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.

//! "Collection" is the process of determining the type and other external
//! details of each item in Rust. Collection is specifically concerned
//! with *interprocedural* things -- for example, for a function
//! definition, collection will figure out the type and signature of the
//! function, but it will not visit the *body* of the function in any way,
//! nor examine type annotations on local variables (that's the job of
//! type *checking*).
//!
//! Collecting is ultimately defined by a bundle of queries that
//! inquire after various facts about the items in the crate (e.g.,
//! `type_of`, `generics_of`, `predicates_of`, etc). See the `provide` function
//! for the full set.
//!
//! At present, however, we do run collection across all items in the
//! crate as a kind of pass. This should eventually be factored away.

use astconv::{AstConv, Bounds};
use lint;
use constrained_type_params as ctp;
use middle::lang_items::SizedTraitLangItem;
use middle::const_val::ConstVal;
use middle::resolve_lifetime as rl;
use rustc::traits::Reveal;
use rustc::ty::subst::Substs;
use rustc::ty::{ToPredicate, ReprOptions};
use rustc::ty::{self, AdtKind, ToPolyTraitRef, Ty, TyCtxt};
use rustc::ty::maps::Providers;
use rustc::ty::util::IntTypeExt;
use util::nodemap::FxHashMap;

use rustc_const_math::ConstInt;

use std::collections::BTreeMap;

use syntax::{abi, ast};
use syntax::codemap::Spanned;
use syntax::symbol::{Symbol, keywords};
use syntax_pos::{Span, DUMMY_SP};

use rustc::hir::{self, map as hir_map};
use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
use rustc::hir::def::{Def, CtorKind};
use rustc::hir::def_id::DefId;

///////////////////////////////////////////////////////////////////////////
// Main entry point

pub fn collect_item_types<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
    let mut visitor = CollectItemTypesVisitor { tcx: tcx };
    tcx.hir.krate().visit_all_item_likes(&mut visitor.as_deep_visitor());
}

pub fn provide(providers: &mut Providers) {
    *providers = Providers {
        type_of,
        generics_of,
        predicates_of,
        super_predicates_of,
        type_param_predicates,
        trait_def,
        adt_def,
        fn_sig,
        impl_trait_ref,
        impl_polarity,
        is_foreign_item,
        is_default_impl,
        ..*providers
    };
}

///////////////////////////////////////////////////////////////////////////

/// Context specific to some particular item. This is what implements
/// AstConv. It has information about the predicates that are defined
/// on the trait. Unfortunately, this predicate information is
/// available in various different forms at various points in the
/// process. So we can't just store a pointer to e.g. the AST or the
/// parsed ty form, we have to be more flexible. To this end, the
/// `ItemCtxt` is parameterized by a `DefId` that it uses to satisfy
/// `get_type_parameter_bounds` requests, drawing the information from
/// the AST (`hir::Generics`), recursively.
pub struct ItemCtxt<'a,'tcx:'a> {
    tcx: TyCtxt<'a, 'tcx, 'tcx>,
    item_def_id: DefId,
}

///////////////////////////////////////////////////////////////////////////

struct CollectItemTypesVisitor<'a, 'tcx: 'a> {
    tcx: TyCtxt<'a, 'tcx, 'tcx>
}

impl<'a, 'tcx> Visitor<'tcx> for CollectItemTypesVisitor<'a, 'tcx> {
    fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
        NestedVisitorMap::OnlyBodies(&self.tcx.hir)
    }

    fn visit_item(&mut self, item: &'tcx hir::Item) {
        convert_item(self.tcx, item.id);
        intravisit::walk_item(self, item);
    }

    fn visit_generics(&mut self, generics: &'tcx hir::Generics) {
        for param in &generics.ty_params {
            if param.default.is_some() {
                let def_id = self.tcx.hir.local_def_id(param.id);
                self.tcx.type_of(def_id);
            }
        }
        intravisit::walk_generics(self, generics);
    }

    fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
        if let hir::ExprClosure(..) = expr.node {
            let def_id = self.tcx.hir.local_def_id(expr.id);
            self.tcx.generics_of(def_id);
            self.tcx.type_of(def_id);
        }
        intravisit::walk_expr(self, expr);
    }

    fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
        if let hir::TyImplTrait(..) = ty.node {
            let def_id = self.tcx.hir.local_def_id(ty.id);
            self.tcx.generics_of(def_id);
            self.tcx.predicates_of(def_id);
        }
        intravisit::walk_ty(self, ty);
    }

    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
        convert_trait_item(self.tcx, trait_item.id);
        intravisit::walk_trait_item(self, trait_item);
    }

    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
        convert_impl_item(self.tcx, impl_item.id);
        intravisit::walk_impl_item(self, impl_item);
    }
}

///////////////////////////////////////////////////////////////////////////
// Utility types and common code for the above passes.

impl<'a, 'tcx> ItemCtxt<'a, 'tcx> {
    pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>, item_def_id: DefId)
           -> ItemCtxt<'a,'tcx> {
        ItemCtxt {
            tcx,
            item_def_id,
        }
    }
}

impl<'a,'tcx> ItemCtxt<'a,'tcx> {
    pub fn to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
        AstConv::ast_ty_to_ty(self, ast_ty)
    }
}

impl<'a, 'tcx> AstConv<'tcx, 'tcx> for ItemCtxt<'a, 'tcx> {
    fn tcx<'b>(&'b self) -> TyCtxt<'b, 'tcx, 'tcx> { self.tcx }

    fn get_type_parameter_bounds(&self,
                                 span: Span,
                                 def_id: DefId)
                                 -> ty::GenericPredicates<'tcx>
    {
        self.tcx.at(span).type_param_predicates((self.item_def_id, def_id))
    }

    fn re_infer(&self, _span: Span, _def: Option<&ty::RegionParameterDef>)
                -> Option<ty::Region<'tcx>> {
        None
    }

    fn ty_infer(&self, span: Span) -> Ty<'tcx> {
        struct_span_err!(
            self.tcx().sess,
            span,
            E0121,
            "the type placeholder `_` is not allowed within types on item signatures"
        ).span_label(span, "not allowed in type signatures")
        .emit();
        self.tcx().types.err
    }

    fn projected_ty_from_poly_trait_ref(&self,
                                        span: Span,
                                        item_def_id: DefId,
                                        poly_trait_ref: ty::PolyTraitRef<'tcx>)
                                        -> Ty<'tcx>
    {
        if let Some(trait_ref) = self.tcx().no_late_bound_regions(&poly_trait_ref) {
            self.tcx().mk_projection(item_def_id, trait_ref.substs)
        } else {
            // no late-bound regions, we can just ignore the binder
            span_err!(self.tcx().sess, span, E0212,
                "cannot extract an associated type from a higher-ranked trait bound \
                 in this context");
            self.tcx().types.err
        }
    }

    fn normalize_ty(&self, _span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
        // types in item signatures are not normalized, to avoid undue
        // dependencies.
        ty
    }

    fn set_tainted_by_errors(&self) {
        // no obvious place to track this, just let it go
    }

    fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
        // no place to record types from signatures?
    }
}

fn type_param_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                   (item_def_id, def_id): (DefId, DefId))
                                   -> ty::GenericPredicates<'tcx> {
    use rustc::hir::map::*;
    use rustc::hir::*;

