Auto merge of #116435 - compiler-errors:re-erased, r=lcnr

Handle `ReErased` in responses in new solver

There are legitimate cases in the compiler where we return `ReErased` for lifetimes that are uncaptured in the hidden type of an opaque. For example, in the test committed below, we ignore ignore the bivariant lifetimes of an opaque when it's inferred as the hidden type of another opaque. This may result in a `type_of(Opaque)` call returning a type that references `ReErased`. Let's handle this gracefully in the new solver.

Also added a `rustc_hidden_type_of_opaques` attr to print hidden types. This seems useful for opaques.

r? lcnr

3 files changed, 51 insertions, 0 deletions

diff --git a/tests/ui/impl-trait/erased-regions-in-hidden-ty.current.stderr b/tests/ui/impl-trait/erased-regions-in-hidden-ty.current.stderr
new file mode 100644
index 00000000000..84b61dc5044
--- /dev/null
+++ b/tests/ui/impl-trait/erased-regions-in-hidden-ty.current.stderr
@@ -0,0 +1,14 @@
+error: {foo<ReEarlyBound(DefId(..), 0, 'a)>::{closure#0} closure_kind_ty=i8 closure_sig_as_fn_ptr_ty=extern "rust-call" fn(()) upvar_tys=()}
+  --> $DIR/erased-regions-in-hidden-ty.rs:11:36
+   |
+LL | fn foo<'a: 'a>(x: &'a Vec<i32>) -> impl Fn() + 'static {
+   |                                    ^^^^^^^^^^^^^^^^^^^
+
+error: Opaque(DefId(..), [ReErased])
+  --> $DIR/erased-regions-in-hidden-ty.rs:17:13
+   |
+LL | fn bar() -> impl Fn() + 'static {
+   |             ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
diff --git a/tests/ui/impl-trait/erased-regions-in-hidden-ty.next.stderr b/tests/ui/impl-trait/erased-regions-in-hidden-ty.next.stderr
new file mode 100644
index 00000000000..84b61dc5044
--- /dev/null
+++ b/tests/ui/impl-trait/erased-regions-in-hidden-ty.next.stderr
@@ -0,0 +1,14 @@
+error: {foo<ReEarlyBound(DefId(..), 0, 'a)>::{closure#0} closure_kind_ty=i8 closure_sig_as_fn_ptr_ty=extern "rust-call" fn(()) upvar_tys=()}
+  --> $DIR/erased-regions-in-hidden-ty.rs:11:36
+   |
+LL | fn foo<'a: 'a>(x: &'a Vec<i32>) -> impl Fn() + 'static {
+   |                                    ^^^^^^^^^^^^^^^^^^^
+
+error: Opaque(DefId(..), [ReErased])
+  --> $DIR/erased-regions-in-hidden-ty.rs:17:13
+   |
+LL | fn bar() -> impl Fn() + 'static {
+   |             ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
diff --git a/tests/ui/impl-trait/erased-regions-in-hidden-ty.rs b/tests/ui/impl-trait/erased-regions-in-hidden-ty.rs
new file mode 100644
index 00000000000..698123a932d
--- /dev/null
+++ b/tests/ui/impl-trait/erased-regions-in-hidden-ty.rs
@@ -0,0 +1,23 @@
+// revisions: current next
+// compile-flags: -Zverbose
+//[next] compile-flags: -Ztrait-solver=next
+// normalize-stderr-test "DefId\([^\)]+\)" -> "DefId(..)"
+
+#![feature(rustc_attrs)]
+#![rustc_hidden_type_of_opaques]
+
+// Make sure that the compiler can handle `ReErased` in the hidden type of an opaque.
+
+fn foo<'a: 'a>(x: &'a Vec<i32>) -> impl Fn() + 'static {
+//~^ ERROR 0, 'a)>::{closure#0} closure_kind_ty=i8 closure_sig_as_fn_ptr_ty=extern "rust-call" fn(()) upvar_tys=()}
+// Can't write whole type because of lack of path sanitization
+    || ()
+}
+
+fn bar() -> impl Fn() + 'static {
+//~^ ERROR , [ReErased])
+// Can't write whole type because of lack of path sanitization
+    foo(&vec![])
+}
+
+fn main() {}