Enforce supertrait outlives obligations hold when confirming impl

compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs

@@ -7,7 +7,7 @@ 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 _};
+use rustc_type_ir::{self as ty, elaborate, Interner, Upcast as _};
 use rustc_type_ir_macros::{TypeFoldable_Generic, TypeVisitable_Generic};
 use tracing::instrument;
 
@@ -671,11 +671,19 @@ where
 {
     let cx = ecx.cx();
     let mut requirements = vec![];
-    requirements.extend(
+    // 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.

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -87,6 +87,19 @@ where
                 .map(|pred| goal.with(cx, pred));
             ecx.add_goals(GoalSource::ImplWhereBound, where_clause_bounds);
 
+            // We currently elaborate all supertrait outlives obligations from impls.
+            // This can be removed when we actually do coinduction correctly, and prove
+            // all supertrait obligations unconditionally.
+            let goal_clause: I::Clause = goal.predicate.upcast(cx);
+            for clause in elaborate::elaborate(cx, [goal_clause]) {
+                if matches!(
+                    clause.kind().skip_binder(),
+                    ty::ClauseKind::TypeOutlives(..) | ty::ClauseKind::RegionOutlives(..)
+                ) {
+                    ecx.add_goal(GoalSource::Misc, goal.with(cx, clause));
+                }
+            }
+
             ecx.evaluate_added_goals_and_make_canonical_response(maximal_certainty)
         })
     }

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -7,15 +7,17 @@ use std::fmt::{self, Display};
 use std::ops::ControlFlow;
 use std::{cmp, iter};
 
+use hir::def::DefKind;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{Diag, EmissionGuarantee};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::LangItem;
 use rustc_infer::infer::relate::TypeRelation;
-use rustc_infer::infer::BoundRegionConversionTime::HigherRankedType;
-use rustc_infer::infer::{BoundRegionConversionTime, DefineOpaqueTypes};
+use rustc_infer::infer::BoundRegionConversionTime::{self, HigherRankedType};
+use rustc_infer::infer::DefineOpaqueTypes;
+use rustc_infer::traits::util::elaborate;
 use rustc_infer::traits::TraitObligation;
 use rustc_middle::bug;
 use rustc_middle::dep_graph::{dep_kinds, DepNodeIndex};
@@ -2798,6 +2800,35 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             });
         }
 
+        // Register any outlives obligations from the trait here, cc #124336.
+        if matches!(self.tcx().def_kind(def_id), DefKind::Impl { of_trait: true })
+            && let Some(header) = self.tcx().impl_trait_header(def_id)
+        {
+            let trait_clause: ty::Clause<'tcx> =
+                header.trait_ref.instantiate(self.tcx(), args).upcast(self.tcx());
+            for clause in elaborate(self.tcx(), [trait_clause]) {
+                if matches!(
+                    clause.kind().skip_binder(),
+                    ty::ClauseKind::TypeOutlives(..) | ty::ClauseKind::RegionOutlives(..)
+                ) {
+                    let clause = normalize_with_depth_to(
+                        self,
+                        param_env,
+                        cause.clone(),
+                        recursion_depth,
+                        clause,
+                        &mut obligations,
+                    );
+                    obligations.push(Obligation {
+                        cause: cause.clone(),
+                        recursion_depth,
+                        param_env,
+                        predicate: clause.as_predicate(),
+                    });
+                }
+            }
+        }
+
         obligations
     }
 }

compiler/rustc_type_ir/src/inherent.rs

@@ -451,6 +451,8 @@ pub trait Clause<I: Interner<Clause = Self>>:
     + UpcastFrom<I, ty::Binder<I, ty::ClauseKind<I>>>
     + UpcastFrom<I, ty::TraitRef<I>>
     + UpcastFrom<I, ty::Binder<I, ty::TraitRef<I>>>
+    + UpcastFrom<I, ty::TraitPredicate<I>>
+    + UpcastFrom<I, ty::Binder<I, ty::TraitPredicate<I>>>
     + UpcastFrom<I, ty::ProjectionPredicate<I>>
     + UpcastFrom<I, ty::Binder<I, ty::ProjectionPredicate<I>>>
     + IntoKind<Kind = ty::Binder<I, ty::ClauseKind<I>>>

tests/ui/fn/implied-bounds-unnorm-associated-type-5.rs

@@ -5,6 +5,7 @@ trait Trait<'a>: 'a {
 // if the `T: 'a` bound gets implied we would probably get ub here again
 impl<'a, T> Trait<'a> for T {
     //~^ ERROR the parameter type `T` may not live long enough
+    //~| ERROR the parameter type `T` may not live long enough
     type Type = ();
 }
 

tests/ui/fn/implied-bounds-unnorm-associated-type-5.stderr

@@ -16,8 +16,21 @@ help: consider adding an explicit lifetime bound
 LL | impl<'a, T: 'a> Trait<'a> for T {
    |           ++++
 
