rust/src/librustc/metadata/decoder.rs

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

// Decoding metadata from a single crate's metadata


use metadata::cstore::crate_metadata;
use metadata::common::*;
use metadata::csearch::StaticMethodInfo;
use metadata::csearch;
use metadata::cstore;
use metadata::decoder;
use metadata::tydecode::{parse_ty_data, parse_def_id,
                         parse_type_param_def_data,
                         parse_bare_fn_ty_data, parse_trait_ref_data};
use middle::ty::{ImplContainer, TraitContainer};
use middle::ty;
use middle::typeck;
use middle::astencode::vtable_decoder_helpers;


use std::u64;
use std::io::WriterUtil;
use std::io;
use std::option;
use std::str;
use std::vec;
use extra::ebml::reader;
use extra::ebml;
use extra::serialize::Decodable;
use syntax::ast_map;
use syntax::attr;
use syntax::parse::token::{ident_interner, special_idents};
use syntax::print::pprust;
use syntax::ast;
use syntax::codemap;
use syntax::parse::token;

type Cmd = @crate_metadata;

// A function that takes a def_id relative to the crate being searched and
// returns a def_id relative to the compilation environment, i.e. if we hit a
// def_id for an item defined in another crate, somebody needs to figure out
// what crate that's in and give us a def_id that makes sense for the current
// build.

fn lookup_hash(d: ebml::Doc, eq_fn: &fn(x:&[u8]) -> bool, hash: u64) ->
   Option<ebml::Doc> {
    let index = reader::get_doc(d, tag_index);
    let table = reader::get_doc(index, tag_index_table);
    let hash_pos = table.start + (hash % 256 * 4) as uint;
    let pos = io::u64_from_be_bytes(*d.data, hash_pos, 4) as uint;
    let tagged_doc = reader::doc_at(d.data, pos);

    let belt = tag_index_buckets_bucket_elt;

    let mut ret = None;
    do reader::tagged_docs(tagged_doc.doc, belt) |elt| {
        let pos = io::u64_from_be_bytes(*elt.data, elt.start, 4) as uint;
        if eq_fn(elt.data.slice(elt.start + 4, elt.end)) {
            ret = Some(reader::doc_at(d.data, pos).doc);
            false
        } else {
            true
        }
    };
    ret
}

pub type GetCrateDataCb<'self> = &'self fn(ast::CrateNum) -> Cmd;

pub fn maybe_find_item(item_id: int, items: ebml::Doc) -> Option<ebml::Doc> {
    fn eq_item(bytes: &[u8], item_id: int) -> bool {
        return io::u64_from_be_bytes(
            bytes.slice(0u, 4u), 0u, 4u) as int
            == item_id;
    }
    lookup_hash(items,
                |a| eq_item(a, item_id),
                (item_id as i64).hash())
}

fn find_item(item_id: int, items: ebml::Doc) -> ebml::Doc {
    match maybe_find_item(item_id, items) {
       None => fail!("lookup_item: id not found: {}", item_id),
       Some(d) => d
    }
}

// Looks up an item in the given metadata and returns an ebml doc pointing
// to the item data.
pub fn lookup_item(item_id: int, data: @~[u8]) -> ebml::Doc {
    let items = reader::get_doc(reader::Doc(data), tag_items);
    find_item(item_id, items)
}

#[deriving(Eq)]
enum Family {
    ImmStatic,             // c
    MutStatic,             // b
    Fn,                    // f
    UnsafeFn,              // u
    StaticMethod,          // F
    UnsafeStaticMethod,    // U
    ForeignFn,             // e
    Type,                  // y
    ForeignType,           // T
    Mod,                   // m
    ForeignMod,            // n
    Enum,                  // t
    TupleVariant,          // v
    StructVariant,         // V
    Impl,                  // i
    Trait,                 // I
    Struct,                // S
    PublicField,           // g
    PrivateField,          // j
    InheritedField         // N
}

fn item_family(item: ebml::Doc) -> Family {
    let fam = reader::get_doc(item, tag_items_data_item_family);
    match reader::doc_as_u8(fam) as char {
      'c' => ImmStatic,
      'b' => MutStatic,
      'f' => Fn,
      'u' => UnsafeFn,
      'F' => StaticMethod,
      'U' => UnsafeStaticMethod,
      'e' => ForeignFn,
      'y' => Type,
      'T' => ForeignType,
      'm' => Mod,
      'n' => ForeignMod,
      't' => Enum,
      'v' => TupleVariant,
      'V' => StructVariant,
      'i' => Impl,
      'I' => Trait,
      'S' => Struct,
      'g' => PublicField,
      'j' => PrivateField,
      'N' => InheritedField,
       c => fail!("unexpected family char: {}", c)
    }
}

fn item_visibility(item: ebml::Doc) -> ast::visibility {
    match reader::maybe_get_doc(item, tag_items_data_item_visibility) {
        None => ast::public,
        Some(visibility_doc) => {
            match reader::doc_as_u8(visibility_doc) as char {
                'y' => ast::public,
                'n' => ast::private,
                'i' => ast::inherited,
                _ => fail!("unknown visibility character")
            }
        }
    }
}

fn item_method_sort(item: ebml::Doc) -> char {
    let mut ret = 'r';
    do reader::tagged_docs(item, tag_item_trait_method_sort) |doc| {
        ret = doc.as_str_slice()[0] as char;
        false
    };
    ret
}

fn item_symbol(item: ebml::Doc) -> ~str {
    reader::get_doc(item, tag_items_data_item_symbol).as_str()
}

fn item_parent_item(d: ebml::Doc) -> Option<ast::DefId> {
    let mut ret = None;
    do reader::tagged_docs(d, tag_items_data_parent_item) |did| {
        ret = Some(reader::with_doc_data(did, parse_def_id));
        false
    };
    ret
}

fn item_reqd_and_translated_parent_item(cnum: ast::CrateNum,
                                        d: ebml::Doc) -> ast::DefId {
    let trait_did = item_parent_item(d).expect("item without parent");
    ast::DefId { crate: cnum, node: trait_did.node }
}

fn item_def_id(d: ebml::Doc, cdata: Cmd) -> ast::DefId {
    let tagdoc = reader::get_doc(d, tag_def_id);
    return translate_def_id(cdata, reader::with_doc_data(tagdoc, parse_def_id));
}

fn get_provided_source(d: ebml::Doc, cdata: Cmd) -> Option<ast::DefId> {
    do reader::maybe_get_doc(d, tag_item_method_provided_source).map |doc| {
        translate_def_id(cdata, reader::with_doc_data(doc, parse_def_id))
    }
}

fn each_reexport(d: ebml::Doc, f: &fn(ebml::Doc) -> bool) -> bool {
    reader::tagged_docs(d, tag_items_data_item_reexport, f)
}

