Recurse into nested impl-trait when computing variance.

2 files changed, 28 insertions, 0 deletions

diff --git a/src/test/ui/impl-trait/nested-return-type4.rs b/src/test/ui/impl-trait/nested-return-type4.rs
new file mode 100644
index 00000000000..cec70bb1a0d
--- /dev/null
+++ b/src/test/ui/impl-trait/nested-return-type4.rs
@@ -0,0 +1,8 @@
+// edition: 2021
+
+fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized> {
+    async move { let _s = s; }
+    //~^ ERROR hidden type for `impl Future<Output = impl Sized>` captures lifetime that does not appear in bounds
+}
+
+fn main() {}
diff --git a/src/test/ui/impl-trait/nested-return-type4.stderr b/src/test/ui/impl-trait/nested-return-type4.stderr
new file mode 100644
index 00000000000..e761a60e79c
--- /dev/null
+++ b/src/test/ui/impl-trait/nested-return-type4.stderr
@@ -0,0 +1,20 @@
+error[E0700]: hidden type for `impl Future<Output = impl Sized>` captures lifetime that does not appear in bounds
+  --> $DIR/nested-return-type4.rs:4:5
+   |
+LL | fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized> {
+   |         -- hidden type `[async block@$DIR/nested-return-type4.rs:4:5: 4:31]` captures the lifetime `'s` as defined here
+LL |     async move { let _s = s; }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: to declare that `impl Future<Output = impl Sized>` captures `'s`, you can add an explicit `'s` lifetime bound
+   |
+LL | fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized> + 's {
+   |                                                                              ++++
+help: to declare that `impl Sized` captures `'s`, you can add an explicit `'s` lifetime bound
+   |
+LL | fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized + 's> {
+   |                                                                             ++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0700`.