src/rustc/metadata/encoder.rs

// Metadata encoding

import std::{ebml, map, list};
import std::map::hashmap;
import io::writer_util;
import ebml::writer;
import syntax::ast::*;
import syntax::print::pprust;
import syntax::{ast_util, visit};
import syntax::ast_util::local_def;
import common::*;
import middle::trans::common::crate_ctxt;
import middle::ty;
import middle::ty::node_id_to_type;
import middle::ast_map;
import front::attr;
import driver::session::session;
import std::serialization::serializer;

export encode_metadata;
export encoded_ty;

// used by astencode:
export def_to_str;
export encode_ctxt;
export write_type;
export encode_def_id;

type abbrev_map = map::hashmap<ty::t, tyencode::ty_abbrev>;

type encode_ctxt = {ccx: @crate_ctxt,
                    type_abbrevs: abbrev_map,
                    reachable: reachable::map};

// Path table encoding
fn encode_name(ebml_w: ebml::writer, name: str) {
    ebml_w.wr_tagged_str(tag_paths_data_name, name);
}

fn encode_def_id(ebml_w: ebml::writer, id: def_id) {
    ebml_w.wr_tagged_str(tag_def_id, def_to_str(id));
}

fn encode_named_def_id(ebml_w: ebml::writer, name: str, id: def_id) {
    ebml_w.wr_tag(tag_paths_data_item) {||
        encode_name(ebml_w, name);
        encode_def_id(ebml_w, id);
    }
}

type entry<T> = {val: T, pos: uint};

fn encode_enum_variant_paths(ebml_w: ebml::writer, variants: [variant],
                            path: [str], &index: [entry<str>]) {
    for variant: variant in variants {
        add_to_index(ebml_w, path, index, variant.node.name);
        ebml_w.wr_tag(tag_paths_data_item) {||
            encode_name(ebml_w, variant.node.name);
            encode_def_id(ebml_w, local_def(variant.node.id));
        }
    }
}

fn add_to_index(ebml_w: ebml::writer, path: [str], &index: [entry<str>],
                name: str) {
    let full_path = path + [name];
    index +=
        [{val: str::connect(full_path, "::"), pos: ebml_w.writer.tell()}];
}

fn encode_native_module_item_paths(ebml_w: ebml::writer, nmod: native_mod,
                                   path: [str], &index: [entry<str>]) {
    for nitem: @native_item in nmod.items {
        add_to_index(ebml_w, path, index, nitem.ident);
        encode_named_def_id(ebml_w, nitem.ident, local_def(nitem.id));
    }
}

