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 parameters. See the [rustc guide]
12 //! chapter for more info.
14 //! [rustc guide]: https://rust-lang-nursery.github.io/rustc-guide/variance.html
19 use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
20 use rustc::ty::{self, CrateVariancesMap, TyCtxt};
21 use rustc::ty::query::Providers;
22 use rustc_data_structures::sync::Lrc;
24 /// Defines the `TermsContext` basically houses an arena where we can
28 /// Code to gather up constraints.
31 /// Code to solve constraints and write out the results.
34 /// Code to write unit tests of variance.
37 /// Code for transforming variances.
40 pub fn provide(providers: &mut Providers) {
41 *providers = Providers {
48 fn crate_variances<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum)
49 -> Lrc<CrateVariancesMap> {
50 assert_eq!(crate_num, LOCAL_CRATE);
51 let mut arena = arena::TypedArena::new();
52 let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &mut arena);
53 let constraints_cx = constraints::add_constraints_from_crate(terms_cx);
54 Lrc::new(solve::solve_constraints(constraints_cx))
57 fn variances_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item_def_id: DefId)
58 -> Lrc<Vec<ty::Variance>> {
59 let id = tcx.hir.as_local_node_id(item_def_id).expect("expected local def-id");
60 let unsupported = || {
61 // Variance not relevant.
62 span_bug!(tcx.hir.span(id), "asked to compute variance for wrong kind of item")
64 match tcx.hir.get(id) {
65 Node::Item(item) => match item.node {
66 hir::ItemKind::Enum(..) |
67 hir::ItemKind::Struct(..) |
68 hir::ItemKind::Union(..) |
69 hir::ItemKind::Fn(..) => {}
74 Node::TraitItem(item) => match item.node {
75 hir::TraitItemKind::Method(..) => {}
80 Node::ImplItem(item) => match item.node {
81 hir::ImplItemKind::Method(..) => {}
86 Node::ForeignItem(item) => match item.node {
87 hir::ForeignItemKind::Fn(..) => {}
92 Node::Variant(_) | Node::StructCtor(_) => {}
97 // Everything else must be inferred.
99 let crate_map = tcx.crate_variances(LOCAL_CRATE);
100 crate_map.variances.get(&item_def_id)
101 .unwrap_or(&crate_map.empty_variance)