// A pass that annotates for each loops and functions with the free
// variables that they contain.

use syntax::print::pprust::path_to_str;
use std::map::*;
use option::*;
use syntax::{ast, ast_util, visit};
use syntax::codemap::span;

export annotate_freevars;
export freevar_map;
export freevar_info;
export freevar_entry;
export get_freevars;
export has_freevars;

// A vector of defs representing the free variables referred to in a function.
// (The def_upvar will already have been stripped).
#[auto_serialize]
#[auto_deserialize]
type freevar_entry = {
    def: ast::def, //< The variable being accessed free.
    span: span     //< First span where it is accessed (there can be multiple)
};
type freevar_info = @~[@freevar_entry];
type freevar_map = HashMap<ast::node_id, freevar_info>;

// Searches through part of the AST for all references to locals or
// upvars in this frame and returns the list of definition IDs thus found.
// Since we want to be able to collect upvars in some arbitrary piece
// of the AST, we take a walker function that we invoke with a visitor
// in order to start the search.
fn collect_freevars(def_map: resolve::DefMap, blk: ast::blk)
    -> freevar_info {
    let seen = HashMap();
    let refs = @mut ~[];

    fn ignore_item(_i: @ast::item, &&_depth: int, _v: visit::vt<int>) { }

    let walk_expr = fn@(expr: @ast::expr, &&depth: int, v: visit::vt<int>) {
            match expr.node {
              ast::expr_fn(proto, _, _, _) => {
                if proto != ast::proto_bare {
                    visit::visit_expr(expr, depth + 1, v);
                }
              }
              ast::expr_fn_block(*) => {
                visit::visit_expr(expr, depth + 1, v);
              }
              ast::expr_path(*) => {
                  let mut i = 0;
                  match def_map.find(expr.id) {
                    None => fail ~"path not found",
                    Some(df) => {
                      let mut def = df;
                      while i < depth {
                        match copy def {
                          ast::def_upvar(_, inner, _, _) => { def = *inner; }
                          _ => break
                        }
                        i += 1;
                      }
                      if i == depth { // Made it to end of loop
                        let dnum = ast_util::def_id_of_def(def).node;
                        if !seen.contains_key(dnum) {
                            refs.push(@{def:def, span:expr.span});
                            seen.insert(dnum, ());
                        }
                      }
                    }
                  }
              }
              _ => visit::visit_expr(expr, depth, v)
            }
        };

    let v = visit::mk_vt(@{visit_item: ignore_item, visit_expr: walk_expr,
                           .. *visit::default_visitor()});
    v.visit_block(blk, 1, v);
    return @*refs;
}

// Build a map from every function and for-each body to a set of the
// freevars contained in it. The implementation is not particularly
// efficient as it fully recomputes the free variables at every
// node of interest rather than building up the free variables in
// one pass. This could be improved upon if it turns out to matter.
fn annotate_freevars(def_map: resolve::DefMap, crate: @ast::crate) ->
   freevar_map {
    let freevars = HashMap();

    let walk_fn = fn@(_fk: visit::fn_kind, _decl: ast::fn_decl,
                      blk: ast::blk, _sp: span, nid: ast::node_id) {
        let vars = collect_freevars(def_map, blk);
        freevars.insert(nid, vars);
    };

    let visitor =
        visit::mk_simple_visitor(@{visit_fn: walk_fn,
                                   .. *visit::default_simple_visitor()});
    visit::visit_crate(*crate, (), visitor);

    return freevars;
}

fn get_freevars(tcx: ty::ctxt, fid: ast::node_id) -> freevar_info {
    match tcx.freevars.find(fid) {
      None => fail ~"get_freevars: " + int::str(fid) + ~" has no freevars",
      Some(d) => return d
    }
}
fn has_freevars(tcx: ty::ctxt, fid: ast::node_id) -> bool {
    return vec::len(*get_freevars(tcx, fid)) != 0u;
}

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