Rollup merge of #116379 - fmease:opaq-hid-inf-bnds-non-lt-bndrs, r=compiler-errors

non_lifetime_binders: fix ICE in lint opaque-hidden-inferred-bound

Opaque types like `impl for<T> Trait<T>` would previously lead to an ICE.

r? `@compiler-errors`

compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs

@@ -37,8 +37,6 @@
     ///     type Assoc: Duh;
     /// }
     ///
-    /// struct Struct;
-    ///
     /// impl<F: Duh> Trait for F {
     ///     type Assoc = F;
     /// }
@@ -53,12 +51,12 @@
     /// {{produces}}
     ///
     /// In this example, `test` declares that the associated type `Assoc` for
-    /// `impl Trait` is `impl Sized`, which does not satisfy the `Send` bound
+    /// `impl Trait` is `impl Sized`, which does not satisfy the bound `Duh`
     /// on the associated type.
     ///
     /// Although the hidden type, `i32` does satisfy this bound, we do not
     /// consider the return type to be well-formed with this lint. It can be
-    /// fixed by changing `Tait = impl Sized` into `Tait = impl Sized + Send`.
+    /// fixed by changing `Tait = impl Sized` into `Tait = impl Sized + Duh`.
     pub OPAQUE_HIDDEN_INFERRED_BOUND,
     Warn,
     "detects the use of nested `impl Trait` types in associated type bounds that are not general enough"
@@ -79,9 +77,7 @@ fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
         for (pred, pred_span) in
             cx.tcx.explicit_item_bounds(def_id).instantiate_identity_iter_copied()
         {
-            // Liberate bound regions in the predicate since we
-            // don't actually care about lifetimes in this check.
-            let predicate = cx.tcx.liberate_late_bound_regions(def_id, pred.kind());
+            let predicate = infcx.instantiate_binder_with_placeholders(pred.kind());
             let ty::ClauseKind::Projection(proj) = predicate else {
                 continue;
             };

tests/ui/traits/non_lifetime_binders/on-rpit.rs

@@ -0,0 +1,16 @@
+// check-pass
+
+#![feature(non_lifetime_binders)]
+//~^ WARN the feature `non_lifetime_binders` is incomplete
+
+trait Trait<T: ?Sized> {}
+
+impl<T: ?Sized> Trait<T> for i32 {}
+
+fn produce() -> impl for<T> Trait<T> {
+    16
+}
+
+fn main() {
+    let _ = produce();
+}

tests/ui/traits/non_lifetime_binders/on-rpit.stderr

@@ -0,0 +1,11 @@
+warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/on-rpit.rs:3:12
+   |
+LL | #![feature(non_lifetime_binders)]
+   |            ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+