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Uplift trait_ref_is_knowable and friends

This commit is contained in:
Michael Goulet 2024-07-06 18:24:51 -04:00
parent b2e30bdec4
commit a982471e07
13 changed files with 508 additions and 458 deletions
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15
compiler/rustc_hir_analysis/src/coherence/orphan.rs
View File

@ -286,7 +286,7 @@ fn orphan_check<'tcx>(
tcx: TyCtxt<'tcx>,
impl_def_id: LocalDefId,
mode: OrphanCheckMode,
) -> Result<(), OrphanCheckErr<'tcx, FxIndexSet<DefId>>> {
) -> 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();
@ -326,17 +326,16 @@ fn orphan_check<'tcx>(
ty
};
Ok(ty)
Ok::<_, !>(ty)
};
let Ok(result) = traits::orphan_check_trait_ref::<!>(
let result = traits::orphan_check_trait_ref(
&infcx,
trait_ref,
traits::InCrate::Local { mode },
lazily_normalize_ty,
) else {
unreachable!()
};
)
.into_ok();
// (2) Try to map the remaining inference vars back to generic params.
result.map_err(|err| match err {
@ -369,7 +368,7 @@ fn emit_orphan_check_error<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::TraitRef<'tcx>,
impl_def_id: LocalDefId,
err: traits::OrphanCheckErr<'tcx, FxIndexSet<DefId>>,
err: traits::OrphanCheckErr<TyCtxt<'tcx>, FxIndexSet<DefId>>,
) -> ErrorGuaranteed {
match err {
traits::OrphanCheckErr::NonLocalInputType(tys) => {
@ -482,7 +481,7 @@ fn emit_orphan_check_error<'tcx>(
fn lint_uncovered_ty_params<'tcx>(
tcx: TyCtxt<'tcx>,
UncoveredTyParams { uncovered, local_ty }: UncoveredTyParams<'tcx, FxIndexSet<DefId>>,
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);

1
compiler/rustc_hir_analysis/src/lib.rs
View File

@ -71,6 +71,7 @@ This API is completely unstable and subject to change.
#![feature(rustdoc_internals)]
#![feature(slice_partition_dedup)]
#![feature(try_blocks)]
#![feature(unwrap_infallible)]
// tidy-alphabetical-end
#[macro_use]

4
compiler/rustc_infer/src/infer/context.rs
View File

@ -151,6 +151,10 @@ impl<'tcx> InferCtxtLike for InferCtxt<'tcx> {
.eq_structurally_relating_aliases_no_trace(lhs, rhs)
}
fn shallow_resolve(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
self.shallow_resolve(ty)
}
fn resolve_vars_if_possible<T>(&self, value: T) -> T
where
T: TypeFoldable<TyCtxt<'tcx>>,

4
compiler/rustc_middle/src/ty/adt.rs
View File

@ -229,6 +229,10 @@ impl<'tcx> rustc_type_ir::inherent::AdtDef<TyCtxt<'tcx>> for AdtDef<'tcx> {
fn sized_constraint(self, tcx: TyCtxt<'tcx>) -> Option<ty::EarlyBinder<'tcx, Ty<'tcx>>> {
self.sized_constraint(tcx)
}
fn is_fundamental(self) -> bool {
self.is_fundamental()
}
}
#[derive(Copy, Clone, Debug, Eq, PartialEq, HashStable, TyEncodable, TyDecodable)]

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

@ -524,6 +524,10 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
self.is_object_safe(trait_def_id)
}
fn trait_is_fundamental(self, def_id: DefId) -> bool {
self.trait_def(def_id).is_fundamental
}
fn trait_may_be_implemented_via_object(self, trait_def_id: DefId) -> bool {
self.trait_def(trait_def_id).implement_via_object
}
@ -635,6 +639,10 @@ bidirectional_lang_item_map! {
}
impl<'tcx> rustc_type_ir::inherent::DefId<TyCtxt<'tcx>> for DefId {
fn is_local(self) -> bool {
self.is_local()
}
fn as_local(self) -> Option<LocalDefId> {
self.as_local()
}

