EUV: fix place of deref pattern's interior's scrutinee

The place previously used here was that of the temporary holding the
reference returned by `Deref::deref` or `DerefMut::deref_mut`. However,
since the inner pattern of `deref!(inner)` expects the deref-target type
itself, this would ICE when that type was inspected (e.g. by the EUV
case for slice patterns). This adds a deref projection to fix that.

Since current in-tree consumers of EUV (upvar inference and clippy)
don't care about Rvalues, the place could be simplified to
`self.cat_rvalue(pat.hir_id, self.pat_ty_adjusted(subpat)?)` to save
some cycles. I personally find EUV to be a bit fragile, so I've opted
for pedantic correctness. Maybe a `HACK` comment would suffice though?

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/ui/pattern/deref-patterns/dont-ice-on-slice-in-deref-pat-in-closure.rs b/tests/ui/pattern/deref-patterns/dont-ice-on-slice-in-deref-pat-in-closure.rs
new file mode 100644
index 00000000000..e1a37b9c65f
--- /dev/null
+++ b/tests/ui/pattern/deref-patterns/dont-ice-on-slice-in-deref-pat-in-closure.rs
@@ -0,0 +1,15 @@
+//@ check-pass
+//! Regression test for ICE in `rustc_hir_typeck::expr_use_visitor` on nesting a slice pattern
+//! inside a deref pattern inside a closure: rust-lang/rust#125059
+
+#![feature(deref_patterns)]
+#![allow(incomplete_features, unused)]
+
+fn simple_vec(vec: Vec<u32>) -> u32 {
+   (|| match Vec::<u32>::new() {
+        deref!([]) => 100,
+        _ => 2000,
+    })()
+}
+
+fn main() {}