577 lines
19 KiB
Rust
577 lines
19 KiB
Rust
/*!
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This file actually contains two passes related to regions. The first
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pass builds up the `region_map`, which describes the parent links in
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the region hierarchy. The second pass infers which types must be
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region parameterized.
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*/
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import driver::session::session;
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import middle::ty;
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import syntax::{ast, visit};
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import syntax::codemap::span;
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import syntax::print::pprust;
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import syntax::ast_util::new_def_hash;
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import syntax::ast_map;
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import dvec::{dvec, extensions};
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import metadata::csearch;
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import std::list;
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import std::list::list;
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import std::map::{hashmap, int_hash};
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type parent = option<ast::node_id>;
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/* Records the parameter ID of a region name. */
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type binding = {node_id: ast::node_id,
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name: ~str,
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br: ty::bound_region};
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/// Mapping from a block/expr/binding to the innermost scope that
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/// bounds its lifetime. For a block/expression, this is the lifetime
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/// in which it will be evaluated. For a binding, this is the lifetime
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/// in which is in scope.
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type region_map = hashmap<ast::node_id, ast::node_id>;
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type ctxt = {
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sess: session,
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def_map: resolve3::DefMap,
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region_map: region_map,
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// Generally speaking, expressions are parented to their innermost
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// enclosing block. But some kinds of expressions serve as
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// parents: calls, methods, etc. In addition, some expressions
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// serve as parents by virtue of where they appear. For example,
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// the condition in a while loop is always a parent. In those
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// cases, we add the node id of such an expression to this set so
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// that when we visit it we can view it as a parent.
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root_exprs: hashmap<ast::node_id, ()>,
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// The parent scope is the innermost block, call, or alt
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// expression during the execution of which the current expression
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// will be evaluated. Generally speaking, the innermost parent
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// scope is also the closest suitable ancestor in the AST tree.
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//
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// There is a subtle point concerning call arguments. Imagine
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// you have a call:
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//
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// { // block a
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// foo( // call b
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// x,
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// y);
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// }
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//
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// In what lifetime are the expressions `x` and `y` evaluated? At
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// first, I imagine the answer was the block `a`, as the arguments
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// are evaluated before the call takes place. But this turns out
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// to be wrong. The lifetime of the call must encompass the
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// argument evaluation as well.
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//
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// The reason is that evaluation of an earlier argument could
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// create a borrow which exists during the evaluation of later
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// arguments. Consider this torture test, for example,
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//
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// fn test1(x: @mut ~int) {
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// foo(&**x, *x = ~5);
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// }
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//
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// Here, the first argument `&**x` will be a borrow of the `~int`,
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// but the second argument overwrites that very value! Bad.
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// (This test is borrowck-pure-scope-in-call.rs, btw)
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parent: parent
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};
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/// Returns true if `subscope` is equal to or is lexically nested inside
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/// `superscope` and false otherwise.
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fn scope_contains(region_map: region_map, superscope: ast::node_id,
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subscope: ast::node_id) -> bool {
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let mut subscope = subscope;
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while superscope != subscope {
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alt region_map.find(subscope) {
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none { ret false; }
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some(scope) { subscope = scope; }
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}
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}
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ret true;
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}
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/// Determines whether one region is a subregion of another. This is
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/// intended to run *after inference* and sadly the logic is somewhat
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/// duplicated with the code in infer.rs.
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fn subregion(region_map: region_map,
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super_region: ty::region,
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sub_region: ty::region) -> bool {
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super_region == sub_region ||
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alt (super_region, sub_region) {
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(ty::re_static, _) => {true}
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(ty::re_scope(super_scope), ty::re_scope(sub_scope)) |
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(ty::re_free(super_scope, _), ty::re_scope(sub_scope)) => {
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scope_contains(region_map, super_scope, sub_scope)
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}
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_ => {
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false
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}
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}
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}
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/// Finds the nearest common ancestor (if any) of two scopes. That
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/// is, finds the smallest scope which is greater than or equal to
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/// both `scope_a` and `scope_b`.
