis = m.pe_vis().inherit_from(rcvr_visibility);

        let m_ty_generics =
            ty_generics_for_fn_or_method(ccx, m.pe_generics(),
                                         (*rcvr_ty_generics).clone());
        ty::Method::new(m.pe_ident(),
                        m_ty_generics,
                        fty,
                        explicit_self_category,
                        method_vis,
                        local_def(m.id),
                        container,
                        None)
    }
}

pub fn ensure_no_ty_param_bounds(ccx: &CrateCtxt,
                                 span: Span,
                                 generics: &ast::Generics,
                                 thing: &'static str) {
    for ty_param in generics.ty_params.iter() {
        if ty_param.bounds.len() > 0 {
            span_err!(ccx.tcx.sess, span, E0122,
                      "trait bounds are not allowed in {} definitions", thing);
        }
    }
}

pub fn convert(ccx: &CrateCtxt, it: &ast::Item) {
    let tcx = ccx.tcx;
    debug!("convert: item {} with id {}", token::get_ident(it.ident), it.id);
    match it.node {
        // These don't define types.
        ast::ItemForeignMod(_) | ast::ItemMod(_) | ast::ItemMac(_) => {}
        ast::ItemEnum(ref enum_definition, ref generics) => {
            ensure_no_ty_param_bounds(ccx, it.span, generics, "enumeration");
            let pty = ty_of_item(ccx, it);
            write_ty_to_tcx(tcx, it.id, pty.ty);
            get_enum_variant_types(ccx,
                                   pty.ty,
                                   enum_definition.variants.as_slice(),
                                   generics);
        },
        ast::ItemImpl(ref generics,
                      ref opt_trait_ref,
                      selfty,
                      ref impl_items) => {
            let ty_generics = ty_generics_for_type(ccx, generics);
            let selfty = ccx.to_ty(&ExplicitRscope, &*selfty);
            write_ty_to_tcx(tcx, it.id, selfty);

            tcx.tcache.borrow_mut().insert(local_def(it.id),
                                Polytype {
                                    generics: ty_generics.clone(),
                                    ty: selfty});

            // If there is a trait reference, treat the methods as always public.
            // This is to work around some incorrect behavior in privacy checking:
            // when the method belongs to a trait, it should acquire the privacy
            // from the trait, not the impl. Forcing the visibility to be public
            // makes things sorta work.
            let parent_visibility = if opt_trait_ref.is_some() {
                ast::Public
            } else {
                it.vis
            };

            let mut methods = Vec::new();
            for impl_item in impl_items.iter() {
                match *impl_item {
                    ast::MethodImplItem(ref method) => {
                        check_method_self_type(ccx,
                                               &BindingRscope::new(method.id),
                                               selfty,
                                               method.pe_explicit_self());
                        methods.push(*method);
                    }
                }
            }

            convert_methods(ccx,
                            ImplContainer(local_def(it.id)),
                            methods.as_slice(),
                            selfty,
                            &ty_generics,
                            parent_visibility);

            for trait_ref in opt_trait_ref.iter() {
                instantiate_trait_ref(ccx, trait_ref, selfty);
            }
        },
        ast::ItemTrait(_, _, _, ref trait_methods) => {
            let trait_def = trait_def_of_item(ccx, it);

            for trait_method in trait_methods.iter() {
                let self_type = ty::mk_param(ccx.tcx,
                                             subst::SelfSpace,
                                             0,
                                             local_def(it.id));
                match *trait_method {
                    ast::RequiredMethod(ref type_method) => {
                        let rscope = BindingRscope::new(type_method.id);
                        check_method_self_type(ccx,
                                               &rscope,
                                               self_type,
                                               &type_method.explicit_self)
                    }
                    ast::ProvidedMethod(ref method) => {
                        check_method_self_type(ccx,
                                               &BindingRscope::new(method.id),
                                               self_type,
                                               method.pe_explicit_self())
                    }
                }
            }

            // Run convert_methods on the provided methods.
            let (_, provided_methods) =
                split_trait_methods(trait_methods.as_slice());
            let untransformed_rcvr_ty = ty::mk_self_type(tcx, local_def(it.id));
            convert_methods(ccx,
                            TraitContainer(local_def(it.id)),
                            provided_methods.as_slice(),
                            untransformed_rcvr_ty,
                            &trait_def.generics,
                            it.vis);

