add failing test

Author: ada4a

tests/ui/unnecessary_operation.rs

@@ -163,3 +163,12 @@ fn issue15173_original<MsU>(handler: impl FnOnce() -> MsU + Clone + 'static) {
         None
     }) as Box<dyn Fn(i32) -> Option<i32>>;
 }
+
+// don't lint if any of the fields has an ambiguous type when used by themselves
+fn issue15381() {
+    struct DescriptorSet {
+        slots: Vec<u32>,
+    }
+
+    DescriptorSet { slots: Vec::new() };
+}

tests/ui/unnecessary_operation.stderr

@@ -127,5 +127,11 @@ error: unnecessary operation
 LL |     [42, 55][get_usize()];
    |     ^^^^^^^^^^^^^^^^^^^^^^ help: statement can be written as: `assert!([42, 55].len() > get_usize());`
 
-error: aborting due to 20 previous errors
+error: unnecessary operation
+  --> tests/ui/unnecessary_operation.rs:173:5
+   |
+LL |     DescriptorSet { slots: Vec::new() };
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: statement can be reduced to: `Vec::new();`
+
+error: aborting due to 21 previous errors