rustc_next_trait_solver/solve/assembly/structural_traits.rs
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//! Code which is used by built-in goals that match "structurally", such a auto
//! traits, `Copy`/`Clone`.
use derive_where::derive_where;
use rustc_ast_ir::{Movability, Mutability};
use rustc_type_ir::data_structures::HashMap;
use rustc_type_ir::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
use rustc_type_ir::inherent::*;
use rustc_type_ir::lang_items::TraitSolverLangItem;
use rustc_type_ir::{self as ty, Interner, Upcast as _, elaborate};
use rustc_type_ir_macros::{TypeFoldable_Generic, TypeVisitable_Generic};
use tracing::instrument;
use crate::delegate::SolverDelegate;
use crate::solve::{AdtDestructorKind, EvalCtxt, Goal, NoSolution};
// Calculates the constituent types of a type for `auto trait` purposes.
#[instrument(level = "trace", skip(ecx), ret)]
pub(in crate::solve) fn instantiate_constituent_tys_for_auto_trait<D, I>(
ecx: &EvalCtxt<'_, D>,
ty: I::Ty,
) -> Result<Vec<ty::Binder<I, I::Ty>>, NoSolution>
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
let cx = ecx.cx();
match ty.kind() {
ty::Uint(_)
| ty::Int(_)
| ty::Bool
| ty::Float(_)
| ty::FnDef(..)
| ty::FnPtr(..)
| ty::Error(_)
| ty::Never
| ty::Char => Ok(vec![]),
// Treat `str` like it's defined as `struct str([u8]);`
ty::Str => Ok(vec![ty::Binder::dummy(Ty::new_slice(cx, Ty::new_u8(cx)))]),
ty::Dynamic(..)
| ty::Param(..)
| ty::Foreign(..)
| ty::Alias(ty::Projection | ty::Inherent | ty::Weak, ..)
| ty::Placeholder(..)
| ty::Bound(..)
| ty::Infer(_) => {
panic!("unexpected type `{ty:?}`")
}
ty::RawPtr(element_ty, _) | ty::Ref(_, element_ty, _) => {
Ok(vec![ty::Binder::dummy(element_ty)])
}
ty::Pat(element_ty, _) | ty::Array(element_ty, _) | ty::Slice(element_ty) => {
Ok(vec![ty::Binder::dummy(element_ty)])
}
ty::Tuple(tys) => {
// (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
Ok(tys.iter().map(ty::Binder::dummy).collect())
}
ty::Closure(_, args) => Ok(vec![ty::Binder::dummy(args.as_closure().tupled_upvars_ty())]),
ty::CoroutineClosure(_, args) => {
Ok(vec![ty::Binder::dummy(args.as_coroutine_closure().tupled_upvars_ty())])
}
ty::Coroutine(_, args) => {
let coroutine_args = args.as_coroutine();
Ok(vec![
ty::Binder::dummy(coroutine_args.tupled_upvars_ty()),
ty::Binder::dummy(coroutine_args.witness()),
])
}
ty::CoroutineWitness(def_id, args) => Ok(ecx
.cx()
.bound_coroutine_hidden_types(def_id)
.into_iter()
.map(|bty| bty.instantiate(cx, args))
.collect()),
// For `PhantomData<T>`, we pass `T`.
ty::Adt(def, args) if def.is_phantom_data() => Ok(vec![ty::Binder::dummy(args.type_at(0))]),
ty::Adt(def, args) => {
Ok(def.all_field_tys(cx).iter_instantiated(cx, args).map(ty::Binder::dummy).collect())
}
ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
// We can resolve the `impl Trait` to its concrete type,
// which enforces a DAG between the functions requiring
// the auto trait bounds in question.
Ok(vec![ty::Binder::dummy(cx.type_of(def_id).instantiate(cx, args))])
}
}
}
#[instrument(level = "trace", skip(ecx), ret)]
pub(in crate::solve) fn instantiate_constituent_tys_for_sized_trait<D, I>(
ecx: &EvalCtxt<'_, D>,
ty: I::Ty,
) -> Result<Vec<ty::Binder<I, I::Ty>>, NoSolution>
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
match ty.kind() {
// impl Sized for u*, i*, bool, f*, FnDef, FnPtr, *(const/mut) T, char, &mut? T, [T; N], dyn* Trait, !
