check FnDef return type for WF

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -647,6 +647,8 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  fn visit_ty(&mut self, t: <TyCtxt<'tcx> as ty::Interner>::Ty) -> Self::Result {
  debug!("wf bounds for t={:?} t.kind={:#?}", t, t.kind());
 
+ let tcx = self.tcx();
+
  match *t.kind() {
  ty::Bool
  | ty::Char
@@ -707,6 +709,16 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  }
 
  ty::FnDef(did, args) => {
+ // HACK: Check the return type of function definitions for
+ // well-formedness to mostly fix #84533. This is still not
+ // perfect and there may be ways to abuse the fact that we
+ // ignore requirements with escaping bound vars. That's a
+ // more general issue however.
+ //
+ // FIXME(eddyb) add the type to `walker` instead of recursing.
+ let fn_sig = tcx.fn_sig(did).instantiate(tcx, args);
+ fn_sig.output().skip_binder().visit_with(self);
+
  let obligations = self.nominal_obligations(did, args);
  self.out.extend(obligations);
  }
@@ -716,7 +728,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  if !r.has_escaping_bound_vars() && !rty.has_escaping_bound_vars() {
  let cause = self.cause(traits::ReferenceOutlivesReferent(t));
  self.out.push(traits::Obligation::with_depth(
- self.tcx(),
+ tcx,
  cause,
  self.recursion_depth,
  self.param_env,
@@ -805,12 +817,12 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  // obligations that don't refer to Self and
  // checking those
 
- let defer_to_coercion = self.tcx().features().object_safe_for_dispatch;
+ let defer_to_coercion = tcx.features().object_safe_for_dispatch;
 
  if !defer_to_coercion {
  if let Some(principal) = data.principal_def_id() {
  self.out.push(traits::Obligation::with_depth(
- self.tcx(),
+ tcx,
  self.cause(traits::WellFormed(None)),
  self.recursion_depth,
  self.param_env,
@@ -835,7 +847,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  ty::Infer(_) => {
  let cause = self.cause(traits::WellFormed(None));
  self.out.push(traits::Obligation::with_depth(
- self.tcx(),
+ tcx,
  cause,
  self.recursion_depth,
  self.param_env,
@@ -850,6 +862,8 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  }
 
  fn visit_const(&mut self, c: <TyCtxt<'tcx> as ty::Interner>::Const) -> Self::Result {
+ let tcx = self.tcx();
+
  match c.kind() {
  ty::ConstKind::Unevaluated(uv) => {
  if !c.has_escaping_bound_vars() {
@@ -861,7 +875,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  ));
  let cause = self.cause(traits::WellFormed(None));
  self.out.push(traits::Obligation::with_depth(
- self.tcx(),
+ tcx,
  cause,
  self.recursion_depth,
  self.param_env,
@@ -873,7 +887,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  let cause = self.cause(traits::WellFormed(None));
 
  self.out.push(traits::Obligation::with_depth(
- self.tcx(),
+ tcx,
  cause,
  self.recursion_depth,
  self.param_env,
@@ -895,7 +909,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
  ));
  let cause = self.cause(traits::WellFormed(None));
  self.out.push(traits::Obligation::with_depth(
- self.tcx(),
+ tcx,
  cause,
  self.recursion_depth,
  self.param_env,

tests/ui/proc-macro/bad-projection.rs

@@ -15,4 +15,5 @@ pub fn uwu() -> <() as Project>::Assoc {}
 //~^ ERROR the trait bound `(): Project` is not satisfied
 //~| ERROR the trait bound `(): Project` is not satisfied
 //~| ERROR the trait bound `(): Project` is not satisfied
+//~| ERROR the trait bound `(): Project` is not satisfied
 //~| ERROR function is expected to take 1 argument, but it takes 0 arguments

tests/ui/proc-macro/bad-projection.stderr

@@ -35,6 +35,18 @@ help: this trait has no implementations, consider adding one
 LL | trait Project {
  | ^^^^^^^^^^^^^
 
+error[E0277]: the trait bound `(): Project` is not satisfied
+ --> $DIR/bad-projection.rs:14:1
+ |
+LL | pub fn uwu() -> <() as Project>::Assoc {}
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Project` is not implemented for `()`
+ |
+help: this trait has no implementations, consider adding one
+ --> $DIR/bad-projection.rs:9:1
+ |
+LL | trait Project {
+ | ^^^^^^^^^^^^^
+
 error[E0277]: the trait bound `(): Project` is not satisfied
  --> $DIR/bad-projection.rs:14:40
  |
@@ -47,7 +59,7 @@ help: this trait has no implementations, consider adding one
 LL | trait Project {
  | ^^^^^^^^^^^^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0277, E0593.
 For more information about an error, try `rustc --explain E0277`.

