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