    // In the AST, bounds can derive from two places. Either
    // written inline like `<T:Foo>` or in a where clause like
    // `where T:Foo`.

    let param_id = tcx.hir.as_local_node_id(def_id).unwrap();
    let param_owner = tcx.hir.ty_param_owner(param_id);
    let param_owner_def_id = tcx.hir.local_def_id(param_owner);
    let generics = tcx.generics_of(param_owner_def_id);
    let index = generics.type_param_to_index[&def_id.index];
    let ty = tcx.mk_param(index, tcx.hir.ty_param_name(param_id));

    // Don't look for bounds where the type parameter isn't in scope.
    let parent = if item_def_id == param_owner_def_id {
        None
    } else {
        tcx.generics_of(item_def_id).parent
    };

    let mut result = parent.map_or(ty::GenericPredicates {
        parent: None,
        predicates: vec![]
    }, |parent| {
        let icx = ItemCtxt::new(tcx, parent);
        icx.get_type_parameter_bounds(DUMMY_SP, def_id)
    });

    let item_node_id = tcx.hir.as_local_node_id(item_def_id).unwrap();
    let ast_generics = match tcx.hir.get(item_node_id) {
        NodeTraitItem(item) => {
            match item.node {
                TraitItemKind::Method(ref sig, _) => &sig.generics,
                _ => return result
            }
        }

        NodeImplItem(item) => {
            match item.node {
                ImplItemKind::Method(ref sig, _) => &sig.generics,
                _ => return result
            }
        }

        NodeItem(item) => {
            match item.node {
                ItemFn(.., ref generics, _) |
                ItemImpl(_, _, _, ref generics, ..) |
                ItemTy(_, ref generics) |
                ItemEnum(_, ref generics) |
                ItemStruct(_, ref generics) |
                ItemUnion(_, ref generics) => generics,
                ItemTrait(_, ref generics, ..) => {
                    // Implied `Self: Trait` and supertrait bounds.
                    if param_id == item_node_id {
                        result.predicates.push(ty::TraitRef {
                            def_id: item_def_id,
                            substs: Substs::identity_for_item(tcx, item_def_id)
                        }.to_predicate());
                    }
                    generics
                }
                _ => return result
            }
        }

        NodeForeignItem(item) => {
            match item.node {
                ForeignItemFn(_, _, ref generics) => generics,
                _ => return result
            }
        }

        _ => return result
    };

    let icx = ItemCtxt::new(tcx, item_def_id);
    result.predicates.extend(
        icx.type_parameter_bounds_in_generics(ast_generics, param_id, ty));
    result
}

impl<'a, 'tcx> ItemCtxt<'a, 'tcx> {
    /// Find bounds from hir::Generics. This requires scanning through the
    /// AST. We do this to avoid having to convert *all* the bounds, which
    /// would create artificial cycles. Instead we can only convert the
    /// bounds for a type parameter `X` if `X::Foo` is used.
    fn type_parameter_bounds_in_generics(&self,
                                         ast_generics: &hir::Generics,
                                         param_id: ast::NodeId,
                                         ty: Ty<'tcx>)
                                         -> Vec<ty::Predicate<'tcx>>
    {
        let from_ty_params =
            ast_generics.ty_params
                .iter()
                .filter(|p| p.id == param_id)
                .flat_map(|p| p.bounds.iter())
                .flat_map(|b| predicates_from_bound(self, ty, b));

        let from_where_clauses =
            ast_generics.where_clause
                .predicates
                .iter()
                .filter_map(|wp| match *wp {
                    hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
                    _ => None
                })
                .filter(|bp| is_param(self.tcx, &bp.bounded_ty, param_id))
                .flat_map(|bp| bp.bounds.iter())
                .flat_map(|b| predicates_from_bound(self, ty, b));

        from_ty_params.chain(from_where_clauses).collect()
    }
}

/// Tests whether this is the AST for a reference to the type
/// parameter with id `param_id`. We use this so as to avoid running
/// `ast_ty_to_ty`, because we want to avoid triggering an all-out
/// conversion of the type to avoid inducing unnecessary cycles.
fn is_param<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                      ast_ty: &hir::Ty,
                      param_id: ast::NodeId)
                      -> bool
{
    if let hir::TyPath(hir::QPath::Resolved(None, ref path)) = ast_ty.node {
        match path.def {
            Def::SelfTy(Some(def_id), None) |
            Def::TyParam(def_id) => {
                def_id == tcx.hir.local_def_id(param_id)
            }
            _ => false
        }
    } else {
        false
    }
}

fn ensure_no_ty_param_bounds(tcx: TyCtxt,
                             span: Span,
                             generics: &hir::Generics,
                             thing: &'static str) {
    let mut warn = false;

    for ty_param in generics.ty_params.iter() {
        for bound in ty_param.bounds.iter() {
            match *bound {
                hir::TraitTyParamBound(..) => {
                    warn = true;
                }
                hir::RegionTyParamBound(..) => { }
            }
        }
    }

    for predicate in generics.where_clause.predicates.iter() {
        match *predicate {
            hir::WherePredicate::BoundPredicate(..) => {
                warn = true;
            }
            hir::WherePredicate::RegionPredicate(..) => { }
            hir::WherePredicate::EqPredicate(..) => { }
        }
    }

    if warn {
        // According to accepted RFC #XXX, we should
        // eventually accept these, but it will not be
        // part of this PR. Still, convert to warning to
        // make bootstrapping easier.
        span_warn!(tcx.sess, span, E0122,
                   "trait bounds are not (yet) enforced \
                   in {} definitions",
                   thing);
    }
}

fn convert_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item_id: ast::NodeId) {
    let it = tcx.hir.expect_item(item_id);
    debug!("convert: item {} with id {}", it.name, it.id);
    let def_id = tcx.hir.local_def_id(item_id);
    match it.node {
        // These don't define types.
        hir::ItemExternCrate(_) |
        hir::ItemUse(..) |
        hir::ItemMod(_) |
        hir::ItemGlobalAsm(_) => {}
        hir::ItemForeignMod(ref foreign_mod) => {
            for item in &foreign_mod.items {
                let def_id = tcx.hir.local_def_id(item.id);
                tcx.generics_of(def_id);
                tcx.type_of(def_id);
                tcx.predicates_of(def_id);
                if let hir::ForeignItemFn(..) = item.node {
                    tcx.fn_sig(def_id);
                }
            }
        }
        hir::ItemEnum(ref enum_definition, _) => {
            tcx.generics_of(def_id);
            tcx.type_of(def_id);
            tcx.predicates_of(def_id);
            convert_enum_variant_types(tcx, def_id, &enum_definition.variants);
        },
        hir::ItemDefaultImpl(..) => {
            tcx.impl_trait_ref(def_id);
        }
        hir::ItemImpl(..) => {
            tcx.generics_of(def_id);
            tcx.type_of(def_id);
            tcx.impl_trait_ref(def_id);
            tcx.predicates_of(def_id);
        },
        hir::ItemTrait(..) => {
            tcx.generics_of(def_id);
            tcx.trait_def(def_id);
            tcx.at(it.span).super_predicates_of(def_id);
            tcx.predicates_of(def_id);
        },
        hir::ItemStruct(ref struct_def, _) |
        hir::ItemUnion(ref struct_def, _) => {
            tcx.generics_of(def_id);
            tcx.type_of(def_id);
            tcx.predicates_of(def_id);