469
compiler/rustc_next_trait_solver/src/coherence.rs Normal file
View File

@ -0,0 +1,469 @@
use std::fmt::Debug;
use std::ops::ControlFlow;
use rustc_type_ir::inherent::*;
use rustc_type_ir::visit::{TypeVisitable, TypeVisitableExt, TypeVisitor};
use rustc_type_ir::{self as ty, InferCtxtLike, Interner};
use tracing::instrument;
/// Whether we do the orphan check relative to this crate or to some remote crate.
#[derive(Copy, Clone, Debug)]
pub enum InCrate {
Local { mode: OrphanCheckMode },
Remote,
}
#[derive(Copy, Clone, Debug)]
pub enum OrphanCheckMode {
/// Proper orphan check.
Proper,
/// Improper orphan check for backward compatibility.
///
/// In this mode, type params inside projections are considered to be covered
/// even if the projection may normalize to a type that doesn't actually cover
/// them. This is unsound. See also [#124559] and [#99554].
///
/// [#124559]: https://github.com/rust-lang/rust/issues/124559
/// [#99554]: https://github.com/rust-lang/rust/issues/99554
Compat,
}
#[derive(Debug, Copy, Clone)]
pub enum Conflict {
Upstream,
Downstream,
}
/// Returns whether all impls which would apply to the `trait_ref`
/// e.g. `Ty: Trait<Arg>` are already known in the local crate.
///
/// This both checks whether any downstream or sibling crates could
/// implement it and whether an upstream crate can add this impl
/// without breaking backwards compatibility.
#[instrument(level = "debug", skip(infcx, lazily_normalize_ty), ret)]
pub fn trait_ref_is_knowable<Infcx, I, E>(
infcx: &Infcx,
trait_ref: ty::TraitRef<I>,
mut lazily_normalize_ty: impl FnMut(I::Ty) -> Result<I::Ty, E>,
) -> Result<Result<(), Conflict>, E>
where
Infcx: InferCtxtLike<Interner = I>,
I: Interner,
E: Debug,
{
if orphan_check_trait_ref(infcx, trait_ref, InCrate::Remote, &mut lazily_normalize_ty)?.is_ok()
{
// A downstream or cousin crate is allowed to implement some
// generic parameters of this trait-ref.
return Ok(Err(Conflict::Downstream));
}
if trait_ref_is_local_or_fundamental(infcx.cx(), trait_ref) {
// This is a local or fundamental trait, so future-compatibility
// is no concern. We know that downstream/cousin crates are not
// allowed to implement a generic parameter of this trait ref,
// which means impls could only come from dependencies of this
// crate, which we already know about.
return Ok(Ok(()));
}
// This is a remote non-fundamental trait, so if another crate
// can be the "final owner" of the generic parameters of this trait-ref,
// they are allowed to implement it future-compatibly.
//
// However, if we are a final owner, then nobody else can be,
// and if we are an intermediate owner, then we don't care
// about future-compatibility, which means that we're OK if
// we are an owner.
if orphan_check_trait_ref(
infcx,
trait_ref,
InCrate::Local { mode: OrphanCheckMode::Proper },
&mut lazily_normalize_ty,
)?
.is_ok()
{
Ok(Ok(()))
} else {
Ok(Err(Conflict::Upstream))
}
}
pub fn trait_ref_is_local_or_fundamental<I: Interner>(tcx: I, trait_ref: ty::TraitRef<I>) -> bool {
trait_ref.def_id.is_local() || tcx.trait_is_fundamental(trait_ref.def_id)
}
#[derive(Debug, Copy, Clone)]
pub enum IsFirstInputType {
No,
Yes,
}
impl From<bool> for IsFirstInputType {
fn from(b: bool) -> IsFirstInputType {
match b {
false => IsFirstInputType::No,
true => IsFirstInputType::Yes,
}
}
}
#[derive(derivative::Derivative)]
#[derivative(Debug(bound = "T: Debug"))]
pub enum OrphanCheckErr<I: Interner, T> {
NonLocalInputType(Vec<(I::Ty, IsFirstInputType)>),
UncoveredTyParams(UncoveredTyParams<I, T>),
}
#[derive(derivative::Derivative)]
#[derivative(Debug(bound = "T: Debug"))]
pub struct UncoveredTyParams<I: Interner, T> {
pub uncovered: T,
pub local_ty: Option<I::Ty>,
}
/// Checks whether a trait-ref is potentially implementable by a crate.
///
/// The current rule is that a trait-ref orphan checks in a crate C:
///
/// 1. Order the parameters in the trait-ref in generic parameters order
/// - Self first, others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
/// 2. Of these type parameters, there is at least one type parameter
/// in which, walking the type as a tree, you can reach a type local
/// to C where all types in-between are fundamental types. Call the
/// first such parameter the "local key parameter".
/// - e.g., `Box<LocalType>` is OK, because you can visit LocalType
/// going through `Box`, which is fundamental.
/// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
/// the same reason.
/// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
/// not local), `Vec<LocalType>` is bad, because `Vec<->` is between
/// the local type and the type parameter.
/// 3. Before this local type, no generic type parameter of the impl must
/// be reachable through fundamental types.
/// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
/// - while `impl<T> Trait<LocalType> for Box<T>` results in an error, as `T` is
/// reachable through the fundamental type `Box`.
/// 4. Every type in the local key parameter not known in C, going
/// through the parameter's type tree, must appear only as a subtree of
/// a type local to C, with only fundamental types between the type
/// local to C and the local key parameter.
/// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
/// is bad, because the only local type with `T` as a subtree is
/// `LocalType<T>`, and `Vec<->` is between it and the type parameter.
/// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
/// the second occurrence of `T` is not a subtree of *any* local type.
/// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
