diff options
Diffstat (limited to 'compiler/rustc_middle/src/ty/opaque_types.rs')
| -rw-r--r-- | compiler/rustc_middle/src/ty/opaque_types.rs | 218 |
1 files changed, 218 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/opaque_types.rs b/compiler/rustc_middle/src/ty/opaque_types.rs new file mode 100644 index 000000000..b05c63109 --- /dev/null +++ b/compiler/rustc_middle/src/ty/opaque_types.rs @@ -0,0 +1,218 @@ +use rustc_data_structures::fx::FxHashMap; +use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable}; +use rustc_middle::ty::subst::{GenericArg, GenericArgKind}; +use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable}; +use rustc_span::Span; + +/// Converts generic params of a TypeFoldable from one +/// item's generics to another. Usually from a function's generics +/// list to the opaque type's own generics. +pub(super) struct ReverseMapper<'tcx> { + tcx: TyCtxt<'tcx>, + map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>, + /// see call sites to fold_kind_no_missing_regions_error + /// for an explanation of this field. + do_not_error: bool, + + /// We do not want to emit any errors in typeck because + /// the spans in typeck are subpar at the moment. + /// Borrowck will do the same work again (this time with + /// lifetime information) and thus report better errors. + ignore_errors: bool, + + /// Span of function being checked. + span: Span, +} + +impl<'tcx> ReverseMapper<'tcx> { + pub(super) fn new( + tcx: TyCtxt<'tcx>, + map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>, + span: Span, + ignore_errors: bool, + ) -> Self { + Self { tcx, map, do_not_error: false, ignore_errors, span } + } + + fn fold_kind_no_missing_regions_error(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> { + assert!(!self.do_not_error); + self.do_not_error = true; + let kind = kind.fold_with(self); + self.do_not_error = false; + kind + } + + fn fold_kind_normally(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> { + assert!(!self.do_not_error); + kind.fold_with(self) + } +} + +impl<'tcx> TypeFolder<'tcx> for ReverseMapper<'tcx> { + fn tcx(&self) -> TyCtxt<'tcx> { + self.tcx + } + + #[instrument(skip(self), level = "debug")] + fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { + match *r { + // Ignore bound regions and `'static` regions that appear in the + // type, we only need to remap regions that reference lifetimes + // from the function declaration. + // This would ignore `'r` in a type like `for<'r> fn(&'r u32)`. + ty::ReLateBound(..) | ty::ReStatic => return r, + + // If regions have been erased (by writeback), don't try to unerase + // them. + ty::ReErased => return r, + + // The regions that we expect from borrow checking. + ty::ReEarlyBound(_) | ty::ReFree(_) => {} + + ty::RePlaceholder(_) | ty::ReVar(_) => { + // All of the regions in the type should either have been + // erased by writeback, or mapped back to named regions by + // borrow checking. + bug!("unexpected region kind in opaque type: {:?}", r); + } + } + + match self.map.get(&r.into()).map(|k| k.unpack()) { + Some(GenericArgKind::Lifetime(r1)) => r1, + Some(u) => panic!("region mapped to unexpected kind: {:?}", u), + None if self.do_not_error => self.tcx.lifetimes.re_static, + None => { + self.tcx + .sess + .struct_span_err(self.span, "non-defining opaque type use in defining scope") + .span_label( + self.span, + format!( + "lifetime `{}` is part of concrete type but not used in \ + parameter list of the `impl Trait` type alias", + r + ), + ) + .emit(); + + self.tcx().lifetimes.re_static + } + } + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + match *ty.kind() { + ty::Closure(def_id, substs) => { + // I am a horrible monster and I pray for death. When + // we encounter a closure here, it is always a closure + // from within the function that we are currently + // type-checking -- one that is now being encapsulated + // in an opaque type. Ideally, we would + // go through the types/lifetimes that it references + // and treat them just like we would any other type, + // which means we would error out if we find any + // reference to a type/region that is not in the + // "reverse map". + // + // **However,** in the case of closures, there is a + // somewhat subtle (read: hacky) consideration. The + // problem is that our closure types currently include + // all the lifetime parameters declared on the + // enclosing function, even if they are unused by the + // closure itself. We can't readily filter them out, + // so here we replace those values with `'empty`. This + // can't really make a difference to the rest of the + // compiler; those regions are ignored for the + // outlives relation, and hence don't affect trait + // selection or auto traits, and they are erased + // during codegen. + + let generics = self.tcx.generics_of(def_id); + let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| { + if index < generics.parent_count { + // Accommodate missing regions in the parent kinds... + self.fold_kind_no_missing_regions_error(kind) + } else { + // ...but not elsewhere. + self.fold_kind_normally(kind) + } + })); + + self.tcx.mk_closure(def_id, substs) + } + + ty::Generator(def_id, substs, movability) => { + let generics = self.tcx.generics_of(def_id); + let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| { + if index < generics.parent_count { + // Accommodate missing regions in the parent kinds... + self.fold_kind_no_missing_regions_error(kind) + } else { + // ...but not elsewhere. + self.fold_kind_normally(kind) + } + })); + + self.tcx.mk_generator(def_id, substs, movability) + } + + ty::Param(param) => { + // Look it up in the substitution list. + match self.map.get(&ty.into()).map(|k| k.unpack()) { + // Found it in the substitution list; replace with the parameter from the + // opaque type. + Some(GenericArgKind::Type(t1)) => t1, + Some(u) => panic!("type mapped to unexpected kind: {:?}", u), + None => { + debug!(?param, ?self.map); + if !self.ignore_errors { + self.tcx + .sess + .struct_span_err( + self.span, + &format!( + "type parameter `{}` is part of concrete type but not \ + used in parameter list for the `impl Trait` type alias", + ty + ), + ) + .emit(); + } + + self.tcx().ty_error() + } + } + } + + _ => ty.super_fold_with(self), + } + } + + fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> { + trace!("checking const {:?}", ct); + // Find a const parameter + match ct.kind() { + ty::ConstKind::Param(..) => { + // Look it up in the substitution list. + match self.map.get(&ct.into()).map(|k| k.unpack()) { + // Found it in the substitution list, replace with the parameter from the + // opaque type. + Some(GenericArgKind::Const(c1)) => c1, + Some(u) => panic!("const mapped to unexpected kind: {:?}", u), + None => { + if !self.ignore_errors { + self.tcx.sess.emit_err(ty::ConstNotUsedTraitAlias { + ct: ct.to_string(), + span: self.span, + }); + } + + self.tcx().const_error(ct.ty()) + } + } + } + + _ => ct, + } + } +} |