            for f in struct_def.fields() {
                let def_id = tcx.hir.local_def_id(f.id);
                tcx.generics_of(def_id);
                tcx.type_of(def_id);
                tcx.predicates_of(def_id);
            }

            if !struct_def.is_struct() {
                convert_variant_ctor(tcx, struct_def.id());
            }
        },
        hir::ItemTy(_, ref generics) => {
            ensure_no_ty_param_bounds(tcx, it.span, generics, "type");
            tcx.generics_of(def_id);
            tcx.type_of(def_id);
            tcx.predicates_of(def_id);
        }
        hir::ItemStatic(..) | hir::ItemConst(..) | hir::ItemFn(..) => {
            tcx.generics_of(def_id);
            tcx.type_of(def_id);
            tcx.predicates_of(def_id);
            if let hir::ItemFn(..) = it.node {
                tcx.fn_sig(def_id);
            }
        }
    }
}

fn convert_trait_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, trait_item_id: ast::NodeId) {
    let trait_item = tcx.hir.expect_trait_item(trait_item_id);
    let def_id = tcx.hir.local_def_id(trait_item.id);
    tcx.generics_of(def_id);

    match trait_item.node {
        hir::TraitItemKind::Const(..) |
        hir::TraitItemKind::Type(_, Some(_)) |
        hir::TraitItemKind::Method(..) => {
            tcx.type_of(def_id);
            if let hir::TraitItemKind::Method(..) = trait_item.node {
                tcx.fn_sig(def_id);
            }
        }

        hir::TraitItemKind::Type(_, None) => {}
    };

    tcx.predicates_of(def_id);
}

fn convert_impl_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, impl_item_id: ast::NodeId) {
    let def_id = tcx.hir.local_def_id(impl_item_id);
    tcx.generics_of(def_id);
    tcx.type_of(def_id);
    tcx.predicates_of(def_id);
    if let hir::ImplItemKind::Method(..) = tcx.hir.expect_impl_item(impl_item_id).node {
        tcx.fn_sig(def_id);
    }
}

fn convert_variant_ctor<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                  ctor_id: ast::NodeId) {
    let def_id = tcx.hir.local_def_id(ctor_id);
    tcx.generics_of(def_id);
    tcx.type_of(def_id);
    tcx.predicates_of(def_id);
}

fn convert_enum_variant_types<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                        def_id: DefId,
                                        variants: &[hir::Variant]) {
    let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
    let def = tcx.adt_def(def_id);
    let repr_type = def.repr.discr_type();
    let initial = repr_type.initial_discriminant(tcx);
    let mut prev_discr = None::<ConstInt>;

    // fill the discriminant values and field types
    for variant in variants {
        let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr());
        prev_discr = Some(if let Some(e) = variant.node.disr_expr {
            let expr_did = tcx.hir.local_def_id(e.node_id);
            let substs = Substs::identity_for_item(tcx, expr_did);
            let result = tcx.at(variant.span).const_eval(param_env.and((expr_did, substs)));

            // enum variant evaluation happens before the global constant check
            // so we need to report the real error
            if let Err(ref err) = result {
                err.report(tcx, variant.span, "enum discriminant");
            }

            match result {
                Ok(&ty::Const { val: ConstVal::Integral(x), .. }) => Some(x),
                _ => None
            }
        } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
            Some(discr)
        } else {
            struct_span_err!(tcx.sess, variant.span, E0370,
                             "enum discriminant overflowed")
                .span_label(variant.span, format!("overflowed on value after {}",
                                                   prev_discr.unwrap()))
                .note(&format!("explicitly set `{} = {}` if that is desired outcome",
                               variant.node.name, wrapped_discr))
                .emit();
            None
        }.unwrap_or(wrapped_discr));

        for f in variant.node.data.fields() {
            let def_id = tcx.hir.local_def_id(f.id);
            tcx.generics_of(def_id);
            tcx.type_of(def_id);
            tcx.predicates_of(def_id);
        }

        // Convert the ctor, if any. This also registers the variant as
        // an item.
        convert_variant_ctor(tcx, variant.node.data.id());
    }
}

fn convert_struct_variant<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                    did: DefId,
                                    name: ast::Name,
                                    discr: ty::VariantDiscr,
                                    def: &hir::VariantData)
                                    -> ty::VariantDef {
    let mut seen_fields: FxHashMap<ast::Name, Span> = FxHashMap();
    let node_id = tcx.hir.as_local_node_id(did).unwrap();
    let fields = def.fields().iter().map(|f| {
        let fid = tcx.hir.local_def_id(f.id);
        let dup_span = seen_fields.get(&f.name).cloned();
        if let Some(prev_span) = dup_span {
            struct_span_err!(tcx.sess, f.span, E0124,
                             "field `{}` is already declared",
                             f.name)
                .span_label(f.span, "field already declared")
                .span_label(prev_span, format!("`{}` first declared here", f.name))
                .emit();
        } else {
            seen_fields.insert(f.name, f.span);
        }

        ty::FieldDef {
            did: fid,
            name: f.name,
            vis: ty::Visibility::from_hir(&f.vis, node_id, tcx)
        }
    }).collect();
    ty::VariantDef {
        did,
        name,
        discr,
        fields,
        ctor_kind: CtorKind::from_hir(def),
    }
}

fn adt_def<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                     def_id: DefId)
                     -> &'tcx ty::AdtDef {
    use rustc::hir::map::*;
    use rustc::hir::*;

    let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
    let item = match tcx.hir.get(node_id) {
        NodeItem(item) => item,
        _ => bug!()
    };

    let repr = ReprOptions::new(tcx, def_id);
    let (kind, variants) = match item.node {
        ItemEnum(ref def, _) => {
            let mut distance_from_explicit = 0;
            (AdtKind::Enum, def.variants.iter().map(|v| {
                let did = tcx.hir.local_def_id(v.node.data.id());
                let discr = if let Some(e) = v.node.disr_expr {
                    distance_from_explicit = 0;
                    ty::VariantDiscr::Explicit(tcx.hir.local_def_id(e.node_id))
                } else {
                    ty::VariantDiscr::Relative(distance_from_explicit)
                };
                distance_from_explicit += 1;

                convert_struct_variant(tcx, did, v.node.name, discr, &v.node.data)
            }).collect())
        }
        ItemStruct(ref def, _) => {
            // Use separate constructor id for unit/tuple structs and reuse did for braced structs.
            let ctor_id = if !def.is_struct() {
                Some(tcx.hir.local_def_id(def.id()))
            } else {
                None
            };
            (AdtKind::Struct, vec![
                convert_struct_variant(tcx, ctor_id.unwrap_or(def_id), item.name,
                                       ty::VariantDiscr::Relative(0), def)
            ])
        }
        ItemUnion(ref def, _) => {
            (AdtKind::Union, vec![
                convert_struct_variant(tcx, def_id, item.name,
                                       ty::VariantDiscr::Relative(0), def)
            ])
        }
        _ => bug!()
    };
    tcx.alloc_adt_def(def_id, kind, variants, repr)
}

