Better errors for implied static bound

3 files changed, 67 insertions, 0 deletions

diff --git a/src/test/ui/generic-associated-types/bugs/hrtb-implied-1.rs b/src/test/ui/generic-associated-types/bugs/hrtb-implied-1.rs
new file mode 100644
index 00000000000..719d1bd5a4c
--- /dev/null
+++ b/src/test/ui/generic-associated-types/bugs/hrtb-implied-1.rs
@@ -0,0 +1,35 @@
+// check-fail
+// known-bug
+
+// This gives us problems because `for<'a> I::Item<'a>: Debug` should mean "for
+// all 'a where I::Item<'a> is WF", but really means "for all 'a possible"
+
+use std::fmt::Debug;
+
+pub trait LendingIterator {
+    type Item<'this>
+    where
+        Self: 'this;
+}
+
+pub struct WindowsMut<'x> {
+    slice: &'x (),
+}
+
+impl<'y> LendingIterator for WindowsMut<'y> {
+    type Item<'this> = &'this mut () where 'y: 'this;
+}
+
+fn print_items<I>(_iter: I)
+where
+    I: LendingIterator,
+    for<'a> I::Item<'a>: Debug,
+{
+}
+
+fn main() {
+    let slice = &mut ();
+    //~^ temporary value dropped while borrowed
+    let windows = WindowsMut { slice };
+    print_items::<WindowsMut<'_>>(windows);
+}
diff --git a/src/test/ui/generic-associated-types/bugs/hrtb-implied-1.stderr b/src/test/ui/generic-associated-types/bugs/hrtb-implied-1.stderr
new file mode 100644
index 00000000000..414999881d4
--- /dev/null
+++ b/src/test/ui/generic-associated-types/bugs/hrtb-implied-1.stderr
@@ -0,0 +1,20 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/hrtb-implied-1.rs:31:22
+   |
+LL |     let slice = &mut ();
+   |                      ^^ creates a temporary which is freed while still in use
+...
+LL |     print_items::<WindowsMut<'_>>(windows);
+   |     -------------------------------------- argument requires that borrow lasts for `'static`
+LL | }
+   | - temporary value is freed at the end of this statement
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/hrtb-implied-1.rs:26:26
+   |
+LL |     for<'a> I::Item<'a>: Debug,
+   |                          ^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0716`.
diff --git a/src/test/ui/nll/local-outlives-static-via-hrtb.stderr b/src/test/ui/nll/local-outlives-static-via-hrtb.stderr
index 61009da49ff..f5c10f3ddea 100644
--- a/src/test/ui/nll/local-outlives-static-via-hrtb.stderr
+++ b/src/test/ui/nll/local-outlives-static-via-hrtb.stderr
@@ -9,6 +9,12 @@ LL |     assert_static_via_hrtb(&local);
 LL |     assert_static_via_hrtb_with_assoc_type(&&local);
 LL | }
    | - `local` dropped here while still borrowed
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/local-outlives-static-via-hrtb.rs:15:53
+   |
+LL | fn assert_static_via_hrtb<G>(_: G) where for<'a> G: Outlives<'a> {}
+   |                                                     ^^^^^^^^^^^^
 
 error[E0597]: `local` does not live long enough
   --> $DIR/local-outlives-static-via-hrtb.rs:25:45
@@ -20,6 +26,12 @@ LL |     assert_static_via_hrtb_with_assoc_type(&&local);
    |     argument requires that `local` is borrowed for `'static`
 LL | }
    | - `local` dropped here while still borrowed
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/local-outlives-static-via-hrtb.rs:19:20
+   |
+LL |     for<'a> &'a T: Reference<AssociatedType = &'a ()>,
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors