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//! Orphan checker: every impl either implements a trait defined in this
//! crate or pertains to a type defined in this crate.
use rustc_data_structures::fx::FxIndexSet;
use rustc_errors::ErrorGuaranteed;
use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
use rustc_lint_defs::builtin::UNCOVERED_PARAM_IN_PROJECTION;
use rustc_middle::ty::{
self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeSuperVisitable,
TypeVisitable, TypeVisitableExt, TypeVisitor,
};
use rustc_middle::{bug, span_bug};
use rustc_span::def_id::{DefId, LocalDefId};
use rustc_trait_selection::traits::{
self, IsFirstInputType, OrphanCheckErr, OrphanCheckMode, UncoveredTyParams,
};
use tracing::{debug, instrument};
use crate::errors;
#[instrument(level = "debug", skip(tcx))]
pub(crate) fn orphan_check_impl(
tcx: TyCtxt<'_>,
impl_def_id: LocalDefId,
) -> Result<(), ErrorGuaranteed> {
let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().instantiate_identity();
trait_ref.error_reported()?;
match orphan_check(tcx, impl_def_id, OrphanCheckMode::Proper) {
Ok(()) => {}
Err(err) => match orphan_check(tcx, impl_def_id, OrphanCheckMode::Compat) {
Ok(()) => match err {
OrphanCheckErr::UncoveredTyParams(uncovered_ty_params) => {
lint_uncovered_ty_params(tcx, uncovered_ty_params, impl_def_id)
}
OrphanCheckErr::NonLocalInputType(_) => {
bug!("orphanck: shouldn't've gotten non-local input tys in compat mode")
}
},
Err(err) => return Err(emit_orphan_check_error(tcx, trait_ref, impl_def_id, err)),
},
}
let trait_def_id = trait_ref.def_id;
// In addition to the above rules, we restrict impls of auto traits
// so that they can only be implemented on nominal types, such as structs,
// enums or foreign types. To see why this restriction exists, consider the
// following example (#22978). Imagine that crate A defines an auto trait
// `Foo` and a fn that operates on pairs of types:
//
// ```
// // Crate A
// auto trait Foo { }
// fn two_foos<A:Foo,B:Foo>(..) {
// one_foo::<(A,B)>(..)
// }
// fn one_foo<T:Foo>(..) { .. }
// ```
//
// This type-checks fine; in particular the fn
// `two_foos` is able to conclude that `(A,B):Foo`
// because `A:Foo` and `B:Foo`.
//
// Now imagine that crate B comes along and does the following:
//
// ```
// struct A { }
// struct B { }
// impl Foo for A { }
// impl Foo for B { }
// impl !Foo for (A, B) { }
// ```
//
// This final impl is legal according to the orphan
// rules, but it invalidates the reasoning from
// `two_foos` above.
debug!(
"trait_ref={:?} trait_def_id={:?} trait_is_auto={}",
trait_ref,
trait_def_id,
tcx.trait_is_auto(trait_def_id)
);
if tcx.trait_is_auto(trait_def_id) {
let self_ty = trait_ref.self_ty();
// If the impl is in the same crate as the auto-trait, almost anything
// goes.
//
// impl MyAuto for Rc<Something> {} // okay
// impl<T> !MyAuto for *const T {} // okay
// impl<T> MyAuto for T {} // okay
//
// But there is one important exception: implementing for a trait object
// is not allowed.
//
// impl MyAuto for dyn Trait {} // NOT OKAY
// impl<T: ?Sized> MyAuto for T {} // NOT OKAY
//
// With this restriction, it's guaranteed that an auto-trait is
// implemented for a trait object if and only if the auto-trait is one
// of the trait object's trait bounds (or a supertrait of a bound). In
// other words `dyn Trait + AutoTrait` always implements AutoTrait,
// while `dyn Trait` never implements AutoTrait.
//
// This is necessary in order for autotrait bounds on methods of trait
// objects to be sound.
//
// auto trait AutoTrait {}
//
// trait ObjectSafeTrait {
// fn f(&self) where Self: AutoTrait;
// }
//
// We can allow f to be called on `dyn ObjectSafeTrait + AutoTrait`.
//
// If we didn't deny `impl AutoTrait for dyn Trait`, it would be unsound
// for the ObjectSafeTrait shown above to be object safe because someone
// could take some type implementing ObjectSafeTrait but not AutoTrait,
// unsize it to `dyn ObjectSafeTrait`, and call .f() which has no
// concrete implementation (issue #50781).
enum LocalImpl {
Allow,
Disallow { problematic_kind: &'static str },
}
// If the auto-trait is from a dependency, it must only be getting
// implemented for a nominal type, and specifically one local to the
// current crate.
