Add feature gate.

4 files changed, 90 insertions, 2 deletions

diff --git a/src/test/ui/suggestions/impl-trait-missing-lifetime-gated.rs b/src/test/ui/suggestions/impl-trait-missing-lifetime-gated.rs
new file mode 100644
index 00000000000..fe291e021bc
--- /dev/null
+++ b/src/test/ui/suggestions/impl-trait-missing-lifetime-gated.rs
@@ -0,0 +1,21 @@
+// edition:2021
+// gate-test-anonymous_lifetime_in_impl_trait
+// Verify the behaviour of `feature(anonymous_lifetime_in_impl_trait)`.
+
+fn f(_: impl Iterator<Item = &'_ ()>) {}
+//~^ ERROR anonymous lifetimes in `impl Trait` are unstable
+
+fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+//~^ ERROR anonymous lifetimes in `impl Trait` are unstable
+//~| ERROR missing lifetime specifier
+
+// Anonymous lifetimes in async fn are already allowed.
+// This is understood as `fn foo<'_1>(_: impl Iterator<Item = &'_1 ()>) {}`.
+async fn h(_: impl Iterator<Item = &'_ ()>) {}
+
+// Anonymous lifetimes in async fn are already allowed.
+// But that lifetime does not participate in resolution.
+async fn i(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+//~^ ERROR missing lifetime specifier
+
+fn main() {}
diff --git a/src/test/ui/suggestions/impl-trait-missing-lifetime-gated.stderr b/src/test/ui/suggestions/impl-trait-missing-lifetime-gated.stderr
new file mode 100644
index 00000000000..9adc9679eee
--- /dev/null
+++ b/src/test/ui/suggestions/impl-trait-missing-lifetime-gated.stderr
@@ -0,0 +1,44 @@
+error[E0658]: anonymous lifetimes in `impl Trait` are unstable
+  --> $DIR/impl-trait-missing-lifetime-gated.rs:5:31
+   |
+LL | fn f(_: impl Iterator<Item = &'_ ()>) {}
+   |                               ^^
+   |
+   = help: add `#![feature(anonymous_lifetime_in_impl_trait)]` to the crate attributes to enable
+
+error[E0106]: missing lifetime specifier
+  --> $DIR/impl-trait-missing-lifetime-gated.rs:8:50
+   |
+LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+   |                                                  ^^ expected named lifetime parameter
+   |
+   = help: this function's return type contains a borrowed value with an elided lifetime, but the lifetime cannot be derived from the arguments
+help: consider using the `'static` lifetime
+   |
+LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'static ()> { x.next() }
+   |                                                  ~~~~~~~
+
+error[E0658]: anonymous lifetimes in `impl Trait` are unstable
+  --> $DIR/impl-trait-missing-lifetime-gated.rs:8:31
+   |
+LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+   |                               ^^
+   |
+   = help: add `#![feature(anonymous_lifetime_in_impl_trait)]` to the crate attributes to enable
+
+error[E0106]: missing lifetime specifier
+  --> $DIR/impl-trait-missing-lifetime-gated.rs:18:56
+   |
+LL | async fn i(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+   |                                                        ^^ expected named lifetime parameter
+   |
+   = help: this function's return type contains a borrowed value with an elided lifetime, but the lifetime cannot be derived from the arguments
+help: consider using the `'static` lifetime
+   |
+LL | async fn i(x: impl Iterator<Item = &'_ ()>) -> Option<&'static ()> { x.next() }
+   |                                                        ~~~~~~~
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0106, E0658.
+For more information about an error, try `rustc --explain E0106`.
diff --git a/src/test/ui/suggestions/impl-trait-missing-lifetime.rs b/src/test/ui/suggestions/impl-trait-missing-lifetime.rs
index 2ef0f5a4853..dcc716f56b7 100644
--- a/src/test/ui/suggestions/impl-trait-missing-lifetime.rs
+++ b/src/test/ui/suggestions/impl-trait-missing-lifetime.rs
@@ -1,3 +1,7 @@
+// edition:2021
+
+#![feature(anonymous_lifetime_in_impl_trait)]
+
 // This is understood as `fn foo<'_1>(_: impl Iterator<Item = &'_1 ()>) {}`.
 fn f(_: impl Iterator<Item = &'_ ()>) {}
 
@@ -5,4 +9,11 @@ fn f(_: impl Iterator<Item = &'_ ()>) {}
 fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
 //~^ ERROR missing lifetime specifier
 
+// This is understood as `fn foo<'_1>(_: impl Iterator<Item = &'_1 ()>) {}`.
+async fn h(_: impl Iterator<Item = &'_ ()>) {}
+
+// But that lifetime does not participate in resolution.
+async fn i(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+//~^ ERROR missing lifetime specifier
+
 fn main() {}
diff --git a/src/test/ui/suggestions/impl-trait-missing-lifetime.stderr b/src/test/ui/suggestions/impl-trait-missing-lifetime.stderr
index a09ef8121d7..d3c64cb466d 100644
--- a/src/test/ui/suggestions/impl-trait-missing-lifetime.stderr
+++ b/src/test/ui/suggestions/impl-trait-missing-lifetime.stderr
@@ -1,5 +1,5 @@
 error[E0106]: missing lifetime specifier
-  --> $DIR/impl-trait-missing-lifetime.rs:5:50
+  --> $DIR/impl-trait-missing-lifetime.rs:9:50
    |
 LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
    |                                                  ^^ expected named lifetime parameter
@@ -10,6 +10,18 @@ help: consider using the `'static` lifetime
 LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'static ()> { x.next() }
    |                                                  ~~~~~~~
 
-error: aborting due to previous error
+error[E0106]: missing lifetime specifier
+  --> $DIR/impl-trait-missing-lifetime.rs:16:56
+   |
+LL | async fn i(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+   |                                                        ^^ expected named lifetime parameter
+   |
+   = help: this function's return type contains a borrowed value with an elided lifetime, but the lifetime cannot be derived from the arguments
+help: consider using the `'static` lifetime
+   |
+LL | async fn i(x: impl Iterator<Item = &'_ ()>) -> Option<&'static ()> { x.next() }
+   |                                                        ~~~~~~~
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0106`.