fn encode_module_item_paths(ebml_w: ebml::writer, ecx: @encode_ctxt,
                            module: _mod, path: [str], &index: [entry<str>]) {
    // FIXME factor out add_to_index/start/encode_name/encode_def_id/end ops
    for it: @item in module.items {
        if !ecx.reachable.contains_key(it.id) ||
           !ast_util::is_exported(it.ident, module) { cont; }
        alt it.node {
          item_const(_, _) {
            add_to_index(ebml_w, path, index, it.ident);
            encode_named_def_id(ebml_w, it.ident, local_def(it.id));
          }
          item_fn(_, tps, _) {
            add_to_index(ebml_w, path, index, it.ident);
            encode_named_def_id(ebml_w, it.ident, local_def(it.id));
          }
          item_mod(_mod) {
            add_to_index(ebml_w, path, index, it.ident);
            ebml_w.start_tag(tag_paths_data_mod);
            encode_name(ebml_w, it.ident);
            encode_def_id(ebml_w, local_def(it.id));
            encode_module_item_paths(ebml_w, ecx, _mod, path + [it.ident],
                                     index);
            ebml_w.end_tag();
          }
          item_native_mod(nmod) {
            add_to_index(ebml_w, path, index, it.ident);
            ebml_w.start_tag(tag_paths_data_mod);
            encode_name(ebml_w, it.ident);
            encode_def_id(ebml_w, local_def(it.id));
            encode_native_module_item_paths(ebml_w, nmod, path + [it.ident],
                                            index);
            ebml_w.end_tag();
          }
          item_ty(_, tps) {
            add_to_index(ebml_w, path, index, it.ident);
            ebml_w.start_tag(tag_paths_data_item);
            encode_name(ebml_w, it.ident);
            encode_def_id(ebml_w, local_def(it.id));
            ebml_w.end_tag();
          }
          item_res(_, tps, _, _, ctor_id) {
            add_to_index(ebml_w, path, index, it.ident);
            ebml_w.start_tag(tag_paths_data_item);
            encode_name(ebml_w, it.ident);
            encode_def_id(ebml_w, local_def(ctor_id));
            ebml_w.end_tag();
            add_to_index(ebml_w, path, index, it.ident);
            ebml_w.start_tag(tag_paths_data_item);
            encode_name(ebml_w, it.ident);
            encode_def_id(ebml_w, local_def(it.id));
            ebml_w.end_tag();
          }
          item_class(_,_,_) {
              fail "encode: implement item_class";
          }
          item_enum(variants, tps) {
            add_to_index(ebml_w, path, index, it.ident);
            ebml_w.start_tag(tag_paths_data_item);
            encode_name(ebml_w, it.ident);
            encode_def_id(ebml_w, local_def(it.id));
            ebml_w.end_tag();
            encode_enum_variant_paths(ebml_w, variants, path, index);
          }
          item_iface(_, _) {
            add_to_index(ebml_w, path, index, it.ident);
            ebml_w.start_tag(tag_paths_data_item);
            encode_name(ebml_w, it.ident);
            encode_def_id(ebml_w, local_def(it.id));
            ebml_w.end_tag();
          }
          item_impl(_, _, _, _) {}
        }
    }
}

fn encode_item_paths(ebml_w: ebml::writer, ecx: @encode_ctxt, crate: @crate)
    -> [entry<str>] {
    let index: [entry<str>] = [];
    let path: [str] = [];
    ebml_w.start_tag(tag_paths);
    encode_module_item_paths(ebml_w, ecx, crate.node.module, path, index);
    encode_reexport_paths(ebml_w, ecx, index);
    ebml_w.end_tag();
    ret index;
}

fn encode_reexport_paths(ebml_w: ebml::writer,
                         ecx: @encode_ctxt, &index: [entry<str>]) {
    let tcx = ecx.ccx.tcx;
    ecx.ccx.exp_map.items {|exp_id, defs|
        for def in defs {
            if !def.reexp { cont; }
            let path = alt check tcx.items.get(exp_id) {
              ast_map::node_export(_, path) { ast_map::path_to_str(*path) }
            };
            index += [{val: path, pos: ebml_w.writer.tell()}];
            ebml_w.start_tag(tag_paths_data_item);
            encode_name(ebml_w, path);
            encode_def_id(ebml_w, def.id);
            ebml_w.end_tag();
        }
    }
}


// Item info table encoding
fn encode_family(ebml_w: ebml::writer, c: char) {
    ebml_w.start_tag(tag_items_data_item_family);
    ebml_w.writer.write([c as u8]);
    ebml_w.end_tag();
}

fn def_to_str(did: def_id) -> str { ret #fmt["%d:%d", did.crate, did.node]; }

fn encode_type_param_bounds(ebml_w: ebml::writer, ecx: @encode_ctxt,
                            params: [ty_param]) {
    let ty_str_ctxt = @{ds: def_to_str,
                        tcx: ecx.ccx.tcx,
                        abbrevs: tyencode::ac_use_abbrevs(ecx.type_abbrevs)};
    for param in params {
        ebml_w.start_tag(tag_items_data_item_ty_param_bounds);
        let bs = ecx.ccx.tcx.ty_param_bounds.get(param.id);
        tyencode::enc_bounds(ebml_w.writer, ty_str_ctxt, bs);
        ebml_w.end_tag();
    }
}