            // We need to do this *after* converting methods, since
            // convert_methods produces a tcache entry that is wrong for
            // static trait methods. This is somewhat unfortunate.
            ensure_trait_methods(ccx, it.id, &*trait_def);
        },
        ast::ItemStruct(struct_def, ref generics) => {
            ensure_no_ty_param_bounds(ccx, it.span, generics, "structure");

            // Write the class type.
            let pty = ty_of_item(ccx, it);
            write_ty_to_tcx(tcx, it.id, pty.ty);

            tcx.tcache.borrow_mut().insert(local_def(it.id), pty.clone());

            // Write the super-struct type, if it exists.
            match struct_def.super_struct {
                Some(ty) => {
                    let supserty = ccx.to_ty(&ExplicitRscope, &*ty);
                    write_ty_to_tcx(tcx, it.id, supserty);
                },
                _ => {},
            }

            convert_struct(ccx, &*struct_def, pty, it.id);
        },
        ast::ItemTy(_, ref generics) => {
            ensure_no_ty_param_bounds(ccx, it.span, generics, "type");
            let tpt = ty_of_item(ccx, it);
            write_ty_to_tcx(tcx, it.id, tpt.ty);
        },
        _ => {
            // This call populates the type cache with the converted type
            // of the item in passing. All we have to do here is to write
            // it into the node type table.
            let pty = ty_of_item(ccx, it);
            write_ty_to_tcx(tcx, it.id, pty.ty);
        },
    }
}

pub fn convert_struct(ccx: &CrateCtxt,
                      struct_def: &ast::StructDef,
                      pty: ty::Polytype,
                      id: ast::NodeId) {
    let tcx = ccx.tcx;

    // Write the type of each of the members and check for duplicate fields.
    let mut seen_fields: HashMap<ast::Name, Span> = HashMap::new();
    let field_tys = struct_def.fields.iter().map(|f| {
        let result = convert_field(ccx, &pty.generics, f, local_def(id));

        if result.name != special_idents::unnamed_field.name {
            let dup = match seen_fields.find(&result.name) {
                Some(prev_span) => {
                    span_err!(tcx.sess, f.span, E0124,
                              "field `{}` is already declared",
                              token::get_name(result.name));
                    span_note!(tcx.sess, *prev_span, "previously declared here");
                    true
                },
                None => false,
            };
            // FIXME(#6393) this whole dup thing is just to satisfy
            // the borrow checker :-(
            if !dup {
                seen_fields.insert(result.name, f.span);
            }
        }

        result
    }).collect();

    tcx.struct_fields.borrow_mut().insert(local_def(id), Rc::new(field_tys));

    let super_struct = match struct_def.super_struct {
        Some(t) => match t.node {
            ast::TyPath(_, _, path_id) => {
                let def_map = tcx.def_map.borrow();
                match def_map.find(&path_id) {
                    Some(&def::DefStruct(def_id)) => {
                        // FIXME(#12511) Check for cycles in the inheritance hierarchy.
                        // Check super-struct is virtual.
                        match tcx.map.find(def_id.node) {
                            Some(ast_map::NodeItem(i)) => match i.node {
                                ast::ItemStruct(struct_def, _) => {
                                    if !struct_def.is_virtual {
                                        span_err!(tcx.sess, t.span, E0126,
                                                  "struct inheritance is only \
                                                   allowed from virtual structs");
                                    }
                                },
                                _ => {},
                            },
                            _ => {},
                        }

                        Some(def_id)
                    },
                    _ => None,
                }
            }
            _ => None,
        },
        None => None,
    };
    tcx.superstructs.borrow_mut().insert(local_def(id), super_struct);

    let substs = mk_item_substs(ccx, &pty.generics);
    let selfty = ty::mk_struct(tcx, local_def(id), substs);

