rust/src/comp/middle/freevars.rs

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// A pass that annotates for each loops and functions with the free
// variables that they contain.
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import int;
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import std::map::*;
import option::*;
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import syntax::{ast, ast_util, visit};
import middle::resolve;
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import syntax::codemap::span;
export annotate_freevars;
export freevar_map;
export freevar_info;
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export get_freevars;
export has_freevars;
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// A vector of defs representing the free variables referred to in a function.
// (The def_upvar will already have been stripped).
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>;
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// 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::def_map, walker: fn@(visit::vt<int>)) ->
freevar_info {
let seen = new_int_hash();
let refs = @mutable [];
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fn ignore_item(_i: @ast::item, &&_depth: int, _v: visit::vt<int>) { }
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let walk_expr =
lambda (expr: @ast::expr, &&depth: int, v: visit::vt<int>) {
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alt expr.node {
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ast::expr_fn(f, captures) {
if f.proto != ast::proto_bare {
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visit::visit_expr(expr, depth + 1, v);
}
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}
ast::expr_path(path) {
let def = def_map.get(expr.id), i = 0;
while i < depth {
alt copy def {
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ast::def_upvar(_, inner, _) { def = *inner; }
_ { break; }
}
i += 1;
}
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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 += [@{def:def, span:expr.span}];
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seen.insert(dnum, ());
}
}
}
_ { visit::visit_expr(expr, depth, v); }
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}
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};
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walker(visit::mk_vt(@{visit_item: ignore_item, visit_expr: walk_expr
with *visit::default_visitor()}));
ret @*refs;
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}
// 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::def_map, crate: @ast::crate) ->
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freevar_map {
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let freevars = new_int_hash();
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let walk_fn =
lambda (f: ast::_fn, tps: [ast::ty_param], sp: span, i: ast::fn_ident,
nid: ast::node_id) {
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let start_walk =
lambda (v: visit::vt<int>) {
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v.visit_fn(f, tps, sp, i, nid, 1, v);
};
let vars = collect_freevars(def_map, start_walk);
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freevars.insert(nid, vars);
};
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let visitor =
visit::mk_simple_visitor(@{visit_fn: walk_fn
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with *visit::default_simple_visitor()});
visit::visit_crate(*crate, (), visitor);
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ret freevars;
}
fn get_freevars(tcx: ty::ctxt, fid: ast::node_id) -> freevar_info {
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alt tcx.freevars.find(fid) {
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none. { fail "get_freevars: " + int::str(fid) + " has no freevars"; }
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some(d) { ret d; }
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}
}
fn has_freevars(tcx: ty::ctxt, fid: ast::node_id) -> bool {
ret vec::len(*get_freevars(tcx, fid)) != 0u;
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}
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// Local Variables:
// mode: rust
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End: