Forbid lifetime bounds in nested opaque types in binders

compiler/rustc_ast_lowering/src/item.rs

@@ -1353,6 +1353,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 &param.kind,
                 bounds,
                 PredicateOrigin::GenericParam,
+                itctx.reborrow(),
             )
         }));
         predicates.extend(
@@ -1388,6 +1389,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         kind: &GenericParamKind,
         bounds: &'hir [hir::GenericBound<'hir>],
         origin: PredicateOrigin,
+        itctx: ImplTraitContext<'_, 'hir>,
     ) -> Option<hir::WherePredicate<'hir>> {
         // Do not create a clause if we do not have anything inside it.
         if bounds.is_empty() {
@@ -1437,7 +1439,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     panic!("Missing resolution for lifetime {:?} at {:?}", id, ident.span)
                 });
                 let lt_id = self.resolver.next_node_id();
-                let lifetime = self.new_named_lifetime_with_res(lt_id, ident_span, ident, res);
+                let lifetime =
+                    self.new_named_lifetime_with_res(lt_id, ident_span, ident, res, itctx);
                 Some(hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
                     lifetime,
                     span,
@@ -1474,7 +1477,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 span,
             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
                 span: self.lower_span(span),
-                lifetime: self.lower_lifetime(lifetime),
+                lifetime: self.lower_lifetime(
+                    lifetime,
+                    ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
+                ),
                 bounds: self.lower_param_bounds(
                     bounds,
                     ImplTraitContext::Disallowed(ImplTraitPosition::Bound),

compiler/rustc_ast_lowering/src/path.rs

@@ -180,14 +180,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         segment: &PathSegment,
         param_mode: ParamMode,
         parenthesized_generic_args: ParenthesizedGenericArgs,
-        itctx: ImplTraitContext<'_, 'hir>,
+        mut itctx: ImplTraitContext<'_, 'hir>,
     ) -> hir::PathSegment<'hir> {
         debug!("path_span: {:?}, lower_path_segment(segment: {:?})", path_span, segment,);
         let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
             let msg = "parenthesized type parameters may only be used with a `Fn` trait";
             match **generic_args {
                 GenericArgs::AngleBracketed(ref data) => {
-                    self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
+                    self.lower_angle_bracketed_parameter_data(data, param_mode, itctx.reborrow())
                 }
                 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
                     ParenthesizedGenericArgs::Ok => {
@@ -220,7 +220,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             self.lower_angle_bracketed_parameter_data(
                                 &data.as_angle_bracketed_args(),
                                 param_mode,
-                                itctx,
+                                itctx.reborrow(),
                             )
                             .0,
                             false,
@@ -248,6 +248,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 segment.id,
                 segment.ident.span,
                 &mut generic_args,
+                itctx,
             );
         }
 
@@ -277,6 +278,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         segment_id: NodeId,
         segment_ident_span: Span,
         generic_args: &mut GenericArgsCtor<'hir>,
+        mut itctx: ImplTraitContext<'_, 'hir>,
     ) {
         let (start, end) = match self.resolver.get_lifetime_res(segment_id) {
             Some(LifetimeRes::ElidedAnchor { start, end }) => (start, end),
@@ -305,10 +307,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             0,
             (start.as_u32()..end.as_u32()).map(|i| {
                 let id = NodeId::from_u32(i);
-                let l = self.lower_lifetime(&Lifetime {
-                    id,
-                    ident: Ident::new(kw::UnderscoreLifetime, elided_lifetime_span),
-                });
+                let l = self.lower_lifetime(
+                    &Lifetime {
+                        id,
+                        ident: Ident::new(kw::UnderscoreLifetime, elided_lifetime_span),
+                    },
+                    itctx.reborrow(),
+                );
                 GenericArg::Lifetime(l)
             }),
         );

src/test/ui/associated-type-bounds/rpit.rs

@@ -1,5 +1,3 @@
-// run-pass
-
 #![feature(associated_type_bounds)]
 
 use std::ops::Add;
@@ -42,6 +40,7 @@ pub fn use_et3() {
 }
 
 fn def_et4() -> impl Tr1<As1: for<'a> Tr2<'a>> {
+    //~^ ERROR lifetime bounds on nested opaque types are not supported yet
     #[derive(Copy, Clone)]
     struct A;
     impl Tr1 for A {

src/test/ui/associated-type-bounds/rpit.stderr

@@ -0,0 +1,10 @@
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/rpit.rs:42:43
+   |
+LL | fn def_et4() -> impl Tr1<As1: for<'a> Tr2<'a>> {
+   |                                           ^^
+   |
+   = help: See https://github.com/rust-lang/rust/issues/96194 for further details
+
+error: aborting due to previous error
+

src/test/ui/impl-trait/issues/issue-54895.rs

@@ -1,5 +1,3 @@
-// check-pass
-
 trait Trait<'a> {
     type Out;
     fn call(&'a self) -> Self::Out;
@@ -15,6 +13,7 @@ impl<'a> Trait<'a> for X {
 }
 
 fn f() -> impl for<'a> Trait<'a, Out = impl Sized + 'a> {
+    //~^ ERROR lifetime bounds on nested opaque types are not supported yet
     X(())
 }
 

src/test/ui/impl-trait/issues/issue-54895.stderr

@@ -0,0 +1,10 @@
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-54895.rs:15:53
+   |
+LL | fn f() -> impl for<'a> Trait<'a, Out = impl Sized + 'a> {
+   |                                                     ^^
+   |
+   = help: See https://github.com/rust-lang/rust/issues/96194 for further details
+
+error: aborting due to previous error
+

