From b6cbe33aeb526d6437304f4810762c947bddcd4a Mon Sep 17 00:00:00 2001
From: lcnr <rust@lcnr.de>
Date: Fri, 25 Jul 2025 12:38:54 +0000
Subject: handle region dependent goals due to infer vars

---
 .../ambiguity-due-to-uniquification-3.next.stderr  | 19 +++++++++++++
 .../assembly/ambiguity-due-to-uniquification-3.rs  | 33 ++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.next.stderr
 create mode 100644 tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.rs

(limited to 'tests')

diff --git a/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.next.stderr b/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.next.stderr
new file mode 100644
index 00000000000..e25f892b365
--- /dev/null
+++ b/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.next.stderr
@@ -0,0 +1,19 @@
+error[E0283]: type annotations needed: cannot satisfy `(dyn Object<&(), &()> + 'static): Trait<&()>`
+  --> $DIR/ambiguity-due-to-uniquification-3.rs:28:17
+   |
+LL |     impls_trait(obj, t);
+   |     ----------- ^^^
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = note: cannot satisfy `(dyn Object<&(), &()> + 'static): Trait<&()>`
+   = help: the trait `Trait<T>` is implemented for `()`
+note: required by a bound in `impls_trait`
+  --> $DIR/ambiguity-due-to-uniquification-3.rs:24:19
+   |
+LL | fn impls_trait<T: Trait<U>, U>(_: Inv<T>, _: Inv<U>) {}
+   |                   ^^^^^^^^ required by this bound in `impls_trait`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0283`.
diff --git a/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.rs b/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.rs
new file mode 100644
index 00000000000..6dcd9d5bdf4
--- /dev/null
+++ b/tests/ui/traits/next-solver/assembly/ambiguity-due-to-uniquification-3.rs
@@ -0,0 +1,33 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[current] check-pass
+
+// Regression test from trait-system-refactor-initiative#27.
+//
+// Unlike in the previous two tests, `dyn Object<?x, ?y>: Trait<?x>` relies
+// on structural identity of type inference variables. This inference variable
+// gets constrained to a type containing a region later on. To prevent this
+// from causing an ICE during MIR borrowck, we stash goals which depend on
+// inference variables and then reprove them at the end of HIR typeck.
+
+#![feature(rustc_attrs)]
+#![rustc_no_implicit_bounds]
+trait Trait<T> {}
+impl<T> Trait<T> for () {}
+
+trait Object<T, U>: Trait<T> + Trait<U> {}
+
+#[derive(Clone, Copy)]
+struct Inv<T>(*mut T);
+fn foo<T: Sized, U: Sized>() -> (Inv<dyn Object<T, U>>, Inv<T>) { todo!() }
+fn impls_trait<T: Trait<U>, U>(_: Inv<T>, _: Inv<U>) {}
+
+fn bar() {
+    let (obj, t) = foo();
+    impls_trait(obj, t);
+    //[next]~^ ERROR type annotations needed
+    let _: Inv<dyn Object<&(), &()>> = obj;
+}
+
+fn main() {}
-- 
cgit 1.4.1-3-g733a5