fn encode_variant_id(ebml_w: ebml::writer, vid: def_id) {
    ebml_w.start_tag(tag_items_data_item_variant);
    ebml_w.writer.write(str::bytes(def_to_str(vid)));
    ebml_w.end_tag();
}

fn write_type(ecx: @encode_ctxt, ebml_w: ebml::writer, typ: ty::t) {
    let ty_str_ctxt =
        @{ds: def_to_str,
          tcx: ecx.ccx.tcx,
          abbrevs: tyencode::ac_use_abbrevs(ecx.type_abbrevs)};
    tyencode::enc_ty(ebml_w.writer, ty_str_ctxt, typ);
}

fn encode_type(ecx: @encode_ctxt, ebml_w: ebml::writer, typ: ty::t) {
    ebml_w.start_tag(tag_items_data_item_type);
    write_type(ecx, ebml_w, typ);
    ebml_w.end_tag();
}

fn encode_symbol(ecx: @encode_ctxt, ebml_w: ebml::writer, id: node_id) {
    ebml_w.start_tag(tag_items_data_item_symbol);
    ebml_w.writer.write(str::bytes(ecx.ccx.item_symbols.get(id)));
    ebml_w.end_tag();
}

fn encode_discriminant(ecx: @encode_ctxt, ebml_w: ebml::writer, id: node_id) {
    ebml_w.start_tag(tag_items_data_item_symbol);
    ebml_w.writer.write(str::bytes(ecx.ccx.discrim_symbols.get(id)));
    ebml_w.end_tag();
}

fn encode_disr_val(_ecx: @encode_ctxt, ebml_w: ebml::writer, disr_val: int) {
    ebml_w.start_tag(tag_disr_val);
    ebml_w.writer.write(str::bytes(int::to_str(disr_val,10u)));
    ebml_w.end_tag();
}

fn encode_parent_item(ebml_w: ebml::writer, id: def_id) {
    ebml_w.start_tag(tag_items_data_parent_item);
    ebml_w.writer.write(str::bytes(def_to_str(id)));
    ebml_w.end_tag();
}

fn encode_enum_variant_info(ecx: @encode_ctxt, ebml_w: ebml::writer,
                            id: node_id, variants: [variant],
                            path: ast_map::path, index: @mutable [entry<int>],
                            ty_params: [ty_param]) {
    let disr_val = 0;
    let i = 0;
    let vi = ty::enum_variants(ecx.ccx.tcx, {crate: local_crate, node: id});
    for variant: variant in variants {
        *index += [{val: variant.node.id, pos: ebml_w.writer.tell()}];
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(variant.node.id));
        encode_family(ebml_w, 'v');
        encode_name(ebml_w, variant.node.name);
        encode_parent_item(ebml_w, local_def(id));
        encode_type(ecx, ebml_w,
                    node_id_to_type(ecx.ccx.tcx, variant.node.id));
        if vec::len(variant.node.args) > 0u && ty_params.len() == 0u {
            encode_symbol(ecx, ebml_w, variant.node.id);
        }
        encode_discriminant(ecx, ebml_w, variant.node.id);
        if vi[i].disr_val != disr_val {
            encode_disr_val(ecx, ebml_w, vi[i].disr_val);
            disr_val = vi[i].disr_val;
        }
        encode_type_param_bounds(ebml_w, ecx, ty_params);
        encode_path(ebml_w, path, ast_map::path_name(variant.node.name));
        ebml_w.end_tag();
        disr_val += 1;
        i += 1;
    }
}

fn encode_path(ebml_w: ebml::writer,
               path: ast_map::path,
               name: ast_map::path_elt) {
    fn encode_path_elt(ebml_w: ebml::writer, elt: ast_map::path_elt) {
        let (tag, name) = alt elt {
          ast_map::path_mod(name) { (tag_path_elt_mod, name) }
          ast_map::path_name(name) { (tag_path_elt_name, name) }
        };