fn variant_disr_val(d: ebml::Doc) -> Option<ty::Disr> {
    do reader::maybe_get_doc(d, tag_disr_val).and_then |val_doc| {
        do reader::with_doc_data(val_doc) |data| { u64::parse_bytes(data, 10u) }
    }
}

fn doc_type(doc: ebml::Doc, tcx: ty::ctxt, cdata: Cmd) -> ty::t {
    let tp = reader::get_doc(doc, tag_items_data_item_type);
    parse_ty_data(*tp.data, cdata.cnum, tp.start, tcx,
                  |_, did| translate_def_id(cdata, did))
}

fn doc_method_fty(doc: ebml::Doc, tcx: ty::ctxt, cdata: Cmd) -> ty::BareFnTy {
    let tp = reader::get_doc(doc, tag_item_method_fty);
    parse_bare_fn_ty_data(*tp.data, cdata.cnum, tp.start, tcx,
                          |_, did| translate_def_id(cdata, did))
}

fn doc_transformed_self_ty(doc: ebml::Doc,
                           tcx: ty::ctxt,
                           cdata: Cmd) -> Option<ty::t>
{
    do reader::maybe_get_doc(doc, tag_item_method_transformed_self_ty).map |tp| {
        parse_ty_data(*tp.data, cdata.cnum, tp.start, tcx,
                      |_, did| translate_def_id(cdata, did))
    }
}

pub fn item_type(_item_id: ast::DefId, item: ebml::Doc,
                 tcx: ty::ctxt, cdata: Cmd) -> ty::t {
    doc_type(item, tcx, cdata)
}

fn doc_trait_ref(doc: ebml::Doc, tcx: ty::ctxt, cdata: Cmd) -> ty::TraitRef {
    parse_trait_ref_data(*doc.data, cdata.cnum, doc.start, tcx,
                         |_, did| translate_def_id(cdata, did))
}

fn item_trait_ref(doc: ebml::Doc, tcx: ty::ctxt, cdata: Cmd) -> ty::TraitRef {
    let tp = reader::get_doc(doc, tag_item_trait_ref);
    doc_trait_ref(tp, tcx, cdata)
}

fn item_ty_param_defs(item: ebml::Doc, tcx: ty::ctxt, cdata: Cmd,
                      tag: uint)
    -> @~[ty::TypeParameterDef] {
    let mut bounds = ~[];
    do reader::tagged_docs(item, tag) |p| {
        let bd = parse_type_param_def_data(
            *p.data, p.start, cdata.cnum, tcx,
            |_, did| translate_def_id(cdata, did));
        bounds.push(bd);
        true
    };
    @bounds
}

fn item_ty_region_param(item: ebml::Doc) -> Option<ty::region_variance> {
    do reader::maybe_get_doc(item, tag_region_param).map |doc| {
        let mut decoder = reader::Decoder(doc);
        Decodable::decode(&mut decoder)
    }
}

fn item_ty_param_count(item: ebml::Doc) -> uint {
    let mut n = 0u;
    reader::tagged_docs(item, tag_items_data_item_ty_param_bounds,
                      |_p| { n += 1u; true } );
    n
}

fn enum_variant_ids(item: ebml::Doc, cdata: Cmd) -> ~[ast::DefId] {
    let mut ids: ~[ast::DefId] = ~[];
    let v = tag_items_data_item_variant;
    do reader::tagged_docs(item, v) |p| {
        let ext = reader::with_doc_data(p, parse_def_id);
        ids.push(ast::DefId { crate: cdata.cnum, node: ext.node });
        true
    };
    return ids;
}

pub fn item_path(item_doc: ebml::Doc) -> ast_map::path {
    let path_doc = reader::get_doc(item_doc, tag_path);

    let len_doc = reader::get_doc(path_doc, tag_path_len);
    let len = reader::doc_as_u32(len_doc) as uint;

    let mut result = vec::with_capacity(len);
    do reader::docs(path_doc) |tag, elt_doc| {
        if tag == tag_path_elt_mod {
            let str = elt_doc.as_str_slice();
            result.push(ast_map::path_mod(token::str_to_ident(str)));
        } else if tag == tag_path_elt_name {
            let str = elt_doc.as_str_slice();
            result.push(ast_map::path_name(token::str_to_ident(str)));
        } else if tag == tag_path_elt_pretty_name {
            let name_doc = reader::get_doc(elt_doc,
                                           tag_path_elt_pretty_name_ident);
            let extra_doc = reader::get_doc(elt_doc,
                                            tag_path_elt_pretty_name_extra);
            let str = name_doc.as_str_slice();
            let extra = reader::doc_as_u64(extra_doc);
            result.push(ast_map::path_pretty_name(token::str_to_ident(str),
                                                  extra));
        } else {
            // ignore tag_path_len element
        }
        true
    };

    return result;
}

fn item_name(intr: @ident_interner, item: ebml::Doc) -> ast::Ident {
    let name = reader::get_doc(item, tag_paths_data_name);
    let string = name.as_str_slice();
    match intr.find_equiv(&string) {
        None => token::str_to_ident(string),
        Some(val) => ast::Ident::new(val),
    }
}

pub fn item_to_def_like(item: ebml::Doc, did: ast::DefId, cnum: ast::CrateNum)
    -> DefLike {
    let fam = item_family(item);
    match fam {
        ImmStatic => DlDef(ast::DefStatic(did, false)),
        MutStatic => DlDef(ast::DefStatic(did, true)),
        Struct    => DlDef(ast::DefStruct(did)),
        UnsafeFn  => DlDef(ast::DefFn(did, ast::unsafe_fn)),
        Fn        => DlDef(ast::DefFn(did, ast::impure_fn)),
        ForeignFn => DlDef(ast::DefFn(did, ast::extern_fn)),
        StaticMethod | UnsafeStaticMethod => {
            let purity = if fam == UnsafeStaticMethod { ast::unsafe_fn } else
                { ast::impure_fn };
            // def_static_method carries an optional field of its enclosing
            // trait or enclosing impl (if this is an inherent static method).
            // So we need to detect whether this is in a trait or not, which
            // we do through the mildly hacky way of checking whether there is
            // a trait_method_sort.
            let provenance = if reader::maybe_get_doc(
                  item, tag_item_trait_method_sort).is_some() {
                ast::FromTrait(item_reqd_and_translated_parent_item(cnum,
                                                                    item))
            } else {
                ast::FromImpl(item_reqd_and_translated_parent_item(cnum,
                                                                   item))
            };
            DlDef(ast::DefStaticMethod(did, provenance, purity))
        }
        Type | ForeignType => DlDef(ast::DefTy(did)),
        Mod => DlDef(ast::DefMod(did)),
        ForeignMod => DlDef(ast::DefForeignMod(did)),
        StructVariant => {
            let enum_did = item_reqd_and_translated_parent_item(cnum, item);
            DlDef(ast::DefVariant(enum_did, did, true))
        }
        TupleVariant => {
            let enum_did = item_reqd_and_translated_parent_item(cnum, item);
            DlDef(ast::DefVariant(enum_did, did, false))
        }
        Trait => DlDef(ast::DefTrait(did)),
        Enum => DlDef(ast::DefTy(did)),
        Impl => DlImpl(did),
        PublicField | PrivateField | InheritedField => DlField,
    }
}

