bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

remove assembly context and impl a bit more

Browse source
This commit is contained in:
lcnr 2023-01-17 11:47:47 +01:00
parent bf7dbff921
commit 660c28391c
8 changed files with 322 additions and 168 deletions
Download patch file Download diff file Expand all files Collapse all files

264
compiler/rustc_trait_selection/src/solve/assembly.rs
View file

@ -12,18 +12,73 @@ use std::fmt::Debug;
///
/// It consists of both the `source`, which describes how that goal would be proven,
/// and the `result` when using the given `source`.
///
/// For the list of possible candidates, please look at the documentation of
/// [super::trait_goals::CandidateSource] and [super::project_goals::CandidateSource].
#[derive(Debug, Clone)]
pub(super) struct Candidate<'tcx, G: GoalKind<'tcx>> {
pub(super) source: G::CandidateSource,
pub(super) struct Candidate<'tcx> {
pub(super) source: CandidateSource,
pub(super) result: CanonicalResponse<'tcx>,
}
pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy {
type CandidateSource: Debug + Copy;
/// Possible ways the given goal can be proven.
#[derive(Debug, Clone, Copy)]
pub(super) enum CandidateSource {
/// A user written impl.
///
/// ## Examples
///
/// ```rust
/// fn main() {
/// let x: Vec<u32> = Vec::new();
/// // This uses the impl from the standard library to prove `Vec<T>: Clone`.
/// let y = x.clone();
/// }
/// ```
Impl(DefId),
/// A builtin impl generated by the compiler. When adding a new special
/// trait, try to use actual impls whenever possible. Builtin impls should
/// only be used in cases where the impl cannot be manually be written.
///
/// Notable examples are auto traits, `Sized`, and `DiscriminantKind`.
/// For a list of all traits with builtin impls, check out the
/// [`EvalCtxt::assemble_builtin_impl_candidates`] method. Not
BuiltinImpl,
/// An assumption from the environment.
///
/// More precicely we've used the `n-th` assumption in the `param_env`.
///
/// ## Examples
///
/// ```rust
/// fn is_clone<T: Clone>(x: T) -> (T, T) {
/// // This uses the assumption `T: Clone` from the `where`-bounds
/// // to prove `T: Clone`.
/// (x.clone(), x)
/// }
/// ```
ParamEnv(usize),
/// If the self type is an alias type, e.g. an opaque type or a projection,
/// we know the bounds on that alias to hold even without knowing its concrete
/// underlying type.
///
/// More precisely this candidate is using the `n-th` bound in the `item_bounds` of
/// the self type.
///
/// ## Examples
///
/// ```rust
/// trait Trait {
/// type Assoc: Clone;
/// }
///
/// fn foo<T: Trait>(x: <T as Trait>::Assoc) {
/// // We prove `<T as Trait>::Assoc` by looking at the bounds on `Assoc` in
/// // in the trait definition.
/// let _y = x.clone();
/// }
/// ```
AliasBound(usize),
}
pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy {
fn self_ty(self) -> Ty<'tcx>;
fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self;
@ -31,43 +86,40 @@ pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy {
fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId;
fn consider_impl_candidate(
acx: &mut AssemblyCtxt<'_, '_, 'tcx, Self>,
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
impl_def_id: DefId,
);
) -> Result<Certainty, NoSolution>;
fn consider_builtin_sized_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
) -> Result<Certainty, NoSolution>;
fn consider_assumption(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
assumption: ty::Predicate<'tcx>,
) -> Result<Certainty, NoSolution>;
}
/// An abstraction which correctly deals with the canonical results for candidates.