/// `LocalType<Vec<T>>`, which is local and has no types between it and
/// the type parameter.
///
/// The orphan rules actually serve several different purposes:
///
/// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
/// every type local to one crate is unknown in the other) can't implement
/// the same trait-ref. This follows because it can be seen that no such
/// type can orphan-check in 2 such crates.
///
/// To check that a local impl follows the orphan rules, we check it in
/// InCrate::Local mode, using type parameters for the "generic" types.
///
/// In InCrate::Local mode the orphan check succeeds if the current crate
/// is definitely allowed to implement the given trait (no false positives).
///
/// 2. They ground negative reasoning for coherence. If a user wants to
/// write both a conditional blanket impl and a specific impl, we need to
/// make sure they do not overlap. For example, if we write
/// ```ignore (illustrative)
/// impl<T> IntoIterator for Vec<T>
/// impl<T: Iterator> IntoIterator for T
/// ```
/// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
/// We can observe that this holds in the current crate, but we need to make
/// sure this will also hold in all unknown crates (both "independent" crates,
/// which we need for link-safety, and also child crates, because we don't want
/// child crates to get error for impl conflicts in a *dependency*).
///
/// For that, we only allow negative reasoning if, for every assignment to the
/// inference variables, every unknown crate would get an orphan error if they
/// try to implement this trait-ref. To check for this, we use InCrate::Remote
/// mode. That is sound because we already know all the impls from known crates.
///
/// In InCrate::Remote mode the orphan check succeeds if a foreign crate
/// *could* implement the given trait (no false negatives).
///
/// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
/// add "non-blanket" impls without breaking negative reasoning in dependent
/// crates. This is the "rebalancing coherence" (RFC 1023) restriction.
///
/// For that, we only allow a crate to perform negative reasoning on
/// non-local-non-`#[fundamental]` if there's a local key parameter as per (2).
///
/// Because we never perform negative reasoning generically (coherence does
/// not involve type parameters), this can be interpreted as doing the full
/// orphan check (using InCrate::Local mode), instantiating non-local known
/// types for all inference variables.
///
/// This allows for crates to future-compatibly add impls as long as they
/// can't apply to types with a key parameter in a child crate - applying
/// the rules, this basically means that every type parameter in the impl
/// must appear behind a non-fundamental type (because this is not a
/// type-system requirement, crate owners might also go for "semantic
/// future-compatibility" involving things such as sealed traits, but
/// the above requirement is sufficient, and is necessary in "open world"
/// cases).
///
/// Note that this function is never called for types that have both type
/// parameters and inference variables.
#[instrument(level = "trace", skip(infcx, lazily_normalize_ty), ret)]
pub fn orphan_check_trait_ref<Infcx, I, E: Debug>(
infcx: &Infcx,
trait_ref: ty::TraitRef<I>,
in_crate: InCrate,
lazily_normalize_ty: impl FnMut(I::Ty) -> Result<I::Ty, E>,
) -> Result<Result<(), OrphanCheckErr<I, I::Ty>>, E>
where
Infcx: InferCtxtLike<Interner = I>,
I: Interner,
E: Debug,
{
if trait_ref.has_param() {
panic!("orphan check only expects inference variables: {trait_ref:?}");
}
let mut checker = OrphanChecker::new(infcx, in_crate, lazily_normalize_ty);
Ok(match trait_ref.visit_with(&mut checker) {
ControlFlow::Continue(()) => Err(OrphanCheckErr::NonLocalInputType(checker.non_local_tys)),
ControlFlow::Break(residual) => match residual {
OrphanCheckEarlyExit::NormalizationFailure(err) => return Err(err),
OrphanCheckEarlyExit::UncoveredTyParam(ty) => {
// Does there exist some local type after the `ParamTy`.
checker.search_first_local_ty = true;
let local_ty = match trait_ref.visit_with(&mut checker) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(local_ty)) => Some(local_ty),
_ => None,
};
Err(OrphanCheckErr::UncoveredTyParams(UncoveredTyParams {
uncovered: ty,
local_ty,
}))
}
OrphanCheckEarlyExit::LocalTy(_) => Ok(()),
},
})
}
struct OrphanChecker<'a, Infcx, I: Interner, F> {
infcx: &'a Infcx,
in_crate: InCrate,
in_self_ty: bool,
lazily_normalize_ty: F,
/// Ignore orphan check failures and exclusively search for the first local type.
search_first_local_ty: bool,
non_local_tys: Vec<(I::Ty, IsFirstInputType)>,
}
impl<'a, Infcx, I, F, E> OrphanChecker<'a, Infcx, I, F>
where
Infcx: InferCtxtLike<Interner = I>,
I: Interner,
F: FnOnce(I::Ty) -> Result<I::Ty, E>,
{
fn new(infcx: &'a Infcx, in_crate: InCrate, lazily_normalize_ty: F) -> Self {
OrphanChecker {
infcx,
in_crate,
in_self_ty: true,
lazily_normalize_ty,
search_first_local_ty: false,
non_local_tys: Vec::new(),
}
}
fn found_non_local_ty(&mut self, t: I::Ty) -> ControlFlow<OrphanCheckEarlyExit<I, E>> {
self.non_local_tys.push((t, self.in_self_ty.into()));
ControlFlow::Continue(())
}
fn found_uncovered_ty_param(&mut self, ty: I::Ty) -> ControlFlow<OrphanCheckEarlyExit<I, E>> {
if self.search_first_local_ty {
return ControlFlow::Continue(());
}
ControlFlow::Break(OrphanCheckEarlyExit::UncoveredTyParam(ty))
}
fn def_id_is_local(&mut self, def_id: I::DefId) -> bool {
match self.in_crate {
InCrate::Local { .. } => def_id.is_local(),
InCrate::Remote => false,