pub fn lookup_def(cnum: ast::CrateNum, data: @~[u8], did_: ast::DefId) ->
   ast::Def {
    let item = lookup_item(did_.node, data);
    let did = ast::DefId { crate: cnum, node: did_.node };
    // We treat references to enums as references to types.
    return def_like_to_def(item_to_def_like(item, did, cnum));
}

pub fn get_trait_def(cdata: Cmd,
                     item_id: ast::NodeId,
                     tcx: ty::ctxt) -> ty::TraitDef
{
    let item_doc = lookup_item(item_id, cdata.data);
    let tp_defs = item_ty_param_defs(item_doc, tcx, cdata,
                                     tag_items_data_item_ty_param_bounds);
    let rp = item_ty_region_param(item_doc);
    let mut bounds = ty::EmptyBuiltinBounds();
    // Collect the builtin bounds from the encoded supertraits.
    // FIXME(#8559): They should be encoded directly.
    do reader::tagged_docs(item_doc, tag_item_super_trait_ref) |trait_doc| {
        // NB. Bypasses real supertraits. See get_supertraits() if you wanted them.
        let trait_ref = doc_trait_ref(trait_doc, tcx, cdata);
        do tcx.lang_items.to_builtin_kind(trait_ref.def_id).map |bound| {
            bounds.add(bound);
        };
        true
    };
    ty::TraitDef {
        generics: ty::Generics {type_param_defs: tp_defs,
                                region_param: rp},
        bounds: bounds,
        trait_ref: @item_trait_ref(item_doc, tcx, cdata)
    }
}

pub fn get_type(cdata: Cmd, id: ast::NodeId, tcx: ty::ctxt)
    -> ty::ty_param_bounds_and_ty {

    let item = lookup_item(id, cdata.data);
    let t = item_type(ast::DefId { crate: cdata.cnum, node: id }, item, tcx,
                      cdata);
    let tp_defs = if family_has_type_params(item_family(item)) {
        item_ty_param_defs(item, tcx, cdata, tag_items_data_item_ty_param_bounds)
    } else { @~[] };
    let rp = item_ty_region_param(item);
    ty::ty_param_bounds_and_ty {
        generics: ty::Generics {type_param_defs: tp_defs,
                                region_param: rp},
        ty: t
    }
}

pub fn get_region_param(cdata: Cmd, id: ast::NodeId)
    -> Option<ty::region_variance> {

    let item = lookup_item(id, cdata.data);
    return item_ty_region_param(item);
}

pub fn get_type_param_count(data: @~[u8], id: ast::NodeId) -> uint {
    item_ty_param_count(lookup_item(id, data))
}

pub fn get_impl_trait(cdata: Cmd,
                       id: ast::NodeId,
                       tcx: ty::ctxt) -> Option<@ty::TraitRef>
{
    let item_doc = lookup_item(id, cdata.data);
    do reader::maybe_get_doc(item_doc, tag_item_trait_ref).map |tp| {
        @doc_trait_ref(tp, tcx, cdata)
    }
}

pub fn get_impl_vtables(cdata: Cmd,
                        id: ast::NodeId,
                        tcx: ty::ctxt) -> typeck::impl_res
{
    let item_doc = lookup_item(id, cdata.data);
    let vtables_doc = reader::get_doc(item_doc, tag_item_impl_vtables);
    let mut decoder = reader::Decoder(vtables_doc);

    typeck::impl_res {
        trait_vtables: decoder.read_vtable_res(tcx, cdata),
        self_vtables: decoder.read_vtable_param_res(tcx, cdata)
    }
}


pub fn get_impl_method(intr: @ident_interner, cdata: Cmd, id: ast::NodeId,
                       name: ast::Ident) -> Option<ast::DefId> {
    let items = reader::get_doc(reader::Doc(cdata.data), tag_items);
    let mut found = None;
    do reader::tagged_docs(find_item(id, items), tag_item_impl_method) |mid| {
        let m_did = reader::with_doc_data(mid, parse_def_id);
        if item_name(intr, find_item(m_did.node, items)) == name {
            found = Some(translate_def_id(cdata, m_did));
        }
        true
    };
    found
}

pub fn get_symbol(data: @~[u8], id: ast::NodeId) -> ~str {
    return item_symbol(lookup_item(id, data));
}

// Something that a name can resolve to.
pub enum DefLike {
    DlDef(ast::Def),
    DlImpl(ast::DefId),
    DlField
}

pub fn def_like_to_def(def_like: DefLike) -> ast::Def {
    match def_like {
        DlDef(def) => return def,
        DlImpl(*) => fail!("found impl in def_like_to_def"),
        DlField => fail!("found field in def_like_to_def")
    }
}

/// Iterates over the language items in the given crate.
pub fn each_lang_item(cdata: Cmd, f: &fn(ast::NodeId, uint) -> bool) -> bool {
    let root = reader::Doc(cdata.data);
    let lang_items = reader::get_doc(root, tag_lang_items);
    do reader::tagged_docs(lang_items, tag_lang_items_item) |item_doc| {
        let id_doc = reader::get_doc(item_doc, tag_lang_items_item_id);
        let id = reader::doc_as_u32(id_doc) as uint;
        let node_id_doc = reader::get_doc(item_doc,
                                          tag_lang_items_item_node_id);
        let node_id = reader::doc_as_u32(node_id_doc) as ast::NodeId;

        f(node_id, id)
    }
}

struct EachItemContext<'self> {
    intr: @ident_interner,
    cdata: Cmd,
    get_crate_data: GetCrateDataCb<'self>,
    path_builder: &'self mut ~str,
    callback: &'self fn(&str, DefLike, ast::visibility) -> bool,
}

impl<'self> EachItemContext<'self> {
    // Pushes the given name and returns the old length.
    fn push_name(&mut self, string: &str) -> uint {
        let path_len = self.path_builder.len();
        if path_len != 0 {
            self.path_builder.push_str("::")
        }
        self.path_builder.push_str(string);
        path_len
    }

