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use rustc_data_structures::fx::FxIndexMap;
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::LocalDefId;
use rustc_hir::OpaqueTyOrigin;
use rustc_infer::infer::TyCtxtInferExt as _;
use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin};
use rustc_infer::traits::{Obligation, ObligationCause};
use rustc_macros::extension;
use rustc_middle::ty::visit::TypeVisitableExt;
use rustc_middle::ty::{self, OpaqueHiddenType, OpaqueTypeKey, Ty, TyCtxt, TypeFoldable};
use rustc_middle::ty::{GenericArgKind, GenericArgs};
use rustc_span::Span;
use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
use rustc_trait_selection::traits::ObligationCtxt;
use crate::session_diagnostics::LifetimeMismatchOpaqueParam;
use crate::session_diagnostics::NonGenericOpaqueTypeParam;
use crate::universal_regions::RegionClassification;
use super::RegionInferenceContext;
impl<'tcx> RegionInferenceContext<'tcx> {
/// Resolve any opaque types that were encountered while borrow checking
/// this item. This is then used to get the type in the `type_of` query.
///
/// For example consider `fn f<'a>(x: &'a i32) -> impl Sized + 'a { x }`.
/// This is lowered to give HIR something like
///
/// type f<'a>::_Return<'_x> = impl Sized + '_x;
/// fn f<'a>(x: &'a i32) -> f<'a>::_Return<'a> { x }
///
/// When checking the return type record the type from the return and the
/// type used in the return value. In this case they might be `_Return<'1>`
/// and `&'2 i32` respectively.
///
/// Once we to this method, we have completed region inference and want to
/// call `infer_opaque_definition_from_instantiation` to get the inferred
/// type of `_Return<'_x>`. `infer_opaque_definition_from_instantiation`
/// compares lifetimes directly, so we need to map the inference variables
/// back to concrete lifetimes: `'static`, `ReEarlyParam` or `ReLateParam`.
///
/// First we map the regions in the the generic parameters `_Return<'1>` to
/// their `external_name` giving `_Return<'a>`. This step is a bit involved.
/// See the [rustc-dev-guide chapter] for more info.
///
/// Then we map all the lifetimes in the concrete type to an equal
/// universal region that occurs in the opaque type's args, in this case
/// this would result in `&'a i32`. We only consider regions in the args
/// in case there is an equal region that does not. For example, this should
/// be allowed:
/// `fn f<'a: 'b, 'b: 'a>(x: *mut &'b i32) -> impl Sized + 'a { x }`
///
/// This will then allow `infer_opaque_definition_from_instantiation` to
/// determine that `_Return<'_x> = &'_x i32`.
///
/// There's a slight complication around closures. Given
/// `fn f<'a: 'a>() { || {} }` the closure's type is something like
/// `f::<'a>::{{closure}}`. The region parameter from f is essentially
/// ignored by type checking so ends up being inferred to an empty region.
/// Calling `universal_upper_bound` for such a region gives `fr_fn_body`,
/// which has no `external_name` in which case we use `'{erased}` as the
/// region to pass to `infer_opaque_definition_from_instantiation`.
///
/// [rustc-dev-guide chapter]:
/// https://rustc-dev-guide.rust-lang.org/opaque-types-region-infer-restrictions.html
#[instrument(level = "debug", skip(self, infcx), ret)]
pub(crate) fn infer_opaque_types(
&self,
infcx: &InferCtxt<'tcx>,
opaque_ty_decls: FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>>,
) -> FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>> {
let mut result: FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>> = FxIndexMap::default();
let mut decls_modulo_regions: FxIndexMap<OpaqueTypeKey<'tcx>, (OpaqueTypeKey<'tcx>, Span)> =
FxIndexMap::default();
for (opaque_type_key, concrete_type) in opaque_ty_decls {
debug!(?opaque_type_key, ?concrete_type);
let mut arg_regions: Vec<(ty::RegionVid, ty::Region<'_>)> =
vec![(self.universal_regions.fr_static, infcx.tcx.lifetimes.re_static)];
let opaque_type_key =
opaque_type_key.fold_captured_lifetime_args(infcx.tcx, |region| {
// Use the SCC representative instead of directly using `region`.
