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Rollup merge of #125501 - compiler-errors:opaque-opaque-anon-ct, r=Bo…
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Resolve anon const's parent predicates to direct parent instead of opaque's parent

When an anon const is inside of an opaque, #99801 added a hack to resolve the anon const's parent predicates *not* to the opaque's predicates, but to the opaque's *parent's* predicates. This is insufficient when considering nested opaques.

This means that the `predicates_of` an anon const might reference duplicated lifetimes (installed by `compute_bidirectional_outlives_predicates`) when computing known outlives in MIR borrowck, leading to these ICEs:
Fixes #121574
Fixes #118403

~~Instead, we should be using the `OpaqueTypeOrigin` to acquire the owner item (fn/type alias/etc) of the opaque, whose predicates we're fine to mention.~~

~~I think it's a bit sketchy that we're doing this at all, tbh; I think it *should* be fine for the anon const to inherit the predicates of the opaque it's located inside. However, that would also mean that we need to make sure the `generics_of` that anon const line up in the same way.~~

~~None of this is important to solve right now; I just want to fix these ICEs so we can land #125468, which accidentally fixes these issues in a different and unrelated way.~~

edit: We don't need this special case anyways because we install the right parent item in `generics_of` anyways:
https://github.com/rust-lang/rust/blob/213ad10c8f0fc275648552366275dc4e07f97462/compiler/rustc_hir_analysis/src/collect/generics_of.rs#L150

r? `@BoxyUwU`
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@matthiaskrgr
matthiaskrgr authored May 24, 2024
2 parents 363fbb9 + de517b7 commit 104e1a4
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122 changes: 47 additions & 75 deletions compiler/rustc_hir_analysis/src/collect/predicates_of.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -461,83 +461,55 @@ pub(super) fn explicit_predicates_of<'tcx>(
}
}
} else {
if matches!(def_kind, DefKind::AnonConst) && tcx.features().generic_const_exprs {
let hir_id = tcx.local_def_id_to_hir_id(def_id);
let parent_def_id = tcx.hir().get_parent_item(hir_id);

if let Some(defaulted_param_def_id) =
tcx.hir().opt_const_param_default_param_def_id(hir_id)
{
// In `generics_of` we set the generics' parent to be our parent's parent which means that
// we lose out on the predicates of our actual parent if we dont return those predicates here.
// (See comment in `generics_of` for more information on why the parent shenanigans is necessary)
//
// struct Foo<T, const N: usize = { <T as Trait>::ASSOC }>(T) where T: Trait;
// ^^^ ^^^^^^^^^^^^^^^^^^^^^^^ the def id we are calling
// ^^^ explicit_predicates_of on
// parent item we dont have set as the
// parent of generics returned by `generics_of`
//
// In the above code we want the anon const to have predicates in its param env for `T: Trait`
// and we would be calling `explicit_predicates_of(Foo)` here
let parent_preds = tcx.explicit_predicates_of(parent_def_id);

// If we dont filter out `ConstArgHasType` predicates then every single defaulted const parameter
// will ICE because of #106994. FIXME(generic_const_exprs): remove this when a more general solution
// to #106994 is implemented.
let filtered_predicates = parent_preds
.predicates
.into_iter()
.filter(|(pred, _)| {
if let ty::ClauseKind::ConstArgHasType(ct, _) = pred.kind().skip_binder() {
match ct.kind() {
ty::ConstKind::Param(param_const) => {
let defaulted_param_idx = tcx
.generics_of(parent_def_id)
.param_def_id_to_index[&defaulted_param_def_id.to_def_id()];
param_const.index < defaulted_param_idx
}
_ => bug!(
"`ConstArgHasType` in `predicates_of`\
that isn't a `Param` const"
),
if matches!(def_kind, DefKind::AnonConst)
&& tcx.features().generic_const_exprs
&& let Some(defaulted_param_def_id) =
tcx.hir().opt_const_param_default_param_def_id(tcx.local_def_id_to_hir_id(def_id))
{
// In `generics_of` we set the generics' parent to be our parent's parent which means that
// we lose out on the predicates of our actual parent if we dont return those predicates here.
// (See comment in `generics_of` for more information on why the parent shenanigans is necessary)
//
// struct Foo<T, const N: usize = { <T as Trait>::ASSOC }>(T) where T: Trait;
// ^^^ ^^^^^^^^^^^^^^^^^^^^^^^ the def id we are calling
// ^^^ explicit_predicates_of on
// parent item we dont have set as the
// parent of generics returned by `generics_of`
//
// In the above code we want the anon const to have predicates in its param env for `T: Trait`
// and we would be calling `explicit_predicates_of(Foo)` here
let parent_def_id = tcx.local_parent(def_id);
let parent_preds = tcx.explicit_predicates_of(parent_def_id);