/// Ensures that the super-predicates of the trait with def-id
/// trait_def_id are converted and stored. This also ensures that
/// the transitive super-predicates are converted;
fn super_predicates_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                 trait_def_id: DefId)
                                 -> ty::GenericPredicates<'tcx> {
    debug!("super_predicates(trait_def_id={:?})", trait_def_id);
    let trait_node_id = tcx.hir.as_local_node_id(trait_def_id).unwrap();

    let item = match tcx.hir.get(trait_node_id) {
        hir_map::NodeItem(item) => item,
        _ => bug!("trait_node_id {} is not an item", trait_node_id)
    };

    let (generics, bounds) = match item.node {
        hir::ItemTrait(_, ref generics, ref supertraits, _) => (generics, supertraits),
        _ => span_bug!(item.span,
                       "super_predicates invoked on non-trait"),
    };

    let icx = ItemCtxt::new(tcx, trait_def_id);

    // Convert the bounds that follow the colon, e.g. `Bar+Zed` in `trait Foo : Bar+Zed`.
    let self_param_ty = tcx.mk_self_type();
    let superbounds1 = compute_bounds(&icx,
                                      self_param_ty,
                                      bounds,
                                      SizedByDefault::No,
                                      item.span);

    let superbounds1 = superbounds1.predicates(tcx, self_param_ty);

    // Convert any explicit superbounds in the where clause,
    // e.g. `trait Foo where Self : Bar`:
    let superbounds2 = icx.type_parameter_bounds_in_generics(generics, item.id, self_param_ty);

    // Combine the two lists to form the complete set of superbounds:
    let superbounds: Vec<_> = superbounds1.into_iter().chain(superbounds2).collect();

    // Now require that immediate supertraits are converted,
    // which will, in turn, reach indirect supertraits.
    for bound in superbounds.iter().filter_map(|p| p.to_opt_poly_trait_ref()) {
        tcx.at(item.span).super_predicates_of(bound.def_id());
    }

    ty::GenericPredicates {
        parent: None,
        predicates: superbounds
    }
}

fn trait_def<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                       def_id: DefId)
                       -> &'tcx ty::TraitDef {
    let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
    let item = tcx.hir.expect_item(node_id);

    let unsafety = match item.node {
        hir::ItemTrait(unsafety, ..) => unsafety,
        _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
    };

    let paren_sugar = tcx.has_attr(def_id, "rustc_paren_sugar");
    if paren_sugar && !tcx.sess.features.borrow().unboxed_closures {
        let mut err = tcx.sess.struct_span_err(
            item.span,
            "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
             which traits can use parenthetical notation");
        help!(&mut err,
            "add `#![feature(unboxed_closures)]` to \
             the crate attributes to use it");
        err.emit();
    }

    let def_path_hash = tcx.def_path_hash(def_id);
    let has_default_impl = tcx.hir.trait_is_auto(def_id);
    let def = ty::TraitDef::new(def_id,
                                unsafety,
                                paren_sugar,
                                has_default_impl,
                                def_path_hash);
    tcx.alloc_trait_def(def)
}

fn has_late_bound_regions<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                    node: hir_map::Node<'tcx>)
                                    -> Option<Span> {
    struct LateBoundRegionsDetector<'a, 'tcx: 'a> {
        tcx: TyCtxt<'a, 'tcx, 'tcx>,
        binder_depth: u32,
        has_late_bound_regions: Option<Span>,
    }

    impl<'a, 'tcx> Visitor<'tcx> for LateBoundRegionsDetector<'a, 'tcx> {
        fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
            NestedVisitorMap::None
        }

        fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
            if self.has_late_bound_regions.is_some() { return }
            match ty.node {
                hir::TyBareFn(..) => {
                    self.binder_depth += 1;
                    intravisit::walk_ty(self, ty);
                    self.binder_depth -= 1;
                }
                _ => intravisit::walk_ty(self, ty)
            }
        }

        fn visit_poly_trait_ref(&mut self,
                                tr: &'tcx hir::PolyTraitRef,
                                m: hir::TraitBoundModifier) {
            if self.has_late_bound_regions.is_some() { return }
            self.binder_depth += 1;
            intravisit::walk_poly_trait_ref(self, tr, m);
            self.binder_depth -= 1;
        }

        fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
            if self.has_late_bound_regions.is_some() { return }

            let hir_id = self.tcx.hir.node_to_hir_id(lt.id);
            match self.tcx.named_region(hir_id) {
                Some(rl::Region::Static) | Some(rl::Region::EarlyBound(..)) => {}
                Some(rl::Region::LateBound(debruijn, _)) |
                Some(rl::Region::LateBoundAnon(debruijn, _))
                    if debruijn.depth < self.binder_depth => {}
                _ => self.has_late_bound_regions = Some(lt.span),
            }
        }
    }

    fn has_late_bound_regions<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                        generics: &'tcx hir::Generics,
                                        decl: &'tcx hir::FnDecl)
                                        -> Option<Span> {
        let mut visitor = LateBoundRegionsDetector {
            tcx, binder_depth: 1, has_late_bound_regions: None
        };
        for lifetime in &generics.lifetimes {
            let hir_id = tcx.hir.node_to_hir_id(lifetime.lifetime.id);
            if tcx.is_late_bound(hir_id) {
                return Some(lifetime.lifetime.span);
            }
        }
        visitor.visit_fn_decl(decl);
        visitor.has_late_bound_regions
    }

    match node {
        hir_map::NodeTraitItem(item) => match item.node {
            hir::TraitItemKind::Method(ref sig, _) =>
                has_late_bound_regions(tcx, &sig.generics, &sig.decl),
            _ => None,
        },
        hir_map::NodeImplItem(item) => match item.node {
            hir::ImplItemKind::Method(ref sig, _) =>
                has_late_bound_regions(tcx, &sig.generics, &sig.decl),
            _ => None,
        },
        hir_map::NodeForeignItem(item) => match item.node {
            hir::ForeignItemFn(ref fn_decl, _, ref generics) =>
                has_late_bound_regions(tcx, generics, fn_decl),
            _ => None,
        },
        hir_map::NodeItem(item) => match item.node {
            hir::ItemFn(ref fn_decl, .., ref generics, _) =>
                has_late_bound_regions(tcx, generics, fn_decl),
            _ => None,
        },
        _ => None
    }
}

fn generics_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                         def_id: DefId)
                         -> &'tcx ty::Generics {
    use rustc::hir::map::*;
    use rustc::hir::*;

    let node_id = tcx.hir.as_local_node_id(def_id).unwrap();

    let node = tcx.hir.get(node_id);
    let parent_def_id = match node {
        NodeImplItem(_) |
        NodeTraitItem(_) |
        NodeVariant(_) |
        NodeStructCtor(_) |
        NodeField(_) => {
            let parent_id = tcx.hir.get_parent(node_id);
            Some(tcx.hir.local_def_id(parent_id))
        }
        NodeExpr(&hir::Expr { node: hir::ExprClosure(..), .. }) => {
            Some(tcx.closure_base_def_id(def_id))
        }
        NodeTy(&hir::Ty { node: hir::TyImplTrait(..), .. }) => {
            let mut parent_id = node_id;
            loop {
                match tcx.hir.get(parent_id) {
                    NodeItem(_) | NodeImplItem(_) | NodeTraitItem(_) => break,
                    _ => {
                        parent_id = tcx.hir.get_parent_node(parent_id);
                    }
                }
            }
            Some(tcx.hir.local_def_id(parent_id))
        }
        _ => None
    };

    let mut opt_self = None;
    let mut allow_defaults = false;

    let no_generics = hir::Generics::empty();
    let ast_generics = match node {
        NodeTraitItem(item) => {
            match item.node {
                TraitItemKind::Method(ref sig, _) => &sig.generics,
                _ => &no_generics
            }
        }