    // If this struct is enum-like or tuple-like, create the type of its
    // constructor.
    match struct_def.ctor_id {
        None => {}
        Some(ctor_id) => {
            if struct_def.fields.len() == 0 {
                // Enum-like.
                write_ty_to_tcx(tcx, ctor_id, selfty);

                tcx.tcache.borrow_mut().insert(local_def(ctor_id), pty);
            } else if struct_def.fields.get(0).node.kind.is_unnamed() {
                // Tuple-like.
                let inputs: Vec<_> = struct_def.fields.iter().map(
                        |field| tcx.tcache.borrow().get(
                            &local_def(field.node.id)).ty).collect();
                let ctor_fn_ty = ty::mk_ctor_fn(tcx,
                                                ctor_id,
                                                inputs.as_slice(),
                                                selfty);
                write_ty_to_tcx(tcx, ctor_id, ctor_fn_ty);
                tcx.tcache.borrow_mut().insert(local_def(ctor_id),
                                  Polytype {
                    generics: pty.generics,
                    ty: ctor_fn_ty
                });
            }
        }
    }
}

pub fn convert_foreign(ccx: &CrateCtxt, i: &ast::ForeignItem) {
    // As above, this call populates the type table with the converted
    // type of the foreign item. We simply write it into the node type
    // table.

    // For reasons I cannot fully articulate, I do so hate the AST
    // map, and I regard each time that I use it as a personal and
    // moral failing, but at the moment it seems like the only
    // convenient way to extract the ABI. - ndm
    let abi = ccx.tcx.map.get_foreign_abi(i.id);

    let pty = ty_of_foreign_item(ccx, i, abi);
    write_ty_to_tcx(ccx.tcx, i.id, pty.ty);

    ccx.tcx.tcache.borrow_mut().insert(local_def(i.id), pty);
}

pub fn instantiate_trait_ref(ccx: &CrateCtxt,
                             ast_trait_ref: &ast::TraitRef,
                             self_ty: ty::t) -> Rc<ty::TraitRef> {
    /*!
     * Instantiates the path for the given trait reference, assuming that
     * it's bound to a valid trait type. Returns the def_id for the defining
     * trait. Fails if the type is a type other than a trait type.
     */

    // FIXME(#5121) -- distinguish early vs late lifetime params
    let rscope = ExplicitRscope;

    match lookup_def_tcx(ccx.tcx, ast_trait_ref.path.span, ast_trait_ref.ref_id) {
        def::DefTrait(trait_did) => {
            let trait_ref =
                astconv::ast_path_to_trait_ref(
                    ccx, &rscope, trait_did, Some(self_ty), &ast_trait_ref.path);

            ccx.tcx.trait_refs.borrow_mut().insert(ast_trait_ref.ref_id,
                                                   trait_ref.clone());
            trait_ref
        }
        _ => {
            ccx.tcx.sess.span_fatal(
                ast_trait_ref.path.span,
                format!("`{}` is not a trait",
                        path_to_string(&ast_trait_ref.path)).as_slice());
        }
    }
}

fn get_trait_def(ccx: &CrateCtxt, trait_id: ast::DefId) -> Rc<ty::TraitDef> {
    if trait_id.krate != ast::LOCAL_CRATE {
        return ty::lookup_trait_def(ccx.tcx, trait_id)
    }

    match ccx.tcx.map.get(trait_id.node) {
        ast_map::NodeItem(item) => trait_def_of_item(ccx, &*item),
        _ => {
            ccx.tcx.sess.bug(format!("get_trait_def({}): not an item",
                                     trait_id.node).as_slice())
        }
    }
}

pub fn trait_def_of_item(ccx: &CrateCtxt, it: &ast::Item) -> Rc<ty::TraitDef> {
    let def_id = local_def(it.id);
    let tcx = ccx.tcx;
    match tcx.trait_defs.borrow().find(&def_id) {
        Some(def) => return def.clone(),
        _ => {}
    }

    let (generics, unbound, supertraits) = match it.node {
        ast::ItemTrait(ref generics, ref unbound, ref supertraits, _) => {
            (generics, unbound, supertraits)
        }
        ref s => {
            tcx.sess.span_bug(
                it.span,
                format!("trait_def_of_item invoked on {:?}", s).as_slice());
        }
    };

    let substs = mk_trait_substs(ccx, it.id, generics);