    // Pops the given name.
    fn pop_name(&mut self, old_len: uint) {
        // XXX(pcwalton): There's no safe function to do this. :(
        unsafe {
            str::raw::set_len(self.path_builder, old_len)
        }
    }

    fn process_item_and_pop_name(&mut self,
                                 doc: ebml::Doc,
                                 def_id: ast::DefId,
                                 old_len: uint,
                                 vis: ast::visibility)
                                 -> bool {
        let def_like = item_to_def_like(doc, def_id, self.cdata.cnum);
        match def_like {
            DlDef(def) => {
                debug!("(iterating over each item of a module) processing \
                        `{}` (def {:?})",
                       *self.path_builder,
                       def);
            }
            _ => {
                debug!("(iterating over each item of a module) processing \
                        `{}` ({}:{})",
                       *self.path_builder,
                       def_id.crate,
                       def_id.node);
            }
        }

        let mut continue_ = (self.callback)(*self.path_builder, def_like, vis);

        let family = item_family(doc);
        if family == ForeignMod {
            // These are unnamed; pop the name now.
            self.pop_name(old_len)
        }

        if continue_ {
            // Recurse if necessary.
            match family {
                Mod | ForeignMod | Trait | Impl => {
                    continue_ = self.each_item_of_module(def_id);
                }
                ImmStatic | MutStatic | Struct | UnsafeFn | Fn | ForeignFn |
                UnsafeStaticMethod | StaticMethod | Type | ForeignType |
                TupleVariant | StructVariant | Enum | PublicField |
                PrivateField | InheritedField => {}
            }
        }

        if family != ForeignMod {
            self.pop_name(old_len)
        }

        continue_
    }

    fn each_item_of_module(&mut self, def_id: ast::DefId) -> bool {
        // This item might not be in this crate. If it's not, look it up.
        let items = if def_id.crate == self.cdata.cnum {
            reader::get_doc(reader::Doc(self.cdata.data), tag_items)
        } else {
            let crate_data = (self.get_crate_data)(def_id.crate);
            let root = reader::Doc(crate_data.data);
            reader::get_doc(root, tag_items)
        };

        // Look up the item.
        let item_doc = match maybe_find_item(def_id.node, items) {
            None => return false,
            Some(item_doc) => item_doc,
        };

        self.each_child_of_module_or_crate(item_doc)
    }

    fn each_child_of_module_or_crate(&mut self, item_doc: ebml::Doc) -> bool {
        let mut continue_ = true;

        // Iterate over all children.
        do reader::tagged_docs(item_doc, tag_mod_child) |child_info_doc| {
            let child_def_id = reader::with_doc_data(child_info_doc,
                                                     parse_def_id);
            let child_def_id = translate_def_id(self.cdata, child_def_id);

            // This item may be in yet another crate, if it was the child of
            // a reexport.
            let other_crates_items = if child_def_id.crate ==
                    self.cdata.cnum {
                reader::get_doc(reader::Doc(self.cdata.data), tag_items)
            } else {
                let crate_data = (self.get_crate_data)(child_def_id.crate);
                let root = reader::Doc(crate_data.data);
                reader::get_doc(root, tag_items)
            };

            debug!("(iterating over each item of a module) looking up item \
                    {}:{} in `{}`, crate {}",
                   child_def_id.crate,
                   child_def_id.node,
                   *self.path_builder,
                   self.cdata.cnum);

            // Get the item.
            match maybe_find_item(child_def_id.node, other_crates_items) {
                None => {}
                Some(child_item_doc) => {
                    // Push the name.
                    let child_name = item_name(self.intr, child_item_doc);
                    debug!("(iterating over each item of a module) pushing \
                            name `{}` onto `{}`",
                           token::ident_to_str(&child_name),
                           *self.path_builder);
                    let old_len =
                        self.push_name(token::ident_to_str(&child_name));

                    // Process this item.

                    let vis = item_visibility(child_item_doc);
                    continue_ = self.process_item_and_pop_name(child_item_doc,
                                                              child_def_id,
                                                              old_len,
                                                              vis);
                }
            }
            continue_
        };

        if !continue_ {
            return false
        }

        // Iterate over reexports.
        do each_reexport(item_doc) |reexport_doc| {
            let def_id_doc = reader::get_doc(
                reexport_doc,
                tag_items_data_item_reexport_def_id);
            let orig_def_id = reader::with_doc_data(def_id_doc, parse_def_id);

            // NB: was "cdata"
            let def_id = translate_def_id(self.cdata, orig_def_id);

            let name_doc = reader::get_doc(reexport_doc,
                                           tag_items_data_item_reexport_name);
            let name = name_doc.as_str_slice();

            // Push the name.
            debug!("(iterating over each item of a module) pushing \
                    reexported name `{}` onto `{}` (crate {}, orig {}, \
                    in crate {})",
                   name,
                   *self.path_builder,
                   def_id.crate,
                   orig_def_id.crate,
                   self.cdata.cnum);
            let old_len = self.push_name(name);

            // This reexport may be in yet another crate.
            let other_crates_items = if def_id.crate == self.cdata.cnum {
                reader::get_doc(reader::Doc(self.cdata.data), tag_items)
            } else {
                let crate_data = (self.get_crate_data)(def_id.crate);
                let root = reader::Doc(crate_data.data);
                reader::get_doc(root, tag_items)
            };

            // Get the item.
            match maybe_find_item(def_id.node, other_crates_items) {
                None => { self.pop_name(old_len); }
                Some(reexported_item_doc) => {
                    continue_ = self.process_item_and_pop_name(
                        reexported_item_doc,
                        def_id,
                        old_len,
                        ast::public);
                }
            }

            continue_
        };

        continue_
    }
}

fn each_child_of_item_or_crate(intr: @ident_interner,
                               cdata: Cmd,
                               item_doc: ebml::Doc,
                               get_crate_data: GetCrateDataCb,
                               callback: &fn(DefLike, ast::Ident,
                                             ast::visibility)) {
    // Iterate over all children.
    let _ = do reader::tagged_docs(item_doc, tag_mod_child) |child_info_doc| {
        let child_def_id = reader::with_doc_data(child_info_doc,
                                                 parse_def_id);
        let child_def_id = translate_def_id(cdata, child_def_id);

        // This item may be in yet another crate if it was the child of a
        // reexport.
        let other_crates_items = if child_def_id.crate == cdata.cnum {
            reader::get_doc(reader::Doc(cdata.data), tag_items)
        } else {
            let crate_data = get_crate_data(child_def_id.crate);
            reader::get_doc(reader::Doc(crate_data.data), tag_items)
        };