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fn nearest_common_ancestor(region_map: region_map, scope_a: ast::node_id,
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scope_b: ast::node_id) -> option<ast::node_id> {
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fn ancestors_of(region_map: region_map, scope: ast::node_id)
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-> ~[ast::node_id] {
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let mut result = ~[scope];
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let mut scope = scope;
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loop {
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alt region_map.find(scope) {
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none { ret result; }
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some(superscope) {
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vec::push(result, superscope);
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scope = superscope;
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}
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}
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}
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}
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if scope_a == scope_b { ret some(scope_a); }
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let a_ancestors = ancestors_of(region_map, scope_a);
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let b_ancestors = ancestors_of(region_map, scope_b);
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let mut a_index = vec::len(a_ancestors) - 1u;
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let mut b_index = vec::len(b_ancestors) - 1u;
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// Here, ~[ab]_ancestors is a vector going from narrow to broad.
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// The end of each vector will be the item where the scope is
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// defined; if there are any common ancestors, then the tails of
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// the vector will be the same. So basically we want to walk
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// backwards from the tail of each vector and find the first point
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// where they diverge. If one vector is a suffix of the other,
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// then the corresponding scope is a superscope of the other.
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if a_ancestors[a_index] != b_ancestors[b_index] {
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ret none;
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}
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loop {
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// Loop invariant: a_ancestors[a_index] == b_ancestors[b_index]
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// for all indices between a_index and the end of the array
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if a_index == 0u { ret some(scope_a); }
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if b_index == 0u { ret some(scope_b); }
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a_index -= 1u;
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b_index -= 1u;
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if a_ancestors[a_index] != b_ancestors[b_index] {
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ret some(a_ancestors[a_index + 1u]);
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}
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}
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}
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/// Extracts that current parent from cx, failing if there is none.
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fn parent_id(cx: ctxt, span: span) -> ast::node_id {
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alt cx.parent {
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none {
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cx.sess.span_bug(span, ~"crate should not be parent here");
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}
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some(parent_id) {
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parent_id
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}
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}
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}
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/// Records the current parent (if any) as the parent of `child_id`.
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fn record_parent(cx: ctxt, child_id: ast::node_id) {
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alt cx.parent {
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none { /* no-op */ }
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some(parent_id) {
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debug!{"parent of node %d is node %d", child_id, parent_id};
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cx.region_map.insert(child_id, parent_id);
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}
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}
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}
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fn resolve_block(blk: ast::blk, cx: ctxt, visitor: visit::vt<ctxt>) {
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// Record the parent of this block.
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record_parent(cx, blk.node.id);
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// Descend.
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let new_cx: ctxt = {parent: some(blk.node.id) with cx};
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visit::visit_block(blk, new_cx, visitor);
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}
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fn resolve_arm(arm: ast::arm, cx: ctxt, visitor: visit::vt<ctxt>) {
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visit::visit_arm(arm, cx, visitor);
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}
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fn resolve_pat(pat: @ast::pat, cx: ctxt, visitor: visit::vt<ctxt>) {
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alt pat.node {
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ast::pat_ident(_, path, _) {
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let defn_opt = cx.def_map.find(pat.id);
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alt defn_opt {
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some(ast::def_variant(_,_)) {
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/* Nothing to do; this names a variant. */
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}
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_ {
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/* This names a local. Bind it to the containing scope. */
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record_parent(cx, pat.id);
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}
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}
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}
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_ { /* no-op */ }
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}
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visit::visit_pat(pat, cx, visitor);
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}
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fn resolve_expr(expr: @ast::expr, cx: ctxt, visitor: visit::vt<ctxt>) {
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record_parent(cx, expr.id);
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let mut new_cx = cx;
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alt expr.node {
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ast::expr_call(*) => {
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debug!{"node %d: %s", expr.id, pprust::expr_to_str(expr)};
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new_cx.parent = some(expr.id);
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}
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ast::expr_alt(subexpr, _, _) => {
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debug!{"node %d: %s", expr.id, pprust::expr_to_str(expr)};
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new_cx.parent = some(expr.id);
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}
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ast::expr_fn(_, _, _, cap_clause) |
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ast::expr_fn_block(_, _, cap_clause) => {
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// although the capture items are not expressions per se, they
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// do get "evaluated" in some sense as copies or moves of the
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// relevant variables so we parent them like an expression
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for (*cap_clause).each |cap_item| {
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record_parent(new_cx, cap_item.id);
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}
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}
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ast::expr_while(cond, _) => {
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new_cx.root_exprs.insert(cond.id, ());
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}
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_ => {}
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};
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if new_cx.root_exprs.contains_key(expr.id) {
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new_cx.parent = some(expr.id);
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}
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visit::visit_expr(expr, new_cx, visitor);
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}
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fn resolve_local(local: @ast::local, cx: ctxt, visitor: visit::vt<ctxt>) {
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record_parent(cx, local.node.id);
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visit::visit_local(local, cx, visitor);
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}
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fn resolve_item(item: @ast::item, cx: ctxt, visitor: visit::vt<ctxt>) {
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// Items create a new outer block scope as far as we're concerned.