}
}
}
enum OrphanCheckEarlyExit<I: Interner, E> {
NormalizationFailure(E),
UncoveredTyParam(I::Ty),
LocalTy(I::Ty),
}
impl<'a, Infcx, I, F, E> TypeVisitor<I> for OrphanChecker<'a, Infcx, I, F>
where
Infcx: InferCtxtLike<Interner = I>,
I: Interner,
F: FnMut(I::Ty) -> Result<I::Ty, E>,
{
type Result = ControlFlow<OrphanCheckEarlyExit<I, E>>;
fn visit_region(&mut self, _r: I::Region) -> Self::Result {
ControlFlow::Continue(())
}
fn visit_ty(&mut self, ty: I::Ty) -> Self::Result {
let ty = self.infcx.shallow_resolve(ty);
let ty = match (self.lazily_normalize_ty)(ty) {
Ok(norm_ty) if norm_ty.is_ty_var() => ty,
Ok(norm_ty) => norm_ty,
Err(err) => return ControlFlow::Break(OrphanCheckEarlyExit::NormalizationFailure(err)),
};
let result = match ty.kind() {
ty::Bool
| ty::Char
| ty::Int(..)
| ty::Uint(..)
| ty::Float(..)
| ty::Str
| ty::FnDef(..)
| ty::Pat(..)
| ty::FnPtr(_)
| ty::Array(..)
| ty::Slice(..)
| ty::RawPtr(..)
| ty::Never
| ty::Tuple(..) => self.found_non_local_ty(ty),
ty::Param(..) => panic!("unexpected ty param"),
ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => {
match self.in_crate {
InCrate::Local { .. } => self.found_uncovered_ty_param(ty),
// The inference variable might be unified with a local
// type in that remote crate.
InCrate::Remote => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
}
}
// A rigid alias may normalize to anything.
// * If it references an infer var, placeholder or bound ty, it may
// normalize to that, so we have to treat it as an uncovered ty param.
// * Otherwise it may normalize to any non-type-generic type
// be it local or non-local.
ty::Alias(kind, _) => {
if ty.has_type_flags(
ty::TypeFlags::HAS_TY_PLACEHOLDER
| ty::TypeFlags::HAS_TY_BOUND
| ty::TypeFlags::HAS_TY_INFER,
) {
match self.in_crate {
InCrate::Local { mode } => match kind {
ty::Projection => {
if let OrphanCheckMode::Compat = mode {
ControlFlow::Continue(())
} else {
self.found_uncovered_ty_param(ty)
}
}
_ => self.found_uncovered_ty_param(ty),
},
InCrate::Remote => {
// The inference variable might be unified with a local
// type in that remote crate.
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
}
}
} else {
// Regarding *opaque types* specifically, we choose to treat them as non-local,
// even those that appear within the same crate. This seems somewhat surprising
// at first, but makes sense when you consider that opaque types are supposed
// to hide the underlying type *within the same crate*. When an opaque type is
// used from outside the module where it is declared, it should be impossible to
// observe anything about it other than the traits that it implements.
//
// The alternative would be to look at the underlying type to determine whether
// or not the opaque type itself should be considered local.
//
// However, this could make it a breaking change to switch the underlying hidden
// type from a local type to a remote type. This would violate the rule that
// opaque types should be completely opaque apart from the traits that they
// implement, so we don't use this behavior.
// Addendum: Moreover, revealing the underlying type is likely to cause cycle
// errors as we rely on coherence / the specialization graph during typeck.
self.found_non_local_ty(ty)
}
}
// For fundamental types, we just look inside of them.
ty::Ref(_, ty, _) => ty.visit_with(self),
ty::Adt(def, args) => {
if self.def_id_is_local(def.def_id()) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
} else if def.is_fundamental() {
args.visit_with(self)
} else {
self.found_non_local_ty(ty)
}
}
ty::Foreign(def_id) => {
if self.def_id_is_local(def_id) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
} else {
self.found_non_local_ty(ty)
}
}
ty::Dynamic(tt, ..) => {
let principal = tt.principal().map(|p| p.def_id());
if principal.is_some_and(|p| self.def_id_is_local(p)) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
} else {
self.found_non_local_ty(ty)
}
}
ty::Error(_) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
ty::Closure(did, ..) | ty::CoroutineClosure(did, ..) | ty::Coroutine(did, ..) => {
if self.def_id_is_local(did) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
} else {
self.found_non_local_ty(ty)
}
}
// This should only be created when checking whether we have to check whether some
// auto trait impl applies. There will never be multiple impls, so we can just
// act as if it were a local type here.
ty::CoroutineWitness(..) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
};
// A bit of a hack, the `OrphanChecker` is only used to visit a `TraitRef`, so
// the first type we visit is always the self type.
self.in_self_ty = false;
result
}
/// All possible values for a constant parameter already exist
/// in the crate defining the trait, so they are always non-local[^1].
///
/// Because there's no way to have an impl where the first local
/// generic argument is a constant, we also don't have to fail
/// the orphan check when encountering a parameter or a generic constant.
///
/// This means that we can completely ignore constants during the orphan check.
///
/// See `tests/ui/coherence/const-generics-orphan-check-ok.rs` for examples.
///
/// [^1]: This might not hold for function pointers or trait objects in the future.
/// As these should be quite rare as const arguments and especially rare as impl
/// parameters, allowing uncovered const parameters in impls seems more useful
/// than allowing `impl<T> Trait<local_fn_ptr, T> for i32` to compile.
fn visit_const(&mut self, _c: I::Const) -> Self::Result {
ControlFlow::Continue(())
}
}

1
compiler/rustc_next_trait_solver/src/lib.rs
View File

@ -5,6 +5,7 @@
//! So if you got to this crate from the old solver, it's totally normal.
pub mod canonicalizer;
pub mod coherence;
pub mod delegate;
pub mod relate;
pub mod resolve;

1
compiler/rustc_trait_selection/src/lib.rs
View File

@ -26,6 +26,7 @@
#![feature(never_type)]
#![feature(rustdoc_internals)]
#![feature(type_alias_impl_trait)]
#![feature(unwrap_infallible)]
#![recursion_limit = "512"] // For rustdoc
// tidy-alphabetical-end

450
compiler/rustc_trait_selection/src/traits/coherence.rs
View File

@ -25,42 +25,14 @@ use rustc_middle::traits::specialization_graph::OverlapMode;
use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};
use rustc_middle::ty::{self, Ty, TyCtxt};
pub use rustc_next_trait_solver::coherence::*;
use rustc_span::symbol::sym;
use rustc_span::{Span, DUMMY_SP};
use std::fmt::Debug;
use std::ops::ControlFlow;
use super::error_reporting::suggest_new_overflow_limit;
use super::ObligationCtxt;
/// Whether we do the orphan check relative to this crate or to some remote crate.
#[derive(Copy, Clone, Debug)]
pub enum InCrate {
Local { mode: OrphanCheckMode },
Remote,
}
#[derive(Copy, Clone, Debug)]
pub enum OrphanCheckMode {
/// Proper orphan check.
Proper,
/// Improper orphan check for backward compatibility.
///
/// In this mode, type params inside projections are considered to be covered
/// even if the projection may normalize to a type that doesn't actually cover
/// them. This is unsound. See also [#124559] and [#99554].
///
/// [#124559]: https://github.com/rust-lang/rust/issues/124559
/// [#99554]: https://github.com/rust-lang/rust/issues/99554
Compat,
}
#[derive(Debug, Copy, Clone)]
pub enum Conflict {
Upstream,
Downstream,
}
pub struct OverlapResult<'tcx> {
pub impl_header: ty::ImplHeader<'tcx>,
pub intercrate_ambiguity_causes: FxIndexSet<IntercrateAmbiguityCause<'tcx>>,
@ -612,426 +584,6 @@ fn try_prove_negated_where_clause<'tcx>(
true
}
/// Returns whether all impls which would apply to the `trait_ref`
/// e.g. `Ty: Trait<Arg>` are already known in the local crate.
///
/// This both checks whether any downstream or sibling crates could
/// implement it and whether an upstream crate can add this impl
/// without breaking backwards compatibility.
#[instrument(level = "debug", skip(infcx, lazily_normalize_ty), ret)]
pub fn trait_ref_is_knowable<'tcx, E: Debug>(
infcx: &InferCtxt<'tcx>,
trait_ref: ty::TraitRef<'tcx>,
mut lazily_normalize_ty: impl FnMut(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
) -> Result<Result<(), Conflict>, E> {
if orphan_check_trait_ref(infcx, trait_ref, InCrate::Remote, &mut lazily_normalize_ty)?.is_ok()
{
// A downstream or cousin crate is allowed to implement some
// generic parameters of this trait-ref.
return Ok(Err(Conflict::Downstream));
}
if trait_ref_is_local_or_fundamental(infcx.tcx, trait_ref) {
// This is a local or fundamental trait, so future-compatibility
// is no concern. We know that downstream/cousin crates are not
// allowed to implement a generic parameter of this trait ref,
// which means impls could only come from dependencies of this
// crate, which we already know about.
return Ok(Ok(()));
}
// This is a remote non-fundamental trait, so if another crate
// can be the "final owner" of the generic parameters of this trait-ref,
// they are allowed to implement it future-compatibly.
//
// However, if we are a final owner, then nobody else can be,
// and if we are an intermediate owner, then we don't care
// about future-compatibility, which means that we're OK if
// we are an owner.
if orphan_check_trait_ref(
infcx,
trait_ref,
InCrate::Local { mode: OrphanCheckMode::Proper },
&mut lazily_normalize_ty,
)?
.is_ok()
{
Ok(Ok(()))
} else {
Ok(Err(Conflict::Upstream))
}
}
pub fn trait_ref_is_local_or_fundamental<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::TraitRef<'tcx>,
) -> bool {
trait_ref.def_id.is_local() || tcx.trait_def(trait_ref.def_id).is_fundamental
}
#[derive(Debug, Copy, Clone)]
pub enum IsFirstInputType {
No,
Yes,
}
impl From<bool> for IsFirstInputType {
fn from(b: bool) -> IsFirstInputType {
match b {
false => IsFirstInputType::No,
true => IsFirstInputType::Yes,
}
}
}
#[derive(Debug)]
pub enum OrphanCheckErr<'tcx, T> {
NonLocalInputType(Vec<(Ty<'tcx>, IsFirstInputType)>),
UncoveredTyParams(UncoveredTyParams<'tcx, T>),
}
#[derive(Debug)]
pub struct UncoveredTyParams<'tcx, T> {
pub uncovered: T,
pub local_ty: Option<Ty<'tcx>>,
}
/// Checks whether a trait-ref is potentially implementable by a crate.
///
/// The current rule is that a trait-ref orphan checks in a crate C:
///
/// 1. Order the parameters in the trait-ref in generic parameters order
/// - Self first, others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
/// 2. Of these type parameters, there is at least one type parameter
/// in which, walking the type as a tree, you can reach a type local
/// to C where all types in-between are fundamental types. Call the
/// first such parameter the "local key parameter".
/// - e.g., `Box<LocalType>` is OK, because you can visit LocalType
/// going through `Box`, which is fundamental.
/// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
/// the same reason.
/// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
/// not local), `Vec<LocalType>` is bad, because `Vec<->` is between
/// the local type and the type parameter.
/// 3. Before this local type, no generic type parameter of the impl must
/// be reachable through fundamental types.
/// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
/// - while `impl<T> Trait<LocalType> for Box<T>` results in an error, as `T` is
/// reachable through the fundamental type `Box`.
/// 4. Every type in the local key parameter not known in C, going
/// through the parameter's type tree, must appear only as a subtree of