        NodeImplItem(item) => {
            match item.node {
                ImplItemKind::Method(ref sig, _) => &sig.generics,
                _ => &no_generics
            }
        }

        NodeItem(item) => {
            match item.node {
                ItemFn(.., ref generics, _) |
                ItemImpl(_, _, _, ref generics, ..) => generics,

                ItemTy(_, ref generics) |
                ItemEnum(_, ref generics) |
                ItemStruct(_, ref generics) |
                ItemUnion(_, ref generics) => {
                    allow_defaults = true;
                    generics
                }

                ItemTrait(_, ref generics, ..) => {
                    // Add in the self type parameter.
                    //
                    // Something of a hack: use the node id for the trait, also as
                    // the node id for the Self type parameter.
                    let param_id = item.id;

                    opt_self = Some(ty::TypeParameterDef {
                        index: 0,
                        name: keywords::SelfType.name(),
                        def_id: tcx.hir.local_def_id(param_id),
                        has_default: false,
                        object_lifetime_default: rl::Set1::Empty,
                        pure_wrt_drop: false,
                        synthetic: None,
                    });

                    allow_defaults = true;
                    generics
                }

                _ => &no_generics
            }
        }

        NodeForeignItem(item) => {
            match item.node {
                ForeignItemStatic(..) => &no_generics,
                ForeignItemFn(_, _, ref generics) => generics
            }
        }

        _ => &no_generics
    };

    let has_self = opt_self.is_some();
    let mut parent_has_self = false;
    let mut own_start = has_self as u32;
    let (parent_regions, parent_types) = parent_def_id.map_or((0, 0), |def_id| {
        let generics = tcx.generics_of(def_id);
        assert_eq!(has_self, false);
        parent_has_self = generics.has_self;
        own_start = generics.count() as u32;
        (generics.parent_regions + generics.regions.len() as u32,
            generics.parent_types + generics.types.len() as u32)
    });

    let early_lifetimes = early_bound_lifetimes_from_generics(tcx, ast_generics);
    let regions = early_lifetimes.enumerate().map(|(i, l)| {
        ty::RegionParameterDef {
            name: l.lifetime.name.name(),
            index: own_start + i as u32,
            def_id: tcx.hir.local_def_id(l.lifetime.id),
            pure_wrt_drop: l.pure_wrt_drop,
        }
    }).collect::<Vec<_>>();

    let hir_id = tcx.hir.node_to_hir_id(node_id);
    let object_lifetime_defaults = tcx.object_lifetime_defaults(hir_id);

    // Now create the real type parameters.
    let type_start = own_start + regions.len() as u32;
    let types = ast_generics.ty_params.iter().enumerate().map(|(i, p)| {
        if p.name == keywords::SelfType.name() {
            span_bug!(p.span, "`Self` should not be the name of a regular parameter");
        }

        if !allow_defaults && p.default.is_some() {
            if !tcx.sess.features.borrow().default_type_parameter_fallback {
                tcx.lint_node(
                    lint::builtin::INVALID_TYPE_PARAM_DEFAULT,
                    p.id,
                    p.span,
                    &format!("defaults for type parameters are only allowed in `struct`, \
                              `enum`, `type`, or `trait` definitions."));
            }
        }

        ty::TypeParameterDef {
            index: type_start + i as u32,
            name: p.name,
            def_id: tcx.hir.local_def_id(p.id),
            has_default: p.default.is_some(),
            object_lifetime_default:
                object_lifetime_defaults.as_ref().map_or(rl::Set1::Empty, |o| o[i]),
            pure_wrt_drop: p.pure_wrt_drop,
            synthetic: p.synthetic,
        }
    });
    let mut types: Vec<_> = opt_self.into_iter().chain(types).collect();

    // provide junk type parameter defs - the only place that
    // cares about anything but the length is instantiation,
    // and we don't do that for closures.
    if let NodeExpr(&hir::Expr { node: hir::ExprClosure(..), .. }) = node {
        tcx.with_freevars(node_id, |fv| {
            types.extend(fv.iter().enumerate().map(|(i, _)| ty::TypeParameterDef {
                index: type_start + i as u32,
                name: Symbol::intern("<upvar>"),
                def_id,
                has_default: false,
                object_lifetime_default: rl::Set1::Empty,
                pure_wrt_drop: false,
                synthetic: None,
            }));
        });
    }

    let mut type_param_to_index = BTreeMap::new();
    for param in &types {
        type_param_to_index.insert(param.def_id.index, param.index);
    }

    tcx.alloc_generics(ty::Generics {
        parent: parent_def_id,
        parent_regions,
        parent_types,
        regions,
        types,
        type_param_to_index,
        has_self: has_self || parent_has_self,
        has_late_bound_regions: has_late_bound_regions(tcx, node),
    })
}

fn type_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                     def_id: DefId)
                     -> Ty<'tcx> {
    use rustc::hir::map::*;
    use rustc::hir::*;

    let node_id = tcx.hir.as_local_node_id(def_id).unwrap();

    let icx = ItemCtxt::new(tcx, def_id);

    match tcx.hir.get(node_id) {
        NodeTraitItem(item) => {
            match item.node {
                TraitItemKind::Method(..) => {
                    let substs = Substs::identity_for_item(tcx, def_id);
                    tcx.mk_fn_def(def_id, substs)
                }
                TraitItemKind::Const(ref ty, _) |
                TraitItemKind::Type(_, Some(ref ty)) => icx.to_ty(ty),
                TraitItemKind::Type(_, None) => {
                    span_bug!(item.span, "associated type missing default");
                }
            }
        }