// impl Sized for Coroutine, CoroutineWitness, Closure, CoroutineClosure
ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Uint(_)
| ty::Int(_)
| ty::Bool
| ty::Float(_)
| ty::FnDef(..)
| ty::FnPtr(..)
| ty::RawPtr(..)
| ty::Char
| ty::Ref(..)
| ty::Coroutine(..)
| ty::CoroutineWitness(..)
| ty::Array(..)
| ty::Pat(..)
| ty::Closure(..)
| ty::CoroutineClosure(..)
| ty::Never
| ty::Dynamic(_, _, ty::DynStar)
| ty::Error(_) => Ok(vec![]),
ty::Str
| ty::Slice(_)
| ty::Dynamic(..)
| ty::Foreign(..)
| ty::Alias(..)
| ty::Param(_)
| ty::Placeholder(..) => Err(NoSolution),
ty::Bound(..)
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
panic!("unexpected type `{ty:?}`")
}
// impl Sized for ()
// impl Sized for (T1, T2, .., Tn) where Tn: Sized if n >= 1
ty::Tuple(tys) => Ok(tys.last().map_or_else(Vec::new, |ty| vec![ty::Binder::dummy(ty)])),
// impl Sized for Adt<Args...> where sized_constraint(Adt)<Args...>: Sized
// `sized_constraint(Adt)` is the deepest struct trail that can be determined
// by the definition of `Adt`, independent of the generic args.
// impl Sized for Adt<Args...> if sized_constraint(Adt) == None
// As a performance optimization, `sized_constraint(Adt)` can return `None`
// if the ADTs definition implies that it is sized by for all possible args.
// In this case, the builtin impl will have no nested subgoals. This is a
// "best effort" optimization and `sized_constraint` may return `Some`, even
// if the ADT is sized for all possible args.
ty::Adt(def, args) => {
if let Some(sized_crit) = def.sized_constraint(ecx.cx()) {
Ok(vec![ty::Binder::dummy(sized_crit.instantiate(ecx.cx(), args))])
} else {
Ok(vec![])
}
}
}
}
#[instrument(level = "trace", skip(ecx), ret)]
pub(in crate::solve) fn instantiate_constituent_tys_for_copy_clone_trait<D, I>(
ecx: &EvalCtxt<'_, D>,
ty: I::Ty,
) -> Result<Vec<ty::Binder<I, I::Ty>>, NoSolution>
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
match ty.kind() {
// impl Copy/Clone for FnDef, FnPtr
ty::FnDef(..) | ty::FnPtr(..) | ty::Error(_) => Ok(vec![]),
// Implementations are provided in core
ty::Uint(_)
| ty::Int(_)
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Bool
| ty::Float(_)
| ty::Char
| ty::RawPtr(..)
| ty::Never
| ty::Ref(_, _, Mutability::Not)
| ty::Array(..) => Err(NoSolution),
// Cannot implement in core, as we can't be generic over patterns yet,
// so we'd have to list all patterns and type combinations.
ty::Pat(ty, ..) => Ok(vec![ty::Binder::dummy(ty)]),
ty::Dynamic(..)
| ty::Str
| ty::Slice(_)
| ty::Foreign(..)
| ty::Ref(_, _, Mutability::Mut)
| ty::Adt(_, _)
| ty::Alias(_, _)
| ty::Param(_)
| ty::Placeholder(..) => Err(NoSolution),
ty::Bound(..)