// See [rustc-dev-guide chapter] § "Strict lifetime equality".
let scc = self.constraint_sccs.scc(region.as_var());
let vid = self.scc_representatives[scc];
let named = match self.definitions[vid].origin {
// Iterate over all universal regions in a consistent order and find the
// *first* equal region. This makes sure that equal lifetimes will have
// the same name and simplifies subsequent handling.
// See [rustc-dev-guide chapter] § "Semantic lifetime equality".
NllRegionVariableOrigin::FreeRegion => self
.universal_regions
.universal_regions()
.filter(|&ur| {
// See [rustc-dev-guide chapter] § "Closure restrictions".
!matches!(
self.universal_regions.region_classification(ur),
Some(RegionClassification::External)
)
})
.find(|&ur| self.universal_region_relations.equal(vid, ur))
.map(|ur| self.definitions[ur].external_name.unwrap()),
NllRegionVariableOrigin::Placeholder(placeholder) => {
Some(ty::Region::new_placeholder(infcx.tcx, placeholder))
}
NllRegionVariableOrigin::Existential { .. } => None,
}
.unwrap_or_else(|| {
ty::Region::new_error_with_message(
infcx.tcx,
concrete_type.span,
"opaque type with non-universal region args",
)
});
arg_regions.push((vid, named));
named
});
debug!(?opaque_type_key, ?arg_regions);
let concrete_type = infcx.tcx.fold_regions(concrete_type, |region, _| {
arg_regions
.iter()
.find(|&&(arg_vid, _)| self.eval_equal(region.as_var(), arg_vid))
.map(|&(_, arg_named)| arg_named)
.unwrap_or(infcx.tcx.lifetimes.re_erased)
});
debug!(?concrete_type);
let ty =
infcx.infer_opaque_definition_from_instantiation(opaque_type_key, concrete_type);
// Sometimes, when the hidden type is an inference variable, it can happen that
// the hidden type becomes the opaque type itself. In this case, this was an opaque
// usage of the opaque type and we can ignore it. This check is mirrored in typeck's
// writeback.
// FIXME(-Znext-solver): This should be unnecessary with the new solver.
if let ty::Alias(ty::Opaque, alias_ty) = ty.kind()
&& alias_ty.def_id == opaque_type_key.def_id.to_def_id()
&& alias_ty.args == opaque_type_key.args
{
continue;
}
// Sometimes two opaque types are the same only after we remap the generic parameters
// back to the opaque type definition. E.g. we may have `OpaqueType<X, Y>` mapped to `(X, Y)`
// and `OpaqueType<Y, X>` mapped to `(Y, X)`, and those are the same, but we only know that
// once we convert the generic parameters to those of the opaque type.
if let Some(prev) = result.get_mut(&opaque_type_key.def_id) {
if prev.ty != ty {
let guar = ty.error_reported().err().unwrap_or_else(|| {
let (Ok(e) | Err(e)) = prev
.build_mismatch_error(
&OpaqueHiddenType { ty, span: concrete_type.span },
opaque_type_key.def_id,
infcx.tcx,
)
.map(|d| d.emit());
e
});
prev.ty = Ty::new_error(infcx.tcx, guar);
}
// Pick a better span if there is one.
// FIXME(oli-obk): collect multiple spans for better diagnostics down the road.
prev.span = prev.span.substitute_dummy(concrete_type.span);
} else {
result.insert(
opaque_type_key.def_id,
OpaqueHiddenType { ty, span: concrete_type.span },
);
}
// Check that all opaque types have the same region parameters if they have the same
// non-region parameters. This is necessary because within the new solver we perform
// various query operations modulo regions, and thus could unsoundly select some impls
// that don't hold.