/// a type local to C, with only fundamental types between the type
/// local to C and the local key parameter.
/// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
/// is bad, because the only local type with `T` as a subtree is
/// `LocalType<T>`, and `Vec<->` is between it and the type parameter.
/// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
/// the second occurrence of `T` is not a subtree of *any* local type.
/// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
/// `LocalType<Vec<T>>`, which is local and has no types between it and
/// the type parameter.
///
/// The orphan rules actually serve several different purposes:
///
/// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
/// every type local to one crate is unknown in the other) can't implement
/// the same trait-ref. This follows because it can be seen that no such
/// type can orphan-check in 2 such crates.
///
/// To check that a local impl follows the orphan rules, we check it in
/// InCrate::Local mode, using type parameters for the "generic" types.
///
/// In InCrate::Local mode the orphan check succeeds if the current crate
/// is definitely allowed to implement the given trait (no false positives).
///
/// 2. They ground negative reasoning for coherence. If a user wants to
/// write both a conditional blanket impl and a specific impl, we need to
/// make sure they do not overlap. For example, if we write
/// ```ignore (illustrative)
/// impl<T> IntoIterator for Vec<T>
/// impl<T: Iterator> IntoIterator for T
/// ```
/// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
/// We can observe that this holds in the current crate, but we need to make
/// sure this will also hold in all unknown crates (both "independent" crates,
/// which we need for link-safety, and also child crates, because we don't want
/// child crates to get error for impl conflicts in a *dependency*).
///
/// For that, we only allow negative reasoning if, for every assignment to the
/// inference variables, every unknown crate would get an orphan error if they
/// try to implement this trait-ref. To check for this, we use InCrate::Remote
/// mode. That is sound because we already know all the impls from known crates.
///
/// In InCrate::Remote mode the orphan check succeeds if a foreign crate
/// *could* implement the given trait (no false negatives).
///
/// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
/// add "non-blanket" impls without breaking negative reasoning in dependent
/// crates. This is the "rebalancing coherence" (RFC 1023) restriction.
///
/// For that, we only allow a crate to perform negative reasoning on
/// non-local-non-`#[fundamental]` if there's a local key parameter as per (2).
///
/// Because we never perform negative reasoning generically (coherence does
/// not involve type parameters), this can be interpreted as doing the full
/// orphan check (using InCrate::Local mode), instantiating non-local known
/// types for all inference variables.
///
/// This allows for crates to future-compatibly add impls as long as they
/// can't apply to types with a key parameter in a child crate - applying
/// the rules, this basically means that every type parameter in the impl
/// must appear behind a non-fundamental type (because this is not a
/// type-system requirement, crate owners might also go for "semantic
/// future-compatibility" involving things such as sealed traits, but
/// the above requirement is sufficient, and is necessary in "open world"
/// cases).
///
/// Note that this function is never called for types that have both type
/// parameters and inference variables.
#[instrument(level = "trace", skip(infcx, lazily_normalize_ty), ret)]
pub fn orphan_check_trait_ref<'tcx, E: Debug>(
infcx: &InferCtxt<'tcx>,
trait_ref: ty::TraitRef<'tcx>,
in_crate: InCrate,
lazily_normalize_ty: impl FnMut(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
) -> Result<Result<(), OrphanCheckErr<'tcx, Ty<'tcx>>>, E> {
if trait_ref.has_param() {
bug!("orphan check only expects inference variables: {trait_ref:?}");
}
let mut checker = OrphanChecker::new(infcx, in_crate, lazily_normalize_ty);
Ok(match trait_ref.visit_with(&mut checker) {
ControlFlow::Continue(()) => Err(OrphanCheckErr::NonLocalInputType(checker.non_local_tys)),
ControlFlow::Break(residual) => match residual {
OrphanCheckEarlyExit::NormalizationFailure(err) => return Err(err),
OrphanCheckEarlyExit::UncoveredTyParam(ty) => {
// Does there exist some local type after the `ParamTy`.
checker.search_first_local_ty = true;
let local_ty = match trait_ref.visit_with(&mut checker).break_value() {
Some(OrphanCheckEarlyExit::LocalTy(local_ty)) => Some(local_ty),
_ => None,
};
Err(OrphanCheckErr::UncoveredTyParams(UncoveredTyParams {
uncovered: ty,
local_ty,
}))
}
OrphanCheckEarlyExit::LocalTy(_) => Ok(()),
},
})
}
struct OrphanChecker<'a, 'tcx, F> {
infcx: &'a InferCtxt<'tcx>,
in_crate: InCrate,
in_self_ty: bool,
lazily_normalize_ty: F,
/// Ignore orphan check failures and exclusively search for the first local type.
search_first_local_ty: bool,
non_local_tys: Vec<(Ty<'tcx>, IsFirstInputType)>,
}
impl<'a, 'tcx, F, E> OrphanChecker<'a, 'tcx, F>
where
F: FnOnce(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
{
fn new(infcx: &'a InferCtxt<'tcx>, in_crate: InCrate, lazily_normalize_ty: F) -> Self {
OrphanChecker {
infcx,
in_crate,
in_self_ty: true,
lazily_normalize_ty,
search_first_local_ty: false,
non_local_tys: Vec::new(),
}
}
fn found_non_local_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<OrphanCheckEarlyExit<'tcx, E>> {
self.non_local_tys.push((t, self.in_self_ty.into()));
ControlFlow::Continue(())
}
fn found_uncovered_ty_param(
&mut self,
ty: Ty<'tcx>,
) -> ControlFlow<OrphanCheckEarlyExit<'tcx, E>> {
if self.search_first_local_ty {
return ControlFlow::Continue(());