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
panic!("unexpected type `{ty:?}`")
}
// impl Copy/Clone for (T1, T2, .., Tn) where T1: Copy/Clone, T2: Copy/Clone, .. Tn: Copy/Clone
ty::Tuple(tys) => Ok(tys.iter().map(ty::Binder::dummy).collect()),
// impl Copy/Clone for Closure where Self::TupledUpvars: Copy/Clone
ty::Closure(_, args) => Ok(vec![ty::Binder::dummy(args.as_closure().tupled_upvars_ty())]),
// impl Copy/Clone for CoroutineClosure where Self::TupledUpvars: Copy/Clone
ty::CoroutineClosure(_, args) => {
Ok(vec![ty::Binder::dummy(args.as_coroutine_closure().tupled_upvars_ty())])
}
// only when `coroutine_clone` is enabled and the coroutine is movable
// impl Copy/Clone for Coroutine where T: Copy/Clone forall T in (upvars, witnesses)
ty::Coroutine(def_id, args) => match ecx.cx().coroutine_movability(def_id) {
Movability::Static => Err(NoSolution),
Movability::Movable => {
if ecx.cx().features().coroutine_clone() {
let coroutine = args.as_coroutine();
Ok(vec![
ty::Binder::dummy(coroutine.tupled_upvars_ty()),
ty::Binder::dummy(coroutine.witness()),
])
} else {
Err(NoSolution)
}
}
},
// impl Copy/Clone for CoroutineWitness where T: Copy/Clone forall T in coroutine_hidden_types
ty::CoroutineWitness(def_id, args) => Ok(ecx
.cx()
.bound_coroutine_hidden_types(def_id)
.into_iter()
.map(|bty| bty.instantiate(ecx.cx(), args))
.collect()),
}
}
// Returns a binder of the tupled inputs types and output type from a builtin callable type.
pub(in crate::solve) fn extract_tupled_inputs_and_output_from_callable<I: Interner>(
cx: I,
self_ty: I::Ty,
goal_kind: ty::ClosureKind,
) -> Result<Option<ty::Binder<I, (I::Ty, I::Ty)>>, NoSolution> {
match self_ty.kind() {
// keep this in sync with assemble_fn_pointer_candidates until the old solver is removed.
ty::FnDef(def_id, args) => {
let sig = cx.fn_sig(def_id);
if sig.skip_binder().is_fn_trait_compatible() && !cx.has_target_features(def_id) {
Ok(Some(
sig.instantiate(cx, args)
.map_bound(|sig| (Ty::new_tup(cx, sig.inputs().as_slice()), sig.output())),
))
} else {
Err(NoSolution)
}
}
// keep this in sync with assemble_fn_pointer_candidates until the old solver is removed.
ty::FnPtr(sig_tys, hdr) => {
let sig = sig_tys.with(hdr);
if sig.is_fn_trait_compatible() {
Ok(Some(
sig.map_bound(|sig| (Ty::new_tup(cx, sig.inputs().as_slice()), sig.output())),
))
} else {
Err(NoSolution)
}
}
ty::Closure(_, args) => {
let closure_args = args.as_closure();
match closure_args.kind_ty().to_opt_closure_kind() {
// If the closure's kind doesn't extend the goal kind,
// then the closure doesn't implement the trait.
Some(closure_kind) => {
if !closure_kind.extends(goal_kind) {
return Err(NoSolution);
}
}
// Closure kind is not yet determined, so we return ambiguity unless
// the expected kind is `FnOnce` as that is always implemented.
None => {
if goal_kind != ty::ClosureKind::FnOnce {
return Ok(None);
}
}
}
Ok(Some(
closure_args.sig().map_bound(|sig| (sig.inputs().get(0).unwrap(), sig.output())),
))
}
// Coroutine-closures don't implement `Fn` traits the normal way.
// Instead, they always implement `FnOnce`, but only implement
// `FnMut`/`Fn` if they capture no upvars, since those may borrow
// from the closure.
ty::CoroutineClosure(def_id, args) => {
let args = args.as_coroutine_closure();
let kind_ty = args.kind_ty();
let sig = args.coroutine_closure_sig().skip_binder();
// FIXME: let_chains
let kind = kind_ty.to_opt_closure_kind();
let coroutine_ty = if kind.is_some() && !args.tupled_upvars_ty().is_ty_var() {
let closure_kind = kind.unwrap();
if !closure_kind.extends(goal_kind) {
return Err(NoSolution);
}
// A coroutine-closure implements `FnOnce` *always*, since it may
// always be called once. It additionally implements `Fn`/`FnMut`
// only if it has no upvars referencing the closure-env lifetime,
// and if the closure kind permits it.
if closure_kind != ty::ClosureKind::FnOnce && args.has_self_borrows() {
return Err(NoSolution);
}
coroutine_closure_to_certain_coroutine(
cx,
goal_kind,
// No captures by ref, so this doesn't matter.