    let ty_generics = ty_generics_for_trait(ccx,
                                            it.id,
                                            &substs,
                                            generics);

    let builtin_bounds =
        ensure_supertraits(ccx, it.id, it.span, supertraits, unbound);

    let substs = mk_item_substs(ccx, &ty_generics);
    let trait_def = Rc::new(ty::TraitDef {
        generics: ty_generics,
        bounds: builtin_bounds,
        trait_ref: Rc::new(ty::TraitRef {
            def_id: def_id,
            substs: substs
        })
    });
    tcx.trait_defs.borrow_mut().insert(def_id, trait_def.clone());

    return trait_def;

    fn mk_trait_substs(ccx: &CrateCtxt,
                       trait_id: ast::NodeId,
                       generics: &ast::Generics)
                        -> subst::Substs
    {
        // Creates a no-op substitution for the trait's type parameters.
        let regions =
            generics.lifetimes
                    .iter()
                    .enumerate()
                    .map(|(i, def)| ty::ReEarlyBound(def.lifetime.id,
                                                     subst::TypeSpace,
                                                     i,
                                                     def.lifetime.name))
                    .collect();

        let types =
            generics.ty_params
                    .iter()
                    .enumerate()
                    .map(|(i, def)| ty::mk_param(ccx.tcx, subst::TypeSpace,
                                                 i, local_def(def.id)))
                    .collect();

        let self_ty =
            ty::mk_param(ccx.tcx, subst::SelfSpace, 0, local_def(trait_id));

        subst::Substs::new_trait(types, regions, self_ty)
    }

    fn ensure_supertraits(ccx: &CrateCtxt,
                          id: ast::NodeId,
                          sp: codemap::Span,
                          ast_trait_refs: &Vec<ast::TraitRef>,
                          unbound: &Option<ast::TyParamBound>)
                          -> ty::BuiltinBounds
    {
        let tcx = ccx.tcx;

        // Called only the first time trait_def_of_item is called.
        // Supertraits are ensured at the same time.
        assert!(!tcx.supertraits.borrow().contains_key(&local_def(id)));

        let self_ty = ty::mk_self_type(ccx.tcx, local_def(id));
        let mut ty_trait_refs: Vec<Rc<ty::TraitRef>> = Vec::new();
        let mut bounds = ty::empty_builtin_bounds();
        for ast_trait_ref in ast_trait_refs.iter() {
            let trait_def_id = ty::trait_ref_to_def_id(ccx.tcx, ast_trait_ref);

            // FIXME(#8559): Need to instantiate the trait_ref whether
            // or not it's a builtin trait, so that the trait's node
            // id appears in the tcx trait_ref map. This is only
            // needed for metadata; see the similar fixme in
            // encoder.rs.

            let trait_ref = instantiate_trait_ref(ccx, ast_trait_ref, self_ty);
            if !ty::try_add_builtin_trait(ccx.tcx, trait_def_id, &mut bounds) {

                // FIXME(#5527) Could have same trait multiple times
                if ty_trait_refs.iter().any(
                    |other_trait| other_trait.def_id == trait_ref.def_id)
                {
                    // This means a trait inherited from the same
                    // supertrait more than once.
                    span_err!(tcx.sess, sp, E0127,
                              "duplicate supertrait in trait declaration");
                    break;
                } else {
                    ty_trait_refs.push(trait_ref);
                }
            }
        }

        add_unsized_bound(ccx, unbound, &mut bounds, "trait", sp);
        tcx.supertraits.borrow_mut().insert(local_def(id),
                                            Rc::new(ty_trait_refs));
        bounds
    }
}

pub fn ty_of_item(ccx: &CrateCtxt, it: &ast::Item)
                  -> ty::Polytype {
    let def_id = local_def(it.id);
    let tcx = ccx.tcx;
    match tcx.tcache.borrow().find(&def_id) {
        Some(pty) => return pty.clone(),
        _ => {}
    }
    match it.node {
        ast::ItemStatic(t, _, _) => {
            let typ = ccx.to_ty(&ExplicitRscope, &*t);
            let pty = no_params(typ);

