| //! Module for inferring the variance of type and lifetime parameters. See the [rustc guide] |
| //! chapter for more info. |
| //! |
| //! [rustc guide]: https://rust-lang.github.io/rustc-guide/variance.html |
| |
| use arena; |
| use rustc::hir; |
| use hir::Node; |
| use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE}; |
| use rustc::ty::{self, CrateVariancesMap, TyCtxt}; |
| use rustc::ty::query::Providers; |
| |
| /// Defines the `TermsContext` basically houses an arena where we can |
| /// allocate terms. |
| mod terms; |
| |
| /// Code to gather up constraints. |
| mod constraints; |
| |
| /// Code to solve constraints and write out the results. |
| mod solve; |
| |
| /// Code to write unit tests of variance. |
| pub mod test; |
| |
| /// Code for transforming variances. |
| mod xform; |
| |
| pub fn provide(providers: &mut Providers<'_>) { |
| *providers = Providers { |
| variances_of, |
| crate_variances, |
| ..*providers |
| }; |
| } |
| |
| fn crate_variances(tcx: TyCtxt<'_>, crate_num: CrateNum) -> &CrateVariancesMap<'_> { |
| assert_eq!(crate_num, LOCAL_CRATE); |
| let mut arena = arena::TypedArena::default(); |
| let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &mut arena); |
| let constraints_cx = constraints::add_constraints_from_crate(terms_cx); |
| tcx.arena.alloc(solve::solve_constraints(constraints_cx)) |
| } |
| |
| fn variances_of(tcx: TyCtxt<'_>, item_def_id: DefId) -> &[ty::Variance] { |
| let id = tcx.hir().as_local_hir_id(item_def_id).expect("expected local def-id"); |
| let unsupported = || { |
| // Variance not relevant. |
| span_bug!(tcx.hir().span(id), "asked to compute variance for wrong kind of item") |
| }; |
| match tcx.hir().get(id) { |
| Node::Item(item) => match item.node { |
| hir::ItemKind::Enum(..) | |
| hir::ItemKind::Struct(..) | |
| hir::ItemKind::Union(..) | |
| hir::ItemKind::Fn(..) => {} |
| |
| _ => unsupported() |
| }, |
| |
| Node::TraitItem(item) => match item.node { |
| hir::TraitItemKind::Method(..) => {} |
| |
| _ => unsupported() |
| }, |
| |
| Node::ImplItem(item) => match item.node { |
| hir::ImplItemKind::Method(..) => {} |
| |
| _ => unsupported() |
| }, |
| |
| Node::ForeignItem(item) => match item.node { |
| hir::ForeignItemKind::Fn(..) => {} |
| |
| _ => unsupported() |
| }, |
| |
| Node::Variant(_) | Node::Ctor(..) => {} |
| |
| _ => unsupported() |
| } |
| |
| // Everything else must be inferred. |
| |
| let crate_map = tcx.crate_variances(LOCAL_CRATE); |
| crate_map.variances.get(&item_def_id) |
| .map(|p| *p) |
| .unwrap_or(&[]) |
| } |