1 //! Module for inferring the variance of type and lifetime parameters. See the [rustc guide]
2 //! chapter for more info.
4 //! [rustc guide]: https://rust-lang.github.io/rustc-guide/variance.html
9 use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
10 use rustc::ty::{self, CrateVariancesMap, TyCtxt};
11 use rustc::ty::query::Providers;
13 /// Defines the `TermsContext` basically houses an arena where we can
17 /// Code to gather up constraints.
20 /// Code to solve constraints and write out the results.
23 /// Code to write unit tests of variance.
26 /// Code for transforming variances.
29 pub fn provide(providers: &mut Providers<'_>) {
30 *providers = Providers {
37 fn crate_variances<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum)
38 -> &'tcx CrateVariancesMap<'tcx> {
39 assert_eq!(crate_num, LOCAL_CRATE);
40 let mut arena = arena::TypedArena::default();
41 let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &mut arena);
42 let constraints_cx = constraints::add_constraints_from_crate(terms_cx);
43 tcx.arena.alloc(solve::solve_constraints(constraints_cx))
46 fn variances_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item_def_id: DefId)
47 -> &'tcx [ty::Variance] {
48 let id = tcx.hir().as_local_hir_id(item_def_id).expect("expected local def-id");
49 let unsupported = || {
50 // Variance not relevant.
51 span_bug!(tcx.hir().span_by_hir_id(id), "asked to compute variance for wrong kind of item")
53 match tcx.hir().get_by_hir_id(id) {
54 Node::Item(item) => match item.node {
55 hir::ItemKind::Enum(..) |
56 hir::ItemKind::Struct(..) |
57 hir::ItemKind::Union(..) |
58 hir::ItemKind::Fn(..) => {}
63 Node::TraitItem(item) => match item.node {
64 hir::TraitItemKind::Method(..) => {}
69 Node::ImplItem(item) => match item.node {
70 hir::ImplItemKind::Method(..) => {}
75 Node::ForeignItem(item) => match item.node {
76 hir::ForeignItemKind::Fn(..) => {}
81 Node::Variant(_) | Node::Ctor(..) => {}
86 // Everything else must be inferred.
88 let crate_map = tcx.crate_variances(LOCAL_CRATE);
89 crate_map.variances.get(&item_def_id)