tests/ui/wf/wf-fn-def-check-sig-1.rs

@@ -0,0 +1,44 @@
+// Regression test for #84533.
+
+use std::marker::PhantomData;
+
+fn foo<'b, 'a>() -> PhantomData<&'b &'a ()> {
+ PhantomData
+}
+
+fn extend_lifetime<'a, 'b, T: ?Sized>(x: &'a T) -> &'b T {
+ let f = foo::<'b, 'a>;
+ f.baz(x)
+ //~^ ERROR lifetime may not live long enough
+}
+
+trait Foo<'a, 'b, T: ?Sized> {
+ fn baz(self, s: &'a T) -> &'b T;
+}
+impl<'a, 'b, R, F, T: ?Sized> Foo<'a, 'b, T> for F
+where
+ F: Fn() -> R,
+ R: ProofForConversion<'a, 'b, T>,
+{
+ fn baz(self, s: &'a T) -> &'b T {
+ self().convert(s)
+ }
+}
+
+trait ProofForConversion<'a, 'b, T: ?Sized> {
+ fn convert(self, s: &'a T) -> &'b T;
+}
+impl<'a, 'b, T: ?Sized> ProofForConversion<'a, 'b, T> for PhantomData<&'b &'a ()> {
+ fn convert(self, s: &'a T) -> &'b T {
+ s
+ }
+}
+
+fn main() {
+ let d;
+ {
+ let x = "Hello World".to_string();
+ d = extend_lifetime(&x);
+ }
+ println!("{}", d);
+}

tests/ui/wf/wf-fn-def-check-sig-1.stderr

@@ -0,0 +1,15 @@
+error: lifetime may not live long enough
+ --> $DIR/wf-fn-def-check-sig-1.rs:11:5
+ |
+LL | fn extend_lifetime<'a, 'b, T: ?Sized>(x: &'a T) -> &'b T {
+ | -- -- lifetime `'b` defined here
+ | |
+ | lifetime `'a` defined here
+LL | let f = foo::<'b, 'a>;
+LL | f.baz(x)
+ | ^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
+ |
+ = help: consider adding the following bound: `'a: 'b`
+
+error: aborting due to 1 previous error
+

tests/ui/wf/wf-fn-def-check-sig-2.rs

@@ -0,0 +1,44 @@
+// Regression test for #84533 involving higher-ranked regions
+// in the return type.
+use std::marker::PhantomData;
+
+fn foo<'c, 'b, 'a>(_: &'c ()) -> (&'c (), PhantomData<&'b &'a ()>) {
+ (&(), PhantomData)
+}
+
+fn extend_lifetime<'a, 'b, T: ?Sized>(x: &'a T) -> &'b T {
+ let f = foo;
+ f.baz(x)
+ //~^ ERROR lifetime may not live long enough
+}
+
+trait Foo<'a, 'b, T: ?Sized> {
+ fn baz(self, s: &'a T) -> &'b T;
+}
+impl<'a, 'b, R, F, T: ?Sized> Foo<'a, 'b, T> for F
+where
+ F: for<'c> Fn(&'c ()) -> (&'c (), R),
+ R: ProofForConversion<'a, 'b, T>,
+{
+ fn baz(self, s: &'a T) -> &'b T {
+ self(&()).1.convert(s)
+ }
+}
+
+trait ProofForConversion<'a, 'b, T: ?Sized> {
+ fn convert(self, s: &'a T) -> &'b T;
+}
+impl<'a, 'b, T: ?Sized> ProofForConversion<'a, 'b, T> for PhantomData<&'b &'a ()> {
+ fn convert(self, s: &'a T) -> &'b T {
+ s
+ }
+}
+
+fn main() {
+ let d;
+ {
+ let x = "Hello World".to_string();
+ d = extend_lifetime(&x);
+ }
+ println!("{}", d);
+}

tests/ui/wf/wf-fn-def-check-sig-2.stderr

@@ -0,0 +1,15 @@
+error: lifetime may not live long enough
+ --> $DIR/wf-fn-def-check-sig-2.rs:11:5
+ |
+LL | fn extend_lifetime<'a, 'b, T: ?Sized>(x: &'a T) -> &'b T {
+ | -- -- lifetime `'b` defined here
+ | |
+ | lifetime `'a` defined here
+LL | let f = foo;
+LL | f.baz(x)
+ | ^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
+ |
+ = help: consider adding the following bound: `'a: 'b`
+
+error: aborting due to 1 previous error
+