        NodeImplItem(item) => {
            match item.node {
                ImplItemKind::Method(..) => {
                    let substs = Substs::identity_for_item(tcx, def_id);
                    tcx.mk_fn_def(def_id, substs)
                }
                ImplItemKind::Const(ref ty, _) => icx.to_ty(ty),
                ImplItemKind::Type(ref ty) => {
                    if tcx.impl_trait_ref(tcx.hir.get_parent_did(node_id)).is_none() {
                        span_err!(tcx.sess, item.span, E0202,
                                  "associated types are not allowed in inherent impls");
                    }

                    icx.to_ty(ty)
                }
            }
        }

        NodeItem(item) => {
            match item.node {
                ItemStatic(ref t, ..) | ItemConst(ref t, _) |
                ItemTy(ref t, _) | ItemImpl(.., ref t, _) => {
                    icx.to_ty(t)
                }
                ItemFn(..) => {
                    let substs = Substs::identity_for_item(tcx, def_id);
                    tcx.mk_fn_def(def_id, substs)
                }
                ItemEnum(..) |
                ItemStruct(..) |
                ItemUnion(..) => {
                    let def = tcx.adt_def(def_id);
                    let substs = Substs::identity_for_item(tcx, def_id);
                    tcx.mk_adt(def, substs)
                }
                ItemDefaultImpl(..) |
                ItemTrait(..) |
                ItemMod(..) |
                ItemForeignMod(..) |
                ItemGlobalAsm(..) |
                ItemExternCrate(..) |
                ItemUse(..) => {
                    span_bug!(
                        item.span,
                        "compute_type_of_item: unexpected item type: {:?}",
                        item.node);
                }
            }
        }

        NodeForeignItem(foreign_item) => {
            match foreign_item.node {
                ForeignItemFn(..) => {
                    let substs = Substs::identity_for_item(tcx, def_id);
                    tcx.mk_fn_def(def_id, substs)
                }
                ForeignItemStatic(ref t, _) => icx.to_ty(t)
            }
        }

        NodeStructCtor(&ref def) |
        NodeVariant(&Spanned { node: hir::Variant_ { data: ref def, .. }, .. }) => {
            match *def {
                VariantData::Unit(..) | VariantData::Struct(..) => {
                    tcx.type_of(tcx.hir.get_parent_did(node_id))
                }
                VariantData::Tuple(..) => {
                    let substs = Substs::identity_for_item(tcx, def_id);
                    tcx.mk_fn_def(def_id, substs)
                }
            }
        }

        NodeField(field) => icx.to_ty(&field.ty),

        NodeExpr(&hir::Expr { node: hir::ExprClosure(.., is_generator), .. }) => {
            if is_generator {
                let hir_id = tcx.hir.node_to_hir_id(node_id);
                return tcx.typeck_tables_of(def_id).node_id_to_type(hir_id);
            }

            tcx.mk_closure(def_id, Substs::for_item(
                tcx, def_id,
                |def, _| {
                    let region = def.to_early_bound_region_data();
                    tcx.mk_region(ty::ReEarlyBound(region))
                },
                |def, _| tcx.mk_param_from_def(def)
            ))
        }

        NodeExpr(_) => match tcx.hir.get(tcx.hir.get_parent_node(node_id)) {
            NodeTy(&hir::Ty { node: TyArray(_, body), .. }) |
            NodeTy(&hir::Ty { node: TyTypeof(body), .. }) |
            NodeExpr(&hir::Expr { node: ExprRepeat(_, body), .. })
                if body.node_id == node_id => tcx.types.usize,

            NodeVariant(&Spanned { node: Variant_ { disr_expr: Some(e), .. }, .. })
                if e.node_id == node_id => {
                    tcx.adt_def(tcx.hir.get_parent_did(node_id))
                        .repr.discr_type().to_ty(tcx)
                }

            x => {
                bug!("unexpected expr parent in type_of_def_id(): {:?}", x);
            }
        },

        NodeTyParam(&hir::TyParam { default: Some(ref ty), .. }) => {
            icx.to_ty(ty)
        }

        NodeTy(&hir::Ty { node: TyImplTrait(..), .. }) => {
            let owner = tcx.hir.get_parent_did(node_id);
            let hir_id = tcx.hir.node_to_hir_id(node_id);
            tcx.typeck_tables_of(owner).node_id_to_type(hir_id)
        }

        x => {
            bug!("unexpected sort of node in type_of_def_id(): {:?}", x);
        }
    }
}

fn fn_sig<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                    def_id: DefId)
                    -> ty::PolyFnSig<'tcx> {
    use rustc::hir::map::*;
    use rustc::hir::*;

    let node_id = tcx.hir.as_local_node_id(def_id).unwrap();

    let icx = ItemCtxt::new(tcx, def_id);

    match tcx.hir.get(node_id) {
        NodeTraitItem(&hir::TraitItem { node: TraitItemKind::Method(ref sig, _), .. }) |
        NodeImplItem(&hir::ImplItem { node: ImplItemKind::Method(ref sig, _), .. }) => {
            AstConv::ty_of_fn(&icx, sig.unsafety, sig.abi, &sig.decl)
        }

        NodeItem(&hir::Item { node: ItemFn(ref decl, unsafety, _, abi, _, _), .. }) => {
            AstConv::ty_of_fn(&icx, unsafety, abi, decl)
        }

        NodeForeignItem(&hir::ForeignItem { node: ForeignItemFn(ref fn_decl, _, _), .. }) => {
            let abi = tcx.hir.get_foreign_abi(node_id);
            compute_sig_of_foreign_fn_decl(tcx, def_id, fn_decl, abi)
        }

        NodeStructCtor(&VariantData::Tuple(ref fields, _)) |
        NodeVariant(&Spanned { node: hir::Variant_ {
            data: VariantData::Tuple(ref fields, _), ..
        }, .. }) => {
            let ty = tcx.type_of(tcx.hir.get_parent_did(node_id));
            let inputs = fields.iter().map(|f| {
                tcx.type_of(tcx.hir.local_def_id(f.id))
            });
            ty::Binder(tcx.mk_fn_sig(
                inputs,
                ty,
                false,
                hir::Unsafety::Normal,
                abi::Abi::Rust
            ))
        }

        NodeExpr(&hir::Expr { node: hir::ExprClosure(..), hir_id, .. }) => {
            tcx.typeck_tables_of(def_id).closure_tys()[hir_id]
        }

        x => {
            bug!("unexpected sort of node in fn_sig(): {:?}", x);
        }
    }
}

fn impl_trait_ref<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                            def_id: DefId)
                            -> Option<ty::TraitRef<'tcx>> {
    let icx = ItemCtxt::new(tcx, def_id);

    let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
    match tcx.hir.expect_item(node_id).node {
        hir::ItemDefaultImpl(_, ref ast_trait_ref) => {
            Some(AstConv::instantiate_mono_trait_ref(&icx,
                                                     ast_trait_ref,
                                                     tcx.mk_self_type()))
        }
        hir::ItemImpl(.., ref opt_trait_ref, _, _) => {
            opt_trait_ref.as_ref().map(|ast_trait_ref| {
                let selfty = tcx.type_of(def_id);
                AstConv::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
            })
        }
        _ => bug!()
    }
}

fn impl_polarity<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                           def_id: DefId)
                           -> hir::ImplPolarity {
    let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
    match tcx.hir.expect_item(node_id).node {
        hir::ItemImpl(_, polarity, ..) => polarity,
        ref item => bug!("impl_polarity: {:?} not an impl", item)
    }
}

// Is it marked with ?Sized
fn is_unsized<'gcx: 'tcx, 'tcx>(astconv: &AstConv<'gcx, 'tcx>,
                                ast_bounds: &[hir::TyParamBound],
                                span: Span) -> bool
{
    let tcx = astconv.tcx();