///
/// It also deduplicates the behavior between trait and projection predicates.
pub(super) struct AssemblyCtxt<'a, 'b, 'tcx, G: GoalKind<'tcx>> {
pub(super) cx: &'a mut EvalCtxt<'b, 'tcx>,
candidates: Vec<Candidate<'tcx, G>>,
}
impl<'a, 'b, 'tcx, G: GoalKind<'tcx>> AssemblyCtxt<'a, 'b, 'tcx, G> {
pub(super) fn assemble_and_evaluate_candidates(
cx: &'a mut EvalCtxt<'b, 'tcx>,
goal: Goal<'tcx, G>,
) -> Vec<Candidate<'tcx, G>> {
let mut acx = AssemblyCtxt { cx, candidates: Vec::new() };
acx.assemble_candidates_after_normalizing_self_ty(goal);
acx.assemble_impl_candidates(goal);
acx.candidates
}
pub(super) fn try_insert_candidate(
impl<'tcx> EvalCtxt<'_, 'tcx> {
pub(super) fn assemble_and_evaluate_candidates<G: GoalKind<'tcx>>(
&mut self,
source: G::CandidateSource,
certainty: Certainty,
) {
match self.cx.make_canonical_response(certainty) {
Ok(result) => self.candidates.push(Candidate { source, result }),
Err(NoSolution) => debug!(?source, ?certainty, "failed leakcheck"),
}
goal: Goal<'tcx, G>,
) -> Vec<Candidate<'tcx>> {
let mut candidates = Vec::new();
self.assemble_candidates_after_normalizing_self_ty(goal, &mut candidates);
self.assemble_impl_candidates(goal, &mut candidates);
self.assemble_builtin_impl_candidates(goal, &mut candidates);
self.assemble_param_env_candidates(goal, &mut candidates);
self.assemble_alias_bound_candidates(goal, &mut candidates);
candidates
}
/// If the self type of a goal is a projection, computing the relevant candidates is difficult.
@ -75,15 +127,18 @@ impl<'a, 'b, 'tcx, G: GoalKind<'tcx>> AssemblyCtxt<'a, 'b, 'tcx, G> {
/// To deal with this, we first try to normalize the self type and add the candidates for the normalized
/// self type to the list of candidates in case that succeeds. Note that we can't just eagerly return in
/// this case as projections as self types add `
fn assemble_candidates_after_normalizing_self_ty(&mut self, goal: Goal<'tcx, G>) {
let tcx = self.cx.tcx();
let infcx = self.cx.infcx;
fn assemble_candidates_after_normalizing_self_ty<G: GoalKind<'tcx>>(
&mut self,
goal: Goal<'tcx, G>,
candidates: &mut Vec<Candidate<'tcx>>,
) {
let tcx = self.tcx();
// FIXME: We also have to normalize opaque types, not sure where to best fit that in.
let &ty::Alias(ty::Projection, projection_ty) = goal.predicate.self_ty().kind() else {
return
};
infcx.probe(|_| {
let normalized_ty = infcx.next_ty_infer();
self.infcx.probe(|_| {
let normalized_ty = self.infcx.next_ty_infer();
let normalizes_to_goal = goal.with(
tcx,
ty::Binder::dummy(ty::ProjectionPredicate {
@ -91,33 +146,136 @@ impl<'a, 'b, 'tcx, G: GoalKind<'tcx>> AssemblyCtxt<'a, 'b, 'tcx, G> {
term: normalized_ty.into(),
}),
);
let normalization_certainty = match self.cx.evaluate_goal(normalizes_to_goal) {
let normalization_certainty = match self.evaluate_goal(normalizes_to_goal) {
Ok((_, certainty)) => certainty,
Err(NoSolution) => return,
};
// NOTE: Alternatively we could call `evaluate_goal` here and only have a `Normalized` candidate.
// This doesn't work as long as we use `CandidateSource` in both winnowing and to resolve associated items.