        ebml_w.wr_tagged_str(tag, name);
    }

    ebml_w.wr_tag(tag_path) {||
        ebml_w.wr_tagged_u32(tag_path_len, (vec::len(path) + 1u) as u32);
        vec::iter(path) {|pe| encode_path_elt(ebml_w, pe); }
        encode_path_elt(ebml_w, name);
    }
}

fn encode_info_for_mod(ecx: @encode_ctxt, ebml_w: ebml::writer, md: _mod,
                       id: node_id, path: ast_map::path, name: ident) {
    ebml_w.start_tag(tag_items_data_item);
    encode_def_id(ebml_w, local_def(id));
    encode_family(ebml_w, 'm');
    encode_name(ebml_w, name);
    alt ecx.ccx.maps.impl_map.get(id) {
      list::cons(impls, @list::nil) {
        for i in *impls {
            if ast_util::is_exported(i.ident, md) {
                ebml_w.wr_tagged_str(tag_mod_impl, def_to_str(i.did));
            }
        }
      }
      _ { ecx.ccx.tcx.sess.bug("encode_info_for_mod: \
             undocumented invariant"); }
    }
    encode_path(ebml_w, path, ast_map::path_mod(name));
    ebml_w.end_tag();
}

fn purity_fn_family(p: purity) -> char {
    alt p {
      unsafe_fn { 'u' }
      pure_fn { 'p' }
      impure_fn { 'f' }
      crust_fn { 'c' }
    }
}

fn encode_info_for_item(ecx: @encode_ctxt, ebml_w: ebml::writer, item: @item,
                        index: @mutable [entry<int>], path: ast_map::path) {

    fn should_inline(attrs: [attribute]) -> bool {
        alt attr::find_inline_attr(attrs) {
          attr::ia_none { false }
          attr::ia_hint | attr::ia_always { true }
        }
    }

    let tcx = ecx.ccx.tcx;
    let must_write = alt item.node { item_enum(_, _) { true } _ { false } };
    if !must_write && !ecx.reachable.contains_key(item.id) { ret; }
    *index += [{val: item.id, pos: ebml_w.writer.tell()}];

    alt item.node {
      item_const(_, _) {
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(item.id));
        encode_family(ebml_w, 'c');
        encode_type(ecx, ebml_w, node_id_to_type(tcx, item.id));
        encode_symbol(ecx, ebml_w, item.id);
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        ebml_w.end_tag();
      }
      item_fn(decl, tps, _) {
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(item.id));
        encode_family(ebml_w, purity_fn_family(decl.purity));
        encode_type_param_bounds(ebml_w, ecx, tps);
        encode_type(ecx, ebml_w, node_id_to_type(tcx, item.id));
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        if tps.len() > 0u || should_inline(item.attrs) {
            astencode::encode_inlined_item(ecx, ebml_w, path, ii_item(item));
        } else {
            encode_symbol(ecx, ebml_w, item.id);
        }
        ebml_w.end_tag();
      }
      item_mod(m) {
        encode_info_for_mod(ecx, ebml_w, m, item.id, path, item.ident);
      }
      item_native_mod(_) {
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(item.id));
        encode_family(ebml_w, 'n');
        encode_name(ebml_w, item.ident);
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        ebml_w.end_tag();
      }
      item_ty(_, tps) {
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(item.id));
        encode_family(ebml_w, 'y');
        encode_type_param_bounds(ebml_w, ecx, tps);
        encode_type(ecx, ebml_w, node_id_to_type(tcx, item.id));
        encode_name(ebml_w, item.ident);
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        ebml_w.end_tag();
      }
      item_enum(variants, tps) {
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(item.id));
        encode_family(ebml_w, 't');
        encode_type_param_bounds(ebml_w, ecx, tps);
        encode_type(ecx, ebml_w, node_id_to_type(tcx, item.id));
        encode_name(ebml_w, item.ident);
        for v: variant in variants {
            encode_variant_id(ebml_w, local_def(v.node.id));
        }
        astencode::encode_inlined_item(ecx, ebml_w, path, ii_item(item));
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        ebml_w.end_tag();
        encode_enum_variant_info(ecx, ebml_w, item.id, variants,
                                 path, index, tps);
      }
      item_class(_,_,_) {
          fail "encode: implement item_class";
      }
      item_res(_, tps, _, _, ctor_id) {
        let fn_ty = node_id_to_type(tcx, ctor_id);