    // Try to find an unbound in bounds.
    let mut unbound = None;
    for ab in ast_bounds {
        if let &hir::TraitTyParamBound(ref ptr, hir::TraitBoundModifier::Maybe) = ab  {
            if unbound.is_none() {
                unbound = Some(ptr.trait_ref.clone());
            } else {
                span_err!(tcx.sess, span, E0203,
                          "type parameter has more than one relaxed default \
                                                bound, only one is supported");
            }
        }
    }

    let kind_id = tcx.lang_items().require(SizedTraitLangItem);
    match unbound {
        Some(ref tpb) => {
            // FIXME(#8559) currently requires the unbound to be built-in.
            if let Ok(kind_id) = kind_id {
                if tpb.path.def != Def::Trait(kind_id) {
                    tcx.sess.span_warn(span,
                                       "default bound relaxed for a type parameter, but \
                                       this does nothing because the given bound is not \
                                       a default. Only `?Sized` is supported");
                }
            }
        }
        _ if kind_id.is_ok() => {
            return false;
        }
        // No lang item for Sized, so we can't add it as a bound.
        None => {}
    }

    true
}

/// Returns the early-bound lifetimes declared in this generics
/// listing.  For anything other than fns/methods, this is just all
/// the lifetimes that are declared. For fns or methods, we have to
/// screen out those that do not appear in any where-clauses etc using
/// `resolve_lifetime::early_bound_lifetimes`.
fn early_bound_lifetimes_from_generics<'a, 'tcx>(
    tcx: TyCtxt<'a, 'tcx, 'tcx>,
    ast_generics: &'a hir::Generics)
    -> impl Iterator<Item=&'a hir::LifetimeDef>
{
    ast_generics
        .lifetimes
        .iter()
        .filter(move |l| {
            let hir_id = tcx.hir.node_to_hir_id(l.lifetime.id);
            !tcx.is_late_bound(hir_id)
        })
}

fn predicates_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                           def_id: DefId)
                           -> ty::GenericPredicates<'tcx> {
    explicit_predicates_of(tcx, def_id)
}

fn explicit_predicates_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                           def_id: DefId)
                           -> ty::GenericPredicates<'tcx> {
    use rustc::hir::map::*;
    use rustc::hir::*;

    let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
    let node = tcx.hir.get(node_id);

    let mut is_trait = None;

    let icx = ItemCtxt::new(tcx, def_id);
    let no_generics = hir::Generics::empty();
    let ast_generics = match node {
        NodeTraitItem(item) => {
            match item.node {
                TraitItemKind::Method(ref sig, _) => &sig.generics,
                _ => &no_generics
            }
        }

        NodeImplItem(item) => {
            match item.node {
                ImplItemKind::Method(ref sig, _) => &sig.generics,
                _ => &no_generics
            }
        }

        NodeItem(item) => {
            match item.node {
                ItemFn(.., ref generics, _) |
                ItemImpl(_, _, _, ref generics, ..) |
                ItemTy(_, ref generics) |
                ItemEnum(_, ref generics) |
                ItemStruct(_, ref generics) |
                ItemUnion(_, ref generics) => {
                    generics
                }

                ItemTrait(_, ref generics, .., ref items) => {
                    is_trait = Some((ty::TraitRef {
                        def_id,
                        substs: Substs::identity_for_item(tcx, def_id)
                    }, items));
                    generics
                }

                _ => &no_generics
            }
        }

        NodeForeignItem(item) => {
            match item.node {
                ForeignItemStatic(..) => &no_generics,
                ForeignItemFn(_, _, ref generics) => generics
            }
        }

        NodeTy(&Ty { node: TyImplTrait(ref bounds), span, .. }) => {
            let substs = Substs::identity_for_item(tcx, def_id);
            let anon_ty = tcx.mk_anon(def_id, substs);

            // Collect the bounds, i.e. the `A+B+'c` in `impl A+B+'c`.
            let bounds = compute_bounds(&icx, anon_ty, bounds,
                                        SizedByDefault::Yes,
                                        span);
            return ty::GenericPredicates {
                parent: None,
                predicates: bounds.predicates(tcx, anon_ty)
            };
        }

        _ => &no_generics
    };

    let generics = tcx.generics_of(def_id);
    let parent_count = generics.parent_count() as u32;
    let has_own_self = generics.has_self && parent_count == 0;

    let mut predicates = vec![];

    // Below we'll consider the bounds on the type parameters (including `Self`)
    // and the explicit where-clauses, but to get the full set of predicates
    // on a trait we need to add in the supertrait bounds and bounds found on
    // associated types.
    if let Some((trait_ref, _)) = is_trait {
        predicates = tcx.super_predicates_of(def_id).predicates;

        // Add in a predicate that `Self:Trait` (where `Trait` is the
        // current trait).  This is needed for builtin bounds.
        predicates.push(trait_ref.to_poly_trait_ref().to_predicate());
    }

    // Collect the region predicates that were declared inline as
    // well. In the case of parameters declared on a fn or method, we
    // have to be careful to only iterate over early-bound regions.
    let mut index = parent_count + has_own_self as u32;
    for param in early_bound_lifetimes_from_generics(tcx, ast_generics) {
        let region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
            def_id: tcx.hir.local_def_id(param.lifetime.id),
            index,
            name: param.lifetime.name.name(),
        }));
        index += 1;

        for bound in &param.bounds {
            let bound_region = AstConv::ast_region_to_region(&icx, bound, None);
            let outlives = ty::Binder(ty::OutlivesPredicate(region, bound_region));
            predicates.push(outlives.to_predicate());
        }
    }

    // Collect the predicates that were written inline by the user on each
    // type parameter (e.g., `<T:Foo>`).
    for param in &ast_generics.ty_params {
        let param_ty = ty::ParamTy::new(index, param.name).to_ty(tcx);
        index += 1;

        let bounds = compute_bounds(&icx,
                                    param_ty,
                                    &param.bounds,
                                    SizedByDefault::Yes,
                                    param.span);
        predicates.extend(bounds.predicates(tcx, param_ty));
    }

    // Add in the bounds that appear in the where-clause
    let where_clause = &ast_generics.where_clause;
    for predicate in &where_clause.predicates {
        match predicate {
            &hir::WherePredicate::BoundPredicate(ref bound_pred) => {
                let ty = icx.to_ty(&bound_pred.bounded_ty);

                for bound in bound_pred.bounds.iter() {
                    match bound {
                        &hir::TyParamBound::TraitTyParamBound(ref poly_trait_ref, _) => {
                            let mut projections = Vec::new();

                            let trait_ref =
                                AstConv::instantiate_poly_trait_ref(&icx,
                                                                    poly_trait_ref,
                                                                    ty,
                                                                    &mut projections);

                            predicates.push(trait_ref.to_predicate());

                            for projection in &projections {
                                predicates.push(projection.to_predicate());
                            }
                        }

                        &hir::TyParamBound::RegionTyParamBound(ref lifetime) => {
                            let region = AstConv::ast_region_to_region(&icx,
                                                                       lifetime,
                                                                       None);
                            let pred = ty::Binder(ty::OutlivesPredicate(ty, region));
                            predicates.push(ty::Predicate::TypeOutlives(pred))
                        }
                    }
                }
            }

