Suggest `assert_ne` for `assert!(x != y)`

clippy_lints/src/should_assert_eq.rs

@@ -2,10 +2,10 @@ use rustc::lint::*;
 use rustc::hir::*;
 use utils::{is_direct_expn_of, implements_trait, span_lint};
 
-/// **What it does:** Checks for `assert!(x == y)` which can be better written
-/// as `assert_eq!(x, y)` if `x` and `y` implement `Debug` trait.
+/// **What it does:** Checks for `assert!(x == y)` or `assert!(x != y)` which can be better written
+/// using `assert_eq` or `assert_ne` if `x` and `y` implement `Debug` trait.
 ///
-/// **Why is this bad?** `assert_eq` provides better assertion failure reporting.
+/// **Why is this bad?** `assert_eq` and `assert_ne` provide better assertion failure reporting.
 ///
 /// **Known problems:** Hopefully none.
 ///
@@ -36,10 +36,15 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ShouldAssertEq {
             let ExprIf(ref cond, ..) = e.node,
             let ExprUnary(UnOp::UnNot, ref cond) = cond.node,
             let ExprBinary(ref binop, ref expr1, ref expr2) = cond.node,
-            binop.node == BinOp_::BiEq,
             is_direct_expn_of(cx, e.span, "assert").is_some(),
             let Some(debug_trait) = cx.tcx.lang_items.debug_trait(),
         ], {
+            let sugg = match binop.node {
+                BinOp_::BiEq => "assert_eq",
+                BinOp_::BiNe => "assert_ne",
+                _ => return,
+            };
+
             let ty1 = cx.tables.expr_ty(expr1);
             let ty2 = cx.tables.expr_ty(expr2);
 
@@ -47,7 +52,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ShouldAssertEq {
 
             if implements_trait(cx, ty1, debug_trait, &[], Some(parent)) &&
                 implements_trait(cx, ty2, debug_trait, &[], Some(parent)) {
-                span_lint(cx, SHOULD_ASSERT_EQ, e.span, "use `assert_eq` for better reporting");
+                span_lint(cx, SHOULD_ASSERT_EQ, e.span, &format!("use `{}` for better reporting", sugg));
             }
         }}
     }

tests/ui/should_assert_eq.rs

@@ -14,6 +14,8 @@ fn main() {
     assert!(1 == 2);
     assert!(Debug(1) == Debug(2));
     assert!(NonDebug(1) == NonDebug(1)); // ok
+    assert!(Debug(1) != Debug(2));
+    assert!(NonDebug(1) != NonDebug(2)); // ok
 
     test_generic(1, 2, 3, 4);
 }
@@ -21,4 +23,7 @@ fn main() {
 fn test_generic<T: std::fmt::Debug + Eq, U: Eq>(x: T, y: T, z: U, w: U) {
     assert!(x == y);
     assert!(z == w); // ok
+
+    assert!(x != y);
+    assert!(z != w); // ok
 }

tests/ui/should_assert_eq.stderr

@@ -19,13 +19,29 @@ error: use `assert_eq` for better reporting
    |
    = note: this error originates in a macro outside of the current crate
 
-error: use `assert_eq` for better reporting
-  --> $DIR/should_assert_eq.rs:22:5
+error: use `assert_ne` for better reporting
+  --> $DIR/should_assert_eq.rs:17:5
    |
-22 |     assert!(x == y);
+17 |     assert!(Debug(1) != Debug(2));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro outside of the current crate
+
+error: use `assert_eq` for better reporting
+  --> $DIR/should_assert_eq.rs:24:5
+   |
+24 |     assert!(x == y);
    |     ^^^^^^^^^^^^^^^^
    |
    = note: this error originates in a macro outside of the current crate
 
-error: aborting due to 3 previous errors
+error: use `assert_ne` for better reporting
+  --> $DIR/should_assert_eq.rs:27:5
+   |
+27 |     assert!(x != y);
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro outside of the current crate
+
+error: aborting due to 5 previous errors