        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(ctor_id));
        encode_family(ebml_w, 'y');
        encode_type_param_bounds(ebml_w, ecx, tps);
        encode_type(ecx, ebml_w, ty::ty_fn_ret(fn_ty));
        encode_name(ebml_w, item.ident);
        astencode::encode_inlined_item(ecx, ebml_w, path, ii_item(item));
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        ebml_w.end_tag();

        *index += [{val: ctor_id, pos: ebml_w.writer.tell()}];
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(ctor_id));
        encode_family(ebml_w, 'f');
        encode_type_param_bounds(ebml_w, ecx, tps);
        encode_type(ecx, ebml_w, fn_ty);
        encode_parent_item(ebml_w, local_def(item.id));
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        ebml_w.end_tag();
      }
      item_impl(tps, ifce, _, methods) {
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(item.id));
        encode_family(ebml_w, 'i');
        encode_type_param_bounds(ebml_w, ecx, tps);
        encode_type(ecx, ebml_w, node_id_to_type(tcx, item.id));
        encode_name(ebml_w, item.ident);
        for m in methods {
            ebml_w.start_tag(tag_item_method);
            ebml_w.writer.write(str::bytes(def_to_str(local_def(m.id))));
            ebml_w.end_tag();
        }
        alt ifce {
          some(t) {
            let i_ty = alt check t.node {
              ty_path(_, id) { ty::node_id_to_type(tcx, id) }
            };
            ebml_w.start_tag(tag_impl_iface);
            write_type(ecx, ebml_w, i_ty);
            ebml_w.end_tag();
          }
          _ {}
        }
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        ebml_w.end_tag();

        let impl_path = path + [ast_map::path_name(item.ident)];
        for m in methods {
            *index += [{val: m.id, pos: ebml_w.writer.tell()}];
            ebml_w.start_tag(tag_items_data_item);
            encode_def_id(ebml_w, local_def(m.id));
            encode_family(ebml_w, purity_fn_family(m.decl.purity));
            encode_type_param_bounds(ebml_w, ecx, tps + m.tps);
            encode_type(ecx, ebml_w, node_id_to_type(tcx, m.id));
            encode_name(ebml_w, m.ident);
            encode_path(ebml_w, impl_path, ast_map::path_name(m.ident));
            if tps.len() > 0u || m.tps.len() > 0u || should_inline(m.attrs) {
                astencode::encode_inlined_item(
                    ecx, ebml_w, impl_path,
                    ii_method(local_def(item.id), m));
            } else {
                encode_symbol(ecx, ebml_w, m.id);
            }
            ebml_w.end_tag();
        }
      }
      item_iface(tps, ms) {
        ebml_w.start_tag(tag_items_data_item);
        encode_def_id(ebml_w, local_def(item.id));
        encode_family(ebml_w, 'I');
        encode_type_param_bounds(ebml_w, ecx, tps);
        encode_type(ecx, ebml_w, node_id_to_type(tcx, item.id));
        encode_name(ebml_w, item.ident);
        let i = 0u;
        for mty in *ty::iface_methods(tcx, local_def(item.id)) {
            ebml_w.start_tag(tag_item_method);
            encode_name(ebml_w, mty.ident);
            encode_type_param_bounds(ebml_w, ecx, ms[i].tps);
            encode_type(ecx, ebml_w, ty::mk_fn(tcx, mty.fty));
            encode_family(ebml_w, purity_fn_family(mty.purity));
            ebml_w.end_tag();
            i += 1u;
        }
        encode_path(ebml_w, path, ast_map::path_name(item.ident));
        ebml_w.end_tag();
      }
    }
}