Region::new_static(cx),
def_id,
args,
sig,
)
} else {
// Closure kind is not yet determined, so we return ambiguity unless
// the expected kind is `FnOnce` as that is always implemented.
if goal_kind != ty::ClosureKind::FnOnce {
return Ok(None);
}
coroutine_closure_to_ambiguous_coroutine(
cx,
goal_kind, // No captures by ref, so this doesn't matter.
Region::new_static(cx),
def_id,
args,
sig,
)
};
Ok(Some(args.coroutine_closure_sig().rebind((sig.tupled_inputs_ty, coroutine_ty))))
}
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Adt(_, _)
| ty::Foreign(_)
| ty::Str
| ty::Array(_, _)
| ty::Slice(_)
| ty::RawPtr(_, _)
| ty::Ref(_, _, _)
| ty::Dynamic(_, _, _)
| ty::Coroutine(_, _)
| ty::CoroutineWitness(..)
| ty::Never
| ty::Tuple(_)
| ty::Pat(_, _)
| ty::Alias(_, _)
| ty::Param(_)
| ty::Placeholder(..)
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Error(_) => Err(NoSolution),
ty::Bound(..)
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
panic!("unexpected type `{self_ty:?}`")
}
}
}
/// Relevant types for an async callable, including its inputs, output,
/// and the return type you get from awaiting the output.
#[derive_where(Clone, Copy, Debug; I: Interner)]
#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
pub(in crate::solve) struct AsyncCallableRelevantTypes<I: Interner> {
pub tupled_inputs_ty: I::Ty,
/// Type returned by calling the closure
/// i.e. `f()`.
pub output_coroutine_ty: I::Ty,
/// Type returned by `await`ing the output
/// i.e. `f().await`.
pub coroutine_return_ty: I::Ty,
}
// Returns a binder of the tupled inputs types, output type, and coroutine type
// from a builtin coroutine-closure type. If we don't yet know the closure kind of
// the coroutine-closure, emit an additional trait predicate for `AsyncFnKindHelper`
// which enforces the closure is actually callable with the given trait. When we
// know the kind already, we can short-circuit this check.
pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I: Interner>(
cx: I,
self_ty: I::Ty,
goal_kind: ty::ClosureKind,
env_region: I::Region,
) -> Result<(ty::Binder<I, AsyncCallableRelevantTypes<I>>, Vec<I::Predicate>), NoSolution> {
match self_ty.kind() {
ty::CoroutineClosure(def_id, args) => {
let args = args.as_coroutine_closure();
let kind_ty = args.kind_ty();
let sig = args.coroutine_closure_sig().skip_binder();
let mut nested = vec![];
// FIXME: let_chains
let kind = kind_ty.to_opt_closure_kind();
let coroutine_ty = if kind.is_some() && !args.tupled_upvars_ty().is_ty_var() {
if !kind.unwrap().extends(goal_kind) {
return Err(NoSolution);
}
coroutine_closure_to_certain_coroutine(cx, goal_kind, env_region, def_id, args, sig)
} else {
// When we don't know the closure kind (and therefore also the closure's upvars,
// which are computed at the same time), we must delay the computation of the
// generator's upvars. We do this using the `AsyncFnKindHelper`, which as a trait
// goal functions similarly to the old `ClosureKind` predicate, and ensures that
// the goal kind <= the closure kind. As a projection `AsyncFnKindHelper::Upvars`
// will project to the right upvars for the generator, appending the inputs and
// coroutine upvars respecting the closure kind.
