test that we do not support higher-ranked regions in opaque type inference

tests/ui/rfcs/impl-trait/higher-ranked-regions-diag.rs

@@ -0,0 +1,25 @@
+// Regression test for #97099.
+// This was an ICE because `impl Sized` captures the lifetime 'a.
+
+// check-fail
+
+trait Trait<E> {
+    type Assoc;
+}
+
+struct Foo;
+
+impl<'a> Trait<&'a ()> for Foo {
+    type Assoc = ();
+}
+
+fn foo() -> impl for<'a> Trait<&'a ()> {
+    Foo
+}
+
+fn bar() -> impl for<'a> Trait<&'a (), Assoc = impl Sized> {
+    foo()
+    //~^ ERROR hidden type for `impl Sized` captures lifetime that does not appear in bounds
+}
+
+fn main() {}

tests/ui/rfcs/impl-trait/higher-ranked-regions-diag.stderr

@@ -0,0 +1,13 @@
+error[E0700]: hidden type for `impl Sized` captures lifetime that does not appear in bounds
+  --> $DIR/higher-ranked-regions-diag.rs:21:5
+   |
+LL | fn bar() -> impl for<'a> Trait<&'a (), Assoc = impl Sized> {
+   |                      --                        ---------- opaque type defined here
+   |                      |
+   |                      hidden type `<impl for<'a> Trait<&'a ()> as Trait<&'a ()>>::Assoc` captures the lifetime `'a` as defined here
+LL |     foo()
+   |     ^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0700`.

tests/ui/rfcs/type-alias-impl-trait/higher-ranked-regions-basic.rs

@@ -0,0 +1,84 @@
+// Basic tests for opaque type inference under for<_> binders.
+
+// check-fail
+
+#![feature(type_alias_impl_trait)]
+
+trait Trait<'a> {
+    type Ty;
+}
+impl<'a, T> Trait<'a> for T {
+    type Ty = &'a ();
+}
+
+mod basic_pass {
+    use super::*;
+    type Opq<'a> = impl Sized + 'a;
+    fn test() -> impl for<'a> Trait<'a, Ty = Opq<'a>> {}
+    //~^ ERROR: expected generic lifetime parameter, found `'a`
+}
+
+mod capture_rpit {
+    use super::*;
+    fn test() -> impl for<'a> Trait<'a, Ty = impl Sized> {}
+    //~^ ERROR hidden type for `impl Sized` captures lifetime that does not appear in bounds
+}
+
+mod capture_tait {
+    use super::*;
+    type Opq0 = impl Sized;
+    type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0>;
+    type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+    fn test() -> Opq2 {}
+    //~^ ERROR hidden type for `capture_tait::Opq0` captures lifetime that does not appear in bounds
+}
+
+mod capture_tait_complex_pass {
+    use super::*;
+    type Opq0<'a> = impl Sized;
+    type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'b>>; // <- Note 'b
+    //~^ ERROR: concrete type differs from previous defining opaque type use
+    type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+    fn test() -> Opq2 {}
+    //~^ ERROR: expected generic lifetime parameter, found `'a`
+}
+
+// Same as the above, but make sure that different placeholder regions are not equal.
+mod capture_tait_complex_fail {
+    use super::*;
+    type Opq0<'a> = impl Sized;
+    type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'a>>; // <- Note 'a
+    type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+    fn test() -> Opq2 {}
+    //~^ ERROR hidden type for `capture_tait_complex_fail::Opq0<'a>` captures lifetime that does not appear in bounds
+}
+
+// non-defining use because 'static is used.
+mod constrain_fail0 {
+    use super::*;
+    type Opq0<'a, 'b> = impl Sized;
+    fn test() -> impl for<'a> Trait<'a, Ty = Opq0<'a, 'static>> {}
+    //~^ ERROR non-defining opaque type use in defining scope
+    //~| ERROR: expected generic lifetime parameter, found `'a`
+}
+
+// non-defining use because generic lifetime is used multiple times.
+mod constrain_fail {
+    use super::*;
+    type Opq0<'a, 'b> = impl Sized;
+    fn test() -> impl for<'a> Trait<'a, Ty = Opq0<'a, 'a>> {}
+    //~^ ERROR non-defining opaque type use in defining scope
+    //~| ERROR: expected generic lifetime parameter, found `'a`
+}
+
+mod constrain_pass {
+    use super::*;
+    type Opq0<'a, 'b> = impl Sized;
+    type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'a, 'b>>;
+    //~^ ERROR concrete type differs
+    type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+    fn test() -> Opq2 {}
+    //~^ ERROR: expected generic lifetime parameter, found `'a`
+}
+
+fn main() {}

