Lint on identical variable used as args in assert_eq! macro call

tests/ui/auxiliary/proc_macro_derive.rs

@@ -3,6 +3,7 @@
 
 #![crate_type = "proc-macro"]
 #![feature(repr128, proc_macro_quote)]
+#![allow(clippy::eq_op)]
 
 extern crate proc_macro;
 

tests/ui/double_parens.rs

@@ -1,5 +1,5 @@
 #![warn(clippy::double_parens)]
-#![allow(dead_code)]
+#![allow(dead_code, clippy::eq_op)]
 #![feature(custom_inner_attributes)]
 #![rustfmt::skip]
 

tests/ui/eq_op_early.rs

@@ -0,0 +1,15 @@
+#![warn(clippy::eq_op)]
+
+fn main() {
+    let a = 1;
+    let b = 2;
+
+    // lint identical args in `assert_eq!` (see #3574)
+    assert_eq!(a, a);
+    assert_eq!(a + 1, a + 1);
+
+    // ok
+    assert_eq!(a, b);
+    assert_eq!(a, a + 1);
+    assert_eq!(a + 1, b + 1);
+}

tests/ui/eq_op_early.stderr

@@ -0,0 +1,16 @@
+error: identical args used in this `assert_eq!` macro call
+  --> $DIR/eq_op_early.rs:8:16
+   |
+LL |     assert_eq!(a, a);
+   |                ^^^^
+   |
+   = note: `-D clippy::eq-op` implied by `-D warnings`
+
+error: identical args used in this `assert_eq!` macro call
+  --> $DIR/eq_op_early.rs:9:16
+   |
+LL |     assert_eq!(a + 1, a + 1);
+   |                ^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+

tests/ui/used_underscore_binding.rs

@@ -3,7 +3,7 @@
 
 #![feature(rustc_private)]
 #![warn(clippy::all)]
-#![allow(clippy::blacklisted_name)]
+#![allow(clippy::blacklisted_name, clippy::eq_op)]
 #![warn(clippy::used_underscore_binding)]
 
 #[macro_use]