            tcx.tcache.borrow_mut().insert(local_def(it.id), pty.clone());
            return pty;
        }
        ast::ItemFn(decl, fn_style, abi, ref generics, _) => {
            let ty_generics = ty_generics_for_fn_or_method(ccx, generics,
                                                           ty::Generics::empty());
            let tofd = astconv::ty_of_bare_fn(ccx,
                                              it.id,
                                              fn_style,
                                              abi,
                                              &*decl);
            let pty = Polytype {
                generics: ty_generics,
                ty: ty::mk_bare_fn(ccx.tcx, tofd)
            };
            debug!("type of {} (id {}) is {}",
                    token::get_ident(it.ident),
                    it.id,
                    ppaux::ty_to_string(tcx, pty.ty));

            ccx.tcx.tcache.borrow_mut().insert(local_def(it.id), pty.clone());
            return pty;
        }
        ast::ItemTy(t, ref generics) => {
            match tcx.tcache.borrow_mut().find(&local_def(it.id)) {
                Some(pty) => return pty.clone(),
                None => { }
            }

            let pty = {
                let ty = ccx.to_ty(&ExplicitRscope, &*t);
                Polytype {
                    generics: ty_generics_for_type(ccx, generics),
                    ty: ty
                }
            };

            tcx.tcache.borrow_mut().insert(local_def(it.id), pty.clone());
            return pty;
        }
        ast::ItemEnum(_, ref generics) => {
            // Create a new generic polytype.
            let ty_generics = ty_generics_for_type(ccx, generics);
            let substs = mk_item_substs(ccx, &ty_generics);
            let t = ty::mk_enum(tcx, local_def(it.id), substs);
            let pty = Polytype {
                generics: ty_generics,
                ty: t
            };

            tcx.tcache.borrow_mut().insert(local_def(it.id), pty.clone());
            return pty;
        }
        ast::ItemTrait(..) => {
            tcx.sess.span_bug(it.span, "invoked ty_of_item on trait");
        }
        ast::ItemStruct(_, ref generics) => {
            let ty_generics = ty_generics_for_type(ccx, generics);
            let substs = mk_item_substs(ccx, &ty_generics);
            let t = ty::mk_struct(tcx, local_def(it.id), substs);
            let pty = Polytype {
                generics: ty_generics,
                ty: t
            };

            tcx.tcache.borrow_mut().insert(local_def(it.id), pty.clone());
            return pty;
        }
        ast::ItemImpl(..) | ast::ItemMod(_) |
        ast::ItemForeignMod(_) | ast::ItemMac(_) => fail!(),
    }
}

pub fn ty_of_foreign_item(ccx: &CrateCtxt,
                          it: &ast::ForeignItem,
                          abi: abi::Abi) -> ty::Polytype
{
    match it.node {
        ast::ForeignItemFn(fn_decl, ref generics) => {
            ty_of_foreign_fn_decl(ccx,
                                  &*fn_decl,
                                  local_def(it.id),
                                  generics,
                                  abi)
        }
        ast::ForeignItemStatic(t, _) => {
            ty::Polytype {
                generics: ty::Generics::empty(),
                ty: ast_ty_to_ty(ccx, &ExplicitRscope, &*t)
            }
        }
    }
}

fn ty_generics_for_type(ccx: &CrateCtxt,
                        generics: &ast::Generics)
                        -> ty::Generics {
    ty_generics(ccx,
                subst::TypeSpace,
                &generics.lifetimes,
                &generics.ty_params,
                ty::Generics::empty(),
                &generics.where_clause)
}

fn ty_generics_for_trait(ccx: &CrateCtxt,
                         trait_id: ast::NodeId,
                         substs: &subst::Substs,
                         generics: &ast::Generics)
                         -> ty::Generics {
    let mut generics = ty_generics(ccx,
                                   subst::TypeSpace,
                                   &generics.lifetimes,
                                   &generics.ty_params,
                                   ty::Generics::empty(),
                                   &generics.where_clause);

