From ee6d5c5cdae8b7cb3198800a615855169fc0b3de Mon Sep 17 00:00:00 2001
From: Alex Ozdemir <aozdemir@hmc.edu>
Date: Tue, 28 Dec 2021 08:32:55 -0800
Subject: contants peel_refs to catch `x << &0`

---
 clippy_lints/src/identity_op.rs | 4 ++--
 clippy_utils/src/consts.rs      | 8 ++++++++
 tests/ui/identity_op.rs         | 3 ++-
 tests/ui/identity_op.stderr     | 8 +++++++-
 4 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/clippy_lints/src/identity_op.rs b/clippy_lints/src/identity_op.rs
index de60e284cad..f824f20ca40 100644
--- a/clippy_lints/src/identity_op.rs
+++ b/clippy_lints/src/identity_op.rs
@@ -71,8 +71,8 @@ fn is_allowed(cx: &LateContext<'_>, cmp: BinOp, left: &Expr<'_>, right: &Expr<'_
 }
 
 fn check(cx: &LateContext<'_>, e: &Expr<'_>, m: i8, span: Span, arg: Span) {
-    if let Some(Constant::Int(v)) = constant_simple(cx, cx.typeck_results(), e) {
-        let check = match *cx.typeck_results().expr_ty(e).kind() {
+    if let Some(Constant::Int(v)) = constant_simple(cx, cx.typeck_results(), e).map(Constant::peel_refs) {
+        let check = match *cx.typeck_results().expr_ty(e).peel_refs().kind() {
             ty::Int(ity) => unsext(cx.tcx, -1_i128, ity),
             ty::Uint(uty) => clip(cx.tcx, !0, uty),
             _ => return,
diff --git a/clippy_utils/src/consts.rs b/clippy_utils/src/consts.rs
index 04347672e0f..1cf8f9721b5 100644
--- a/clippy_utils/src/consts.rs
+++ b/clippy_utils/src/consts.rs
@@ -168,6 +168,14 @@ impl Constant {
             None
         }
     }
+
+    #[must_use]
+    pub fn peel_refs(mut self) -> Self {
+        while let Constant::Ref(r) = self {
+            self = *r;
+        }
+        self
+    }
 }
 
 /// Parses a `LitKind` to a `Constant`.
diff --git a/tests/ui/identity_op.rs b/tests/ui/identity_op.rs
index a3985b68fbb..2ed4b5db574 100644
--- a/tests/ui/identity_op.rs
+++ b/tests/ui/identity_op.rs
@@ -11,11 +11,11 @@ impl std::ops::Shl<i32> for A {
         self
     }
 }
-
 #[allow(
     clippy::eq_op,
     clippy::no_effect,
     clippy::unnecessary_operation,
+    clippy::op_ref,
     clippy::double_parens
 )]
 #[warn(clippy::identity_op)]
@@ -49,6 +49,7 @@ fn main() {
     1 >> 0;
     42 >> 0;
     &x >> 0;
+    x >> &0;
 
     let mut a = A("".into());
     let b = a << 0; // no error: non-integer
diff --git a/tests/ui/identity_op.stderr b/tests/ui/identity_op.stderr
index 5b63eb9cc4f..ff34b38db01 100644
--- a/tests/ui/identity_op.stderr
+++ b/tests/ui/identity_op.stderr
@@ -72,5 +72,11 @@ error: the operation is ineffective. Consider reducing it to `&x`
 LL |     &x >> 0;
    |     ^^^^^^^
 
-error: aborting due to 12 previous errors
+error: the operation is ineffective. Consider reducing it to `x`
+  --> $DIR/identity_op.rs:52:5
+   |
+LL |     x >> &0;
+   |     ^^^^^^^
+
+error: aborting due to 13 previous errors
 
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