// This doesn't work as long as we use `CandidateSource` in winnowing.
let goal = goal.with(tcx, goal.predicate.with_self_ty(tcx, normalized_ty));
let normalized_candidates =
AssemblyCtxt::assemble_and_evaluate_candidates(self.cx, goal);
// FIXME: This is broken if we care about the `usize` of `AliasBound` because the self type
// could be normalized to yet another projection with different item bounds.
let normalized_candidates = self.assemble_and_evaluate_candidates(goal);
for mut normalized_candidate in normalized_candidates {
normalized_candidate.result =
normalized_candidate.result.unchecked_map(|mut response| {
// FIXME: This currently hides overflow in the normalization step of the self type
// which is probably wrong. Maybe `unify_and` should actually keep overflow as
// we treat it as non-fatal anyways.
response.certainty = response.certainty.unify_and(normalization_certainty);
response
});
self.candidates.push(normalized_candidate);
candidates.push(normalized_candidate);
}
})
}
fn assemble_impl_candidates(&mut self, goal: Goal<'tcx, G>) {
let tcx = self.cx.tcx();
fn assemble_impl_candidates<G: GoalKind<'tcx>>(
&mut self,
goal: Goal<'tcx, G>,
candidates: &mut Vec<Candidate<'tcx>>,
) {
let tcx = self.tcx();
tcx.for_each_relevant_impl(
goal.predicate.trait_def_id(tcx),
goal.predicate.self_ty(),
|impl_def_id| G::consider_impl_candidate(self, goal, impl_def_id),
|impl_def_id| match G::consider_impl_candidate(self, goal, impl_def_id)
.and_then(|certainty| self.make_canonical_response(certainty))
{
Ok(result) => candidates
.push(Candidate { source: CandidateSource::Impl(impl_def_id), result }),
Err(NoSolution) => (),
},
);
}
fn assemble_builtin_impl_candidates<G: GoalKind<'tcx>>(
&mut self,
goal: Goal<'tcx, G>,
candidates: &mut Vec<Candidate<'tcx>>,
) {
let lang_items = self.tcx().lang_items();
let trait_def_id = goal.predicate.trait_def_id(self.tcx());
let result = if lang_items.sized_trait() == Some(trait_def_id) {
G::consider_builtin_sized_candidate(self, goal)
} else {
Err(NoSolution)
};
match result.and_then(|certainty| self.make_canonical_response(certainty)) {
Ok(result) => {
candidates.push(Candidate { source: CandidateSource::BuiltinImpl, result })
}
Err(NoSolution) => (),
}
}
fn assemble_param_env_candidates<G: GoalKind<'tcx>>(
&mut self,
goal: Goal<'tcx, G>,
candidates: &mut Vec<Candidate<'tcx>>,
) {
for (i, assumption) in goal.param_env.caller_bounds().iter().enumerate() {
match G::consider_assumption(self, goal, assumption)
.and_then(|certainty| self.make_canonical_response(certainty))
{
Ok(result) => {
candidates.push(Candidate { source: CandidateSource::ParamEnv(i), result })
}
Err(NoSolution) => (),
}
}
}
fn assemble_alias_bound_candidates<G: GoalKind<'tcx>>(
&mut self,
goal: Goal<'tcx, G>,
candidates: &mut Vec<Candidate<'tcx>>,
) {
let alias_ty = match goal.predicate.self_ty().kind() {
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::FnDef(_, _)
| ty::FnPtr(_)
| ty::Dynamic(..)
| ty::Closure(..)
| ty::Generator(..)
| ty::GeneratorWitness(_)
| ty::Never
| ty::Tuple(_)
| ty::Param(_)
| ty::Placeholder(..)
| ty::Infer(_)
| ty::Error(_) => return,
ty::Bound(..) => bug!("unexpected bound type: {goal:?}"),
ty::Alias(_, alias_ty) => alias_ty,
};
for (i, (assumption, _)) in self
.tcx()
.bound_explicit_item_bounds(alias_ty.def_id)
.subst_iter_copied(self.tcx(), alias_ty.substs)
.enumerate()
{
match G::consider_assumption(self, goal, assumption)
.and_then(|certainty| self.make_canonical_response(certainty))
{
Ok(result) => {
candidates.push(Candidate { source: CandidateSource::AliasBound(i), result })
}
Err(NoSolution) => (),
}
}
}
}