//
// impl<T> Sync for MyStruct<T> {} // okay
//
// impl Sync for Rc<MyStruct> {} // NOT OKAY
enum NonlocalImpl {
Allow,
DisallowBecauseNonlocal,
DisallowOther,
}
// Exhaustive match considering that this logic is essential for
// soundness.
let (local_impl, nonlocal_impl) = match self_ty.kind() {
// struct Struct<T>;
// impl AutoTrait for Struct<Foo> {}
ty::Adt(self_def, _) => (
LocalImpl::Allow,
if self_def.did().is_local() {
NonlocalImpl::Allow
} else {
NonlocalImpl::DisallowBecauseNonlocal
},
),
// extern { type OpaqueType; }
// impl AutoTrait for OpaqueType {}
ty::Foreign(did) => (
LocalImpl::Allow,
if did.is_local() {
NonlocalImpl::Allow
} else {
NonlocalImpl::DisallowBecauseNonlocal
},
),
// impl AutoTrait for dyn Trait {}
ty::Dynamic(..) => (
LocalImpl::Disallow { problematic_kind: "trait object" },
NonlocalImpl::DisallowOther,
),
// impl<T> AutoTrait for T {}
// impl<T: ?Sized> AutoTrait for T {}
ty::Param(..) => (
if self_ty.is_sized(tcx, tcx.param_env(impl_def_id)) {
LocalImpl::Allow
} else {
LocalImpl::Disallow { problematic_kind: "generic type" }
},
NonlocalImpl::DisallowOther,
),
ty::Alias(kind, _) => {
let problematic_kind = match kind {
// trait Id { type This: ?Sized; }
// impl<T: ?Sized> Id for T {
// type This = T;
// }
// impl<T: ?Sized> AutoTrait for <T as Id>::This {}
ty::Projection => "associated type",
// type Foo = (impl Sized, bool)
// impl AutoTrait for Foo {}
ty::Weak => "type alias",
// type Opaque = impl Trait;
// impl AutoTrait for Opaque {}
ty::Opaque => "opaque type",
// ```
// struct S<T>(T);
// impl<T: ?Sized> S<T> {
// type This = T;
// }
// impl<T: ?Sized> AutoTrait for S<T>::This {}
// ```
// FIXME(inherent_associated_types): The example code above currently leads to a cycle
ty::Inherent => "associated type",
};
(LocalImpl::Disallow { problematic_kind }, NonlocalImpl::DisallowOther)
}
ty::Pat(..) => (
LocalImpl::Disallow { problematic_kind: "pattern type" },
NonlocalImpl::DisallowOther,
),
ty::Bool
| ty::Char
| ty::Int(..)
| ty::Uint(..)
| ty::Float(..)
| ty::Str
| ty::Array(..)
| ty::Slice(..)
| ty::RawPtr(..)
| ty::Ref(..)
| ty::FnDef(..)
| ty::FnPtr(..)
| ty::Never
| ty::Tuple(..) => (LocalImpl::Allow, NonlocalImpl::DisallowOther),
ty::Closure(..)
| ty::CoroutineClosure(..)
| ty::Coroutine(..)
| ty::CoroutineWitness(..)
| ty::Bound(..)
| ty::Placeholder(..)
| ty::Infer(..) => {
let sp = tcx.def_span(impl_def_id);
span_bug!(sp, "weird self type for autotrait impl")
}
ty::Error(..) => (LocalImpl::Allow, NonlocalImpl::Allow),
};
if trait_def_id.is_local() {
match local_impl {
LocalImpl::Allow => {}
LocalImpl::Disallow { problematic_kind } => {
return Err(tcx.dcx().emit_err(errors::TraitsWithDefaultImpl {
span: tcx.def_span(impl_def_id),
traits: tcx.def_path_str(trait_def_id),
problematic_kind,
self_ty,
}));
}
}
} else {
match nonlocal_impl {
NonlocalImpl::Allow => {}
NonlocalImpl::DisallowBecauseNonlocal => {
return Err(tcx.dcx().emit_err(errors::CrossCrateTraitsDefined {
span: tcx.def_span(impl_def_id),
traits: tcx.def_path_str(trait_def_id),
}));
}
NonlocalImpl::DisallowOther => {
return Err(tcx.dcx().emit_err(errors::CrossCrateTraits {
span: tcx.def_span(impl_def_id),
traits: tcx.def_path_str(trait_def_id),
self_ty,
}));
}
}
}
}
Ok(())
}
/// Checks the coherence orphan rules.
///
/// `impl_def_id` should be the `DefId` of a trait impl.
///
/// To pass, either the trait must be local, or else two conditions must be satisfied:
///
/// 1. All type parameters in `Self` must be "covered" by some local type constructor.
/// 2. Some local type must appear in `Self`.