        // Get the item.
        match maybe_find_item(child_def_id.node, other_crates_items) {
            None => {}
            Some(child_item_doc) => {
                // Hand off the item to the callback.
                let child_name = item_name(intr, child_item_doc);
                let def_like = item_to_def_like(child_item_doc,
                                                child_def_id,
                                                cdata.cnum);
                let visibility = item_visibility(child_item_doc);
                callback(def_like, child_name, visibility);

            }
        }

        true
    };

    // As a special case, iterate over all static methods of
    // associated implementations too. This is a bit of a botch.
    // --pcwalton
    let _ = do reader::tagged_docs(item_doc,
                                   tag_items_data_item_inherent_impl)
            |inherent_impl_def_id_doc| {
        let inherent_impl_def_id = item_def_id(inherent_impl_def_id_doc,
                                               cdata);
        let items = reader::get_doc(reader::Doc(cdata.data), tag_items);
        match maybe_find_item(inherent_impl_def_id.node, items) {
            None => {}
            Some(inherent_impl_doc) => {
                let _ = do reader::tagged_docs(inherent_impl_doc,
                                               tag_item_impl_method)
                        |impl_method_def_id_doc| {
                    let impl_method_def_id =
                        reader::with_doc_data(impl_method_def_id_doc,
                                              parse_def_id);
                    let impl_method_def_id =
                        translate_def_id(cdata, impl_method_def_id);
                    match maybe_find_item(impl_method_def_id.node, items) {
                        None => {}
                        Some(impl_method_doc) => {
                            match item_family(impl_method_doc) {
                                StaticMethod | UnsafeStaticMethod => {
                                    // Hand off the static method
                                    // to the callback.
                                    let static_method_name =
                                        item_name(intr, impl_method_doc);
                                    let static_method_def_like =
                                        item_to_def_like(impl_method_doc,
                                                         impl_method_def_id,
                                                         cdata.cnum);
                                    callback(static_method_def_like,
                                             static_method_name,
                                             item_visibility(impl_method_doc));
                                }
                                _ => {}
                            }
                        }
                    }

                    true
                };
            }
        }

        true
    };

    // Iterate over all reexports.
    let _ = do each_reexport(item_doc) |reexport_doc| {
        let def_id_doc = reader::get_doc(reexport_doc,
                                         tag_items_data_item_reexport_def_id);
        let child_def_id = reader::with_doc_data(def_id_doc,
                                                 parse_def_id);
        let child_def_id = translate_def_id(cdata, child_def_id);

        let name_doc = reader::get_doc(reexport_doc,
                                       tag_items_data_item_reexport_name);
        let name = name_doc.as_str_slice();

        // This reexport may be in yet another crate.
        let other_crates_items = if child_def_id.crate == cdata.cnum {
            reader::get_doc(reader::Doc(cdata.data), tag_items)
        } else {
            let crate_data = get_crate_data(child_def_id.crate);
            reader::get_doc(reader::Doc(crate_data.data), tag_items)
        };

        // Get the item.
        match maybe_find_item(child_def_id.node, other_crates_items) {
            None => {}
            Some(child_item_doc) => {
                // Hand off the item to the callback.
                let def_like = item_to_def_like(child_item_doc,
                                                child_def_id,
                                                cdata.cnum);
                // These items have a public visibility because they're part of
                // a public re-export.
                callback(def_like, token::str_to_ident(name), ast::public);
            }
        }

        true
    };
}

/// Iterates over each child of the given item.
pub fn each_child_of_item(intr: @ident_interner,
                          cdata: Cmd,
                          id: ast::NodeId,
                          get_crate_data: GetCrateDataCb,
                          callback: &fn(DefLike, ast::Ident, ast::visibility)) {
    // Find the item.
    let root_doc = reader::Doc(cdata.data);
    let items = reader::get_doc(root_doc, tag_items);
    let item_doc = match maybe_find_item(id, items) {
        None => return,
        Some(item_doc) => item_doc,
    };

    each_child_of_item_or_crate(intr,
                                cdata,
                                item_doc,
                                get_crate_data,
                                callback)
}

/// Iterates over all the top-level crate items.
pub fn each_top_level_item_of_crate(intr: @ident_interner,
                                    cdata: Cmd,
                                    get_crate_data: GetCrateDataCb,
                                    callback: &fn(DefLike, ast::Ident,
                                                  ast::visibility)) {
    let root_doc = reader::Doc(cdata.data);
    let misc_info_doc = reader::get_doc(root_doc, tag_misc_info);
    let crate_items_doc = reader::get_doc(misc_info_doc,
                                          tag_misc_info_crate_items);

    each_child_of_item_or_crate(intr,
                                cdata,
                                crate_items_doc,
                                get_crate_data,
                                callback)
}

pub fn get_item_path(cdata: Cmd, id: ast::NodeId) -> ast_map::path {
    item_path(lookup_item(id, cdata.data))
}

pub type decode_inlined_item<'self> = &'self fn(
    cdata: @cstore::crate_metadata,
    tcx: ty::ctxt,
    path: ast_map::path,
    par_doc: ebml::Doc) -> Option<ast::inlined_item>;

pub fn maybe_get_item_ast(cdata: Cmd, tcx: ty::ctxt,
                          id: ast::NodeId,
                          decode_inlined_item: decode_inlined_item)
                       -> csearch::found_ast {
    debug!("Looking up item: {}", id);
    let item_doc = lookup_item(id, cdata.data);
    let path = {
        let item_path = item_path(item_doc);
        item_path.init().to_owned()
    };
    match decode_inlined_item(cdata, tcx, /*bad*/path.clone(), item_doc) {
      Some(ref ii) => csearch::found(*ii),
      None => {
        match item_parent_item(item_doc) {
          Some(did) => {
            let did = translate_def_id(cdata, did);
            let parent_item = lookup_item(did.node, cdata.data);
            match decode_inlined_item(cdata, tcx, path, parent_item) {
              Some(ref ii) => csearch::found_parent(did, *ii),
              None => csearch::not_found
            }
          }
          None => csearch::not_found
        }
      }
    }
}

pub fn get_enum_variants(intr: @ident_interner, cdata: Cmd, id: ast::NodeId,
                     tcx: ty::ctxt) -> ~[@ty::VariantInfo] {
    let data = cdata.data;
    let items = reader::get_doc(reader::Doc(data), tag_items);
    let item = find_item(id, items);
    let mut infos: ~[@ty::VariantInfo] = ~[];
    let variant_ids = enum_variant_ids(item, cdata);
    let mut disr_val = 0;
    for did in variant_ids.iter() {
        let item = find_item(did.node, items);
        let ctor_ty = item_type(ast::DefId { crate: cdata.cnum, node: id},
                                item, tcx, cdata);
        let name = item_name(intr, item);
        let arg_tys = match ty::get(ctor_ty).sty {
          ty::ty_bare_fn(ref f) => f.sig.inputs.clone(),
          _ => ~[], // Nullary enum variant.
        };
        match variant_disr_val(item) {
          Some(val) => { disr_val = val; }
          _         => { /* empty */ }
        }
        infos.push(@ty::VariantInfo{
            args: arg_tys,
            arg_names: None,
            ctor_ty: ctor_ty,
            name: name,
            // I'm not even sure if we encode visibility
            // for variants -- TEST -- tjc
            id: *did,
            disr_val: disr_val,
            vis: ast::inherited});
        disr_val += 1;
    }
    return infos;
}

