1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Module for inferring the variance of type and lifetime
12 //! parameters. See README.md for details.
16 use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
17 use rustc::ty::{self, CrateVariancesMap, TyCtxt};
18 use rustc::ty::maps::Providers;
19 use rustc_data_structures::sync::Lrc;
21 /// Defines the `TermsContext` basically houses an arena where we can
25 /// Code to gather up constraints.
28 /// Code to solve constraints and write out the results.
31 /// Code to write unit tests of variance.
34 /// Code for transforming variances.
37 pub fn provide(providers: &mut Providers) {
38 *providers = Providers {
45 fn crate_variances<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum)
46 -> Lrc<CrateVariancesMap> {
47 assert_eq!(crate_num, LOCAL_CRATE);
48 let mut arena = arena::TypedArena::new();
49 let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &mut arena);
50 let constraints_cx = constraints::add_constraints_from_crate(terms_cx);
51 Lrc::new(solve::solve_constraints(constraints_cx))
54 fn variances_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item_def_id: DefId)
55 -> Lrc<Vec<ty::Variance>> {
56 let id = tcx.hir.as_local_node_id(item_def_id).expect("expected local def-id");
57 let unsupported = || {
58 // Variance not relevant.
59 span_bug!(tcx.hir.span(id), "asked to compute variance for wrong kind of item")
61 match tcx.hir.get(id) {
62 hir::map::NodeItem(item) => match item.node {
71 hir::map::NodeTraitItem(item) => match item.node {
72 hir::TraitItemKind::Method(..) => {}
77 hir::map::NodeImplItem(item) => match item.node {
78 hir::ImplItemKind::Method(..) => {}
83 hir::map::NodeForeignItem(item) => match item.node {
84 hir::ForeignItemFn(..) => {}
89 hir::map::NodeVariant(_) | hir::map::NodeStructCtor(_) => {}
94 // Everything else must be inferred.
96 let crate_map = tcx.crate_variances(LOCAL_CRATE);
97 crate_map.variances.get(&item_def_id)
98 .unwrap_or(&crate_map.empty_variance)