    // Something of a hack: use the node id for the trait, also as
    // the node id for the Self type parameter.
    let param_id = trait_id;

    let self_trait_ref =
        Rc::new(ty::TraitRef { def_id: local_def(trait_id),
                               substs: (*substs).clone() });

    let def = ty::TypeParameterDef {
        space: subst::SelfSpace,
        index: 0,
        ident: special_idents::type_self,
        def_id: local_def(param_id),
        bounds: Rc::new(ty::ParamBounds {
            builtin_bounds: ty::empty_builtin_bounds(),
            trait_bounds: vec!(self_trait_ref),
        }),
        default: None
    };

    ccx.tcx.ty_param_defs.borrow_mut().insert(param_id, def.clone());

    generics.types.push(subst::SelfSpace, def);

    generics
}

fn ty_generics_for_fn_or_method(ccx: &CrateCtxt,
                                generics: &ast::Generics,
                                base_generics: ty::Generics)
                                -> ty::Generics {
    let early_lifetimes = resolve_lifetime::early_bound_lifetimes(generics);
    ty_generics(ccx,
                subst::FnSpace,
                &early_lifetimes,
                &generics.ty_params,
                base_generics,
                &generics.where_clause)
}

// Add the Sized bound, unless the type parameter is marked as `Sized?`.
fn add_unsized_bound(ccx: &CrateCtxt,
                     unbound: &Option<ast::TyParamBound>,
                     bounds: &mut ty::BuiltinBounds,
                     desc: &str,
                     span: Span) {
    let kind_id = ccx.tcx.lang_items.require(SizedTraitLangItem);
    match unbound {
        &Some(TraitTyParamBound(ref tpb)) => {
            // #FIXME(8559) currently requires the unbound to be built-in.
            let trait_def_id = ty::trait_ref_to_def_id(ccx.tcx, tpb);
            match kind_id {
                Ok(kind_id) if trait_def_id != kind_id => {
                    ccx.tcx.sess.span_warn(span,
                                           format!("default bound relaxed \
                                                    for a {}, but this does \
                                                    nothing because the given \
                                                    bound is not a default. \
                                                    Only `Sized?` is supported.",
                                                   desc).as_slice());
                    ty::try_add_builtin_trait(ccx.tcx,
                                              kind_id,
                                              bounds);
                }
                _ => {}
            }
        }
        _ if kind_id.is_ok() => {
            ty::try_add_builtin_trait(ccx.tcx,
                                      kind_id.unwrap(),
                                      bounds);
        }
        // No lang item for Sized, so we can't add it as a bound.
        _ => {}
    }
}

fn ty_generics(ccx: &CrateCtxt,
               space: subst::ParamSpace,
               lifetimes: &Vec<ast::LifetimeDef>,
               types: &OwnedSlice<ast::TyParam>,
               base_generics: ty::Generics,
               where_clause: &ast::WhereClause)
               -> ty::Generics {
    let mut result = base_generics;

    for (i, l) in lifetimes.iter().enumerate() {
        let def = ty::RegionParameterDef { name: l.lifetime.name,
                                           space: space,
                                           index: i,
                                           def_id: local_def(l.lifetime.id) };
        debug!("ty_generics: def for region param: {}", def);
        result.regions.push(space, def);
    }

    for (i, param) in types.iter().enumerate() {
        let def = get_or_create_type_parameter_def(ccx,
                                                   space,
                                                   param,
                                                   i,
                                                   where_clause);
        debug!("ty_generics: def for type param: {}", def.repr(ccx.tcx));
        result.types.push(space, def);
    }

    return result;

    fn get_or_create_type_parameter_def(ccx: &CrateCtxt,
                                        space: subst::ParamSpace,
                                        param: &ast::TyParam,
                                        index: uint,
                                        where_clause: &ast::WhereClause)
                                        -> ty::TypeParameterDef {
        match ccx.tcx.ty_param_defs.borrow().find(&param.id) {
            Some(d) => { return (*d).clone(); }
            None => { }
        }

        let param_ty = ty::ParamTy {space: space,
                                    idx: index,
                                    def_id: local_def(param.id)};
        let bounds = Rc::new(compute_bounds(ccx,
                                            param_ty,
                                            &param.bounds,
                                            &param.unbound,
                                            param.ident,
                                            param.span,
                                            where_clause));
        let default = param.default.map(|path| {
            let ty = ast_ty_to_ty(ccx, &ExplicitRscope, &*path);
            let cur_idx = param_ty.idx;

