diff --git a/Cargo.lock b/Cargo.lock
index 85e5e6c97105c..a08d43a014c06 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4259,6 +4259,7 @@ dependencies = [
"rustc_serialize",
"rustc_type_ir",
"rustc_type_ir_macros",
+ "smallvec",
"tracing",
]
diff --git a/compiler/rustc_next_trait_solver/Cargo.toml b/compiler/rustc_next_trait_solver/Cargo.toml
index 451c215566be2..f9168112216ab 100644
--- a/compiler/rustc_next_trait_solver/Cargo.toml
+++ b/compiler/rustc_next_trait_solver/Cargo.toml
@@ -13,6 +13,7 @@ rustc_macros = { path = "../rustc_macros", optional = true }
rustc_serialize = { path = "../rustc_serialize", optional = true }
rustc_type_ir = { path = "../rustc_type_ir", default-features = false }
rustc_type_ir_macros = { path = "../rustc_type_ir_macros" }
+smallvec = "1.8.1"
tracing = "0.1"
# tidy-alphabetical-end
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index f4d7c3ce76cf2..4faa243c02a64 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -8,6 +8,7 @@ use rustc_type_ir::lang_items::TraitSolverLangItem;
use rustc_type_ir::solve::CanonicalResponse;
use rustc_type_ir::visit::TypeVisitableExt as _;
use rustc_type_ir::{self as ty, Interner, TraitPredicate, TypingMode, Upcast as _, elaborate};
+use smallvec::SmallVec;
use tracing::{instrument, trace};
use crate::delegate::SolverDelegate;
@@ -225,7 +226,7 @@ where
}
ecx.probe_and_evaluate_goal_for_constituent_tys(
- CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
+ CandidateSource::BuiltinImpl(BuiltinImplSource::Trivial),
goal,
structural_traits::instantiate_constituent_tys_for_sized_trait,
)
@@ -1194,7 +1195,30 @@ where
};
}
- // FIXME: prefer trivial builtin impls
+ // We prefer trivial builtin candidates, i.e. builtin impls without any
+ // nested requirements, over all others. This is a fix for #53123 and
+ // prevents where-bounds from accidentally extending the lifetime of a
+ // variable.
+ if candidates
+ .iter()
+ .any(|c| matches!(c.source, CandidateSource::BuiltinImpl(BuiltinImplSource::Trivial)))
+ {
+ let trivial_builtin_impls: SmallVec<[_; 1]> = candidates
+ .iter()
+ .filter(|c| {
+ matches!(c.source, CandidateSource::BuiltinImpl(BuiltinImplSource::Trivial))
+ })
+ .map(|c| c.result)
+ .collect();
+ // There should only ever be a single trivial builtin candidate
+ // as they would otherwise overlap.
+ assert_eq!(trivial_builtin_impls.len(), 1);
+ return if let Some(response) = self.try_merge_responses(&trivial_builtin_impls) {
+ Ok((response, Some(TraitGoalProvenVia::Misc)))
+ } else {
+ Ok((self.bail_with_ambiguity(&trivial_builtin_impls), None))
+ };
+ }
// If there are non-global where-bounds, prefer where-bounds
// (including global ones) over everything else.
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index aae0e34ddf393..d59cf88875ea7 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -991,7 +991,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
Err(ErrorGuaranteed { .. }) => true,
}
}
- ImplSource::Builtin(BuiltinImplSource::Misc, _) => {
+ ImplSource::Builtin(BuiltinImplSource::Misc | BuiltinImplSource::Trivial, _) => {
// While a builtin impl may be known to exist, the associated type may not yet
// be known. Any type with multiple potential associated types is therefore
// not eligible.
@@ -1296,7 +1296,7 @@ fn confirm_select_candidate<'cx, 'tcx>(
) -> Progress<'tcx> {
match impl_source {
ImplSource::UserDefined(data) => confirm_impl_candidate(selcx, obligation, data),
- ImplSource::Builtin(BuiltinImplSource::Misc, data) => {
+ ImplSource::Builtin(BuiltinImplSource::Misc | BuiltinImplSource::Trivial, data) => {
let tcx = selcx.tcx();
let trait_def_id = obligation.predicate.trait_def_id(tcx);
if tcx.is_lang_item(trait_def_id, LangItem::Coroutine) {
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index fc76a86f79772..d5e1937efaa45 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -248,7 +248,7 @@ fn resolve_associated_item<'tcx>(
})
}
}
- traits::ImplSource::Builtin(BuiltinImplSource::Misc, _) => {
+ traits::ImplSource::Builtin(BuiltinImplSource::Misc | BuiltinImplSource::Trivial, _) => {
if tcx.is_lang_item(trait_ref.def_id, LangItem::Clone) {
// FIXME(eddyb) use lang items for methods instead of names.
let name = tcx.item_name(trait_item_id);
diff --git a/compiler/rustc_type_ir/src/solve/mod.rs b/compiler/rustc_type_ir/src/solve/mod.rs
index fbb5c7430eb2a..c06004d4d0f6c 100644
--- a/compiler/rustc_type_ir/src/solve/mod.rs
+++ b/compiler/rustc_type_ir/src/solve/mod.rs
@@ -169,6 +169,9 @@ pub enum CandidateSource<I: Interner> {
#[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext, TyEncodable, TyDecodable))]
pub enum BuiltinImplSource {
+ /// A built-in impl that is considered trivial, without any nested requirements. They
+ /// are preferred over where-clauses, and we want to track them explicitly.
+ Trivial,
/// Some built-in impl we don't need to differentiate. This should be used
/// unless more specific information is necessary.
Misc,
diff --git a/tests/ui/regions/issue-26448-1.rs b/tests/ui/regions/issue-26448-1.rs
index 0fa40709a7b95..4d1853a93727e 100644
--- a/tests/ui/regions/issue-26448-1.rs
+++ b/tests/ui/regions/issue-26448-1.rs
@@ -1,4 +1,7 @@
-//@ run-pass
+//@ revisions: current next
+//@ [next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
pub trait Foo<T> {
fn foo(self) -> T;
diff --git a/tests/ui/regions/issue-26448-2.rs b/tests/ui/regions/issue-26448-2.rs
index 5fd1e90ebfd96..2e124555125eb 100644
--- a/tests/ui/regions/issue-26448-2.rs
+++ b/tests/ui/regions/issue-26448-2.rs
@@ -1,3 +1,6 @@
+//@ revisions: current next
+//@ [next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
//@ check-pass
pub struct Bar<T> {