tests/ui/rfcs/type-alias-impl-trait/higher-ranked-regions-basic.stderr

@@ -0,0 +1,125 @@
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/higher-ranked-regions-basic.rs:17:55
+   |
+LL |     type Opq<'a> = impl Sized + 'a;
+   |              -- this generic parameter must be used with a generic lifetime parameter
+LL |     fn test() -> impl for<'a> Trait<'a, Ty = Opq<'a>> {}
+   |                                                       ^^
+
+error[E0700]: hidden type for `impl Sized` captures lifetime that does not appear in bounds
+  --> $DIR/higher-ranked-regions-basic.rs:23:58
+   |
+LL |     fn test() -> impl for<'a> Trait<'a, Ty = impl Sized> {}
+   |                           --                 ----------  ^^
+   |                           |                  |
+   |                           |                  opaque type defined here
+   |                           hidden type `&'a ()` captures the lifetime `'a` as defined here
+
+error[E0700]: hidden type for `capture_tait::Opq0` captures lifetime that does not appear in bounds
+  --> $DIR/higher-ranked-regions-basic.rs:32:23
+   |
+LL |     type Opq0 = impl Sized;
+   |                 ---------- opaque type defined here
+LL |     type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0>;
+   |                              -- hidden type `&'b ()` captures the lifetime `'b` as defined here
+LL |     type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+LL |     fn test() -> Opq2 {}
+   |                       ^^
+
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/higher-ranked-regions-basic.rs:42:23
+   |
+LL |     type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'b>>; // <- Note 'b
+   |               -- this generic parameter must be used with a generic lifetime parameter
+...
+LL |     fn test() -> Opq2 {}
+   |                       ^^
+
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/higher-ranked-regions-basic.rs:39:21
+   |
+LL |     type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'b>>; // <- Note 'b
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&'a ()`, got `{type error}`
+   |
+note: previous use here
+  --> $DIR/higher-ranked-regions-basic.rs:41:17
+   |
+LL |     type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0700]: hidden type for `capture_tait_complex_fail::Opq0<'a>` captures lifetime that does not appear in bounds
+  --> $DIR/higher-ranked-regions-basic.rs:52:23
+   |
+LL |     type Opq0<'a> = impl Sized;
+   |                     ---------- opaque type defined here
+LL |     type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'a>>; // <- Note 'a
+   |                              -- hidden type `&'b ()` captures the lifetime `'b` as defined here
+LL |     type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+LL |     fn test() -> Opq2 {}
+   |                       ^^
+
+error[E0792]: non-defining opaque type use in defining scope
+  --> $DIR/higher-ranked-regions-basic.rs:60:41
+   |
+LL |     fn test() -> impl for<'a> Trait<'a, Ty = Opq0<'a, 'static>> {}
+   |                                         ^^^^^^^^^^^^^^^^^^^^^^ argument `'static` is not a generic parameter
+   |
+note: for this opaque type
+  --> $DIR/higher-ranked-regions-basic.rs:59:25
+   |
+LL |     type Opq0<'a, 'b> = impl Sized;
+   |                         ^^^^^^^^^^
+
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/higher-ranked-regions-basic.rs:60:65
+   |
+LL |     type Opq0<'a, 'b> = impl Sized;
+   |               -- this generic parameter must be used with a generic lifetime parameter
+LL |     fn test() -> impl for<'a> Trait<'a, Ty = Opq0<'a, 'static>> {}
+   |                                                                 ^^
+
+error: non-defining opaque type use in defining scope
+  --> $DIR/higher-ranked-regions-basic.rs:69:41
+   |
+LL |     fn test() -> impl for<'a> Trait<'a, Ty = Opq0<'a, 'a>> {}
+   |                                         ^^^^^^^^^^^^^^^^^ generic argument `'a` used twice
+   |
+note: for this opaque type
+  --> $DIR/higher-ranked-regions-basic.rs:68:25
+   |
+LL |     type Opq0<'a, 'b> = impl Sized;
+   |                         ^^^^^^^^^^
+
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/higher-ranked-regions-basic.rs:69:60
+   |
+LL |     type Opq0<'a, 'b> = impl Sized;
+   |               -- this generic parameter must be used with a generic lifetime parameter
+LL |     fn test() -> impl for<'a> Trait<'a, Ty = Opq0<'a, 'a>> {}
+   |                                                            ^^
+
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/higher-ranked-regions-basic.rs:80:23
+   |
+LL |     type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'a, 'b>>;
+   |               -- this generic parameter must be used with a generic lifetime parameter
+...
+LL |     fn test() -> Opq2 {}
+   |                       ^^
+
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/higher-ranked-regions-basic.rs:77:21
+   |
+LL |     type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'a, 'b>>;
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&'a ()`, got `{type error}`
+   |
+note: previous use here
+  --> $DIR/higher-ranked-regions-basic.rs:79:17
+   |
+LL |     type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 12 previous errors
+
+Some errors have detailed explanations: E0700, E0792.
+For more information about an error, try `rustc --explain E0700`.

