`unit_cmp`: don't lint on explicitly written unit expr (#15562)

Fixes rust-lang/rust-clippy#15559

changelog: [`unit_cmp`]: don't lint on explicitly written unit expr

3 files changed, 42 insertions, 4 deletions

diff --git a/clippy_lints/src/unit_types/unit_cmp.rs b/clippy_lints/src/unit_types/unit_cmp.rs
index 48b532968cb..38716519e23 100644
--- a/clippy_lints/src/unit_types/unit_cmp.rs
+++ b/clippy_lints/src/unit_types/unit_cmp.rs
@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::span_lint;
 use clippy_utils::macros::{find_assert_eq_args, root_macro_call_first_node};
-use clippy_utils::sym;
+use clippy_utils::{is_unit_expr, sym};
 use rustc_hir::{BinOpKind, Expr, ExprKind};
 use rustc_lint::LateContext;
 
@@ -16,10 +16,13 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>) {
                 sym::assert_ne_macro | sym::debug_assert_ne_macro => "fail",
                 _ => return,
             };
-            let Some((left, _, _)) = find_assert_eq_args(cx, expr, macro_call.expn) else {
+            let Some((lhs, rhs, _)) = find_assert_eq_args(cx, expr, macro_call.expn) else {
                 return;
             };
-            if !cx.typeck_results().expr_ty(left).is_unit() {
+            if is_unit_expr(lhs) || is_unit_expr(rhs) {
+                return;
+            }
+            if !cx.typeck_results().expr_ty(lhs).is_unit() {
                 return;
             }
             span_lint(
diff --git a/tests/ui/unit_cmp.rs b/tests/ui/unit_cmp.rs
index 93f5b87c3d2..0a0fe3a1990 100644
--- a/tests/ui/unit_cmp.rs
+++ b/tests/ui/unit_cmp.rs
@@ -68,3 +68,20 @@ fn main() {
         }
     );
 }
+
+fn issue15559() {
+    fn foo() {}
+    assert_eq!(
+        //~^ unit_cmp
+        {
+            1;
+        },
+        foo()
+    );
+    assert_eq!(foo(), foo());
+    //~^ unit_cmp
+
+    // don't lint on explicitly written unit expr
+    assert_eq!(foo(), ());
+    assert_ne!((), ContainsUnit(()).0);
+}
diff --git a/tests/ui/unit_cmp.stderr b/tests/ui/unit_cmp.stderr
index 8f26749fd86..21aa9dce151 100644
--- a/tests/ui/unit_cmp.stderr
+++ b/tests/ui/unit_cmp.stderr
@@ -71,5 +71,23 @@ LL | |             true;
 LL | |     );
    | |_____^
 
-error: aborting due to 6 previous errors
+error: `assert_eq` of unit values detected. This will always succeed
+  --> tests/ui/unit_cmp.rs:74:5
+   |
+LL | /     assert_eq!(
+LL | |
+LL | |         {
+LL | |             1;
+LL | |         },
+LL | |         foo()
+LL | |     );
+   | |_____^
+
+error: `assert_eq` of unit values detected. This will always succeed
+  --> tests/ui/unit_cmp.rs:81:5
+   |
+LL |     assert_eq!(foo(), foo());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 8 previous errors