            ty::walk_ty(ty, |t| {
                match ty::get(t).sty {
                    ty::ty_param(p) => if p.idx > cur_idx {
                    span_err!(ccx.tcx.sess, path.span, E0128,
                              "type parameters with a default cannot use \
                               forward declared identifiers");
                    },
                    _ => {}
                }
            });

            ty
        });

        let def = ty::TypeParameterDef {
            space: space,
            index: index,
            ident: param.ident,
            def_id: local_def(param.id),
            bounds: bounds,
            default: default
        };

        ccx.tcx.ty_param_defs.borrow_mut().insert(param.id, def.clone());

        def
    }

    fn compute_bounds(ccx: &CrateCtxt,
                      param_ty: ty::ParamTy,
                      ast_bounds: &OwnedSlice<ast::TyParamBound>,
                      unbound: &Option<ast::TyParamBound>,
                      ident: ast::Ident,
                      span: Span,
                      where_clause: &ast::WhereClause)
                      -> ty::ParamBounds {
        /*!
         * Translate the AST's notion of ty param bounds (which are an
         * enum consisting of a newtyped Ty or a region) to ty's
         * notion of ty param bounds, which can either be user-defined
         * traits, or the built-in trait (formerly known as kind): Send.
         */

        let mut param_bounds = ty::ParamBounds {
            builtin_bounds: ty::empty_builtin_bounds(),
            trait_bounds: Vec::new()
        };
        for ast_bound in ast_bounds.iter() {
            compute_bound(ccx, &mut param_bounds, param_ty, ast_bound);
        }
        for predicate in where_clause.predicates.iter() {
            let predicate_param_id = ccx.tcx
                                        .def_map
                                        .borrow()
                                        .find(&predicate.id)
                                        .expect("compute_bounds(): resolve \
                                                 didn't resolve the type \
                                                 parameter identifier in a \
                                                 `where` clause")
                                        .def_id();
            if param_ty.def_id != predicate_param_id {
                continue
            }
            for bound in predicate.bounds.iter() {
                compute_bound(ccx, &mut param_bounds, param_ty, bound);
            }
        }

        add_unsized_bound(ccx,
                          unbound,
                          &mut param_bounds.builtin_bounds,
                          "type parameter",
                          span);

        check_bounds_compatible(ccx.tcx, &param_bounds, ident, span);

        param_bounds.trait_bounds.sort_by(|a,b| a.def_id.cmp(&b.def_id));

        param_bounds
    }

    /// Translates the AST's notion of a type parameter bound to
    /// typechecking's notion of the same, and pushes the resulting bound onto
    /// the appropriate section of `param_bounds`.
    fn compute_bound(ccx: &CrateCtxt,
                     param_bounds: &mut ty::ParamBounds,
                     param_ty: ty::ParamTy,
                     ast_bound: &ast::TyParamBound) {
        match *ast_bound {
            TraitTyParamBound(ref b) => {
                let ty = ty::mk_param(ccx.tcx, param_ty.space,
                                      param_ty.idx, param_ty.def_id);
                let trait_ref = instantiate_trait_ref(ccx, b, ty);
                if !ty::try_add_builtin_trait(
                        ccx.tcx, trait_ref.def_id,
                        &mut param_bounds.builtin_bounds) {
                    // Must be a user-defined trait
                    param_bounds.trait_bounds.push(trait_ref);
                }
            }

            StaticRegionTyParamBound => {
                param_bounds.builtin_bounds.add(ty::BoundStatic);
            }

            UnboxedFnTyParamBound(ref unboxed_function) => {
                let rscope = ExplicitRscope;
                let self_ty = ty::mk_param(ccx.tcx,
                                           param_ty.space,
                                           param_ty.idx,
                                           param_ty.def_id);
                let trait_ref =
                    astconv::trait_ref_for_unboxed_function(ccx,
                                                            &rscope,
                                                            unboxed_function,
                                                            Some(self_ty));
                param_bounds.trait_bounds.push(Rc::new(trait_ref));
            }