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let new_cx: ctxt = {parent: none with cx};
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visit::visit_item(item, new_cx, visitor);
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}
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fn resolve_fn(fk: visit::fn_kind, decl: ast::fn_decl, body: ast::blk,
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sp: span, id: ast::node_id, cx: ctxt,
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visitor: visit::vt<ctxt>) {
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let fn_cx = alt fk {
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visit::fk_item_fn(*) | visit::fk_method(*) |
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visit::fk_ctor(*) | visit::fk_dtor(*) {
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// Top-level functions are a root scope.
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{parent: some(id) with cx}
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}
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visit::fk_anon(*) | visit::fk_fn_block(*) {
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// Closures continue with the inherited scope.
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cx
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}
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};
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debug!{"visiting fn with body %d. cx.parent: %? \
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fn_cx.parent: %?",
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body.node.id, cx.parent, fn_cx.parent};
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for decl.inputs.each |input| {
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cx.region_map.insert(input.id, body.node.id);
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}
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visit::visit_fn(fk, decl, body, sp, id, fn_cx, visitor);
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}
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fn resolve_crate(sess: session, def_map: resolve3::DefMap,
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crate: @ast::crate) -> region_map {
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let cx: ctxt = {sess: sess,
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def_map: def_map,
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region_map: int_hash(),
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root_exprs: int_hash(),
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parent: none};
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let visitor = visit::mk_vt(@{
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visit_block: resolve_block,
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visit_item: resolve_item,
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visit_fn: resolve_fn,
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visit_arm: resolve_arm,
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visit_pat: resolve_pat,
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visit_expr: resolve_expr,
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visit_local: resolve_local
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with *visit::default_visitor()
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});
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visit::visit_crate(*crate, cx, visitor);
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ret cx.region_map;
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}
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// ___________________________________________________________________________
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// Determining region parameterization
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//
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// Infers which type defns must be region parameterized---this is done
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// by scanning their contents to see whether they reference a region
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// type, directly or indirectly. This is a fixed-point computation.
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//
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// We do it in two passes. First we walk the AST and construct a map
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// from each type defn T1 to other defns which make use of it. For example,
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// if we have a type like:
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//
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// type S = *int;
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// type T = S;
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//
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// Then there would be a map entry from S to T. During the same walk,
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// we also construct add any types that reference regions to a set and
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// a worklist. We can then process the worklist, propagating indirect
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// dependencies until a fixed point is reached.
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type region_paramd_items = hashmap<ast::node_id, ()>;
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type dep_map = hashmap<ast::node_id, @dvec<ast::node_id>>;
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type determine_rp_ctxt_ = {
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sess: session,
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ast_map: ast_map::map,
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def_map: resolve3::DefMap,
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region_paramd_items: region_paramd_items,
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dep_map: dep_map,
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worklist: dvec<ast::node_id>,
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// the innermost enclosing item id
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mut item_id: ast::node_id,
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// true when we are within an item but not within a method.