fn get_explicit_self(item: ebml::Doc) -> ast::explicit_self_ {
    fn get_mutability(ch: u8) -> ast::Mutability {
        match ch as char {
            'i' => ast::MutImmutable,
            'm' => ast::MutMutable,
            _ => fail!("unknown mutability character: `{}`", ch as char),
        }
    }

    let explicit_self_doc = reader::get_doc(item, tag_item_trait_method_explicit_self);
    let string = explicit_self_doc.as_str_slice();

    let explicit_self_kind = string[0];
    match explicit_self_kind as char {
        's' => { return ast::sty_static; }
        'v' => { return ast::sty_value; }
        '@' => { return ast::sty_box(get_mutability(string[1])); }
        '~' => { return ast::sty_uniq; }
        '&' => {
            // FIXME(#4846) expl. region
            return ast::sty_region(None, get_mutability(string[1]));
        }
        _ => {
            fail!("unknown self type code: `{}`", explicit_self_kind as char);
        }
    }
}

fn item_impl_methods(intr: @ident_interner, cdata: Cmd, item: ebml::Doc,
                     tcx: ty::ctxt) -> ~[@ty::Method] {
    let mut rslt = ~[];
    do reader::tagged_docs(item, tag_item_impl_method) |doc| {
        let m_did = reader::with_doc_data(doc, parse_def_id);
        rslt.push(@get_method(intr, cdata, m_did.node, tcx));
        true
    };

    rslt
}

/// Returns information about the given implementation.
pub fn get_impl(intr: @ident_interner, cdata: Cmd, impl_id: ast::NodeId,
               tcx: ty::ctxt)
                -> ty::Impl {
    let data = cdata.data;
    let impl_item = lookup_item(impl_id, data);
    ty::Impl {
        did: ast::DefId {
            crate: cdata.cnum,
            node: impl_id,
        },
        ident: item_name(intr, impl_item),
        methods: item_impl_methods(intr, cdata, impl_item, tcx),
    }
}

pub fn get_method_name_and_explicit_self(
    intr: @ident_interner,
    cdata: Cmd,
    id: ast::NodeId) -> (ast::Ident, ast::explicit_self_)
{
    let method_doc = lookup_item(id, cdata.data);
    let name = item_name(intr, method_doc);
    let explicit_self = get_explicit_self(method_doc);
    (name, explicit_self)
}

pub fn get_method(intr: @ident_interner, cdata: Cmd, id: ast::NodeId,
                  tcx: ty::ctxt) -> ty::Method
{
    let method_doc = lookup_item(id, cdata.data);
    let def_id = item_def_id(method_doc, cdata);

    let container_id = item_reqd_and_translated_parent_item(cdata.cnum,
                                                            method_doc);
    let container_doc = lookup_item(container_id.node, cdata.data);
    let container = match item_family(container_doc) {
        Trait => TraitContainer(container_id),
        _ => ImplContainer(container_id),
    };

    let name = item_name(intr, method_doc);
    let type_param_defs = item_ty_param_defs(method_doc, tcx, cdata,
                                             tag_item_method_tps);
    let transformed_self_ty = doc_transformed_self_ty(method_doc, tcx, cdata);
    let fty = doc_method_fty(method_doc, tcx, cdata);
    let vis = item_visibility(method_doc);
    let explicit_self = get_explicit_self(method_doc);
    let provided_source = get_provided_source(method_doc, cdata);

    ty::Method::new(
        name,
        ty::Generics {
            type_param_defs: type_param_defs,
            region_param: None
        },
        transformed_self_ty,
        fty,
        explicit_self,
        vis,
        def_id,
        container,
        provided_source
    )
}

pub fn get_trait_method_def_ids(cdata: Cmd,
                                id: ast::NodeId) -> ~[ast::DefId] {
    let data = cdata.data;
    let item = lookup_item(id, data);
    let mut result = ~[];
    do reader::tagged_docs(item, tag_item_trait_method) |mth| {
        result.push(item_def_id(mth, cdata));
        true
    };
    result
}

pub fn get_provided_trait_methods(intr: @ident_interner, cdata: Cmd,
                                  id: ast::NodeId, tcx: ty::ctxt) ->
        ~[@ty::Method] {
    let data = cdata.data;
    let item = lookup_item(id, data);
    let mut result = ~[];

    do reader::tagged_docs(item, tag_item_trait_method) |mth_id| {
        let did = item_def_id(mth_id, cdata);
        let mth = lookup_item(did.node, data);

        if item_method_sort(mth) == 'p' {
            result.push(@get_method(intr, cdata, did.node, tcx));
        }
        true
    };

    return result;
}

/// Returns the supertraits of the given trait.
pub fn get_supertraits(cdata: Cmd, id: ast::NodeId, tcx: ty::ctxt)
                    -> ~[@ty::TraitRef] {
    let mut results = ~[];
    let item_doc = lookup_item(id, cdata.data);
    do reader::tagged_docs(item_doc, tag_item_super_trait_ref) |trait_doc| {
        // NB. Only reads the ones that *aren't* builtin-bounds. See also
        // get_trait_def() for collecting the builtin bounds.
        // FIXME(#8559): The builtin bounds shouldn't be encoded in the first place.
        let trait_ref = doc_trait_ref(trait_doc, tcx, cdata);
        if tcx.lang_items.to_builtin_kind(trait_ref.def_id).is_none() {
            results.push(@trait_ref);
        }
        true
    };
    return results;
}

pub fn get_type_name_if_impl(cdata: Cmd,
                             node_id: ast::NodeId) -> Option<ast::Ident> {
    let item = lookup_item(node_id, cdata.data);
    if item_family(item) != Impl {
        return None;
    }

    let mut ret = None;
    do reader::tagged_docs(item, tag_item_impl_type_basename) |doc| {
        ret = Some(token::str_to_ident(doc.as_str_slice()));
        false
    };

    ret
}

pub fn get_static_methods_if_impl(intr: @ident_interner,
                                  cdata: Cmd,
                                  node_id: ast::NodeId)
                               -> Option<~[StaticMethodInfo]> {
    let item = lookup_item(node_id, cdata.data);
    if item_family(item) != Impl {
        return None;
    }

