Fix FP when coercion kicks in

Author: giraffate

clippy_lints/src/loops.rs

@@ -1140,7 +1140,8 @@ fn detect_same_item_push<'tcx>(
     walk_expr(&mut same_item_push_visitor, body);
     if same_item_push_visitor.should_lint {
         if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
-            let ty = cx.typeck_results().expr_ty(pushed_item);
+            let vec_ty = cx.typeck_results().expr_ty(vec);
+            let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
             if cx
                 .tcx
                 .lang_items()

tests/ui/same_item_push.rs

@@ -100,4 +100,15 @@ fn main() {
     for _ in 0..10 {
         vec14.push(std::fs::File::open("foobar").unwrap());
     }
+    // Fix #5979
+    #[derive(Clone)]
+    struct S {}
+
+    trait T {}
+    impl T for S {}
+
+    let mut vec15: Vec<Box<dyn T>> = Vec::new();
+    for _ in 0..10 {
+        vec15.push(Box::new(S {}));
+    }
 }