Auto merge of #101924 - jackh726:revert-static-hrtb-error, r=compiler-errors

Re-add HRTB implied static bug note

r? `@compiler-errors` since you reviewed it previously

I deleted a `normalize` call and forgot about it. Whoops.

12 files changed, 200 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/generic-associated-types/bugs/hrtb-implied-2.rs b/src/test/ui/generic-associated-types/bugs/hrtb-implied-2.rs
new file mode 100644
index 00000000000..8e6c5348e71
--- /dev/null
+++ b/src/test/ui/generic-associated-types/bugs/hrtb-implied-2.rs
@@ -0,0 +1,40 @@
+// 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"
+
+trait LendingIterator: Sized {
+    type Item<'a>
+    where
+        Self: 'a;
+    fn next(&mut self) -> Self::Item<'_>;
+}
+fn fails<I: LendingIterator, F>(iter: &mut I, f: F) -> bool
+where
+    F: FnMut(I::Item<'_>),
+{
+    let mut iter2 = Eat(iter, f);
+    let _next = iter2.next();
+    //~^ borrowed data escapes
+    true
+}
+impl<I: LendingIterator> LendingIterator for &mut I {
+    type Item<'a> = I::Item<'a> where Self:'a;
+    fn next(&mut self) -> Self::Item<'_> {
+        (**self).next()
+    }
+}
+
+struct Eat<I, F>(I, F);
+impl<I: LendingIterator, F> Iterator for Eat<I, F>
+where
+    F: FnMut(I::Item<'_>),
+{
+    type Item = ();
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/generic-associated-types/bugs/hrtb-implied-2.stderr b/src/test/ui/generic-associated-types/bugs/hrtb-implied-2.stderr
new file mode 100644
index 00000000000..1ee270398de
--- /dev/null
+++ b/src/test/ui/generic-associated-types/bugs/hrtb-implied-2.stderr
@@ -0,0 +1,22 @@
+error[E0521]: borrowed data escapes outside of function
+  --> $DIR/hrtb-implied-2.rs:18:17
+   |
+LL | fn fails<I: LendingIterator, F>(iter: &mut I, f: F) -> bool
+   |                                 ----  - let's call the lifetime of this reference `'1`
+   |                                 |
+   |                                 `iter` is a reference that is only valid in the function body
+...
+LL |     let _next = iter2.next();
+   |                 ^^^^^^^^^^^^
+   |                 |
+   |                 `iter` escapes the function body here
+   |                 argument requires that `'1` must outlive `'static`
+   |
+   = note: requirement occurs because of a mutable reference to `Eat<&mut I, F>`
+   = note: mutable references are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+   = note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0521`.
diff --git a/src/test/ui/generic-associated-types/bugs/hrtb-implied-3.rs b/src/test/ui/generic-associated-types/bugs/hrtb-implied-3.rs
new file mode 100644
index 00000000000..bc9e6c8aea8
--- /dev/null
+++ b/src/test/ui/generic-associated-types/bugs/hrtb-implied-3.rs
@@ -0,0 +1,23 @@
+trait LendingIterator {
+    type Item<'a>
+    where
+        Self: 'a;
+}
+
+impl LendingIterator for &str {
+    type Item<'a> = () where Self:'a;
+}
+
+fn trivial_bound<I>(_: I)
+where
+    I: LendingIterator,
+    for<'a> I::Item<'a>: Sized,
+{
+}
+
+fn fails(iter: &str) {
+    trivial_bound(iter);
+    //~^ borrowed data escapes
+}
+
+fn main() {}
diff --git a/src/test/ui/generic-associated-types/bugs/hrtb-implied-3.stderr b/src/test/ui/generic-associated-types/bugs/hrtb-implied-3.stderr
new file mode 100644
index 00000000000..c67e02437cd
--- /dev/null
+++ b/src/test/ui/generic-associated-types/bugs/hrtb-implied-3.stderr
@@ -0,0 +1,22 @@
+error[E0521]: borrowed data escapes outside of function
+  --> $DIR/hrtb-implied-3.rs:19:5
+   |
+LL | fn fails(iter: &str) {
+   |          ----  - let's call the lifetime of this reference `'1`
+   |          |
+   |          `iter` is a reference that is only valid in the function body
+LL |     trivial_bound(iter);
+   |     ^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     `iter` escapes the function body here
+   |     argument requires that `'1` must outlive `'static`
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/hrtb-implied-3.rs:14:26
+   |
+LL |     for<'a> I::Item<'a>: Sized,
+   |                          ^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0521`.
diff --git a/src/test/ui/generic-associated-types/trait-objects.extended.stderr b/src/test/ui/generic-associated-types/trait-objects.extended.stderr
index 086177cc106..45b64d2b024 100644
--- a/src/test/ui/generic-associated-types/trait-objects.extended.stderr
+++ b/src/test/ui/generic-associated-types/trait-objects.extended.stderr
@@ -11,6 +11,8 @@ LL |     x.size_hint().0
    |     |
    |     `x` escapes the function body here
    |     argument requires that `'1` must outlive `'static`
+   |
+   = note: due to current limitations in the borrow checker, this implies a `'static` lifetime
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/higher-rank-trait-bounds/hrtb-just-for-static.stderr b/src/test/ui/higher-rank-trait-bounds/hrtb-just-for-static.stderr
index b4312091edb..31e11e12835 100644
--- a/src/test/ui/higher-rank-trait-bounds/hrtb-just-for-static.stderr
+++ b/src/test/ui/higher-rank-trait-bounds/hrtb-just-for-static.stderr
@@ -14,6 +14,12 @@ LL | fn give_some<'a>() {
    |              -- lifetime `'a` defined here
 LL |     want_hrtb::<&'a u32>()
    |     ^^^^^^^^^^^^^^^^^^^^ requires that `'a` must outlive `'static`
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/hrtb-just-for-static.rs:9:15
+   |
+LL |     where T : for<'a> Foo<&'a isize>
+   |               ^^^^^^^^^^^^^^^^^^^^^^
 