fn encode_info_for_native_item(ecx: @encode_ctxt, ebml_w: ebml::writer,
                               nitem: @native_item,
                               index: @mutable [entry<int>],
                               path: ast_map::path, abi: native_abi) {
    if !ecx.reachable.contains_key(nitem.id) { ret; }
    *index += [{val: nitem.id, pos: ebml_w.writer.tell()}];

    ebml_w.start_tag(tag_items_data_item);
    alt nitem.node {
      native_item_fn(fn_decl, tps) {
        encode_def_id(ebml_w, local_def(nitem.id));
        encode_family(ebml_w, purity_fn_family(fn_decl.purity));
        encode_type_param_bounds(ebml_w, ecx, tps);
        if abi == native_abi_rust_intrinsic {
            ebml_w.start_tag(tag_item_is_intrinsic);
            ebml_w.end_tag();
        }
        encode_type(ecx, ebml_w, node_id_to_type(ecx.ccx.tcx, nitem.id));
        encode_symbol(ecx, ebml_w, nitem.id);
        encode_path(ebml_w, path, ast_map::path_name(nitem.ident));
      }
    }
    ebml_w.end_tag();
}

fn encode_info_for_items(ecx: @encode_ctxt, ebml_w: ebml::writer,
                         crate: @crate) -> [entry<int>] {
    let index = @mutable [];
    ebml_w.start_tag(tag_items_data);
    *index += [{val: crate_node_id, pos: ebml_w.writer.tell()}];
    encode_info_for_mod(ecx, ebml_w, crate.node.module,
                        crate_node_id, [], "");
    visit::visit_crate(*crate, (), visit::mk_vt(@{
        visit_expr: {|_e, _cx, _v|},
        visit_item: {|i, cx, v|
            visit::visit_item(i, cx, v);
            alt check ecx.ccx.tcx.items.get(i.id) {
              ast_map::node_item(_, pt) {
                encode_info_for_item(ecx, ebml_w, i, index, *pt);
              }
            }
        },
        visit_native_item: {|ni, cx, v|
            visit::visit_native_item(ni, cx, v);
            alt check ecx.ccx.tcx.items.get(ni.id) {
              ast_map::node_native_item(_, abi, pt) {
                encode_info_for_native_item(ecx, ebml_w, ni, index, *pt, abi);
              }
            }
        }
        with *visit::default_visitor()
    }));
    ebml_w.end_tag();
    ret *index;
}


// Path and definition ID indexing

fn create_index<T: copy>(index: [entry<T>], hash_fn: fn@(T) -> uint) ->
   [@[entry<T>]] {
    let buckets: [@mutable [entry<T>]] = [];
    uint::range(0u, 256u) {|_i| buckets += [@mutable []]; };
    for elt: entry<T> in index {
        let h = hash_fn(elt.val);
        *buckets[h % 256u] += [elt];
    }

    let buckets_frozen = [];
    for bucket: @mutable [entry<T>] in buckets {
        buckets_frozen += [@*bucket];
    }
    ret buckets_frozen;
}

fn encode_index<T>(ebml_w: ebml::writer, buckets: [@[entry<T>]],
                   write_fn: fn(io::writer, T)) {
    let writer = ebml_w.writer;
    ebml_w.start_tag(tag_index);
    let bucket_locs: [uint] = [];
    ebml_w.start_tag(tag_index_buckets);
    for bucket: @[entry<T>] in buckets {
        bucket_locs += [ebml_w.writer.tell()];
        ebml_w.start_tag(tag_index_buckets_bucket);
        for elt: entry<T> in *bucket {
            ebml_w.start_tag(tag_index_buckets_bucket_elt);
            writer.write_be_uint(elt.pos, 4u);
            write_fn(writer, elt.val);
            ebml_w.end_tag();
        }
        ebml_w.end_tag();
    }
    ebml_w.end_tag();
    ebml_w.start_tag(tag_index_table);
    for pos: uint in bucket_locs { writer.write_be_uint(pos, 4u); }
    ebml_w.end_tag();
    ebml_w.end_tag();
}