+error[E0309]: the parameter type `T` may not live long enough
+  --> $DIR/implied-bounds-unnorm-associated-type-5.rs:6:27
+   |
+LL | impl<'a, T> Trait<'a> for T {
+   |      --                   ^ ...so that the type `T` will meet its required lifetime bounds
+   |      |
+   |      the parameter type `T` must be valid for the lifetime `'a` as defined here...
+   |
+help: consider adding an explicit lifetime bound
+   |
+LL | impl<'a, T: 'a> Trait<'a> for T {
+   |           ++++
+
 error[E0505]: cannot move out of `x` because it is borrowed
-  --> $DIR/implied-bounds-unnorm-associated-type-5.rs:21:10
+  --> $DIR/implied-bounds-unnorm-associated-type-5.rs:22:10
    |
 LL |     let x = String::from("Hello World!");
    |         - binding `x` declared here
@@ -33,7 +46,7 @@ help: consider cloning the value if the performance cost is acceptable
 LL |     let y = f(&x.clone(), ());
    |                 ++++++++
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0309, E0505.
 For more information about an error, try `rustc --explain E0309`.

tests/ui/static/static-lifetime.rs

@@ -1,6 +1,7 @@
 pub trait Arbitrary: Sized + 'static {}
 
 impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {} //~ ERROR lifetime bound
+//~^ ERROR cannot infer an appropriate lifetime for lifetime parameter `'a`
 
 fn main() {
 }

tests/ui/static/static-lifetime.stderr

@@ -11,6 +11,32 @@ LL | impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {}
    |      ^^
    = note: but lifetime parameter must outlive the static lifetime
 
-error: aborting due to 1 previous error
+error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
+  --> $DIR/static-lifetime.rs:3:34
+   |
+LL | impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {}
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: first, the lifetime cannot outlive the lifetime `'a` as defined here...
+  --> $DIR/static-lifetime.rs:3:6
+   |
+LL | impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {}
+   |      ^^
+note: ...so that the types are compatible
+  --> $DIR/static-lifetime.rs:3:34
+   |
+LL | impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {}
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: expected `<Cow<'a, A> as Arbitrary>`
+              found `<Cow<'_, A> as Arbitrary>`
+   = note: but, the lifetime must be valid for the static lifetime...
+note: ...so that the declared lifetime parameter bounds are satisfied
+  --> $DIR/static-lifetime.rs:3:34
+   |
+LL | impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {}
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0478`.
+Some errors have detailed explanations: E0478, E0495.
+For more information about an error, try `rustc --explain E0478`.

tests/ui/wf/wf-in-where-clause-static.current.stderr

@@ -0,0 +1,12 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/wf-in-where-clause-static.rs:18:18
+   |
+LL |     let s = foo(&String::from("blah blah blah"));
+   |             -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-- temporary value is freed at the end of this statement
+   |             |    |
+   |             |    creates a temporary value which is freed while still in use
+   |             argument requires that borrow lasts for `'static`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0716`.

tests/ui/wf/wf-in-where-clause-static.next.stderr

@@ -0,0 +1,12 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/wf-in-where-clause-static.rs:18:18
+   |
+LL |     let s = foo(&String::from("blah blah blah"));
+   |             -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-- temporary value is freed at the end of this statement
+   |             |    |
+   |             |    creates a temporary value which is freed while still in use
+   |             argument requires that borrow lasts for `'static`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0716`.

tests/ui/wf/wf-in-where-clause-static.rs

@@ -1,9 +1,6 @@
-//@ check-pass
-//@ known-bug: #98117
-
-// Should fail. Functions are responsible for checking the well-formedness of
-// their own where clauses, so this should fail and require an explicit bound
-// `T: 'static`.
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
 
 use std::fmt::Display;
 
@@ -19,5 +16,6 @@ where
 
 fn main() {
     let s = foo(&String::from("blah blah blah"));
+    //~^ ERROR temporary value dropped while borrowed
     println!("{}", s);
 }