Auto merge of rust-lang#129021 - compiler-errors:ptr-cast-outlives, r…

…=<try>

Check WF of source type's signature on fn pointer cast

TODO: description

r? lcnr

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1978,28 +1978,68 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
 
                 match cast_kind {
                     CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer) => {
-                        let fn_sig = op.ty(body, tcx).fn_sig(tcx);
+                        let src_sig = op.ty(body, tcx).fn_sig(tcx);
+
+                        // FIXME: Explained higher-ranked case.
+                        if src_sig.has_bound_regions()
+                            && let ty::FnPtr(target_sig) = *ty.kind()
+                            && let Some(target_sig) = target_sig.no_bound_vars()
+                        {
+                            let src_sig = self.infcx.instantiate_binder_with_fresh_vars(
+                                span,
+                                BoundRegionConversionTime::HigherRankedType,
+                                src_sig,
+                            );
+                            let src_ty = Ty::new_fn_ptr(self.tcx(), ty::Binder::dummy(src_sig));
+                            self.prove_predicate(
+                                ty::ClauseKind::WellFormed(src_ty.into()),
+                                location.to_locations(),
+                                ConstraintCategory::Cast { unsize_to: None },
+                            );
+
+                            let src_ty = self.normalize(src_ty, location);
+                            if let Err(terr) = self.sub_types(
+                                src_ty,
+                                *ty,
+                                location.to_locations(),
+                                ConstraintCategory::Cast { unsize_to: None },
+                            ) {
+                                span_mirbug!(
+                                    self,
+                                    rvalue,
+                                    "equating {:?} with {:?} yields {:?}",
+                                    target_sig,
+                                    src_sig,
+                                    terr
+                                );
+                            };
+                        }
+
+                        let src_ty = Ty::new_fn_ptr(tcx, src_sig);
+                        // FIXME: Explain why this is needed.
+                        self.prove_predicate(
+                            ty::ClauseKind::WellFormed(src_ty.into()),
+                            location.to_locations(),
+                            ConstraintCategory::Cast { unsize_to: None },
+                        );
 
                         // The type that we see in the fcx is like
                         // `foo::<'a, 'b>`, where `foo` is the path to a
                         // function definition. When we extract the
                         // signature, it comes from the `fn_sig` query,
                         // and hence may contain unnormalized results.
-                        let fn_sig = self.normalize(fn_sig, location);
-
-                        let ty_fn_ptr_from = Ty::new_fn_ptr(tcx, fn_sig);
-
-                        if let Err(terr) = self.eq_types(
+                        let src_ty = self.normalize(src_ty, location);
+                        if let Err(terr) = self.sub_types(
+                            src_ty,
                             *ty,
-                            ty_fn_ptr_from,
                             location.to_locations(),
                             ConstraintCategory::Cast { unsize_to: None },
                         ) {
                             span_mirbug!(
                                 self,
                                 rvalue,
                                 "equating {:?} with {:?} yields {:?}",
-                                ty_fn_ptr_from,
+                                src_ty,
                                 ty,
                                 terr
                             );
@@ -2014,9 +2054,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         let ty_fn_ptr_from =
                             Ty::new_fn_ptr(tcx, tcx.signature_unclosure(sig, *safety));
 
-                        if let Err(terr) = self.eq_types(
-                            *ty,
+                        if let Err(terr) = self.sub_types(
                             ty_fn_ptr_from,
+                            *ty,
                             location.to_locations(),
                             ConstraintCategory::Cast { unsize_to: None },
                         ) {

compiler/rustc_hir_typeck/src/coercion.rs

@@ -137,7 +137,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 at.lub(DefineOpaqueTypes::Yes, b, a)
             } else {
                 at.sup(DefineOpaqueTypes::Yes, b, a)
-                    .map(|InferOk { value: (), obligations }| InferOk { value: a, obligations })
+                    .map(|InferOk { value: (), obligations }| InferOk { value: b, obligations })
             };
 