fn write_str(writer: io::writer, &&s: str) { writer.write_str(s); }

fn write_int(writer: io::writer, &&n: int) {
    writer.write_be_uint(n as uint, 4u);
}

fn encode_meta_item(ebml_w: ebml::writer, mi: meta_item) {
    alt mi.node {
      meta_word(name) {
        ebml_w.start_tag(tag_meta_item_word);
        ebml_w.start_tag(tag_meta_item_name);
        ebml_w.writer.write(str::bytes(name));
        ebml_w.end_tag();
        ebml_w.end_tag();
      }
      meta_name_value(name, value) {
        alt value.node {
          lit_str(value) {
            ebml_w.start_tag(tag_meta_item_name_value);
            ebml_w.start_tag(tag_meta_item_name);
            ebml_w.writer.write(str::bytes(name));
            ebml_w.end_tag();
            ebml_w.start_tag(tag_meta_item_value);
            ebml_w.writer.write(str::bytes(value));
            ebml_w.end_tag();
            ebml_w.end_tag();
          }
          _ {/* FIXME (#611) */ }
        }
      }
      meta_list(name, items) {
        ebml_w.start_tag(tag_meta_item_list);
        ebml_w.start_tag(tag_meta_item_name);
        ebml_w.writer.write(str::bytes(name));
        ebml_w.end_tag();
        for inner_item: @meta_item in items {
            encode_meta_item(ebml_w, *inner_item);
        }
        ebml_w.end_tag();
      }
    }
}

fn encode_attributes(ebml_w: ebml::writer, attrs: [attribute]) {
    ebml_w.start_tag(tag_attributes);
    for attr: attribute in attrs {
        ebml_w.start_tag(tag_attribute);
        encode_meta_item(ebml_w, attr.node.value);
        ebml_w.end_tag();
    }
    ebml_w.end_tag();
}

// So there's a special crate attribute called 'link' which defines the
// metadata that Rust cares about for linking crates. This attribute requires
// 'name' and 'vers' items, so if the user didn't provide them we will throw
// them in anyway with default values.
fn synthesize_crate_attrs(ecx: @encode_ctxt, crate: @crate) -> [attribute] {

    fn synthesize_link_attr(ecx: @encode_ctxt, items: [@meta_item]) ->
       attribute {

        assert (ecx.ccx.link_meta.name != "");
        assert (ecx.ccx.link_meta.vers != "");

        let name_item =
            attr::mk_name_value_item_str("name", ecx.ccx.link_meta.name);
        let vers_item =
            attr::mk_name_value_item_str("vers", ecx.ccx.link_meta.vers);

        let other_items =
            {
                let tmp = attr::remove_meta_items_by_name(items, "name");
                attr::remove_meta_items_by_name(tmp, "vers")
            };

        let meta_items = [name_item, vers_item] + other_items;
        let link_item = attr::mk_list_item("link", meta_items);

        ret attr::mk_attr(link_item);
    }

    let attrs: [attribute] = [];
    let found_link_attr = false;
    for attr: attribute in crate.node.attrs {
        attrs +=
            if attr::get_attr_name(attr) != "link" {
                [attr]
            } else {
                alt attr.node.value.node {
                  meta_list(n, l) {
                    found_link_attr = true;;
                    [synthesize_link_attr(ecx, l)]
                  }
                  _ { [attr] }
                }
            };
    }

    if !found_link_attr { attrs += [synthesize_link_attr(ecx, [])]; }

    ret attrs;
}

fn encode_crate_deps(ebml_w: ebml::writer, cstore: cstore::cstore) {

    fn get_ordered_names(cstore: cstore::cstore) -> [str] {
        type hashkv = @{key: crate_num, val: cstore::crate_metadata};
        type numname = {crate: crate_num, ident: str};