if !ty.references_error()
&& let Some((prev_decl_key, prev_span)) = decls_modulo_regions.insert(
infcx.tcx.erase_regions(opaque_type_key),
(opaque_type_key, concrete_type.span),
)
&& let Some((arg1, arg2)) = std::iter::zip(
prev_decl_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
opaque_type_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
)
.find(|(arg1, arg2)| arg1 != arg2)
{
infcx.dcx().emit_err(LifetimeMismatchOpaqueParam {
arg: arg1,
prev: arg2,
span: prev_span,
prev_span: concrete_type.span,
});
}
}
result
}
/// Map the regions in the type to named regions. This is similar to what
/// `infer_opaque_types` does, but can infer any universal region, not only
/// ones from the args for the opaque type. It also doesn't double check
/// that the regions produced are in fact equal to the named region they are
/// replaced with. This is fine because this function is only to improve the
/// region names in error messages.
pub(crate) fn name_regions<T>(&self, tcx: TyCtxt<'tcx>, ty: T) -> T
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
tcx.fold_regions(ty, |region, _| match *region {
ty::ReVar(vid) => {
let scc = self.constraint_sccs.scc(vid);
// Special handling of higher-ranked regions.
if !self.scc_universes[scc].is_root() {
match self.scc_values.placeholders_contained_in(scc).enumerate().last() {
// If the region contains a single placeholder then they're equal.
Some((0, placeholder)) => {
return ty::Region::new_placeholder(tcx, placeholder);
}
// Fallback: this will produce a cryptic error message.
_ => return region,
}
}
// Find something that we can name
let upper_bound = self.approx_universal_upper_bound(vid);
let upper_bound = &self.definitions[upper_bound];
match upper_bound.external_name {
Some(reg) => reg,
None => {
// Nothing exact found, so we pick the first one that we find.
let scc = self.constraint_sccs.scc(vid);
for vid in self.rev_scc_graph.as_ref().unwrap().upper_bounds(scc) {
match self.definitions[vid].external_name {
None => {}
Some(region) if region.is_static() => {}
Some(region) => return region,
}
}
region
}
}
}
_ => region,
})
}
}
#[extension(pub trait InferCtxtExt<'tcx>)]
impl<'tcx> InferCtxt<'tcx> {
/// Given the fully resolved, instantiated type for an opaque
/// type, i.e., the value of an inference variable like C1 or C2
/// (*), computes the "definition type" for an opaque type
/// definition -- that is, the inferred value of `Foo1<'x>` or
/// `Foo2<'x>` that we would conceptually use in its definition:
/// ```ignore (illustrative)
/// type Foo1<'x> = impl Bar<'x> = AAA; // <-- this type AAA
/// type Foo2<'x> = impl Bar<'x> = BBB; // <-- or this type BBB
/// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. }
/// ```
/// Note that these values are defined in terms of a distinct set of
/// generic parameters (`'x` instead of `'a`) from C1 or C2. The main
/// purpose of this function is to do that translation.
///
/// (*) C1 and C2 were introduced in the comments on
/// `register_member_constraints`. Read that comment for more context.
///
/// # Parameters
///
/// - `def_id`, the `impl Trait` type
/// - `args`, the args used to instantiate this opaque type
/// - `instantiated_ty`, the inferred type C1 -- fully resolved, lifted version of
/// `opaque_defn.concrete_ty`
#[instrument(level = "debug", skip(self))]
fn infer_opaque_definition_from_instantiation(
&self,
opaque_type_key: OpaqueTypeKey<'tcx>,
instantiated_ty: OpaqueHiddenType<'tcx>,
) -> Ty<'tcx> {
if let Some(e) = self.tainted_by_errors() {
return Ty::new_error(self.tcx, e);
}
if let Err(guar) =
check_opaque_type_parameter_valid(self.tcx, opaque_type_key, instantiated_ty.span)
{
return Ty::new_error(self.tcx, guar);
}
let definition_ty = instantiated_ty
.remap_generic_params_to_declaration_params(opaque_type_key, self.tcx, false)
.ty;
// `definition_ty` does not live in of the current inference context,
// so lets make sure that we don't accidentally misuse our current `infcx`.
match check_opaque_type_well_formed(
self.tcx,
self.next_trait_solver(),
opaque_type_key.def_id,
instantiated_ty.span,
definition_ty,
) {
Ok(hidden_ty) => hidden_ty,
Err(guar) => Ty::new_error(self.tcx, guar),
}
}
}
/// 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.