             // In the new solver, lazy norm may allow us to shallowly equate

tests/ui/impl-trait/recursive-ice-101862.stderr

@@ -11,13 +11,13 @@ LL |     vec![].append(&mut ice(x.as_ref()));
    = note: `#[warn(unconditional_recursion)]` on by default
 
 error[E0792]: expected generic type parameter, found `&str`
-  --> $DIR/recursive-ice-101862.rs:6:5
+  --> $DIR/recursive-ice-101862.rs:6:19
    |
 LL | pub fn ice(x: impl AsRef<str>) -> impl IntoIterator<Item = ()> {
    |               --------------- this generic parameter must be used with a generic type parameter
 LL |
 LL |     vec![].append(&mut ice(x.as_ref()));
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                   ^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error; 1 warning emitted
 

tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance-early-bound.rs

@@ -0,0 +1,11 @@
+static UNIT: &'static &'static () = &&();
+
+fn foo<'a: 'a, 'b: 'b, T>(_: &'a &'b (), v: &'b T) -> &'a T { v }
+
+fn bad<'a, T>(x: &'a T) -> &'static T {
+    let f: fn(_, &'a T) -> &'static T = foo;
+    //~^ ERROR lifetime may not live long enough
+    f(UNIT, x)
+}
+
+fn main() {}

tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance-early-bound.stderr

@@ -0,0 +1,10 @@
+error: lifetime may not live long enough
+  --> $DIR/implied-bounds-on-nested-references-plus-variance-early-bound.rs:6:12
+   |
+LL | fn bad<'a, T>(x: &'a T) -> &'static T {
+   |        -- lifetime `'a` defined here
+LL |     let f: fn(_, &'a T) -> &'static T = foo;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
+
+error: aborting due to 1 previous error
+

tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance-unnormalized.rs

@@ -0,0 +1,17 @@
+trait ToArg<T> {
+    type Arg;
+}
+impl<T, U> ToArg<T> for U {
+    type Arg = T;
+}
+
+fn extend_inner<'a, 'b>(x: &'a str) -> <&'b &'a () as ToArg<&'b str>>::Arg { x }
+fn extend<'a, 'b>(x: &'a str) -> &'b str {
+    (extend_inner as fn(_) -> _)(x)
+    //~^ ERROR lifetime may not live long enough
+}
+
+fn main() {
+    let y = extend(&String::from("Hello World"));
+    println!("{}", y);
+}

tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance-unnormalized.stderr

@@ -0,0 +1,14 @@
+error: lifetime may not live long enough
+  --> $DIR/implied-bounds-on-nested-references-plus-variance-unnormalized.rs:10:5
+   |
+LL | fn extend<'a, 'b>(x: &'a str) -> &'b str {
+   |           --  -- lifetime `'b` defined here
+   |           |
+   |           lifetime `'a` defined here
+LL |     (extend_inner as fn(_) -> _)(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/implied-bounds/implied-bounds-on-nested-references-plus-variance.rs

@@ -1,15 +1,10 @@
-//@ check-pass
-//@ known-bug: #25860
-
-// Should fail. The combination of variance and implied bounds for nested
-// references allows us to infer a longer lifetime than we can prove.
-
 static UNIT: &'static &'static () = &&();
 
 fn foo<'a, 'b, T>(_: &'a &'b (), v: &'b T) -> &'a T { v }
 
 fn bad<'a, T>(x: &'a T) -> &'static T {
     let f: fn(_, &'a T) -> &'static T = foo;
+    //~^ ERROR lifetime may not live long enough
     f(UNIT, x)
 }
 

tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance.stderr

@@ -0,0 +1,10 @@
+error: lifetime may not live long enough
+  --> $DIR/implied-bounds-on-nested-references-plus-variance.rs:6:12
+   |
+LL | fn bad<'a, T>(x: &'a T) -> &'static T {
+   |        -- lifetime `'a` defined here
+LL |     let f: fn(_, &'a T) -> &'static T = foo;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
+
+error: aborting due to 1 previous error
+

tests/ui/traits/next-solver/alias-bound-unsound.rs

@@ -27,5 +27,6 @@ fn main() {
     //~| ERROR overflow evaluating the requirement `&<() as Foo>::Item well-formed`
     //~| ERROR overflow evaluating the requirement `<() as Foo>::Item == _`
     //~| ERROR overflow evaluating the requirement `<() as Foo>::Item == _`
+    //~| ERROR overflow evaluating the requirement `<() as Foo>::Item == _`
     println!("{x}");
 }

tests/ui/traits/next-solver/alias-bound-unsound.stderr

@@ -44,6 +44,12 @@ LL |     drop(<() as Foo>::copy_me(&x));
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: aborting due to 6 previous errors
+error[E0275]: overflow evaluating the requirement `<() as Foo>::Item == _`
+  --> $DIR/alias-bound-unsound.rs:24:31
+   |
+LL |     drop(<() as Foo>::copy_me(&x));
+   |                               ^^
+
+error: aborting due to 7 previous errors
 
 For more information about this error, try `rustc --explain E0275`.