don't allow fields whose types are uncertain

Author: ada4a

clippy_lints/src/no_effect.rs

@@ -348,7 +348,9 @@ fn reduce_expression<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<Vec
             reduce_expression(cx, inner).or_else(|| Some(vec![inner]))
         },
         ExprKind::Struct(_, fields, ref base) => {
-            if has_drop(cx, cx.typeck_results().expr_ty(expr)) {
+            if fields.iter().any(|f| !expr_type_is_certain(cx, &f.expr))
+                || has_drop(cx, cx.typeck_results().expr_ty(expr))
+            {
                 None
             } else {
                 let base = match base {

tests/ui/unnecessary_operation.fixed

@@ -157,3 +157,15 @@ fn issue15173_original<MsU>(handler: impl FnOnce() -> MsU + Clone + 'static) {
         None
     }) as Box<dyn Fn(i32) -> Option<i32>>;
 }
+
+fn issue15381() {
+    struct Resources;
+    struct DescriptorSet {
+        slots: Vec<Resources>,
+    }
+
+    fn main() {
+        Vec::new();
+        //~^ unnecessary_operation
+    }
+}

tests/ui/unnecessary_operation.stderr

@@ -67,12 +67,6 @@ error: unnecessary operation
 LL |     ..get_number();
    |     ^^^^^^^^^^^^^^^ help: statement can be reduced to: `get_number();`
 
-error: unnecessary operation
-  --> tests/ui/unnecessary_operation.rs:93:5
-   |
-LL |     5..get_number();
-   |     ^^^^^^^^^^^^^^^^ help: statement can be reduced to: `5;get_number();`
-
 error: unnecessary operation
   --> tests/ui/unnecessary_operation.rs:95:5
    |
@@ -112,26 +106,11 @@ LL | |         get_number()
 LL | |     };
    | |______^ help: statement can be reduced to: `get_number();`
 
-error: unnecessary operation
-  --> tests/ui/unnecessary_operation.rs:109:5
-   |
-LL | /     FooString {
-LL | |
-LL | |         s: String::from("blah"),
-LL | |     };
-   | |______^ help: statement can be reduced to: `String::from("blah");`
-
 error: unnecessary operation
   --> tests/ui/unnecessary_operation.rs:150:5
    |
 LL |     [42, 55][get_usize()];
    |     ^^^^^^^^^^^^^^^^^^^^^^ help: statement can be written as: `assert!([42, 55].len() > get_usize());`
 
-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
+error: aborting due to 18 previous errors