tests/ui/rfcs/type-alias-impl-trait/higher-ranked-regions-gat.rs

@@ -0,0 +1,21 @@
+// Regression test for #97098.
+
+#![feature(type_alias_impl_trait)]
+
+pub trait Trait {
+    type Assoc<'a>;
+}
+
+pub type Foo = impl for<'a> Trait<Assoc<'a> = FooAssoc<'a>>;
+pub type FooAssoc<'a> = impl Sized;
+//~^ ERROR: concrete type differs from previous defining opaque type use
+
+struct Struct;
+impl Trait for Struct {
+    type Assoc<'a> = &'a u32;
+}
+
+const FOO: Foo = Struct;
+//~^ ERROR: expected generic lifetime parameter, found `'a`
+
+fn main() {}

tests/ui/rfcs/type-alias-impl-trait/higher-ranked-regions-gat.stderr

@@ -0,0 +1,24 @@
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/higher-ranked-regions-gat.rs:18:18
+   |
+LL | pub type FooAssoc<'a> = impl Sized;
+   |                   -- this generic parameter must be used with a generic lifetime parameter
+...
+LL | const FOO: Foo = Struct;
+   |                  ^^^^^^
+
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/higher-ranked-regions-gat.rs:10:25
+   |
+LL | pub type FooAssoc<'a> = impl Sized;
+   |                         ^^^^^^^^^^ expected `&'a u32`, got `{type error}`
+   |
+note: previous use here
+  --> $DIR/higher-ranked-regions-gat.rs:9:16
+   |
+LL | pub type Foo = impl for<'a> Trait<Assoc<'a> = FooAssoc<'a>>;
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0792`.

tests/ui/type-alias-impl-trait/hkl_forbidden.rs

@@ -0,0 +1,39 @@
+#![feature(type_alias_impl_trait)]
+
+fn id(s: &str) -> &str {
+    s
+}
+
+type Opaque<'a> = impl Sized + 'a;
+
+fn test(s: &str) -> (impl Fn(&str) -> Opaque<'_>, impl Fn(&str) -> Opaque<'_>) {
+    (id, id) //~ ERROR expected generic lifetime parameter, found `'_`
+}
+
+fn id2<'a, 'b>(s: (&'a str, &'b str)) -> (&'a str, &'b str) {
+    s
+}
+
+type Opaque2<'a> = impl Sized + 'a;
+
+fn test2() -> impl for<'a, 'b> Fn((&'a str, &'b str)) -> (Opaque2<'a>, Opaque2<'b>) {
+    id2 //~ ERROR expected generic lifetime parameter, found `'a`
+}
+
+type Opaque3<'a> = impl Sized + 'a;
+
+fn test3(s: &str) -> (impl Fn(&str) -> Opaque3<'_>, Opaque3<'_>) {
+    (id, s) //~ ERROR expected generic lifetime parameter, found `'_`
+}
+
+type Opaque4<'a> = impl Sized + 'a;
+fn test4(s: &str) -> (Opaque4<'_>, impl Fn(&str) -> Opaque4<'_>) {
+    (s, id) //~ ERROR expected generic lifetime parameter, found `'_`
+}
+
+type Inner<'a> = impl Sized;
+fn outer_impl() -> impl for<'a> Fn(&'a ()) -> Inner<'a> {
+    |x| x //~ ERROR expected generic lifetime parameter, found `'a`
+}
+
+fn main() {}

tests/ui/type-alias-impl-trait/hkl_forbidden.stderr

@@ -0,0 +1,48 @@
+error[E0792]: expected generic lifetime parameter, found `'_`
+  --> $DIR/hkl_forbidden.rs:10:5
+   |
+LL | type Opaque<'a> = impl Sized + 'a;
+   |             -- this generic parameter must be used with a generic lifetime parameter
+...
+LL |     (id, id)
+   |     ^^^^^^^^
+
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/hkl_forbidden.rs:20:5
+   |
+LL | type Opaque2<'a> = impl Sized + 'a;
+   |              -- this generic parameter must be used with a generic lifetime parameter
+...
+LL |     id2
+   |     ^^^
+
+error[E0792]: expected generic lifetime parameter, found `'_`
+  --> $DIR/hkl_forbidden.rs:26:5
+   |
+LL | type Opaque3<'a> = impl Sized + 'a;
+   |              -- this generic parameter must be used with a generic lifetime parameter
+...
+LL |     (id, s)
+   |     ^^^^^^^
+
+error[E0792]: expected generic lifetime parameter, found `'_`
+  --> $DIR/hkl_forbidden.rs:31:5
+   |
+LL | type Opaque4<'a> = impl Sized + 'a;
+   |              -- this generic parameter must be used with a generic lifetime parameter
+LL | fn test4(s: &str) -> (Opaque4<'_>, impl Fn(&str) -> Opaque4<'_>) {
+LL |     (s, id)
+   |     ^^^^^^^
+
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/hkl_forbidden.rs:36:5
+   |
+LL | type Inner<'a> = impl Sized;
+   |            -- this generic parameter must be used with a generic lifetime parameter
+LL | fn outer_impl() -> impl for<'a> Fn(&'a ()) -> Inner<'a> {
+LL |     |x| x
+   |     ^^^^^
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0792`.