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Commit c4e05e5

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Auto merge of #136988 - compiler-errors:impossible_predicates, r=lcnr
Use the new solver in the `impossible_predicates` The old solver is unsound for many reasons. One of which was weaponized by `@lcnr` in #140212, where the old solver was incompletely considering a dyn vtable method to be impossible and replacing its vtable entry with a null value. This null function could be called post-mono. The new solver is expected to be less incomplete due to its correct handling of higher-ranked aliases in relate. This PR switches the `impossible_predicates` query to use the new solver, which patches this UB. r? lcnr
2 parents d163a28 + 257f687 commit c4e05e5

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2 files changed

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‎compiler/rustc_trait_selection/src/traits/mod.rs‎

Lines changed: 5 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -690,8 +690,11 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
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/// used during analysis.
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pub fn impossible_predicates<'tcx>(tcx: TyCtxt<'tcx>, predicates: Vec<ty::Clause<'tcx>>) -> bool {
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debug!("impossible_predicates(predicates={:?})", predicates);
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let (infcx, param_env) =
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tcx.infer_ctxt().build_with_typing_env(ty::TypingEnv::fully_monomorphized());
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let (infcx, param_env) = tcx
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.infer_ctxt()
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.with_next_trait_solver(true)
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.build_with_typing_env(ty::TypingEnv::fully_monomorphized());
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let ocx = ObligationCtxt::new(&infcx);
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let predicates = ocx.normalize(&ObligationCause::dummy(), param_env, predicates);
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for predicate in predicates {
@@ -704,13 +707,6 @@ pub fn impossible_predicates<'tcx>(tcx: TyCtxt<'tcx>, predicates: Vec<ty::Clause
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return true;
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}
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// Leak check for any higher-ranked trait mismatches.
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// We only need to do this in the old solver, since the new solver already
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// leak-checks.
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if !infcx.next_trait_solver() && infcx.leak_check(ty::UniverseIndex::ROOT, None).is_err() {
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return true;
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}
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false
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}
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Lines changed: 38 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,38 @@
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//@ run-pass
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//@ revisions: current next
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//@ ignore-compare-mode-next-solver (explicit revisions)
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//@[next] compile-flags: -Znext-solver
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trait Id {
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type This<'a>;
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}
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impl<T> Id for T {
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type This<'a> = T;
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}
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trait Trait<T> {}
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impl<T: Id> Trait<for<'a> fn(T::This<'a>)> for T {}
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trait Method<T: Id> {
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fn call_me(&self)
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where
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T: Trait<for<'a> fn(T::This<'a>)>;
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}
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impl<T, U> Method<U> for T {
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fn call_me(&self) {
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println!("method was reachable");
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}
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}
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fn generic<T: Id>(x: &dyn Method<T>) {
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// Proving `T: Trait<for<'a> fn(T::This<'a>)>` holds.
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x.call_me();
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}
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fn main() {
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// Proving `u32: Trait<fn(u32)>` fails due to incompleteness.
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// We don't add the method to the vtable of `dyn Method`, so
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// calling it causes UB.
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generic::<u32>(&());
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}

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