rustc_hir_typeck: Account for skipped_ref_pats in expr_use_visitor

Fixes #125058

Author: Jules-Bertholet

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -18,12 +18,12 @@ use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, Res};
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::{HirId, PatKind};
-use rustc_middle::{bug, span_bug};
 use rustc_middle::hir::place::ProjectionKind;
 use rustc_middle::mir::FakeReadCause;
 use rustc_middle::ty::{
     self, adjustment, AdtKind, Ty, TyCtxt, TypeFoldable, TypeVisitableExt as _,
 };
+use rustc_middle::{bug, span_bug};
 use rustc_span::{ErrorGuaranteed, Span};
 use rustc_target::abi::{FieldIdx, VariantIdx, FIRST_VARIANT};
 use rustc_trait_selection::infer::InferCtxtExt;
@@ -1181,6 +1181,10 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 debug!("pat_ty(pat={:?}) found adjusted ty `{:?}`", pat, first_ty);
                 return Ok(*first_ty);
             }
+        } else if let PatKind::Ref(subpat, _) = pat.kind
+            && self.cx.typeck_results().skipped_ref_pats().contains(pat.hir_id)
+        {
+            return self.pat_ty_adjusted(subpat);
         }
 
         self.pat_ty_unadjusted(pat)
@@ -1712,6 +1716,12 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 self.cat_pattern(place_with_id, subpat, op)?;
             }
 
+            PatKind::Ref(subpat, _)
+                if self.cx.typeck_results().skipped_ref_pats().contains(pat.hir_id) =>
+            {
+                self.cat_pattern(place_with_id, subpat, op)?;
+            }
+
             PatKind::Box(subpat) | PatKind::Ref(subpat, _) => {
                 // box p1, &p1, &mut p1. we can ignore the mutability of
                 // PatKind::Ref since that information is already contained

tests/ui/pattern/skipped-ref-pats-issue-125058.rs

@@ -0,0 +1,18 @@
+//@ run-pass
+//@ edition: 2024
+//@ compile-flags: -Zunstable-options
+
+#![allow(incomplete_features)]
+#![feature(ref_pat_eat_one_layer_2024)]
+
+struct Foo;
+//~^ WARN struct `Foo` is never constructed
+
+fn main() {
+    || {
+        //~^ WARN unused closure that must be used
+        if let Some(Some(&mut x)) = &mut Some(&mut Some(0)) {
+            let _: u32 = x;
+        }
+    };
+}

tests/ui/pattern/skipped-ref-pats-issue-125058.stderr

@@ -0,0 +1,24 @@
+warning: struct `Foo` is never constructed
+  --> $DIR/skipped-ref-pats-issue-125058.rs:8:8
+   |
+LL | struct Foo;
+   |        ^^^
+   |
+   = note: `#[warn(dead_code)]` on by default
+
+warning: unused closure that must be used
+  --> $DIR/skipped-ref-pats-issue-125058.rs:12:5
+   |
+LL | /     || {
+LL | |
+LL | |         if let Some(Some(&mut x)) = &mut Some(&mut Some(0)) {
+LL | |             let _: u32 = x;
+LL | |         }
+LL | |     };
+   | |_____^
+   |
+   = note: closures are lazy and do nothing unless called
+   = note: `#[warn(unused_must_use)]` on by default
+
+warning: 2 warnings emitted
+