}
ControlFlow::Break(OrphanCheckEarlyExit::UncoveredTyParam(ty))
}
fn def_id_is_local(&mut self, def_id: DefId) -> bool {
match self.in_crate {
InCrate::Local { .. } => def_id.is_local(),
InCrate::Remote => false,
}
}
}
enum OrphanCheckEarlyExit<'tcx, E> {
NormalizationFailure(E),
UncoveredTyParam(Ty<'tcx>),
LocalTy(Ty<'tcx>),
}
impl<'a, 'tcx, F, E> TypeVisitor<TyCtxt<'tcx>> for OrphanChecker<'a, 'tcx, F>
where
F: FnMut(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
{
type Result = ControlFlow<OrphanCheckEarlyExit<'tcx, E>>;
fn visit_region(&mut self, _r: ty::Region<'tcx>) -> Self::Result {
ControlFlow::Continue(())
}
fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
let ty = self.infcx.shallow_resolve(ty);
let ty = match (self.lazily_normalize_ty)(ty) {
Ok(norm_ty) if norm_ty.is_ty_var() => ty,
Ok(norm_ty) => norm_ty,
Err(err) => return ControlFlow::Break(OrphanCheckEarlyExit::NormalizationFailure(err)),
};
let result = match *ty.kind() {
ty::Bool
| ty::Char
| ty::Int(..)
| ty::Uint(..)
| ty::Float(..)
| ty::Str
| ty::FnDef(..)
| ty::Pat(..)
| ty::FnPtr(_)
| ty::Array(..)
| ty::Slice(..)
| ty::RawPtr(..)
| ty::Never
| ty::Tuple(..) => self.found_non_local_ty(ty),
ty::Param(..) => bug!("unexpected ty param"),
ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => {
match self.in_crate {
InCrate::Local { .. } => self.found_uncovered_ty_param(ty),
// The inference variable might be unified with a local
// type in that remote crate.
InCrate::Remote => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
}
}
// A rigid alias may normalize to anything.
// * If it references an infer var, placeholder or bound ty, it may
// normalize to that, so we have to treat it as an uncovered ty param.
// * Otherwise it may normalize to any non-type-generic type
// be it local or non-local.
ty::Alias(kind, _) => {
if ty.has_type_flags(
ty::TypeFlags::HAS_TY_PLACEHOLDER
| ty::TypeFlags::HAS_TY_BOUND
| ty::TypeFlags::HAS_TY_INFER,
) {
match self.in_crate {
InCrate::Local { mode } => match kind {
ty::Projection if let OrphanCheckMode::Compat = mode => {
ControlFlow::Continue(())
}
_ => self.found_uncovered_ty_param(ty),
},
InCrate::Remote => {
// The inference variable might be unified with a local
// type in that remote crate.
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
}
}
} else {
// Regarding *opaque types* specifically, we choose to treat them as non-local,
// even those that appear within the same crate. This seems somewhat surprising
// at first, but makes sense when you consider that opaque types are supposed
// to hide the underlying type *within the same crate*. When an opaque type is
// used from outside the module where it is declared, it should be impossible to
// observe anything about it other than the traits that it implements.
//
// The alternative would be to look at the underlying type to determine whether
// or not the opaque type itself should be considered local.
//
// However, this could make it a breaking change to switch the underlying hidden
// type from a local type to a remote type. This would violate the rule that
// opaque types should be completely opaque apart from the traits that they
// implement, so we don't use this behavior.
// Addendum: Moreover, revealing the underlying type is likely to cause cycle
// errors as we rely on coherence / the specialization graph during typeck.
self.found_non_local_ty(ty)
}
}
// For fundamental types, we just look inside of them.
ty::Ref(_, ty, _) => ty.visit_with(self),
ty::Adt(def, args) => {
if self.def_id_is_local(def.did()) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
} else if def.is_fundamental() {
args.visit_with(self)
} else {
self.found_non_local_ty(ty)
}
}
ty::Foreign(def_id) => {
if self.def_id_is_local(def_id) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
} else {
self.found_non_local_ty(ty)
}
}
ty::Dynamic(tt, ..) => {
let principal = tt.principal().map(|p| p.def_id());
if principal.is_some_and(|p| self.def_id_is_local(p)) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
} else {
self.found_non_local_ty(ty)
}
}
ty::Error(_) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
ty::Closure(did, ..) | ty::CoroutineClosure(did, ..) | ty::Coroutine(did, ..) => {
if self.def_id_is_local(did) {
ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
} else {
self.found_non_local_ty(ty)
}
}
// This should only be created when checking whether we have to check whether some
// auto trait impl applies. There will never be multiple impls, so we can just
// act as if it were a local type here.
ty::CoroutineWitness(..) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)),
};
// A bit of a hack, the `OrphanChecker` is only used to visit a `TraitRef`, so
// the first type we visit is always the self type.
self.in_self_ty = false;
result
}
/// All possible values for a constant parameter already exist
/// in the crate defining the trait, so they are always non-local[^1].
///
/// Because there's no way to have an impl where the first local
/// generic argument is a constant, we also don't have to fail
/// the orphan check when encountering a parameter or a generic constant.
///
/// This means that we can completely ignore constants during the orphan check.
///
/// See `tests/ui/coherence/const-generics-orphan-check-ok.rs` for examples.
///
/// [^1]: This might not hold for function pointers or trait objects in the future.
/// As these should be quite rare as const arguments and especially rare as impl
/// parameters, allowing uncovered const parameters in impls seems more useful
/// than allowing `impl<T> Trait<local_fn_ptr, T> for i32` to compile.
fn visit_const(&mut self, _c: ty::Const<'tcx>) -> Self::Result {
ControlFlow::Continue(())
}
}
/// Compute the `intercrate_ambiguity_causes` for the new solver using
/// "proof trees".
///