 error: implementation of `Foo` is not general enough
   --> $DIR/hrtb-just-for-static.rs:30:5
diff --git a/src/test/ui/higher-rank-trait-bounds/hrtb-perfect-forwarding.stderr b/src/test/ui/higher-rank-trait-bounds/hrtb-perfect-forwarding.stderr
index 1461e7fd2dd..5e75a4cc8af 100644
--- a/src/test/ui/higher-rank-trait-bounds/hrtb-perfect-forwarding.stderr
+++ b/src/test/ui/higher-rank-trait-bounds/hrtb-perfect-forwarding.stderr
@@ -46,6 +46,12 @@ LL | fn foo_hrtb_bar_not<'b, T>(mut t: T)
 ...
 LL |     foo_hrtb_bar_not(&mut t);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'b` must outlive `'static`
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/hrtb-perfect-forwarding.rs:37:8
+   |
+LL |     T: for<'a> Foo<&'a isize> + Bar<&'b isize>,
+   |        ^^^^^^^^^^^^^^^^^^^^^^
 
 error: implementation of `Bar` is not general enough
   --> $DIR/hrtb-perfect-forwarding.rs:43:5
diff --git a/src/test/ui/issues/issue-26217.stderr b/src/test/ui/issues/issue-26217.stderr
index c7601caacdc..73c772205c3 100644
--- a/src/test/ui/issues/issue-26217.stderr
+++ b/src/test/ui/issues/issue-26217.stderr
@@ -5,6 +5,12 @@ LL | fn bar<'a>() {
    |        -- lifetime `'a` defined here
 LL |     foo::<&'a i32>();
    |     ^^^^^^^^^^^^^^ requires that `'a` must outlive `'static`
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/issue-26217.rs:1:30
+   |
+LL | fn foo<T>() where for<'a> T: 'a {}
+   |                              ^^
 
 error: aborting due to previous error
 
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
 
diff --git a/src/test/ui/nll/type-test-universe.stderr b/src/test/ui/nll/type-test-universe.stderr
index 242486c360a..31e17d64b8c 100644
--- a/src/test/ui/nll/type-test-universe.stderr
+++ b/src/test/ui/nll/type-test-universe.stderr
@@ -11,6 +11,12 @@ LL | fn test2<'a>() {
    |          -- lifetime `'a` defined here
 LL |     outlives_forall::<Value<'a>>();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'a` must outlive `'static`
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/type-test-universe.rs:6:16
+   |
+LL |     for<'u> T: 'u,
+   |                ^^
 
 error: aborting due to 2 previous errors