            OtherRegionTyParamBound(span) => {
                if !ccx.tcx.sess.features.issue_5723_bootstrap.get() {
                    ccx.tcx.sess.span_err(
                        span,
                        "only the 'static lifetime is accepted here.");
                }
            }
        }
    }

    fn check_bounds_compatible(tcx: &ty::ctxt,
                               param_bounds: &ty::ParamBounds,
                               ident: ast::Ident,
                               span: Span) {
        // Currently the only bound which is incompatible with other bounds is
        // Sized/Unsized.
        if !param_bounds.builtin_bounds.contains_elem(ty::BoundSized) {
            ty::each_bound_trait_and_supertraits(tcx,
                                                 param_bounds.trait_bounds.as_slice(),
                                                 |trait_ref| {
                let trait_def = ty::lookup_trait_def(tcx, trait_ref.def_id);
                if trait_def.bounds.contains_elem(ty::BoundSized) {
                    span_err!(tcx.sess, span, E0129,
                              "incompatible bounds on type parameter {}, \
                               bound {} does not allow unsized type",
                              token::get_ident(ident),
                              ppaux::trait_ref_to_string(tcx, &*trait_ref));
                }
                true
            });
        }
    }
}

pub fn ty_of_foreign_fn_decl(ccx: &CrateCtxt,
                             decl: &ast::FnDecl,
                             def_id: ast::DefId,
                             ast_generics: &ast::Generics,
                             abi: abi::Abi)
                          -> ty::Polytype {

    for i in decl.inputs.iter() {
        match (*i).pat.node {
            ast::PatIdent(_, _, _) => (),
            ast::PatWild(ast::PatWildSingle) => (),
            _ => {
                span_err!(ccx.tcx.sess, (*i).pat.span, E0130,
                          "patterns aren't allowed in foreign function declarations");
            }
        }
    }

    let ty_generics_for_fn_or_method =
        ty_generics_for_fn_or_method(ccx, ast_generics,
                                     ty::Generics::empty());
    let rb = BindingRscope::new(def_id.node);
    let input_tys = decl.inputs
                        .iter()
                        .map(|a| ty_of_arg(ccx, &rb, a, None))
                        .collect();

    let output_ty = ast_ty_to_ty(ccx, &rb, &*decl.output);

    let t_fn = ty::mk_bare_fn(
        ccx.tcx,
        ty::BareFnTy {
            abi: abi,
            fn_style: ast::UnsafeFn,
            sig: ty::FnSig {binder_id: def_id.node,
                            inputs: input_tys,
                            output: output_ty,
                            variadic: decl.variadic}
        });
    let pty = Polytype {
        generics: ty_generics_for_fn_or_method,
        ty: t_fn
    };

    ccx.tcx.tcache.borrow_mut().insert(def_id, pty.clone());
    return pty;
}

pub fn mk_item_substs(ccx: &CrateCtxt,
                      ty_generics: &ty::Generics)
                      -> subst::Substs
{
    let types =
        ty_generics.types.map(
            |def| ty::mk_param_from_def(ccx.tcx, def));

    let regions =
        ty_generics.regions.map(
            |def| ty::ReEarlyBound(def.def_id.node, def.space,
                                   def.index, def.name));

    subst::Substs::new(types, regions)
}

/// Verifies that the explicit self type of a method matches the impl or
/// trait.
fn check_method_self_type<RS:RegionScope>(
                          crate_context: &CrateCtxt,
                          rs: &RS,
                          required_type: ty::t,
                          explicit_self: &ast::ExplicitSelf) {
    match explicit_self.node {
        ast::SelfExplicit(ref ast_type, _) => {
            let typ = crate_context.to_ty(rs, &**ast_type);
            let base_type = match ty::get(typ).sty {
                ty::ty_rptr(_, tm) => tm.ty,
                ty::ty_uniq(typ) => typ,
                _ => typ,
            };
            let infcx = infer::new_infer_ctxt(crate_context.tcx);
            drop(typeck::require_same_types(crate_context.tcx,
                                            Some(&infcx),
                                            false,
                                            explicit_self.span,
                                            base_type,
                                            required_type,
                                            || {
                format!("mismatched self type: expected `{}`",
                        ppaux::ty_to_string(crate_context.tcx, required_type))
            }));
            infcx.resolve_regions_and_report_errors();
        }
        _ => {}
    }
}