2
compiler/rustc_trait_selection/src/traits/select/mod.rs
View File

@ -1523,7 +1523,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
// bound regions.
let trait_ref = predicate.skip_binder().trait_ref;
coherence::trait_ref_is_knowable::<!>(self.infcx, trait_ref, |ty| Ok(ty)).unwrap()
coherence::trait_ref_is_knowable(self.infcx, trait_ref, |ty| Ok::<_, !>(ty)).into_ok()
}
/// Returns `true` if the global caches can be used.

5
compiler/rustc_type_ir/src/infer_ctxt.rs
View File

@ -73,6 +73,11 @@ pub trait InferCtxtLike {
rhs: T,
) -> Result<Vec<Goal<Self::Interner, <Self::Interner as Interner>::Predicate>>, NoSolution>;
fn shallow_resolve(
&self,
ty: <Self::Interner as Interner>::Ty,
) -> <Self::Interner as Interner>::Ty;
fn resolve_vars_if_possible<T>(&self, value: T) -> T
where
T: TypeFoldable<Self::Interner>;

4
compiler/rustc_type_ir/src/inherent.rs
View File

@ -514,6 +514,8 @@ pub trait AdtDef<I: Interner>: Copy + Debug + Hash + Eq {
fn all_field_tys(self, interner: I) -> ty::EarlyBinder<I, impl IntoIterator<Item = I::Ty>>;
fn sized_constraint(self, interner: I) -> Option<ty::EarlyBinder<I, I::Ty>>;
fn is_fundamental(self) -> bool;
}
pub trait ParamEnv<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
@ -558,6 +560,8 @@ pub trait EvaluationCache<I: Interner> {
}
pub trait DefId<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
fn is_local(self) -> bool;
fn as_local(self) -> Option<I::LocalDefId>;
}

2
compiler/rustc_type_ir/src/interner.rs
View File

@ -246,6 +246,8 @@ pub trait Interner:
fn trait_is_object_safe(self, trait_def_id: Self::DefId) -> bool;
fn trait_is_fundamental(self, def_id: Self::DefId) -> bool;
fn trait_may_be_implemented_via_object(self, trait_def_id: Self::DefId) -> bool;
fn supertrait_def_ids(self, trait_def_id: Self::DefId)