src/test/ui/impl-trait/issues/issue-67830.rs

@@ -20,6 +20,7 @@ where
 struct A;
 fn test() -> impl for<'a> MyFn<&'a A, Output=impl Iterator + 'a> {
     //~^ ERROR implementation of `FnOnce` is not general enough
+    //~| ERROR lifetime bounds on nested opaque types are not supported yet
     Wrap(|a| Some(a).into_iter())
 }
 

src/test/ui/impl-trait/issues/issue-67830.stderr

@@ -1,3 +1,11 @@
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-67830.rs:21:62
+   |
+LL | fn test() -> impl for<'a> MyFn<&'a A, Output=impl Iterator + 'a> {
+   |                                                              ^^
+   |
+   = help: See https://github.com/rust-lang/rust/issues/96194 for further details
+
 error: implementation of `FnOnce` is not general enough
   --> $DIR/issue-67830.rs:21:14
    |
@@ -7,5 +15,5 @@ LL | fn test() -> impl for<'a> MyFn<&'a A, Output=impl Iterator + 'a> {
    = note: closure with signature `fn(&'2 A) -> std::option::IntoIter<&A>` must implement `FnOnce<(&'1 A,)>`, for any lifetime `'1`...
    = note: ...but it actually implements `FnOnce<(&'2 A,)>`, for some specific lifetime `'2`
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 

src/test/ui/impl-trait/issues/issue-88236-2.rs

@@ -13,11 +13,23 @@ impl<'a> Hrtb<'a> for &'a () {
 }
 
 fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+//~^ ERROR lifetime bounds on nested opaque types are not supported yet
 fn make_weird_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
     &() //~^ ERROR implementation of `Hrtb` is not general enough
+    //~| ERROR lifetime bounds on nested opaque types are not supported yet
 }
 fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
     x //~^ ERROR implementation of `Hrtb` is not general enough
+    //~| ERROR lifetime bounds on nested opaque types are not supported yet
+}
+
+trait Zend<'a>: Send {}
+
+impl<'a, T: Send> Zend<'a> for T {}
+
+fn make_bad_impl_2<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Zend<'a>> {
+    x //~^ ERROR implementation of `Hrtb` is not general enough
+    //~| ERROR lifetime bounds on nested opaque types are not supported yet
 }
 
 fn main() {}

src/test/ui/impl-trait/issues/issue-88236-2.stderr

@@ -1,5 +1,37 @@
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236-2.rs:15:61
+   |
+LL | fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+   |                                                             ^^
+   |
+   = help: See https://github.com/rust-lang/rust/issues/96194 for further details
+
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236-2.rs:17:80
+   |
+LL | fn make_weird_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
+   |                                                                                ^^
+   |
+   = help: See https://github.com/rust-lang/rust/issues/96194 for further details
+
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236-2.rs:21:78
+   |
+LL | fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
+   |                                                                              ^^
+   |
+   = help: See https://github.com/rust-lang/rust/issues/96194 for further details
+
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236-2.rs:30:78
+   |
+LL | fn make_bad_impl_2<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Zend<'a>> {
+   |                                                                              ^^
+   |
+   = help: See https://github.com/rust-lang/rust/issues/96194 for further details
+
 error: implementation of `Hrtb` is not general enough
-  --> $DIR/issue-88236-2.rs:16:38
+  --> $DIR/issue-88236-2.rs:17:38
    |
 LL | fn make_weird_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `Hrtb` is not general enough
@@ -8,13 +40,22 @@ LL | fn make_weird_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Sen
    = note: ...but `Hrtb<'1>` is actually implemented for the type `&'1 ()`, for some specific lifetime `'1`
 
 error: implementation of `Hrtb` is not general enough
-  --> $DIR/issue-88236-2.rs:19:36
+  --> $DIR/issue-88236-2.rs:21:36
    |
 LL | fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `Hrtb` is not general enough
    |
    = note: `Hrtb<'1>` would have to be implemented for the type `&()`, for any lifetime `'1`...
    = note: ...but `Hrtb<'_>` is actually implemented for the type `&()`
 
-error: aborting due to 2 previous errors
+error: implementation of `Hrtb` is not general enough
+  --> $DIR/issue-88236-2.rs:30:38
+   |
+LL | fn make_bad_impl_2<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Zend<'a>> {
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `Hrtb` is not general enough
+   |
+   = note: `Hrtb<'1>` would have to be implemented for the type `&()`, for any lifetime `'1`...
+   = note: ...but `Hrtb<'_>` is actually implemented for the type `&()`
+
+error: aborting due to 7 previous errors
 

src/test/ui/impl-trait/issues/issue-88236.rs

@@ -1,5 +1,3 @@
-// check-pass
-
 // this used to cause stack overflows
 
 trait Hrtb<'a> {
@@ -15,5 +13,6 @@ impl<'a> Hrtb<'a> for &'a () {
 }
 
 fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+//~^ ERROR lifetime bounds on nested opaque types are not supported yet
 
 fn main() {}

src/test/ui/impl-trait/issues/issue-88236.stderr

@@ -0,0 +1,10 @@
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236.rs:15:61
+   |
+LL | fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+   |                                                             ^^
+   |
+   = help: See https://github.com/rust-lang/rust/issues/96194 for further details
+
+error: aborting due to previous error
+