Description
rust-analyzer version: 0.3.1631-standalone
rustc version: rustc 1.72.0 (5680fa18f 2023-08-23)
When you have an incomplete match statement (i.e. not covering all pattern variants) and one or more of the arms has unsafe code inside of unsafe { .. } blocks, Rust Analyzer will incorrectly put warnings on each unsafe keyword saying the unsafe block is unnecessary.
This was quite confusing, as when I encountered this, although I was aware my match statement was incomplete and I was in the process of filling in the missing variants, I actually removed the unsafe blocks due to these warnings because I thought "oh, I must be inside an unsafe fn", only to find that once I filled in the missing variants, it wanted the unsafe blocks back.
This toy example reproduces it:
enum MyEnum {
Red,
Blue,
Purple,
Gray,
Orange,
}
fn my_fn(input: MyEnum) -> u32 {
let bytes1 = [1u8, 2u8, 3u8, 4u8];
let bytes2 = [1u8, 3u8, 3u8, 4u8];
let bytes3 = [1u8, 2u8, 0u8, 4u8];
let bytes4 = [1u8, 7u8, 3u8, 4u8];
match input {
MyEnum::Red => unsafe { core::mem::transmute_copy(&bytes1) },
MyEnum::Blue => unsafe { core::mem::transmute_copy(&bytes2) },
MyEnum::Purple => unsafe { core::mem::transmute_copy(&bytes3) },
MyEnum::Gray => unsafe { core::mem::transmute_copy(&bytes4) },
}
}
Once you fill in the missing MyEnum::Orange variant, everything will compile and the warnings disappear.