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 //! Module for inferring the variance of type and lifetime parameters. See the [rustc dev guide] //! chapter for more info. //! //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/variance.html use hir::Node; use rustc_arena::TypedArena; use rustc_hir as hir; use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE}; use rustc_middle::ty::query::Providers; use rustc_middle::ty::{self, CrateVariancesMap, TyCtxt}; /// 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 = TypedArena::default(); let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &mut arena); let constraints_cx = constraints::add_constraints_from_crate(terms_cx); 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_local()); 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.kind { hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Fn(..) => {} _ => unsupported(), }, Node::TraitItem(item) => match item.kind { hir::TraitItemKind::Fn(..) => {} _ => unsupported(), }, Node::ImplItem(item) => match item.kind { hir::ImplItemKind::Fn(..) => {} _ => unsupported(), }, Node::ForeignItem(item) => match item.kind { 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).copied().unwrap_or(&[]) }