Add a regression test for #109071

Signed-off-by: Yuki Okushi <jtitor@2k36.org>

tests/ui/associated-inherent-types/issue-109071.no_gate.stderr

@@ -0,0 +1,35 @@
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/issue-109071.rs:8:17
+   |
+LL |     type Item = &[T];
+   |                 ^ explicit lifetime name needed here
+
+error[E0107]: missing generics for struct `Windows`
+  --> $DIR/issue-109071.rs:7:9
+   |
+LL | impl<T> Windows {
+   |         ^^^^^^^ expected 1 generic argument
+   |
+note: struct defined here, with 1 generic parameter: `T`
+  --> $DIR/issue-109071.rs:5:8
+   |
+LL | struct Windows<T> {}
+   |        ^^^^^^^ -
+help: add missing generic argument
+   |
+LL | impl<T> Windows<T> {
+   |                +++
+
+error[E0658]: inherent associated types are unstable
+  --> $DIR/issue-109071.rs:8:5
+   |
+LL |     type Item = &[T];
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #8995 <https://github.com/rust-lang/rust/issues/8995> for more information
+   = help: add `#![feature(inherent_associated_types)]` to the crate attributes to enable
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0107, E0637, E0658.
+For more information about an error, try `rustc --explain E0107`.

tests/ui/associated-inherent-types/issue-109071.rs

@@ -0,0 +1,18 @@
+// revisions: with_gate no_gate
+#![cfg_attr(with_gate, feature(inherent_associated_types))]
+#![cfg_attr(with_gate, allow(incomplete_features))]
+
+struct Windows<T> {}
+
+impl<T> Windows { //~ ERROR: missing generics for struct `Windows`
+    type Item = &[T]; //~ ERROR: `&` without an explicit lifetime name cannot be used here
+    //[no_gate]~^ ERROR: inherent associated types are unstable
+
+    fn next() -> Option<Self::Item> {}
+}
+
+impl<T> Windows<T> {
+    fn T() -> Option<Self::Item> {}
+}
+
+fn main() {}

tests/ui/associated-inherent-types/issue-109071.with_gate.stderr

@@ -0,0 +1,26 @@
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/issue-109071.rs:8:17
+   |
+LL |     type Item = &[T];
+   |                 ^ explicit lifetime name needed here
+
+error[E0107]: missing generics for struct `Windows`
+  --> $DIR/issue-109071.rs:7:9
+   |
+LL | impl<T> Windows {
+   |         ^^^^^^^ expected 1 generic argument
+   |
+note: struct defined here, with 1 generic parameter: `T`
+  --> $DIR/issue-109071.rs:5:8
+   |
+LL | struct Windows<T> {}
+   |        ^^^^^^^ -
+help: add missing generic argument
+   |
+LL | impl<T> Windows<T> {
+   |                +++
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0107, E0637.
+For more information about an error, try `rustc --explain E0107`.