Enable missing-unsafe-on-extern lint (bytecodealliance#9963)

* Enable `missing-unsafe-on-extern` lint

This'll be a hard error in the 2024 edition so go ahead and opt-in to it
now to ease our future transition.

* Fix adapter build

* Fix custom c-api build

* Fix fuzzer build

* Fix some Windows `extern` blocks

Author: alexcrichton

.github/workflows/main.yml

@@ -936,7 +936,7 @@ jobs:
       with:
         submodules: true
     - uses: ./.github/actions/install-rust
-    - run: cargo install cbindgen --vers "^0.26" --locked
+    - run: cargo install cbindgen --vers "^0.27" --locked
     - run: rustup target add x86_64-unknown-none
     - run: ./build.sh x86_64-unknown-none
       working-directory: ./examples/min-platform

Cargo.toml

@@ -187,6 +187,7 @@ deprecated-safe-2024 = 'warn'
 rust-2024-guarded-string-incompatible-syntax = 'warn'
 rust-2024-prelude-collisions = 'warn'
 rust-2024-incompatible-pat = 'warn'
+missing-unsafe-on-extern = 'warn'
 
 # Don't warn about unknown cfgs for pulley
 [workspace.lints.rust.unexpected_cfgs]

cranelift/filetests/src/function_runner.rs

@@ -111,11 +111,11 @@ impl TestFileCompiler {
         // final binary doesn't link in `libm`.
         #[cfg(unix)]
         {
-            extern "C" {
-                fn ceilf(f: f32) -> f32;
+            unsafe extern "C" {
+                safe fn ceilf(f: f32) -> f32;
             }
             let f = 1.2_f32;
-            assert_eq!(f.ceil(), unsafe { ceilf(f) });
+            assert_eq!(f.ceil(), ceilf(f));
         }
 
         let module = JITModule::new(builder);

crates/fiber/src/stackswitch.rs

@@ -23,7 +23,7 @@ cfg_if::cfg_if! {
     }
 }
 
-extern "C" {
+unsafe extern "C" {
     #[wasmtime_versioned_export_macros::versioned_link]
     pub(crate) fn wasmtime_fiber_init(
         top_of_stack: *mut u8,

crates/fiber/src/unix.rs

@@ -371,7 +371,7 @@ mod asan {
 
     // These intrinsics are provided by the address sanitizer runtime. Their C
     // signatures were translated into Rust-isms here with `Option` and `&mut`.
-    extern "C" {
+    unsafe extern "C" {
         fn __sanitizer_start_switch_fiber(
             private_asan_pointer_save: Option<&mut *mut u8>,
             bottom: *const u8,

crates/fiber/src/windows.rs

@@ -64,7 +64,7 @@ struct StartState {
 
 const FIBER_FLAG_FLOAT_SWITCH: u32 = 1;
 
-extern "C" {
+unsafe extern "C" {
     #[wasmtime_versioned_export_macros::versioned_link]
     fn wasmtime_fiber_get_current() -> *mut c_void;
 }

crates/jit-debug/src/gdb_jit_int.rs

@@ -27,7 +27,7 @@ struct JITDescriptor {
     first_entry: *mut JITCodeEntry,
 }
 
-extern "C" {
+unsafe extern "C" {
     #[versioned_link]
     fn wasmtime_jit_debug_descriptor() -> *mut JITDescriptor;
     fn __jit_debug_register_code();

crates/test-programs/src/bin/preview2_adapter_badfd.rs

@@ -1,6 +1,6 @@
 fn main() {
     #[link(wasm_import_module = "wasi_snapshot_preview1")]
-    extern "C" {
+    unsafe extern "C" {
         #[cfg_attr(target_arch = "wasm32", link_name = "adapter_open_badfd")]
         fn adapter_open_badfd(fd: *mut u32) -> wasi::Errno;
 

crates/wasi-preview1-component-adapter/src/descriptors.rs

@@ -150,7 +150,7 @@ pub struct Descriptors {
 
 #[cfg(not(feature = "proxy"))]
 #[link(wasm_import_module = "wasi:filesystem/preopens@0.2.2")]
-extern "C" {
+unsafe extern "C" {
     #[link_name = "get-directories"]
     fn wasi_filesystem_get_directories(rval: *mut PreopenList);
 }

crates/wasi-preview1-component-adapter/src/lib.rs

@@ -114,12 +114,12 @@ pub mod bindings {
     }
 }
 
-#[export_name = "wasi:cli/run@0.2.3#run"]
+#[unsafe(export_name = "wasi:cli/run@0.2.3#run")]
 #[cfg(feature = "command")]
-pub unsafe extern "C" fn run() -> u32 {
+pub extern "C" fn run() -> u32 {
     #[link(wasm_import_module = "__main_module__")]
-    extern "C" {
-        fn _start();
+    unsafe extern "C" {
+        safe fn _start();
     }
     _start();
     0
@@ -457,7 +457,7 @@ impl BumpAlloc {
 
 #[cfg(not(feature = "proxy"))]
 #[link(wasm_import_module = "wasi:cli/environment@0.2.3")]
-extern "C" {
+unsafe extern "C" {
     #[link_name = "get-arguments"]
     fn wasi_cli_get_arguments(rval: *mut WasmStrList);
     #[link_name = "get-environment"]
@@ -2156,7 +2156,7 @@ pub unsafe extern "C" fn poll_oneoff(
         }
 
         #[link(wasm_import_module = "wasi:io/poll@0.2.3")]
-        extern "C" {
+        unsafe extern "C" {
             #[link_name = "poll"]
             fn poll_import(pollables: *const Pollable, len: usize, rval: *mut ReadyList);
         }
@@ -2731,7 +2731,7 @@ enum AllocationState {
 }
 
 #[expect(improper_ctypes, reason = "types behind pointers")]
-extern "C" {
+unsafe extern "C" {
     fn get_state_ptr() -> *mut State;
     fn set_state_ptr(state: *mut State);
     fn get_allocation_state() -> AllocationState;
@@ -2764,7 +2764,7 @@ impl State {
     #[cold]
     fn new() -> *mut State {
         #[link(wasm_import_module = "__main_module__")]
-        extern "C" {
+        unsafe extern "C" {
             fn cabi_realloc(
                 old_ptr: *mut u8,
                 old_len: usize,