nested.push(
ty::TraitRef::new(
cx,
cx.require_lang_item(TraitSolverLangItem::AsyncFnKindHelper),
[kind_ty, Ty::from_closure_kind(cx, goal_kind)],
)
.upcast(cx),
);
coroutine_closure_to_ambiguous_coroutine(
cx, goal_kind, env_region, def_id, args, sig,
)
};
Ok((
args.coroutine_closure_sig().rebind(AsyncCallableRelevantTypes {
tupled_inputs_ty: sig.tupled_inputs_ty,
output_coroutine_ty: coroutine_ty,
coroutine_return_ty: sig.return_ty,
}),
nested,
))
}
ty::FnDef(def_id, _) => {
let sig = self_ty.fn_sig(cx);
if sig.is_fn_trait_compatible() && !cx.has_target_features(def_id) {
fn_item_to_async_callable(cx, sig)
} else {
Err(NoSolution)
}
}
ty::FnPtr(..) => {
let sig = self_ty.fn_sig(cx);
if sig.is_fn_trait_compatible() {
fn_item_to_async_callable(cx, sig)
} else {
Err(NoSolution)
}
}
ty::Closure(_, args) => {
let args = args.as_closure();
let bound_sig = args.sig();
let sig = bound_sig.skip_binder();
let future_trait_def_id = cx.require_lang_item(TraitSolverLangItem::Future);
// `Closure`s only implement `AsyncFn*` when their return type
// implements `Future`.
let mut nested = vec![
bound_sig
.rebind(ty::TraitRef::new(cx, future_trait_def_id, [sig.output()]))
.upcast(cx),
];
// Additionally, we need to check that the closure kind
// is still compatible.
let kind_ty = args.kind_ty();
if let Some(closure_kind) = kind_ty.to_opt_closure_kind() {
if !closure_kind.extends(goal_kind) {
return Err(NoSolution);
}
} else {
let async_fn_kind_trait_def_id =
cx.require_lang_item(TraitSolverLangItem::AsyncFnKindHelper);
// When we don't know the closure kind (and therefore also the closure's upvars,
// which are computed at the same time), we must delay the computation of the
// generator's upvars. We do this using the `AsyncFnKindHelper`, which as a trait
// goal functions similarly to the old `ClosureKind` predicate, and ensures that
// the goal kind <= the closure kind. As a projection `AsyncFnKindHelper::Upvars`
// will project to the right upvars for the generator, appending the inputs and
// coroutine upvars respecting the closure kind.
nested.push(
ty::TraitRef::new(cx, async_fn_kind_trait_def_id, [
kind_ty,
Ty::from_closure_kind(cx, goal_kind),
])
.upcast(cx),
);
}
let future_output_def_id = cx.require_lang_item(TraitSolverLangItem::FutureOutput);
let future_output_ty = Ty::new_projection(cx, future_output_def_id, [sig.output()]);
Ok((
bound_sig.rebind(AsyncCallableRelevantTypes {
tupled_inputs_ty: sig.inputs().get(0).unwrap(),
output_coroutine_ty: sig.output(),
coroutine_return_ty: future_output_ty,
}),
nested,
))
}
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Adt(_, _)
| ty::Foreign(_)
| ty::Str
| ty::Array(_, _)
| ty::Pat(_, _)
| ty::Slice(_)
| ty::RawPtr(_, _)
| ty::Ref(_, _, _)
| ty::Dynamic(_, _, _)
| ty::Coroutine(_, _)
| ty::CoroutineWitness(..)
| ty::Never
| ty::Tuple(_)
| ty::Alias(_, _)
| ty::Param(_)
| ty::Placeholder(..)
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Error(_) => Err(NoSolution),
ty::Bound(..)
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
panic!("unexpected type `{self_ty:?}`")
}
}
}
fn fn_item_to_async_callable<I: Interner>(
cx: I,
bound_sig: ty::Binder<I, ty::FnSig<I>>,
) -> Result<(ty::Binder<I, AsyncCallableRelevantTypes<I>>, Vec<I::Predicate>), NoSolution> {
let sig = bound_sig.skip_binder();
let future_trait_def_id = cx.require_lang_item(TraitSolverLangItem::Future);
// `FnDef` and `FnPtr` only implement `AsyncFn*` when their
// return type implements `Future`.
