【Rust】edition 2024 移行ログ — cargo fix が直した8箇所と直さなかった1箇所

cargo fix --edition --allow-dirty --allow-no-vcs
# 実行結果（抜粋）
# Migrating Cargo.toml from 2021 edition to 2024
# Migrating src\main.rs from 2021 edition to 2024
#     Fixed src\main.rs (8 fixes)

# Cargo.toml の edition は手で書き換える（この実行では 2021 のままだった）
sed -i 's/edition = "2021"/edition = "2024"/' Cargo.toml
cargo check
# 実行結果（抜粋）
# error: creating a shared reference to mutable static
#   --> src\main.rs:26:5
# 26 |     &TOTAL
# help: use `&raw const` instead to create a raw pointer
# error: could not compile `legacy-app` (bin "legacy-app") due to 1 previous error

use std::env;

static mut TOTAL: u32 = 0;

#[no_mangle]
pub extern "C" fn counter() -> u32 {
    unsafe { TOTAL }
}

extern "C" {
    fn getpid() -> i32;
}

// edition 2021 では `gen` は普通の識別子として使える
fn make_gen() -> usize {
    7
}

unsafe fn read_len(buf: &[u8]) -> usize {
    let gen = make_gen();

    TOTAL += 1;
    buf.len() + gen
}

unsafe fn total_ref() -> &'static u32 {
    &TOTAL
}

fn bump_middle(values: &mut [u32; 3]) -> u32 {
    match &mut values[..] {
        [_, ref mut middle, _] => {
            *middle += 1;

            *middle
        }
        _ => 0,
    }
}

fn main() {
    env::set_var("APP_ENV", "dev");

    let mut values = [1, 2, 3];

    unsafe {
        read_len(b"abc");
    }

    println!("{:?}", values);
    println!("{}", bump_middle(&mut values));
    println!("{}", unsafe { *total_ref() });
    println!("{}", counter());
    println!("{}", env::var("APP_ENV").unwrap());
}

// 実行結果（cargo check: edition 2021）
// warning: function `getpid` is never used
// warning: creating a shared reference to mutable static
// warning: `legacy-app` (bin "legacy-app") generated 2 warnings
//     Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.13s

-#[no_mangle]
+#[unsafe(no_mangle)]

-extern "C" {
+unsafe extern "C" {

-unsafe fn read_len(buf: &[u8]) -> usize {
-    let gen = make_gen();
+unsafe fn read_len(buf: &[u8]) -> usize { unsafe {
+    let r#gen = make_gen();

-        [_, ref mut middle, _] => {
+        [_, middle, _] => {

-    env::set_var("APP_ENV", "dev");
+    // TODO: Audit that the environment access only happens in single-threaded code.
+    unsafe { env::set_var("APP_ENV", "dev") };

cargo check
# 実行結果（抜粋）
# warning: function `getpid` is never used
# error: creating a shared reference to mutable static
#   --> src\main.rs:26:5
# 26 |     &TOTAL
#    |     ^^^^^^ shared reference to mutable static
# help: use `&raw const` instead to create a raw pointer
# 26 |     &raw const TOTAL
# error: could not compile `legacy-app` (bin "legacy-app") due to 1 previous error

// 修正前: static mut への参照を関数の外に持ち出していた
unsafe fn total_ref() -> &'static u32 {
    &TOTAL
}

// 修正後: 生ポインタを取り、参照が要る所でだけ unsafe に戻す
fn total_ptr() -> *const u32 {
    &raw const TOTAL
}

fn main() {
    println!("{}", unsafe { *total_ptr() });
}

// 実行結果
// [1, 2, 3]
// 3
// 1
// 1
// dev

use std::cell::RefCell;

fn last_item_count() -> usize {
    let items = RefCell::new(vec![10, 20, 30]);

    items.borrow().len()
}

// rustc --edition=2021 の出力
// error[E0597]: `items` does not live long enough
//
// rustc --edition=2024 の出力
// （コンパイル成功）