`clippy::vec_init_then_push` can't be ignored

Summary

I'm trying to come up with a configuration array that takes objects that are of a given type. The items in this global list can vary depending on compilation settings. As a result, I'm constructing the values in a LazyLock.

The items that are added to the vec depend on feature flags. As a result, I can't construct a vec![] as it suggests. Additionally, I can't seem to be able to turn them off in the obvious way.

Lint Name

vec_init_then_push

Reproducer

I tried this code:

#![allow(unexpected_cfgs)]
use std::sync::RwLock;
use std::sync::LazyLock;

trait ExampleTrait: Send + Sync {
    fn value(&self) -> u32;
}

struct Object {
    val: u32,
}

impl ExampleTrait for Object {
    fn value(&self) -> u32 {
        self.val
    }
}

fn init_object(val: u32) -> Object {
    Object { val }
}

static OBJECTS: LazyLock<RwLock<Vec<Box<dyn ExampleTrait>>>> = LazyLock::new(|| {
    #[allow(clippy::vec_init_then_push)]
    let mut v: Vec<Box<dyn ExampleTrait>> = vec![];
    
    #[allow(clippy::vec_init_then_push)]
    v.push(Box::new(init_object(1)));

    #[cfg(feature = "other-feature")]
    #[allow(clippy::vec_init_then_push)]
    v.push(Box::new(init_object(2)));
    
    RwLock::new(v)
});

fn main() {
    let test_list = &*OBJECTS.read().unwrap();
    for val in test_list {
        println!("Val: {}", val.value());
    }
}

I saw this happen:

warning: calls to `push` immediately after creation
  --> src/main.rs:25:5
   |
25 | /     let mut v: Vec<Box<dyn ExampleTrait>> = vec![];
26 | |     
27 | |     #[allow(clippy::vec_init_then_push)]
28 | |     v.push(Box::new(init_object(1)));
   | |_____________________________________^ help: consider using the `vec![]` macro: `let v: Vec<Box<dyn ExampleTrait>> = vec![..];`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#vec_init_then_push
   = note: `#[warn(clippy::vec_init_then_push)]` on by default

I expected to see this happen:

No output, especially since I ignored the lint immediately above.

Version

rustc 1.87.0 (17067e9ac 2025-05-09)
binary: rustc
commit-hash: 17067e9ac6d7ecb70e50f92c1944e545188d2359
commit-date: 2025-05-09
host: x86_64-unknown-linux-gnu
release: 1.87.0
LLVM version: 20.1.1

Additional Labels

No response

Start with the vec_init_then_push lint implementation and reproduce the report using the linked Rust Playground example. Check how the lint selects its diagnostic span relative to the #[allow] attributes, including the cfg-gated push. Done means the shown allow attributes suppress the warning without changing the intended conditional initialization behavior.