    // If this impl implements a trait, don't consider it.
    let ret = do reader::tagged_docs(item, tag_item_trait_ref) |_doc| {
        false
    };

    if !ret { return None }

    let mut impl_method_ids = ~[];
    do reader::tagged_docs(item, tag_item_impl_method) |impl_method_doc| {
        impl_method_ids.push(reader::with_doc_data(impl_method_doc, parse_def_id));
        true
    };

    let mut static_impl_methods = ~[];
    for impl_method_id in impl_method_ids.iter() {
        let impl_method_doc = lookup_item(impl_method_id.node, cdata.data);
        let family = item_family(impl_method_doc);
        match family {
            StaticMethod | UnsafeStaticMethod => {
                let purity;
                match item_family(impl_method_doc) {
                    StaticMethod => purity = ast::impure_fn,
                    UnsafeStaticMethod => purity = ast::unsafe_fn,
                    _ => fail!()
                }

                static_impl_methods.push(StaticMethodInfo {
                    ident: item_name(intr, impl_method_doc),
                    def_id: item_def_id(impl_method_doc, cdata),
                    purity: purity,
                    vis: item_visibility(impl_method_doc),
                });
            }
            _ => {}
        }
    }

    return Some(static_impl_methods);
}

pub fn get_item_attrs(cdata: Cmd,
                      node_id: ast::NodeId,
                      f: &fn(~[@ast::MetaItem])) {

    let item = lookup_item(node_id, cdata.data);
    do reader::tagged_docs(item, tag_attributes) |attributes| {
        do reader::tagged_docs(attributes, tag_attribute) |attribute| {
            f(get_meta_items(attribute));
            true
        };
        true
    };
}

fn struct_field_family_to_visibility(family: Family) -> ast::visibility {
    match family {
      PublicField => ast::public,
      PrivateField => ast::private,
      InheritedField => ast::inherited,
      _ => fail!()
    }
}

pub fn get_struct_fields(intr: @ident_interner, cdata: Cmd, id: ast::NodeId)
    -> ~[ty::field_ty] {
    let data = cdata.data;
    let item = lookup_item(id, data);
    let mut result = ~[];
    do reader::tagged_docs(item, tag_item_field) |an_item| {
        let f = item_family(an_item);
        if f == PublicField || f == PrivateField || f == InheritedField {
            // FIXME #6993: name should be of type Name, not Ident
            let name = item_name(intr, an_item);
            let did = item_def_id(an_item, cdata);
            result.push(ty::field_ty {
                name: name.name,
                id: did, vis:
                struct_field_family_to_visibility(f),
            });
        }
        true
    };
    do reader::tagged_docs(item, tag_item_unnamed_field) |an_item| {
        let did = item_def_id(an_item, cdata);
        result.push(ty::field_ty {
            name: special_idents::unnamed_field.name,
            id: did,
            vis: ast::inherited,
        });
        true
    };
    result
}

pub fn get_item_visibility(cdata: Cmd, id: ast::NodeId)
                        -> ast::visibility {
    item_visibility(lookup_item(id, cdata.data))
}

fn family_has_type_params(fam: Family) -> bool {
    match fam {
      ImmStatic | ForeignType | Mod | ForeignMod | PublicField | PrivateField
      | ForeignFn | MutStatic => false,
      _           => true
    }
}

fn family_names_type(fam: Family) -> bool {
    match fam { Type | Mod | Trait => true, _ => false }
}

fn read_path(d: ebml::Doc) -> (~str, uint) {
    do reader::with_doc_data(d) |desc| {
        let pos = io::u64_from_be_bytes(desc, 0u, 4u) as uint;
        let pathbytes = desc.slice(4u, desc.len());
        let path = str::from_utf8(pathbytes);

        (path, pos)
    }
}

fn describe_def(items: ebml::Doc, id: ast::DefId) -> ~str {
    if id.crate != ast::LOCAL_CRATE { return ~"external"; }
    let it = match maybe_find_item(id.node, items) {
        Some(it) => it,
        None => fail!("describe_def: item not found {:?}", id)
    };
    return item_family_to_str(item_family(it));
}

fn item_family_to_str(fam: Family) -> ~str {
    match fam {
      ImmStatic => ~"static",
      MutStatic => ~"static mut",
      Fn => ~"fn",
      UnsafeFn => ~"unsafe fn",
      StaticMethod => ~"static method",
      UnsafeStaticMethod => ~"unsafe static method",
      ForeignFn => ~"foreign fn",
      Type => ~"type",
      ForeignType => ~"foreign type",
      Mod => ~"mod",
      ForeignMod => ~"foreign mod",
      Enum => ~"enum",
      StructVariant => ~"struct variant",
      TupleVariant => ~"tuple variant",
      Impl => ~"impl",
      Trait => ~"trait",
      Struct => ~"struct",
      PublicField => ~"public field",
      PrivateField => ~"private field",
      InheritedField => ~"inherited field",
    }
}

fn get_meta_items(md: ebml::Doc) -> ~[@ast::MetaItem] {
    let mut items: ~[@ast::MetaItem] = ~[];
    do reader::tagged_docs(md, tag_meta_item_word) |meta_item_doc| {
        let nd = reader::get_doc(meta_item_doc, tag_meta_item_name);
        let n = nd.as_str_slice().to_managed();
        items.push(attr::mk_word_item(n));
        true
    };
    do reader::tagged_docs(md, tag_meta_item_name_value) |meta_item_doc| {
        let nd = reader::get_doc(meta_item_doc, tag_meta_item_name);
        let vd = reader::get_doc(meta_item_doc, tag_meta_item_value);
        let n = nd.as_str_slice().to_managed();
        let v = vd.as_str_slice().to_managed();
        // FIXME (#623): Should be able to decode MetaNameValue variants,
        // but currently the encoder just drops them
        items.push(attr::mk_name_value_item_str(n, v));
        true
    };
    do reader::tagged_docs(md, tag_meta_item_list) |meta_item_doc| {
        let nd = reader::get_doc(meta_item_doc, tag_meta_item_name);
        let n = nd.as_str_slice().to_managed();
        let subitems = get_meta_items(meta_item_doc);
        items.push(attr::mk_list_item(n, subitems));
        true
    };
    return items;
}