let nested = vec![
bound_sig.rebind(ty::TraitRef::new(cx, future_trait_def_id, [sig.output()])).upcast(cx),
];
let future_output_def_id = cx.require_lang_item(TraitSolverLangItem::FutureOutput);
let future_output_ty = Ty::new_projection(cx, future_output_def_id, [sig.output()]);
Ok((
bound_sig.rebind(AsyncCallableRelevantTypes {
tupled_inputs_ty: Ty::new_tup(cx, sig.inputs().as_slice()),
output_coroutine_ty: sig.output(),
coroutine_return_ty: future_output_ty,
}),
nested,
))
}
/// Given a coroutine-closure, project to its returned coroutine when we are *certain*
/// that the closure's kind is compatible with the goal.
fn coroutine_closure_to_certain_coroutine<I: Interner>(
cx: I,
goal_kind: ty::ClosureKind,
goal_region: I::Region,
def_id: I::DefId,
args: ty::CoroutineClosureArgs<I>,
sig: ty::CoroutineClosureSignature<I>,
) -> I::Ty {
sig.to_coroutine_given_kind_and_upvars(
cx,
args.parent_args(),
cx.coroutine_for_closure(def_id),
goal_kind,
goal_region,
args.tupled_upvars_ty(),
args.coroutine_captures_by_ref_ty(),
)
}
/// Given a coroutine-closure, project to its returned coroutine when we are *not certain*
/// that the closure's kind is compatible with the goal, and therefore also don't know
/// yet what the closure's upvars are.
///
/// Note that we do not also push a `AsyncFnKindHelper` goal here.
fn coroutine_closure_to_ambiguous_coroutine<I: Interner>(
cx: I,
goal_kind: ty::ClosureKind,
goal_region: I::Region,
def_id: I::DefId,
args: ty::CoroutineClosureArgs<I>,
sig: ty::CoroutineClosureSignature<I>,
) -> I::Ty {
let upvars_projection_def_id = cx.require_lang_item(TraitSolverLangItem::AsyncFnKindUpvars);
let tupled_upvars_ty = Ty::new_projection(cx, upvars_projection_def_id, [
I::GenericArg::from(args.kind_ty()),
Ty::from_closure_kind(cx, goal_kind).into(),
goal_region.into(),
sig.tupled_inputs_ty.into(),
args.tupled_upvars_ty().into(),
args.coroutine_captures_by_ref_ty().into(),
]);
sig.to_coroutine(
cx,
args.parent_args(),
Ty::from_closure_kind(cx, goal_kind),
cx.coroutine_for_closure(def_id),
tupled_upvars_ty,
)
}
/// This duplicates `extract_tupled_inputs_and_output_from_callable` but needs
/// to return different information (namely, the def id and args) so that we can
/// create const conditions.
///
/// Doing so on all calls to `extract_tupled_inputs_and_output_from_callable`
/// would be wasteful.
pub(in crate::solve) fn extract_fn_def_from_const_callable<I: Interner>(
cx: I,
self_ty: I::Ty,
) -> Result<(ty::Binder<I, (I::FnInputTys, I::Ty)>, I::DefId, I::GenericArgs), NoSolution> {
match self_ty.kind() {
ty::FnDef(def_id, args) => {
let sig = cx.fn_sig(def_id);
if sig.skip_binder().is_fn_trait_compatible()
&& !cx.has_target_features(def_id)
&& cx.fn_is_const(def_id)
{
Ok((
sig.instantiate(cx, args).map_bound(|sig| (sig.inputs(), sig.output())),
def_id,
args,
))
} else {
return Err(NoSolution);
}
}
// `FnPtr`s are not const for now.
ty::FnPtr(..) => {
return Err(NoSolution);
}
// `Closure`s are not const for now.
ty::Closure(..) => {
return Err(NoSolution);
}
// `CoroutineClosure`s are not const for now.
ty::CoroutineClosure(..) => {
return Err(NoSolution);
}
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Adt(_, _)
| ty::Foreign(_)
| ty::Str
| ty::Array(_, _)
| ty::Slice(_)
| ty::RawPtr(_, _)
| ty::Ref(_, _, _)
| ty::Dynamic(_, _, _)
| ty::Coroutine(_, _)
| ty::CoroutineWitness(..)
| ty::Never
| ty::Tuple(_)
| ty::Pat(_, _)
| ty::Alias(_, _)
| ty::Param(_)
| ty::Placeholder(..)