        // Pull the cnums and names out of cstore
        let pairs: [mutable numname] = [mutable];
        cstore::iter_crate_data(cstore) {|key, val|
            pairs += [mutable {crate: key, ident: val.name}];
        };

        // Sort by cnum
        fn lteq(kv1: numname, kv2: numname) -> bool { kv1.crate <= kv2.crate }
        std::sort::quick_sort(lteq, pairs);

        // Sanity-check the crate numbers
        let expected_cnum = 1;
        for n: numname in pairs {
            assert (n.crate == expected_cnum);
            expected_cnum += 1;
        }

        // Return just the names
        fn name(kv: numname) -> str { kv.ident }
        // mutable -> immutable hack for vec::map
        let immpairs = vec::slice(pairs, 0u, vec::len(pairs));
        ret vec::map(immpairs, name);
    }

    // We're just going to write a list of crate names, with the assumption
    // that they are numbered 1 to n.
    // FIXME: This is not nearly enough to support correct versioning
    // but is enough to get transitive crate dependencies working.
    ebml_w.start_tag(tag_crate_deps);
    for cname: str in get_ordered_names(cstore) {
        ebml_w.start_tag(tag_crate_dep);
        ebml_w.writer.write(str::bytes(cname));
        ebml_w.end_tag();
    }
    ebml_w.end_tag();
}

fn encode_hash(ebml_w: ebml::writer, hash: str) {
    ebml_w.start_tag(tag_crate_hash);
    ebml_w.writer.write(str::bytes(hash));
    ebml_w.end_tag();
}

fn encode_metadata(cx: @crate_ctxt, crate: @crate) -> [u8] {

    let reachable = reachable::find_reachable(cx, crate.node.module);
    let abbrevs = ty::new_ty_hash();
    let ecx = @{ccx: cx,
                type_abbrevs: abbrevs,
                reachable: reachable};

    let buf = io::mem_buffer();
    let buf_w = io::mem_buffer_writer(buf);
    let ebml_w = ebml::writer(buf_w);

    encode_hash(ebml_w, cx.link_meta.extras_hash);

    let crate_attrs = synthesize_crate_attrs(ecx, crate);
    encode_attributes(ebml_w, crate_attrs);

    encode_crate_deps(ebml_w, cx.sess.cstore);

    // Encode and index the paths.
    ebml_w.start_tag(tag_paths);
    let paths_index = encode_item_paths(ebml_w, ecx, crate);
    let paths_buckets = create_index(paths_index, hash_path);
    encode_index(ebml_w, paths_buckets, write_str);
    ebml_w.end_tag();

    // Encode and index the items.
    ebml_w.start_tag(tag_items);
    let items_index = encode_info_for_items(ecx, ebml_w, crate);
    let items_buckets = create_index(items_index, hash_node_id);
    encode_index(ebml_w, items_buckets, write_int);
    ebml_w.end_tag();

    // Pad this, since something (LLVM, presumably) is cutting off the
    // remaining % 4 bytes.
    buf_w.write([0u8, 0u8, 0u8, 0u8]);
    io::mem_buffer_buf(buf)
}

// Get the encoded string for a type
fn encoded_ty(tcx: ty::ctxt, t: ty::t) -> str {
    let cx = @{ds: def_to_str, tcx: tcx, abbrevs: tyencode::ac_no_abbrevs};
    let buf = io::mem_buffer();
    tyencode::enc_ty(io::mem_buffer_writer(buf), cx, t);
    ret io::mem_buffer_str(buf);
}


// Local Variables:
// mode: rust
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End: