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#![allow(unused)]
#![warn(clippy::collection_is_never_read)]
use std::collections::{HashMap, HashSet};
fn main() {}
fn not_a_collection() {
// TODO: Expand `collection_is_never_read` beyond collections?
let mut x = 10; // Ok
x += 1;
}
fn no_access_at_all() {
// Other lints should catch this.
let x = vec![1, 2, 3]; // Ok
}
fn write_without_read() {
// The main use case for `collection_is_never_read`.
let mut x = HashMap::new(); // WARNING
x.insert(1, 2);
}
fn read_without_write() {
let mut x = vec![1, 2, 3]; // Ok
let _ = x.len();
}
fn write_and_read() {
let mut x = vec![1, 2, 3]; // Ok
x.push(4);
let _ = x.len();
}
fn write_after_read() {
// TODO: Warn here, but this requires more extensive data flow analysis.
let mut x = vec![1, 2, 3]; // Ok
let _ = x.len();
x.push(4); // Pointless
}
fn write_before_reassign() {
// TODO: Warn here, but this requires more extensive data flow analysis.
let mut x = HashMap::new(); // Ok
x.insert(1, 2); // Pointless
x = HashMap::new();
let _ = x.len();
}
fn read_in_closure() {
let mut x = HashMap::new(); // Ok
x.insert(1, 2);
let _ = || {
let _ = x.len();
};
}
fn write_in_closure() {
let mut x = vec![1, 2, 3]; // WARNING
let _ = || {
x.push(4);
};
}
fn read_in_format() {
let mut x = HashMap::new(); // Ok
x.insert(1, 2);
format!("{x:?}");
}
fn shadowing_1() {
let x = HashMap::<usize, usize>::new(); // Ok
let _ = x.len();
let mut x = HashMap::new(); // WARNING
x.insert(1, 2);
}
fn shadowing_2() {
let mut x = HashMap::new(); // WARNING
x.insert(1, 2);
let x = HashMap::<usize, usize>::new(); // Ok
let _ = x.len();
}
#[allow(clippy::let_unit_value)]
fn fake_read_1() {
let mut x = vec![1, 2, 3]; // WARNING
x.reverse();
let _: () = x.clear();
}
fn fake_read_2() {
let mut x = vec![1, 2, 3]; // WARNING
x.reverse();
println!("{:?}", x.push(5));
}
fn assignment() {
let mut x = vec![1, 2, 3]; // WARNING
let y = vec![4, 5, 6]; // Ok
x = y;
}
#[allow(clippy::self_assignment)]
fn self_assignment() {
let mut x = vec![1, 2, 3]; // WARNING
x = x;
}
fn method_argument_but_not_target() {
struct MyStruct;
impl MyStruct {
fn my_method(&self, _argument: &[usize]) {}
}
let my_struct = MyStruct;
let mut x = vec![1, 2, 3]; // Ok
x.reverse();
my_struct.my_method(&x);
}
fn insert_is_not_a_read() {
let mut x = HashSet::new(); // WARNING
x.insert(5);
}
fn insert_is_a_read() {
let mut x = HashSet::new(); // Ok
if x.insert(5) {
println!("5 was inserted");
}
}
fn not_read_if_return_value_not_used() {
// `is_empty` does not modify the set, so it's a query. But since the return value is not used, the
// lint does not consider it a read here.
let x = vec![1, 2, 3]; // WARNING
x.is_empty();
}
fn extension_traits() {
trait VecExt<T> {
fn method_with_side_effect(&self);
fn method_without_side_effect(&self);
}
impl<T> VecExt<T> for Vec<T> {
fn method_with_side_effect(&self) {
println!("my length: {}", self.len());
}
fn method_without_side_effect(&self) {}
}
let x = vec![1, 2, 3]; // Ok
x.method_with_side_effect();
let y = vec![1, 2, 3]; // Ok (false negative)
y.method_without_side_effect();
}
fn function_argument() {
#[allow(clippy::ptr_arg)]
fn foo<T>(v: &Vec<T>) -> usize {
v.len()
}
let x = vec![1, 2, 3]; // Ok
foo(&x);
}
fn string() {
// Do lint (write without read)
let mut s = String::new();
s.push_str("Hello, World!");
// Do not lint (read without write)
let mut s = String::from("Hello, World!");
let _ = s.len();
// Do not lint (write and read)
let mut s = String::from("Hello, World!");
s.push_str("foo, bar");
let _ = s.len();
// Do lint the first line, but not the second
let mut s = String::from("Hello, World!");
let t = String::from("foo, bar");
s = t;
}
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