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Error(_) => return Err(NoSolution),
ty::Bound(..)
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
panic!("unexpected type `{self_ty:?}`")
}
}
}
pub(in crate::solve) fn const_conditions_for_destruct<I: Interner>(
cx: I,
self_ty: I::Ty,
) -> Result<Vec<ty::TraitRef<I>>, NoSolution> {
let destruct_def_id = cx.require_lang_item(TraitSolverLangItem::Destruct);
match self_ty.kind() {
// An ADT is `~const Destruct` only if all of the fields are,
// *and* if there is a `Drop` impl, that `Drop` impl is also `~const`.
ty::Adt(adt_def, args) => {
let mut const_conditions: Vec<_> = adt_def
.all_field_tys(cx)
.iter_instantiated(cx, args)
.map(|field_ty| ty::TraitRef::new(cx, destruct_def_id, [field_ty]))
.collect();
match adt_def.destructor(cx) {
// `Drop` impl exists, but it's not const. Type cannot be `~const Destruct`.
Some(AdtDestructorKind::NotConst) => return Err(NoSolution),
// `Drop` impl exists, and it's const. Require `Ty: ~const Drop` to hold.
Some(AdtDestructorKind::Const) => {
let drop_def_id = cx.require_lang_item(TraitSolverLangItem::Drop);
let drop_trait_ref = ty::TraitRef::new(cx, drop_def_id, [self_ty]);
const_conditions.push(drop_trait_ref);
}
// No `Drop` impl, no need to require anything else.
None => {}
}
Ok(const_conditions)
}
ty::Array(ty, _) | ty::Pat(ty, _) | ty::Slice(ty) => {
Ok(vec![ty::TraitRef::new(cx, destruct_def_id, [ty])])
}
ty::Tuple(tys) => Ok(tys
.iter()
.map(|field_ty| ty::TraitRef::new(cx, destruct_def_id, [field_ty]))
.collect()),
// Trivially implement `~const Destruct`
ty::Bool
| ty::Char
| ty::Int(..)
| ty::Uint(..)
| ty::Float(..)
| ty::Str
| ty::RawPtr(..)
| ty::Ref(..)
| ty::FnDef(..)
| ty::FnPtr(..)
| ty::Never
| ty::Infer(ty::InferTy::FloatVar(_) | ty::InferTy::IntVar(_))
| ty::Error(_) => Ok(vec![]),
// Coroutines and closures could implement `~const Drop`,
// but they don't really need to right now.
ty::Closure(_, _)
| ty::CoroutineClosure(_, _)
| ty::Coroutine(_, _)
| ty::CoroutineWitness(_, _) => Err(NoSolution),
ty::Dynamic(..) | ty::Param(_) | ty::Alias(..) | ty::Placeholder(_) | ty::Foreign(_) => {
Err(NoSolution)
}
ty::Bound(..)
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
panic!("unexpected type `{self_ty:?}`")
}
}
}
/// Assemble a list of predicates that would be present on a theoretical
/// user impl for an object type. These predicates must be checked any time
/// we assemble a built-in object candidate for an object type, since they
/// are not implied by the well-formedness of the type.
///
/// For example, given the following traits:
///
/// ```rust,ignore (theoretical code)
/// trait Foo: Baz {
/// type Bar: Copy;
/// }
///
/// trait Baz {}
/// ```
///
/// For the dyn type `dyn Foo<Item = Ty>`, we can imagine there being a
/// pair of theoretical impls:
///
/// ```rust,ignore (theoretical code)
/// impl Foo for dyn Foo<Item = Ty>
/// where
/// Self: Baz,
/// <Self as Foo>::Bar: Copy,
/// {
/// type Bar = Ty;
/// }
///
/// impl Baz for dyn Foo<Item = Ty> {}
/// ```
///
/// However, in order to make such impls well-formed, we need to do an
/// additional step of eagerly folding the associated types in the where
/// clauses of the impl. In this example, that means replacing
/// `<Self as Foo>::Bar` with `Ty` in the first impl.