fn check_opaque_type_well_formed<'tcx>(
tcx: TyCtxt<'tcx>,
next_trait_solver: bool,
def_id: LocalDefId,
definition_span: Span,
definition_ty: Ty<'tcx>,
) -> Result<Ty<'tcx>, ErrorGuaranteed> {
// Only check this for TAIT. RPIT already supports `tests/ui/impl-trait/nested-return-type2.rs`
// on stable and we'd break that.
let opaque_ty_hir = tcx.hir().expect_item(def_id);
let OpaqueTyOrigin::TyAlias { .. } = opaque_ty_hir.expect_opaque_ty().origin else {
return Ok(definition_ty);
};
let param_env = tcx.param_env(def_id);
let mut parent_def_id = def_id;
while tcx.def_kind(parent_def_id) == DefKind::OpaqueTy {
parent_def_id = tcx.local_parent(parent_def_id);
}
// FIXME(-Znext-solver): We probably should use `&[]` instead of
// and prepopulate this `InferCtxt` with known opaque values, rather than
// allowing opaque types to be defined and checking them after the fact.
let infcx = tcx
.infer_ctxt()
.with_next_trait_solver(next_trait_solver)
.with_opaque_type_inference(parent_def_id)
.build();
let ocx = ObligationCtxt::new(&infcx);
let identity_args = GenericArgs::identity_for_item(tcx, def_id);
// Require that the hidden type actually fulfills all the bounds of the opaque type, even without
// the bounds that the function supplies.
let opaque_ty = Ty::new_opaque(tcx, def_id.to_def_id(), identity_args);
ocx.eq(&ObligationCause::misc(definition_span, def_id), param_env, opaque_ty, definition_ty)
.map_err(|err| {
infcx
.err_ctxt()
.report_mismatched_types(
&ObligationCause::misc(definition_span, def_id),
opaque_ty,
definition_ty,
err,
)
.emit()
})?;
// Require the hidden type to be well-formed with only the generics of the opaque type.
// Defining use functions may have more bounds than the opaque type, which is ok, as long as the
// hidden type is well formed even without those bounds.
let predicate = ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(
definition_ty.into(),
)));
ocx.register_obligation(Obligation::misc(tcx, definition_span, def_id, param_env, predicate));
// Check that all obligations are satisfied by the implementation's
// version.
let errors = ocx.select_all_or_error();
// This is fishy, but we check it again in `check_opaque_meets_bounds`.
// Remove once we can prepopulate with known hidden types.
let _ = infcx.take_opaque_types();
if errors.is_empty() {
Ok(definition_ty)
} else {
Err(infcx.err_ctxt().report_fulfillment_errors(errors))
}
}
/// Opaque type parameter validity check as documented in the [rustc-dev-guide chapter].
///
/// [rustc-dev-guide chapter]:
/// https://rustc-dev-guide.rust-lang.org/opaque-types-region-infer-restrictions.html
fn check_opaque_type_parameter_valid<'tcx>(
tcx: TyCtxt<'tcx>,
opaque_type_key: OpaqueTypeKey<'tcx>,
span: Span,
) -> Result<(), ErrorGuaranteed> {
let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
let opaque_env = LazyOpaqueTyEnv::new(tcx, opaque_type_key.def_id);
let mut seen_params: FxIndexMap<_, Vec<_>> = FxIndexMap::default();
for (i, arg) in opaque_type_key.iter_captured_args(tcx) {
let arg_is_param = match arg.unpack() {
GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
GenericArgKind::Lifetime(lt) => {
matches!(*lt, ty::ReEarlyParam(_) | ty::ReLateParam(_))
|| (lt.is_static() && opaque_env.param_equal_static(i))
}
GenericArgKind::Const(ct) => matches!(ct.kind(), ty::ConstKind::Param(_)),
};
if arg_is_param {
// Register if the same lifetime appears multiple times in the generic args.
// There is an exception when the opaque type *requires* the lifetimes to be equal.