            &hir::WherePredicate::RegionPredicate(ref region_pred) => {
                let r1 = AstConv::ast_region_to_region(&icx, &region_pred.lifetime, None);
                for bound in &region_pred.bounds {
                    let r2 = AstConv::ast_region_to_region(&icx, bound, None);
                    let pred = ty::Binder(ty::OutlivesPredicate(r1, r2));
                    predicates.push(ty::Predicate::RegionOutlives(pred))
                }
            }

            &hir::WherePredicate::EqPredicate(..) => {
                // FIXME(#20041)
            }
        }
    }

    // Add predicates from associated type bounds.
    if let Some((self_trait_ref, trait_items)) = is_trait {
        predicates.extend(trait_items.iter().flat_map(|trait_item_ref| {
            let trait_item = tcx.hir.trait_item(trait_item_ref.id);
            let bounds = match trait_item.node {
                hir::TraitItemKind::Type(ref bounds, _) => bounds,
                _ => {
                    return vec![].into_iter();
                }
            };

            let assoc_ty = tcx.mk_projection(
                tcx.hir.local_def_id(trait_item.id),
                self_trait_ref.substs,
            );

            let bounds = compute_bounds(&ItemCtxt::new(tcx, def_id),
                                        assoc_ty,
                                        bounds,
                                        SizedByDefault::Yes,
                                        trait_item.span);

            bounds.predicates(tcx, assoc_ty).into_iter()
        }))
    }

    // Subtle: before we store the predicates into the tcx, we
    // sort them so that predicates like `T: Foo<Item=U>` come
    // before uses of `U`.  This avoids false ambiguity errors
    // in trait checking. See `setup_constraining_predicates`
    // for details.
    if let NodeItem(&Item { node: ItemImpl(..), .. }) = node {
        let self_ty = tcx.type_of(def_id);
        let trait_ref = tcx.impl_trait_ref(def_id);
        ctp::setup_constraining_predicates(tcx,
                                           &mut predicates,
                                           trait_ref,
                                           &mut ctp::parameters_for_impl(self_ty, trait_ref));
    }

    ty::GenericPredicates {
        parent: generics.parent,
        predicates,
    }
}

pub enum SizedByDefault { Yes, No, }

/// 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.
pub fn compute_bounds<'gcx: 'tcx, 'tcx>(astconv: &AstConv<'gcx, 'tcx>,
                                        param_ty: Ty<'tcx>,
                                        ast_bounds: &[hir::TyParamBound],
                                        sized_by_default: SizedByDefault,
                                        span: Span)
                                        -> Bounds<'tcx>
{
    let mut region_bounds = vec![];
    let mut trait_bounds = vec![];
    for ast_bound in ast_bounds {
        match *ast_bound {
            hir::TraitTyParamBound(ref b, hir::TraitBoundModifier::None) => {
                trait_bounds.push(b);
            }
            hir::TraitTyParamBound(_, hir::TraitBoundModifier::Maybe) => {}
            hir::RegionTyParamBound(ref l) => {
                region_bounds.push(l);
            }
        }
    }

    let mut projection_bounds = vec![];

    let mut trait_bounds: Vec<_> = trait_bounds.iter().map(|&bound| {
        astconv.instantiate_poly_trait_ref(bound,
                                           param_ty,
                                           &mut projection_bounds)
    }).collect();

    let region_bounds = region_bounds.into_iter().map(|r| {
        astconv.ast_region_to_region(r, None)
    }).collect();

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

    let implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
        !is_unsized(astconv, ast_bounds, span)
    } else {
        false
    };

    Bounds {
        region_bounds,
        implicitly_sized,
        trait_bounds,
        projection_bounds,
    }
}

/// Converts a specific TyParamBound from the AST into a set of
/// predicates that apply to the self-type. A vector is returned
/// because this can be anywhere from 0 predicates (`T:?Sized` adds no
/// predicates) to 1 (`T:Foo`) to many (`T:Bar<X=i32>` adds `T:Bar`
/// and `<T as Bar>::X == i32`).
fn predicates_from_bound<'tcx>(astconv: &AstConv<'tcx, 'tcx>,
                               param_ty: Ty<'tcx>,
                               bound: &hir::TyParamBound)
                               -> Vec<ty::Predicate<'tcx>>
{
    match *bound {
        hir::TraitTyParamBound(ref tr, hir::TraitBoundModifier::None) => {
            let mut projections = Vec::new();
            let pred = astconv.instantiate_poly_trait_ref(tr,
                                                          param_ty,
                                                          &mut projections);
            projections.into_iter()
                       .map(|p| p.to_predicate())
                       .chain(Some(pred.to_predicate()))
                       .collect()
        }
        hir::RegionTyParamBound(ref lifetime) => {
            let region = astconv.ast_region_to_region(lifetime, None);
            let pred = ty::Binder(ty::OutlivesPredicate(param_ty, region));
            vec![ty::Predicate::TypeOutlives(pred)]
        }
        hir::TraitTyParamBound(_, hir::TraitBoundModifier::Maybe) => {
            Vec::new()
        }
    }
}

fn compute_sig_of_foreign_fn_decl<'a, 'tcx>(
    tcx: TyCtxt<'a, 'tcx, 'tcx>,
    def_id: DefId,
    decl: &hir::FnDecl,
    abi: abi::Abi)
    -> ty::PolyFnSig<'tcx>
{
    let fty = AstConv::ty_of_fn(&ItemCtxt::new(tcx, def_id), hir::Unsafety::Unsafe, abi, decl);

    // feature gate SIMD types in FFI, since I (huonw) am not sure the
    // ABIs are handled at all correctly.
    if abi != abi::Abi::RustIntrinsic && abi != abi::Abi::PlatformIntrinsic
            && !tcx.sess.features.borrow().simd_ffi {
        let check = |ast_ty: &hir::Ty, ty: Ty| {
            if ty.is_simd() {
                tcx.sess.struct_span_err(ast_ty.span,
                              &format!("use of SIMD type `{}` in FFI is highly experimental and \
                                        may result in invalid code",
                                       tcx.hir.node_to_pretty_string(ast_ty.id)))
                    .help("add #![feature(simd_ffi)] to the crate attributes to enable")
                    .emit();
            }
        };
        for (input, ty) in decl.inputs.iter().zip(*fty.inputs().skip_binder()) {
            check(&input, ty)
        }
        if let hir::Return(ref ty) = decl.output {
            check(&ty, *fty.output().skip_binder())
        }
    }

    fty
}

fn is_foreign_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                             def_id: DefId)
                             -> bool {
    match tcx.hir.get_if_local(def_id) {
        Some(hir_map::NodeForeignItem(..)) => true,
        Some(_) => false,
        _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id)
    }
}

fn is_default_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                             def_id: DefId)
                             -> bool {
    match tcx.hir.get_if_local(def_id) {
        Some(hir_map::NodeItem(&hir::Item { node: hir::ItemDefaultImpl(..), .. }))
             => true,
        Some(_) => false,
        _ => bug!("is_default_impl applied to non-local def-id {:?}", def_id)
    }
}