///
// FIXME: This is only necessary as `<Self as Trait>::Assoc: ItemBound`
// bounds in impls are trivially proven using the item bound candidates.
// This is unsound in general and once that is fixed, we don't need to
// normalize eagerly here. See https://github.com/lcnr/solver-woes/issues/9
// for more details.
pub(in crate::solve) fn predicates_for_object_candidate<D, I>(
ecx: &EvalCtxt<'_, D>,
param_env: I::ParamEnv,
trait_ref: ty::TraitRef<I>,
object_bounds: I::BoundExistentialPredicates,
) -> Vec<Goal<I, I::Predicate>>
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
let cx = ecx.cx();
let mut requirements = vec![];
// Elaborating all supertrait outlives obligations here is not soundness critical,
// since if we just used the unelaborated set, then the transitive supertraits would
// be reachable when proving the former. However, since we elaborate all supertrait
// outlives obligations when confirming impls, we would end up with a different set
// of outlives obligations here if we didn't do the same, leading to ambiguity.
// FIXME(-Znext-solver=coinductive): Adding supertraits here can be removed once we
// make impls coinductive always, since they'll always need to prove their supertraits.
requirements.extend(elaborate::elaborate(
cx,
cx.explicit_super_predicates_of(trait_ref.def_id)
.iter_instantiated(cx, trait_ref.args)
.map(|(pred, _)| pred),
));
// FIXME(associated_const_equality): Also add associated consts to
// the requirements here.
for associated_type_def_id in cx.associated_type_def_ids(trait_ref.def_id) {
// associated types that require `Self: Sized` do not show up in the built-in
// implementation of `Trait for dyn Trait`, and can be dropped here.
if cx.generics_require_sized_self(associated_type_def_id) {
continue;
}
requirements
.extend(cx.item_bounds(associated_type_def_id).iter_instantiated(cx, trait_ref.args));
}
let mut replace_projection_with = HashMap::default();
for bound in object_bounds.iter() {
if let ty::ExistentialPredicate::Projection(proj) = bound.skip_binder() {
let proj = proj.with_self_ty(cx, trait_ref.self_ty());
let old_ty = replace_projection_with.insert(proj.def_id(), bound.rebind(proj));
assert_eq!(
old_ty,
None,
"{:?} has two generic parameters: {:?} and {:?}",
proj.projection_term,
proj.term,
old_ty.unwrap()
);
}
}
let mut folder =
ReplaceProjectionWith { ecx, param_env, mapping: replace_projection_with, nested: vec![] };
let folded_requirements = requirements.fold_with(&mut folder);
folder
.nested
.into_iter()
.chain(folded_requirements.into_iter().map(|clause| Goal::new(cx, param_env, clause)))
.collect()
}
struct ReplaceProjectionWith<'a, D: SolverDelegate<Interner = I>, I: Interner> {
ecx: &'a EvalCtxt<'a, D>,
param_env: I::ParamEnv,
mapping: HashMap<I::DefId, ty::Binder<I, ty::ProjectionPredicate<I>>>,
nested: Vec<Goal<I, I::Predicate>>,
}
impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I>
for ReplaceProjectionWith<'_, D, I>
{
fn cx(&self) -> I {
self.ecx.cx()
}
fn fold_ty(&mut self, ty: I::Ty) -> I::Ty {
if let ty::Alias(ty::Projection, alias_ty) = ty.kind() {
if let Some(replacement) = self.mapping.get(&alias_ty.def_id) {
// We may have a case where our object type's projection bound is higher-ranked,
// but the where clauses we instantiated are not. We can solve this by instantiating
// the binder at the usage site.
let proj = self.ecx.instantiate_binder_with_infer(*replacement);
// FIXME: Technically this equate could be fallible...
self.nested.extend(
self.ecx
.eq_and_get_goals(
self.param_env,
alias_ty,
proj.projection_term.expect_ty(self.ecx.cx()),
)
.expect(
"expected to be able to unify goal projection with dyn's projection",
),
);
proj.term.expect_ty()
} else {
ty.super_fold_with(self)
}
} else {
ty.super_fold_with(self)
}
}
}