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use crate::error::ConstNotUsedTraitAlias;
use crate::ty::fold::{TypeFolder, TypeSuperFoldable};
use crate::ty::{self, Ty, TyCtxt, TypeFoldable};
use crate::ty::{GenericArg, GenericArgKind};
use rustc_data_structures::fx::FxHashMap;
use rustc_span::def_id::DefId;
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)
}
fn fold_closure_args(
&mut self,
def_id: DefId,
args: ty::GenericArgsRef<'tcx>,
) -> ty::GenericArgsRef<'tcx> {
// 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);
self.tcx.mk_args_from_iter(args.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)
}
}))
}
}
impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ReverseMapper<'tcx> {
fn interner(&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,
ty::ReError(_) => 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 => {
let e = self
.tcx
.sess
.struct_span_err(self.span, "non-defining opaque type use in defining scope")
.span_label(
self.span,
format!(
"lifetime `{r}` is part of concrete type but not used in \
parameter list of the `impl Trait` type alias"
),
)
.emit();
ty::Region::new_error(self.interner(), e)
}
}
}
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
match *ty.kind() {
ty::Closure(def_id, args) => {
let args = self.fold_closure_args(def_id, args);
Ty::new_closure(self.tcx, def_id, args)
}
ty::Generator(def_id, args, movability) => {
let args = self.fold_closure_args(def_id, args);
Ty::new_generator(self.tcx, def_id, args, movability)
}
ty::GeneratorWitness(def_id, args) => {
let args = self.fold_closure_args(def_id, args);
Ty::new_generator_witness(self.tcx, def_id, args)
}
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 `{ty}` is part of concrete type but not \
used in parameter list for the `impl Trait` type alias"
),
)
.emit();
}
Ty::new_misc_error(self.tcx)
}
}
}
_ => 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 => {
let guar = self
.tcx
.sess
.create_err(ConstNotUsedTraitAlias {
ct: ct.to_string(),
span: self.span,
})
.emit_unless(self.ignore_errors);
ty::Const::new_error(self.tcx, guar, ct.ty())
}
}
}
_ => ct,
}
}
}