#[instrument(level = "debug", skip(tcx), ret)]
fn orphan_check<'tcx>(
tcx: TyCtxt<'tcx>,
impl_def_id: LocalDefId,
mode: OrphanCheckMode,
) -> Result<(), OrphanCheckErr<TyCtxt<'tcx>, FxIndexSet<DefId>>> {
// We only accept this routine to be invoked on implementations
// of a trait, not inherent implementations.
let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
debug!(trait_ref = ?trait_ref.skip_binder());
// If the *trait* is local to the crate, ok.
if let Some(def_id) = trait_ref.skip_binder().def_id.as_local() {
debug!("trait {def_id:?} is local to current crate");
return Ok(());
}
// (1) Instantiate all generic params with fresh inference vars.
let infcx = tcx.infer_ctxt().intercrate(true).build();
let cause = traits::ObligationCause::dummy();
let args = infcx.fresh_args_for_item(cause.span, impl_def_id.to_def_id());
let trait_ref = trait_ref.instantiate(tcx, args);
let lazily_normalize_ty = |user_ty: Ty<'tcx>| {
let ty::Alias(..) = user_ty.kind() else { return Ok(user_ty) };
let ocx = traits::ObligationCtxt::new(&infcx);
let ty = ocx.normalize(&cause, ty::ParamEnv::empty(), user_ty);
let ty = infcx.resolve_vars_if_possible(ty);
let errors = ocx.select_where_possible();
if !errors.is_empty() {
return Ok(user_ty);
}
let ty = if infcx.next_trait_solver() {
ocx.structurally_normalize(
&cause,
ty::ParamEnv::empty(),
infcx.resolve_vars_if_possible(ty),
)
.unwrap_or(ty)
} else {
ty
};
Ok::<_, !>(ty)
};
let result = traits::orphan_check_trait_ref(
&infcx,
trait_ref,
traits::InCrate::Local { mode },
lazily_normalize_ty,
)
.into_ok();
// (2) Try to map the remaining inference vars back to generic params.
result.map_err(|err| match err {
OrphanCheckErr::UncoveredTyParams(UncoveredTyParams { uncovered, local_ty }) => {
let mut collector =
UncoveredTyParamCollector { infcx: &infcx, uncovered_params: Default::default() };
uncovered.visit_with(&mut collector);
// FIXME(fmease): This is very likely reachable.
debug_assert!(!collector.uncovered_params.is_empty());
OrphanCheckErr::UncoveredTyParams(UncoveredTyParams {
uncovered: collector.uncovered_params,
local_ty,
})
}
OrphanCheckErr::NonLocalInputType(tys) => {
let generics = tcx.generics_of(impl_def_id);
let tys = tys
.into_iter()
.map(|(ty, is_target_ty)| {
(ty.fold_with(&mut TyVarReplacer { infcx: &infcx, generics }), is_target_ty)
})
.collect();
OrphanCheckErr::NonLocalInputType(tys)
}
})
}
fn emit_orphan_check_error<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::TraitRef<'tcx>,
impl_def_id: LocalDefId,
err: traits::OrphanCheckErr<TyCtxt<'tcx>, FxIndexSet<DefId>>,
) -> ErrorGuaranteed {
match err {
traits::OrphanCheckErr::NonLocalInputType(tys) => {
let item = tcx.hir().expect_item(impl_def_id);
let impl_ = item.expect_impl();
let hir_trait_ref = impl_.of_trait.as_ref().unwrap();
let span = tcx.def_span(impl_def_id);
let mut diag = tcx.dcx().create_err(match trait_ref.self_ty().kind() {
ty::Adt(..) => errors::OnlyCurrentTraits::Outside { span, note: () },
_ if trait_ref.self_ty().is_primitive() => {
errors::OnlyCurrentTraits::Primitive { span, note: () }
}
_ => errors::OnlyCurrentTraits::Arbitrary { span, note: () },
});
for &(mut ty, is_target_ty) in &tys {
let span = if matches!(is_target_ty, IsFirstInputType::Yes) {
// Point at `D<A>` in `impl<A, B> for C<B> in D<A>`
impl_.self_ty.span
} else {
// Point at `C<B>` in `impl<A, B> for C<B> in D<A>`
hir_trait_ref.path.span
};
ty = tcx.erase_regions(ty);
let is_foreign =
!trait_ref.def_id.is_local() && matches!(is_target_ty, IsFirstInputType::No);
match *ty.kind() {
ty::Slice(_) => {
if is_foreign {
diag.subdiagnostic(errors::OnlyCurrentTraitsForeign { span });
} else {
diag.subdiagnostic(errors::OnlyCurrentTraitsName {
span,
name: "slices",
});
}
}
ty::Array(..) => {
if is_foreign {
