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

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: #114936 (comment) Fixes #114936 Fixes #118876 r? types cc ``@BoxyUwU`` ``@lcnr``
rust-lang · Feb 13, 2024 · db9591c · db9591c
2 parents a84bb95 2b4a2b9
commit db9591c
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diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -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.
@@ -1464,15 1464,31 @@ 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(),
  )))
  }),
  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

diff --git a/tests/ui/nll/check-normalized-sig-for-wf.rs b/tests/ui/nll/check-normalized-sig-for-wf.rs
@@ -0,0 1,27 @@
 // <https://github.com/rust-lang/rust/issues/114936>
 fn whoops(
  s: String,
  f: impl for<'s> FnOnce(&'s str) -> (&'static str, [&'static &'s (); 0]),
 ) -> &'static str
 {
  f(&s).0
  //~^ ERROR `s` does not live long enough
 }
 
 // <https://github.com/rust-lang/rust/issues/118876>
 fn extend<T>(input: &T) -> &'static T {
  struct Bounded<'a, 'b: 'static, T>(&'a T, [&'b (); 0]);
  let n: Box<dyn FnOnce(&T) -> Bounded<'static, '_, T>> = Box::new(|x| Bounded(x, []));
  n(input).0
  //~^ ERROR borrowed data escapes outside of function
 }
 
 // <https://github.com/rust-lang/rust/issues/118876>
 fn extend_mut<'a, T>(input: &'a mut T) -> &'static mut T {
  struct Bounded<'a, 'b: 'static, T>(&'a mut T, [&'b (); 0]);
  let mut n: Box<dyn FnMut(&mut T) -> Bounded<'static, '_, T>> = Box::new(|x| Bounded(x, []));
  n(input).0
  //~^ ERROR borrowed data escapes outside of function
 }
 
 fn main() {}
diff --git a/tests/ui/nll/check-normalized-sig-for-wf.stderr b/tests/ui/nll/check-normalized-sig-for-wf.stderr
@@ -0,0 1,47 @@
 error[E0597]: `s` does not live long enough
  --> $DIR/check-normalized-sig-for-wf.rs:7:7
  |
 LL | s: String,
  | - binding `s` declared here
 ...
 LL | f(&s).0
  | --^^-
  | | |
  | | borrowed value does not live long enough
  | argument requires that `s` is borrowed for `'static`
 LL |
 LL | }
  | - `s` dropped here while still borrowed
 
 error[E0521]: borrowed data escapes outside of function
  --> $DIR/check-normalized-sig-for-wf.rs:15:5
  |
 LL | fn extend<T>(input: &T) -> &'static T {
  | ----- - let's call the lifetime of this reference `'1`
  | |
  | `input` is a reference that is only valid in the function body
 ...
 LL | n(input).0
  | ^^^^^^^^
  | |
  | `input` escapes the function body here
  | argument requires that `'1` must outlive `'static`
 
 error[E0521]: borrowed data escapes outside of function
  --> $DIR/check-normalized-sig-for-wf.rs:23:5
  |
 LL | fn extend_mut<'a, T>(input: &'a mut T) -> &'static mut T {
  | -- ----- `input` is a reference that is only valid in the function body
  | |
  | lifetime `'a` defined here
 ...
 LL | n(input).0
  | ^^^^^^^^
  | |
  | `input` escapes the function body here
  | argument requires that `'a` must outlive `'static`
 
 error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0521, E0597.
 For more information about an error, try `rustc --explain E0521`.