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Rollup merge of #118882 - compiler-errors:normalized-sig-wf, r=lcnr

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Check normalized call signature for WF in mir typeck

Unfortunately we don't check that the built-in implementations for `Fn*` traits are actually well-formed in the same way that we do for user-provided impls.

Essentially, when checking a call terminator, we end up with a signature that references an unnormalized `<[closure] as FnOnce<...>>::Output` in its output. That output type, due to the built-in impl, doesn't follow the expected rule that `WF(ty)` implies `WF(normalized(ty))`. We fix this by also checking the normalized signature here.

**See** boxy's detailed and useful explanation comment which explains this in more detail: https://github.com/rust-lang/rust/issues/114936#issuecomment-1710388741

Fixes #114936
Fixes #118876

r? types
cc ``@BoxyUwU`` ``@lcnr``
This commit is contained in:
Matthias Krüger 2024-02-13 22:51:53 +01:00 • committed by GitHub
commit db9591cfb6
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3 changed files with 94 additions and 4 deletions
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24
compiler/rustc_borrowck/src/type_check/mod.rs
View file

@ -1432,7 +1432,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
return;
}
};
let (sig, map) = tcx.instantiate_bound_regions(sig, |br| {
let (unnormalized_sig, map) = tcx.instantiate_bound_regions(sig, |br| {
use crate::renumber::RegionCtxt;
let region_ctxt_fn = || {
@ -1454,7 +1454,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
region_ctxt_fn,
)
});
debug!(?sig);
debug!(?unnormalized_sig);
// IMPORTANT: We have to prove well formed for the function signature before
// we normalize it, as otherwise types like `<&'a &'b () as Trait>::Assoc`
// get normalized away, causing us to ignore the `'b: 'a` bound used by the function.
@ -1464,7 +1464,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
//
// See #91068 for an example.
self.prove_predicates(
sig.inputs_and_output.iter().map(|ty| {
unnormalized_sig.inputs_and_output.iter().map(|ty| {
ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(
ty.into(),
)))
@ -1472,7 +1472,23 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
term_location.to_locations(),
ConstraintCategory::Boring,
);
let sig = self.normalize(sig, term_location);
let sig = self.normalize(unnormalized_sig, term_location);
// HACK(#114936): `WF(sig)` does not imply `WF(normalized(sig))`
// with built-in `Fn` implementations, since the impl may not be
// well-formed itself.
if sig != unnormalized_sig {
self.prove_predicates(
sig.inputs_and_output.iter().map(|ty| {
ty::Binder::dummy(ty::PredicateKind::Clause(
ty::ClauseKind::WellFormed(ty.into()),
))
}),
term_location.to_locations(),
ConstraintCategory::Boring,
);
}
self.check_call_dest(body, term, &sig, *destination, *target, term_location);
// The ordinary liveness rules will ensure that all