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Move ReverseMapper logic onto OpaqueHiddenType

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This commit is contained in:
Oli Scherer 2022-09-27 11:37:10 +00:00
parent d643ae1bbf
commit 9eb69e82e0
5 changed files with 247 additions and 233 deletions
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231
compiler/rustc_borrowck/src/region_infer/opaque_types.rs
View File

@ -5,8 +5,7 @@ use rustc_hir::OpaqueTyOrigin;
use rustc_infer::infer::TyCtxtInferExt as _;
use rustc_infer::infer::{DefiningAnchor, InferCtxt};
use rustc_infer::traits::{Obligation, ObligationCause, TraitEngine};
use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts};
use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
use rustc_middle::ty::visit::TypeVisitable;
use rustc_middle::ty::{
self, OpaqueHiddenType, OpaqueTypeKey, ToPredicate, Ty, TyCtxt, TypeFoldable,
@ -15,8 +14,6 @@ use rustc_span::Span;
use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
use rustc_trait_selection::traits::TraitEngineExt as _;
use crate::session_diagnostics::ConstNotUsedTraitAlias;
use super::RegionInferenceContext;
impl<'tcx> RegionInferenceContext<'tcx> {
@ -228,29 +225,9 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
return self.tcx.ty_error();
}
let OpaqueTypeKey { def_id, substs } = opaque_type_key;
// Use substs to build up a reverse map from regions to their
// identity mappings. This is necessary because of `impl
// Trait` lifetimes are computed by replacing existing
// lifetimes with 'static and remapping only those used in the
// `impl Trait` return type, resulting in the parameters
// shifting.
let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id.to_def_id());
debug!(?id_substs);
let map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>> =
substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect();
debug!("map = {:#?}", map);
// Convert the type from the function into a type valid outside
// the function, by replacing invalid regions with 'static,
// after producing an error for each of them.
let definition_ty = instantiated_ty.ty.fold_with(&mut ReverseMapper::new(
self.tcx,
map,
instantiated_ty.span,
));
debug!(?definition_ty);
let definition_ty = instantiated_ty
.remap_generic_params_to_declaration_params(opaque_type_key, self.tcx)
.ty;
if !check_opaque_type_parameter_valid(
self.tcx,
@ -266,6 +243,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
let OpaqueTyOrigin::TyAlias = origin else {
return definition_ty;
};
let def_id = opaque_type_key.def_id;
// This logic duplicates most of `check_opaque_meets_bounds`.
// FIXME(oli-obk): Also do region checks here and then consider removing `check_opaque_meets_bounds` entirely.
let param_env = self.tcx.param_env(def_id);
@ -281,6 +259,8 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
.to_predicate(infcx.tcx);
let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id.to_def_id());
// Require that the hidden type actually fulfills all the bounds of the opaque type, even without
// the bounds that the function supplies.
match infcx.register_hidden_type(
@ -421,200 +401,3 @@ fn check_opaque_type_parameter_valid(
}
true
}
struct ReverseMapper<'tcx> {
tcx: TyCtxt<'tcx>,
map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
do_not_error: bool,
/// Span of function being checked.
span: Span,
}
impl<'tcx> ReverseMapper<'tcx> {
fn new(
tcx: TyCtxt<'tcx>,
map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
span: Span,
) -> Self {
Self { tcx, map, do_not_error: false, 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);
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 => {
self.tcx.sess.emit_err(ConstNotUsedTraitAlias {
ct: ct.to_string(),
span: self.span,
});
self.tcx().const_error(ct.ty())
}
}
}
_ => ct,
}
}
}

9
compiler/rustc_borrowck/src/session_diagnostics.rs
View File

@ -52,15 +52,6 @@ pub(crate) struct VarNeedNotMut {
#[suggestion_short(applicability = "machine-applicable", code = "")]
pub span: Span,
}
#[derive(Diagnostic)]
#[diag(borrowck::const_not_used_in_type_alias)]
pub(crate) struct ConstNotUsedTraitAlias {
pub ct: String,
#[primary_span]
pub span: Span,
}
#[derive(Diagnostic)]
#[diag(borrowck::var_cannot_escape_closure)]
#[note]

8
compiler/rustc_middle/src/ty/diagnostics.rs
View File

@ -511,3 +511,11 @@ impl<'tcx> TypeVisitor<'tcx> for IsSuggestableVisitor<'tcx> {
c.super_visit_with(self)
}
}
#[derive(Diagnostic)]
#[diag(borrowck::const_not_used_in_type_alias)]
pub(super) struct ConstNotUsedTraitAlias {
pub ct: String,
#[primary_span]
pub span: Span,
}

27
compiler/rustc_middle/src/ty/mod.rs
View File

@ -131,6 +131,7 @@ mod generics;
mod impls_ty;
mod instance;
mod list;
mod opaque_types;
mod parameterized;
mod rvalue_scopes;
mod structural_impls;
@ -1300,6 +1301,32 @@ impl<'tcx> OpaqueHiddenType<'tcx> {
sub: sub_diag,
});
}
#[instrument(level = "debug", skip(tcx), ret)]
pub fn remap_generic_params_to_declaration_params(
self,
opaque_type_key: OpaqueTypeKey<'tcx>,
tcx: TyCtxt<'tcx>,
) -> Self {
let OpaqueTypeKey { def_id, substs } = opaque_type_key;
// Use substs to build up a reverse map from regions to their
// identity mappings. This is necessary because of `impl
// Trait` lifetimes are computed by replacing existing
// lifetimes with 'static and remapping only those used in the
// `impl Trait` return type, resulting in the parameters
// shifting.
let id_substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
debug!(?id_substs);
let map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>> =
substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect();
debug!("map = {:#?}", map);
// Convert the type from the function into a type valid outside
// the function, by replacing invalid regions with 'static,
// after producing an error for each of them.
self.fold_with(&mut opaque_types::ReverseMapper::new(tcx, map, self.span))
}
}
/// The "placeholder index" fully defines a placeholder region, type, or const. Placeholders are

205
compiler/rustc_middle/src/ty/opaque_types.rs Normal file
View File

@ -0,0 +1,205 @@
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>>,
do_not_error: 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,
) -> Self {
Self { tcx, map, do_not_error: false, 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);
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 => {
self.tcx.sess.emit_err(ty::ConstNotUsedTraitAlias {
ct: ct.to_string(),
span: self.span,
});
self.tcx().const_error(ct.ty())
}
}
}
_ => ct,
}
}
}