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// see long discussion on region_is_relevant()
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mut anon_implies_rp: bool
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};
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enum determine_rp_ctxt {
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determine_rp_ctxt_(@determine_rp_ctxt_)
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}
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impl methods for determine_rp_ctxt {
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fn add_rp(id: ast::node_id) {
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assert id != 0;
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if self.region_paramd_items.insert(id, ()) {
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debug!{"add region-parameterized item: %d (%s)",
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id, ast_map::node_id_to_str(self.ast_map, id)};
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self.worklist.push(id);
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} else {
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debug!{"item %d already region-parameterized", id};
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}
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}
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fn add_dep(from: ast::node_id, to: ast::node_id) {
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debug!{"add dependency from %d -> %d (%s -> %s)",
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from, to,
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ast_map::node_id_to_str(self.ast_map, from),
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ast_map::node_id_to_str(self.ast_map, to)};
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let vec = alt self.dep_map.find(from) {
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some(vec) => {vec}
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none => {
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let vec = @dvec();
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self.dep_map.insert(from, vec);
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vec
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}
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};
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if !vec.contains(to) { vec.push(to); }
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}
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// Determines whether a reference to a region that appears in the
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// AST implies that the enclosing type is region-parameterized.
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//
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// This point is subtle. Here are four examples to make it more
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// concrete.
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//
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// 1. impl foo for &int { ... }
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// 2. impl foo for &self/int { ... }
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// 3. impl foo for bar { fn m() -> &self/int { ... } }
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// 4. impl foo for bar { fn m() -> &int { ... } }
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//
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// In case 1, the anonymous region is being referenced,
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// but it appears in a context where the anonymous region
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// resolves to self, so the impl foo is region-parameterized.
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//
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// In case 2, the self parameter is written explicitly.
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//
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// In case 3, the method refers to self, so that implies that the
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// impl must be region parameterized. (If the type bar is not
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// region parameterized, that is an error, because the self region
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// is effectively unconstrained, but that is detected elsewhere).
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//
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// In case 4, the anonymous region is referenced, but it
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// bound by the method, so it does not refer to self. This impl
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// need not be region parameterized.
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//
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// So the rules basically are: the `self` region always implies
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// that the enclosing type is region parameterized. The anonymous
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// region also does, unless it appears within a method, in which
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// case it is bound. We handle this by setting a flag
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// (anon_implies_rp) to true when we enter an item and setting
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// that flag to false when we enter a method.
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fn region_is_relevant(r: @ast::region) -> bool {
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alt r.node {
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ast::re_anon {self.anon_implies_rp}
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ast::re_named(@~"self") {true}
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ast::re_named(_) {false}
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}
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}
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fn with(item_id: ast::node_id, anon_implies_rp: bool, f: fn()) {
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let old_item_id = self.item_id;
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let old_anon_implies_rp = self.anon_implies_rp;
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self.item_id = item_id;
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self.anon_implies_rp = anon_implies_rp;
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debug!{"with_item_id(%d, %b)", item_id, anon_implies_rp};
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let _i = util::common::indenter();
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f();
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self.item_id = old_item_id;
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self.anon_implies_rp = old_anon_implies_rp;
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}
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}
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fn determine_rp_in_item(item: @ast::item,
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&&cx: determine_rp_ctxt,
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visitor: visit::vt<determine_rp_ctxt>) {
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do cx.with(item.id, true) {
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visit::visit_item(item, cx, visitor);
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}
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}
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fn determine_rp_in_fn(fk: visit::fn_kind,
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decl: ast::fn_decl,
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body: ast::blk,
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sp: span,
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id: ast::node_id,
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&&cx: determine_rp_ctxt,
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visitor: visit::vt<determine_rp_ctxt>) {
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do cx.with(cx.item_id, false) {
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visit::visit_fn(fk, decl, body, sp, id, cx, visitor);
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}
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}
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fn determine_rp_in_ty_method(ty_m: ast::ty_method,
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&&cx: determine_rp_ctxt,
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visitor: visit::vt<determine_rp_ctxt>) {
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do cx.with(cx.item_id, false) {
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visit::visit_ty_method(ty_m, cx, visitor);
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}
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}
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fn determine_rp_in_ty(ty: @ast::ty,
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&&cx: determine_rp_ctxt,
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visitor: visit::vt<determine_rp_ctxt>) {
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// we are only interesting in types that will require an item to
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// be region-parameterized. if cx.item_id is zero, then this type
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// is not a member of a type defn nor is it a constitutent of an
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// impl etc. So we can ignore it and its components.