// If we dont filter out `ConstArgHasType` predicates then every single defaulted const parameter
// will ICE because of #106994. FIXME(generic_const_exprs): remove this when a more general solution
// to #106994 is implemented.
let filtered_predicates = parent_preds
.predicates
.into_iter()
.filter(|(pred, _)| {
if let ty::ClauseKind::ConstArgHasType(ct, _) = pred.kind().skip_binder() {
match ct.kind() {
ty::ConstKind::Param(param_const) => {
let defaulted_param_idx = tcx
.generics_of(parent_def_id)
.param_def_id_to_index[&defaulted_param_def_id.to_def_id()];
param_const.index < defaulted_param_idx
}
} else {
true
_ => bug!(
"`ConstArgHasType` in `predicates_of`\
that isn't a `Param` const"
),
}
})
.cloned();
return GenericPredicates {
parent: parent_preds.parent,
predicates: { tcx.arena.alloc_from_iter(filtered_predicates) },
};
}

let parent_def_kind = tcx.def_kind(parent_def_id);
if matches!(parent_def_kind, DefKind::OpaqueTy) {
// In `instantiate_identity` we inherit the predicates of our parent.
// However, opaque types do not have a parent (see `gather_explicit_predicates_of`), which means
// that we lose out on the predicates of our actual parent if we dont return those predicates here.
//
//
// fn foo<T: Trait>() -> impl Iterator<Output = Another<{ <T as Trait>::ASSOC }> > { todo!() }
// ^^^^^^^^^^^^^^^^^^^ the def id we are calling
// explicit_predicates_of on
//
// In the above code we want the anon const to have predicates in its param env for `T: Trait`.
// However, the anon const cannot inherit predicates from its parent since it's opaque.
//
// To fix this, we call `explicit_predicates_of` directly on `foo`, the parent's parent.

// In the above example this is `foo::{opaque#0}` or `impl Iterator`
let parent_hir_id = tcx.local_def_id_to_hir_id(parent_def_id.def_id);

// In the above example this is the function `foo`
let item_def_id = tcx.hir().get_parent_item(parent_hir_id);

// In the above code example we would be calling `explicit_predicates_of(foo)` here
return tcx.explicit_predicates_of(item_def_id);
}
} else {
true
}
})
.cloned();
return GenericPredicates {
parent: parent_preds.parent,
predicates: { tcx.arena.alloc_from_iter(filtered_predicates) },
};
}
gather_explicit_predicates_of(tcx, def_id)
}
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8 changes: 0 additions & 8 deletions tests/crashes/118403.rs
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8 changes: 0 additions & 8 deletions tests/crashes/121574-2.rs
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6 changes: 0 additions & 6 deletions tests/crashes/121574.rs
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13 changes: 13 additions & 0 deletions tests/ui/const-generics/generic_const_exprs/double-opaque-parent-predicates.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
//@ check-pass

#![feature(generic_const_exprs)]
//~^ WARN the feature `generic_const_exprs` is incomplete and may not be safe to use

pub fn y<'a, U: 'a>() -> impl IntoIterator<Item = impl IntoIterator<Item = [u8; { 1 + 2 }]> + 'a> {
[[[1, 2, 3]]]
}
// Make sure that the `predicates_of` for `{ 1 + 2 }` don't mention the duplicated lifetimes of
// the *outer* iterator. Whether they should mention the duplicated lifetimes of the *inner*
// iterator are another question, but not really something we need to answer immediately.

fn main() {}
11 changes: 11 additions & 0 deletions tests/ui/const-generics/generic_const_exprs/double-opaque-parent-predicates.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
--> $DIR/double-opaque-parent-predicates.rs:3:12
|
LL | #![feature(generic_const_exprs)]
| ^^^^^^^^^^^^^^^^^^^
|
= note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information
= note: `#[warn(incomplete_features)]` on by default

warning: 1 warning emitted

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