diag.subdiagnostic(errors::OnlyCurrentTraitsForeign { span });
} else {
diag.subdiagnostic(errors::OnlyCurrentTraitsName {
span,
name: "arrays",
});
}
}
ty::Tuple(..) => {
if is_foreign {
diag.subdiagnostic(errors::OnlyCurrentTraitsForeign { span });
} else {
diag.subdiagnostic(errors::OnlyCurrentTraitsName {
span,
name: "tuples",
});
}
}
ty::Alias(ty::Opaque, ..) => {
diag.subdiagnostic(errors::OnlyCurrentTraitsOpaque { span });
}
ty::RawPtr(ptr_ty, mutbl) => {
if !trait_ref.self_ty().has_param() {
diag.subdiagnostic(errors::OnlyCurrentTraitsPointerSugg {
wrapper_span: impl_.self_ty.span,
struct_span: item.span.shrink_to_lo(),
mut_key: mutbl.prefix_str(),
ptr_ty,
});
}
diag.subdiagnostic(errors::OnlyCurrentTraitsPointer { span, pointer: ty });
}
ty::Adt(adt_def, _) => {
diag.subdiagnostic(errors::OnlyCurrentTraitsAdt {
span,
name: tcx.def_path_str(adt_def.did()),
});
}
_ => {
diag.subdiagnostic(errors::OnlyCurrentTraitsTy { span, ty });
}
}
}
diag.emit()
}
traits::OrphanCheckErr::UncoveredTyParams(UncoveredTyParams { uncovered, local_ty }) => {
let mut reported = None;
for param_def_id in uncovered {
let span = tcx.def_ident_span(param_def_id).unwrap();
let name = tcx.item_name(param_def_id);
reported.get_or_insert(match local_ty {
Some(local_type) => tcx.dcx().emit_err(errors::TyParamFirstLocal {
span,
note: (),
param: name,
local_type,
}),
None => tcx.dcx().emit_err(errors::TyParamSome { span, note: (), param: name }),
});
}
reported.unwrap() // FIXME(fmease): This is very likely reachable.
}
}
}
fn lint_uncovered_ty_params<'tcx>(
tcx: TyCtxt<'tcx>,
UncoveredTyParams { uncovered, local_ty }: UncoveredTyParams<TyCtxt<'tcx>, FxIndexSet<DefId>>,
impl_def_id: LocalDefId,
) {
let hir_id = tcx.local_def_id_to_hir_id(impl_def_id);
for param_def_id in uncovered {
let span = tcx.def_ident_span(param_def_id).unwrap();
let name = tcx.item_name(param_def_id);
match local_ty {
Some(local_type) => tcx.emit_node_span_lint(
UNCOVERED_PARAM_IN_PROJECTION,
hir_id,
span,
errors::TyParamFirstLocalLint { span, note: (), param: name, local_type },
),
None => tcx.emit_node_span_lint(
UNCOVERED_PARAM_IN_PROJECTION,
hir_id,
span,
errors::TyParamSomeLint { span, note: (), param: name },
),
};
}
}
struct UncoveredTyParamCollector<'cx, 'tcx> {
infcx: &'cx InferCtxt<'tcx>,
uncovered_params: FxIndexSet<DefId>,
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for UncoveredTyParamCollector<'_, 'tcx> {
fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
if !ty.has_type_flags(ty::TypeFlags::HAS_TY_INFER) {
return;
}
let ty::Infer(ty::TyVar(vid)) = *ty.kind() else {
return ty.super_visit_with(self);
};
let origin = self.infcx.type_var_origin(vid);
if let Some(def_id) = origin.param_def_id {
self.uncovered_params.insert(def_id);
}
}
fn visit_const(&mut self, ct: ty::Const<'tcx>) -> Self::Result {
if ct.has_type_flags(ty::TypeFlags::HAS_TY_INFER) {
ct.super_visit_with(self)
}
}
}
struct TyVarReplacer<'cx, 'tcx> {
infcx: &'cx InferCtxt<'tcx>,
generics: &'tcx ty::Generics,
}
impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for TyVarReplacer<'cx, 'tcx> {
fn cx(&self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
if !ty.has_type_flags(ty::TypeFlags::HAS_TY_INFER) {
return ty;
}
let ty::Infer(ty::TyVar(vid)) = *ty.kind() else {
return ty.super_fold_with(self);
};
let origin = self.infcx.type_var_origin(vid);
if let Some(def_id) = origin.param_def_id {
// The generics of an `impl` don't have a parent, we can index directly.
let index = self.generics.param_def_id_to_index[&def_id];
let name = self.generics.own_params[index as usize].name;
Ty::new_param(self.infcx.tcx, index, name)
} else {
ty
}
}
fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
if !ct.has_type_flags(ty::TypeFlags::HAS_TY_INFER) {
return ct;
}
ct.super_fold_with(self)
}
}