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if cx.item_id == 0 { ret; }
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// if this type directly references a region, either via a
|
|
// region pointer like &r.ty or a region-parameterized path
|
|
// like path/r, add to the worklist/set
|
|
alt ty.node {
|
|
ast::ty_rptr(r, _) |
|
|
ast::ty_path(@{rp: some(r), _}, _) => {
|
|
debug!{"referenced type with regions %s", pprust::ty_to_str(ty)};
|
|
if cx.region_is_relevant(r) {
|
|
cx.add_rp(cx.item_id);
|
|
}
|
|
}
|
|
|
|
_ => {}
|
|
}
|
|
|
|
// if this references another named type, add the dependency
|
|
// to the dep_map. If the type is not defined in this crate,
|
|
// then check whether it is region-parameterized and consider
|
|
// that as a direct dependency.
|
|
alt ty.node {
|
|
ast::ty_path(_, id) {
|
|
alt cx.def_map.get(id) {
|
|
ast::def_ty(did) | ast::def_class(did, _) {
|
|
if did.crate == ast::local_crate {
|
|
cx.add_dep(did.node, cx.item_id);
|
|
} else {
|
|
let cstore = cx.sess.cstore;
|
|
if csearch::get_region_param(cstore, did) {
|
|
debug!{"reference to external, rp'd type %s",
|
|
pprust::ty_to_str(ty)};
|
|
cx.add_rp(cx.item_id);
|
|
}
|
|
}
|
|
}
|
|
_ {}
|
|
}
|
|
}
|
|
_ {}
|
|
}
|
|
|
|
alt ty.node {
|
|
ast::ty_fn(*) => {
|
|
do cx.with(cx.item_id, false) {
|
|
visit::visit_ty(ty, cx, visitor);
|
|
}
|
|
}
|
|
_ => {
|
|
visit::visit_ty(ty, cx, visitor);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn determine_rp_in_crate(sess: session,
|
|
ast_map: ast_map::map,
|
|
def_map: resolve3::DefMap,
|
|
crate: @ast::crate) -> region_paramd_items {
|
|
let cx = determine_rp_ctxt_(@{sess: sess,
|
|
ast_map: ast_map,
|
|
def_map: def_map,
|
|
region_paramd_items: int_hash(),
|
|
dep_map: int_hash(),
|
|
worklist: dvec(),
|
|
mut item_id: 0,
|
|
mut anon_implies_rp: false});
|
|
|
|
// gather up the base set, worklist and dep_map:
|
|
let visitor = visit::mk_vt(@{
|
|
visit_fn: determine_rp_in_fn,
|
|
visit_item: determine_rp_in_item,
|
|
visit_ty: determine_rp_in_ty,
|
|
visit_ty_method: determine_rp_in_ty_method,
|
|
with *visit::default_visitor()
|
|
});
|
|
visit::visit_crate(*crate, cx, visitor);
|
|
|
|
// propagate indirect dependencies
|
|
while cx.worklist.len() != 0 {
|
|
let id = cx.worklist.pop();
|
|
debug!{"popped %d from worklist", id};
|
|
alt cx.dep_map.find(id) {
|
|
none {}
|
|
some(vec) {
|
|
for vec.each |to_id| {
|
|
cx.add_rp(to_id);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// return final set
|
|
ret cx.region_paramd_items;
|
|
}
|