// See [rustc-dev-guide chapter] § "An exception to uniqueness rule".
let seen_where = seen_params.entry(arg).or_default();
if !seen_where.first().is_some_and(|&prev_i| opaque_env.params_equal(i, prev_i)) {
seen_where.push(i);
}
} else {
// Prevent `fn foo() -> Foo<u32>` from being defining.
let opaque_param = opaque_generics.param_at(i, tcx);
let kind = opaque_param.kind.descr();
if let Err(guar) = opaque_env.param_is_error(i) {
return Err(guar);
}
return Err(tcx.dcx().emit_err(NonGenericOpaqueTypeParam {
ty: arg,
kind,
span,
param_span: tcx.def_span(opaque_param.def_id),
}));
}
}
for (_, indices) in seen_params {
if indices.len() > 1 {
let descr = opaque_generics.param_at(indices[0], tcx).kind.descr();
let spans: Vec<_> = indices
.into_iter()
.map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id))
.collect();
#[allow(rustc::diagnostic_outside_of_impl)]
#[allow(rustc::untranslatable_diagnostic)]
return Err(tcx
.dcx()
.struct_span_err(span, "non-defining opaque type use in defining scope")
.with_span_note(spans, format!("{descr} used multiple times"))
.emit());
}
}
Ok(())
}
/// Computes if an opaque type requires a lifetime parameter to be equal to
/// another one or to the `'static` lifetime.
/// These requirements are derived from the explicit and implied bounds.
struct LazyOpaqueTyEnv<'tcx> {
tcx: TyCtxt<'tcx>,
def_id: LocalDefId,
/// Equal parameters will have the same name. Computed Lazily.
/// Example:
/// `type Opaque<'a: 'static, 'b: 'c, 'c: 'b> = impl Sized;`
/// Identity args: `['a, 'b, 'c]`
/// Canonical args: `['static, 'b, 'b]`
canonical_args: std::cell::OnceCell<ty::GenericArgsRef<'tcx>>,
}
impl<'tcx> LazyOpaqueTyEnv<'tcx> {
pub fn new(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self {
Self { tcx, def_id, canonical_args: std::cell::OnceCell::new() }
}
pub fn param_equal_static(&self, param_index: usize) -> bool {
self.get_canonical_args()[param_index].expect_region().is_static()
}
pub fn params_equal(&self, param1: usize, param2: usize) -> bool {
let canonical_args = self.get_canonical_args();
canonical_args[param1] == canonical_args[param2]
}
pub fn param_is_error(&self, param_index: usize) -> Result<(), ErrorGuaranteed> {
self.get_canonical_args()[param_index].error_reported()
}
fn get_canonical_args(&self) -> ty::GenericArgsRef<'tcx> {
use rustc_hir as hir;
use rustc_infer::infer::outlives::env::OutlivesEnvironment;
use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
if let Some(&canonical_args) = self.canonical_args.get() {
return canonical_args;
}
let &Self { tcx, def_id, .. } = self;
let origin = tcx.opaque_type_origin(def_id);
let parent = match origin {
hir::OpaqueTyOrigin::FnReturn(parent)
| hir::OpaqueTyOrigin::AsyncFn(parent)
| hir::OpaqueTyOrigin::TyAlias { parent, .. } => parent,
};
let param_env = tcx.param_env(parent);
let args = GenericArgs::identity_for_item(tcx, parent).extend_to(
tcx,
def_id.to_def_id(),
|param, _| {
tcx.map_opaque_lifetime_to_parent_lifetime(param.def_id.expect_local()).into()
},
);
let infcx = tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(&infcx);
let wf_tys = ocx.assumed_wf_types(param_env, parent).unwrap_or_else(|_| {
tcx.dcx().span_delayed_bug(tcx.def_span(def_id), "error getting implied bounds");
Default::default()
});
let implied_bounds = infcx.implied_bounds_tys(param_env, parent, &wf_tys);
let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
let mut seen = vec![tcx.lifetimes.re_static];
let canonical_args = tcx.fold_regions(args, |r1, _| {
if r1.is_error() {
r1
} else if let Some(&r2) = seen.iter().find(|&&r2| {
let free_regions = outlives_env.free_region_map();
free_regions.sub_free_regions(tcx, r1, r2)
&& free_regions.sub_free_regions(tcx, r2, r1)
}) {
r2
} else {
seen.push(r1);
r1
}
});
self.canonical_args.set(canonical_args).unwrap();
canonical_args
}
}