fn get_attributes(md: ebml::Doc) -> ~[ast::Attribute] {
    let mut attrs: ~[ast::Attribute] = ~[];
    match reader::maybe_get_doc(md, tag_attributes) {
      option::Some(attrs_d) => {
        do reader::tagged_docs(attrs_d, tag_attribute) |attr_doc| {
            let meta_items = get_meta_items(attr_doc);
            // Currently it's only possible to have a single meta item on
            // an attribute
            assert_eq!(meta_items.len(), 1u);
            let meta_item = meta_items[0];
            attrs.push(
                codemap::Spanned {
                    node: ast::Attribute_ {
                        style: ast::AttrOuter,
                        value: meta_item,
                        is_sugared_doc: false,
                    },
                    span: codemap::dummy_sp()
                });
            true
        };
      }
      option::None => ()
    }
    return attrs;
}

fn list_meta_items(intr: @ident_interner,
                   meta_items: ebml::Doc,
                   out: @io::Writer) {
    let r = get_meta_items(meta_items);
    for mi in r.iter() {
        out.write_str(format!("{}\n", pprust::meta_item_to_str(*mi, intr)));
    }
}

fn list_crate_attributes(intr: @ident_interner, md: ebml::Doc, hash: &str,
                         out: @io::Writer) {
    out.write_str(format!("=Crate Attributes ({})=\n", hash));

    let r = get_attributes(md);
    for attr in r.iter() {
        out.write_str(format!("{}\n", pprust::attribute_to_str(attr, intr)));
    }

    out.write_str("\n\n");
}

pub fn get_crate_attributes(data: @~[u8]) -> ~[ast::Attribute] {
    return get_attributes(reader::Doc(data));
}

#[deriving(Clone)]
pub struct CrateDep {
    cnum: ast::CrateNum,
    name: ast::Ident,
    vers: @str,
    hash: @str
}

pub fn get_crate_deps(data: @~[u8]) -> ~[CrateDep] {
    let mut deps: ~[CrateDep] = ~[];
    let cratedoc = reader::Doc(data);
    let depsdoc = reader::get_doc(cratedoc, tag_crate_deps);
    let mut crate_num = 1;
    fn docstr(doc: ebml::Doc, tag_: uint) -> @str {
        let d = reader::get_doc(doc, tag_);
        d.as_str_slice().to_managed()
    }
    do reader::tagged_docs(depsdoc, tag_crate_dep) |depdoc| {
        deps.push(CrateDep {cnum: crate_num,
                  name: token::str_to_ident(docstr(depdoc, tag_crate_dep_name)),
                  vers: docstr(depdoc, tag_crate_dep_vers),
                  hash: docstr(depdoc, tag_crate_dep_hash)});
        crate_num += 1;
        true
    };
    return deps;
}

fn list_crate_deps(data: @~[u8], out: @io::Writer) {
    out.write_str("=External Dependencies=\n");

    let r = get_crate_deps(data);
    for dep in r.iter() {
        out.write_str(
            format!("{} {}-{}-{}\n",
                 dep.cnum, token::ident_to_str(&dep.name), dep.hash, dep.vers));
    }

    out.write_str("\n");
}

pub fn get_crate_hash(data: @~[u8]) -> @str {
    let cratedoc = reader::Doc(data);
    let hashdoc = reader::get_doc(cratedoc, tag_crate_hash);
    hashdoc.as_str_slice().to_managed()
}

pub fn get_crate_vers(data: @~[u8]) -> @str {
    let attrs = decoder::get_crate_attributes(data);
    let linkage_attrs = attr::find_linkage_metas(attrs);

    match attr::last_meta_item_value_str_by_name(linkage_attrs, "vers") {
        Some(ver) => ver,
        None => @"0.0"
    }
}

pub fn list_crate_metadata(intr: @ident_interner, bytes: @~[u8],
                           out: @io::Writer) {
    let hash = get_crate_hash(bytes);
    let md = reader::Doc(bytes);
    list_crate_attributes(intr, md, hash, out);
    list_crate_deps(bytes, out);
}

// Translates a def_id from an external crate to a def_id for the current
// compilation environment. We use this when trying to load types from
// external crates - if those types further refer to types in other crates
// then we must translate the crate number from that encoded in the external
// crate to the correct local crate number.
pub fn translate_def_id(cdata: Cmd, did: ast::DefId) -> ast::DefId {
    if did.crate == ast::LOCAL_CRATE {
        return ast::DefId { crate: cdata.cnum, node: did.node };
    }

    match cdata.cnum_map.find(&did.crate) {
      option::Some(&n) => ast::DefId { crate: n, node: did.node },
      option::None => fail!("didn't find a crate in the cnum_map")
    }
}

pub fn get_link_args_for_crate(cdata: Cmd) -> ~[~str] {
    let link_args = reader::get_doc(reader::Doc(cdata.data), tag_link_args);
    let mut result = ~[];
    do reader::tagged_docs(link_args, tag_link_args_arg) |arg_doc| {
        result.push(arg_doc.as_str());
        true
    };
    result
}

pub fn each_impl(cdata: Cmd, callback: &fn(ast::DefId)) {
    let impls_doc = reader::get_doc(reader::Doc(cdata.data), tag_impls);
    let _ = do reader::tagged_docs(impls_doc, tag_impls_impl) |impl_doc| {
        callback(item_def_id(impl_doc, cdata));
        true
    };
}

pub fn each_implementation_for_type(cdata: Cmd,
                                    id: ast::NodeId,
                                    callback: &fn(ast::DefId)) {
    let item_doc = lookup_item(id, cdata.data);
    do reader::tagged_docs(item_doc, tag_items_data_item_inherent_impl)
            |impl_doc| {
        let implementation_def_id = item_def_id(impl_doc, cdata);
        callback(implementation_def_id);
        true
    };
}

pub fn each_implementation_for_trait(cdata: Cmd,
                                     id: ast::NodeId,
                                     callback: &fn(ast::DefId)) {
    let item_doc = lookup_item(id, cdata.data);

    let _ = do reader::tagged_docs(item_doc,
                                   tag_items_data_item_extension_impl)
            |impl_doc| {
        let implementation_def_id = item_def_id(impl_doc, cdata);
        callback(implementation_def_id);
        true
    };
}

pub fn get_trait_of_method(cdata: Cmd, id: ast::NodeId, tcx: ty::ctxt)
                           -> Option<ast::DefId> {
    let item_doc = lookup_item(id, cdata.data);
    let parent_item_id = match item_parent_item(item_doc) {
        None => return None,
        Some(item_id) => item_id,
    };
    let parent_item_id = translate_def_id(cdata, parent_item_id);
    let parent_item_doc = lookup_item(parent_item_id.node, cdata.data);
    match item_family(parent_item_doc) {
        Trait => Some(item_def_id(parent_item_doc, cdata)),
        Impl => {
            do reader::maybe_get_doc(parent_item_doc, tag_item_trait_ref).map
                    |_| {
                item_trait_ref(parent_item_doc, tcx, cdata).def_id
            }
        }
        _ => None
    }
}