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Auto merge of #17999 - ShoyuVanilla:issue-17998, r=Veykril
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fix: `std::error::Error` is object unsafe

Fixes #17998

I tried to get generic predicates of assoc function itself, not inherited from the parent here;

https://github.com/rust-lang/rust-analyzer/blob/0ae42bd42576566540a84c62e118aa823edcf2ec/crates/hir-ty/src/object_safety.rs#L420-L442

But this naive equality check approach doesn't work when the assoc function has one or more generic paramters like;

```rust
trait Foo {}
trait Bar: Foo {
    fn bar(&self);
}
```

because the generic predicates of the parent, `Bar` is `[^1.0 implements Foo]` and the generic predicates of `fn bar` is `[^1.1 implements Foo]`, which are different.

This PR implements a correct logic for filtering out parent generic predicates for this.
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bors committed Aug 30, 2024
2 parents 1b48c76 + 2310839 commit aefe34d
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Showing 4 changed files with 45 additions and 21 deletions.
3 changes: 3 additions & 0 deletions crates/hir-ty/src/db.rs
Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,9 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
#[salsa::invoke(crate::lower::generic_predicates_query)]
fn generic_predicates(&self, def: GenericDefId) -> GenericPredicates;

#[salsa::invoke(crate::lower::generic_predicates_without_parent_query)]
fn generic_predicates_without_parent(&self, def: GenericDefId) -> GenericPredicates;

#[salsa::invoke(crate::lower::trait_environment_for_body_query)]
#[salsa::transparent]
fn trait_environment_for_body(&self, def: DefWithBodyId) -> Arc<TraitEnvironment>;
Expand Down
23 changes: 23 additions & 0 deletions crates/hir-ty/src/lower.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1700,6 +1700,28 @@ pub(crate) fn generic_predicates_query(
db: &dyn HirDatabase,
def: GenericDefId,
) -> GenericPredicates {
generic_predicates_filtered_by(db, def, |_, _| true)
}

/// Resolve the where clause(s) of an item with generics,
/// except the ones inherited from the parent
pub(crate) fn generic_predicates_without_parent_query(
db: &dyn HirDatabase,
def: GenericDefId,
) -> GenericPredicates {
generic_predicates_filtered_by(db, def, |_, d| *d == def)
}

/// Resolve the where clause(s) of an item with generics,
/// except the ones inherited from the parent
fn generic_predicates_filtered_by<F>(
db: &dyn HirDatabase,
def: GenericDefId,
filter: F,
) -> GenericPredicates
where
F: Fn(&WherePredicate, &GenericDefId) -> bool,
{
let resolver = def.resolver(db.upcast());
let (impl_trait_lowering, param_lowering) = match def {
GenericDefId::FunctionId(_) => {
Expand All @@ -1714,6 +1736,7 @@ pub(crate) fn generic_predicates_query(

let mut predicates = resolver
.where_predicates_in_scope()
.filter(|(pred, def)| filter(pred, def))
.flat_map(|(pred, def)| {
ctx.lower_where_predicate(pred, def, false).map(|p| make_binders(db, &generics, p))
})
Expand Down
23 changes: 2 additions & 21 deletions crates/hir-ty/src/object_safety.rs
Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ use hir_def::{
lang_item::LangItem, AssocItemId, ConstId, FunctionId, GenericDefId, HasModule, TraitId,
TypeAliasId,
};
use rustc_hash::{FxHashMap, FxHashSet};
use rustc_hash::FxHashSet;
use smallvec::SmallVec;

use crate::{
Expand Down Expand Up @@ -417,30 +417,11 @@ where
cb(MethodViolationCode::UndispatchableReceiver)?;
}

let predicates = &*db.generic_predicates(func.into());
let mut parent_predicates = (*db.generic_predicates(trait_.into()))
.iter()
.map(|b| b.skip_binders().skip_binders().clone())
.fold(FxHashMap::default(), |mut acc, item| {
acc.entry(item)
.and_modify(|cnt| {
*cnt += 1;
})
.or_insert(1);
acc
});
let predicates = &*db.generic_predicates_without_parent(func.into());
let trait_self_idx = trait_self_param_idx(db.upcast(), func.into());
for pred in predicates {
let pred = pred.skip_binders().skip_binders();

// Skip predicates from parent, i.e. the trait that contains this method
if let Some(cnt) = parent_predicates.get_mut(pred) {
if *cnt > 0 {
*cnt -= 1;
continue;
}
}

if matches!(pred, WhereClause::TypeOutlives(_)) {
continue;
}
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17 changes: 17 additions & 0 deletions crates/hir-ty/src/object_safety/tests.rs
Original file line number Diff line number Diff line change
Expand Up @@ -361,3 +361,20 @@ pub trait Trait {
[("Trait", vec![])],
);
}

#[test]
fn std_error_is_object_safe() {
check_object_safety(
r#"
//- minicore: fmt, dispatch_from_dyn
trait Erased<'a>: 'a {}
pub struct Request<'a>(dyn Erased<'a> + 'a);
pub trait Error: core::fmt::Debug + core::fmt::Display {
fn provide<'a>(&'a self, request: &mut Request<'a>);
}
"#,
[("Error", vec![])],
);
}

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