rust: Fix compatibility of generated code with the 2024 edition (bytecodealliance#1119)

This commit fixes compatibility of generated code with the Rust 2024
edition coming up next month. The new edition requires that
`#[export_name]` is notably an `unsafe` attribute and is wrapped in
`#[unsafe(export_name = "...")]` so the generated code is updated to do
that. Note that this syntax is allowed on the 2021 edition as of Rust
1.82.0 but is not required, it's only required in the 2024 edition.

Author: alexcrichton

ci/rebuild-libcabi-realloc.sh

@@ -7,9 +7,9 @@
 # the `cabi_realloc` symbol from the final binary. This library, however,
 # is not stable which means that we're publishing new versions of `wit-bindgen`
 # over its development. This means that if `wit-bindgen`-the-crate were to
-# export a `#[no_mangle]` symbol of `cabi_realloc` then it wouldn't work to
-# have two versions of `wit-bindgen` in the same project. This can arise
-# relatively quickly, however, so this is something we want to solve.
+# export a `#[unsafe(no_mangle)]` symbol of `cabi_realloc` then it wouldn't
+# work to have two versions of `wit-bindgen` in the same project. This can
+# arise relatively quickly, however, so this is something we want to solve.
 #
 # The general idea of the solution here is to ensure that the `cabi_realloc`
 # symbol itself is declared as a weak symbol. A weakly-defined symbol means
@@ -46,7 +46,7 @@ sym=cabi_realloc_wit_bindgen_$version
 cat >./crates/guest-rust/rt/src/cabi_realloc.rs <<-EOF
 // This file is generated by $0
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub unsafe extern "C" fn $sym(
     old_ptr: *mut u8,
     old_len: usize,

crates/guest-rust/rt/src/cabi_realloc.rs

@@ -1,6 +1,6 @@
 // This file is generated by ./ci/rebuild-libcabi-realloc.sh
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub unsafe extern "C" fn cabi_realloc_wit_bindgen_0_36_0(
     old_ptr: *mut u8,
     old_len: usize,

crates/guest-rust/src/lib.rs

@@ -310,7 +310,7 @@
 /// Additionally a macro is generated by `generate!` (macros generating macros)
 /// called `export!`. The `export!` macro is given a component that implements
 /// the export `trait`s and then it will itself generate all necessary
-/// `#[no_mangle]` functions to implement the ABI required.
+/// `#[unsafe(no_mangle)]` functions to implement the ABI required.
 ///
 /// ## Exports: Multiple Interfaces
 ///
@@ -502,9 +502,9 @@
 /// Components are created by having exported WebAssembly functions with
 /// specific names, and these functions are not created when `generate!` is
 /// invoked. Instead these functions are created afterwards once you've defined
-/// your own type an implemented the various `trait`s for it. The `#[no_mangle]`
-/// functions that will become the component are created with the generated
-/// `export!` macro.
+/// your own type an implemented the various `trait`s for it. The
+/// `#[unsafe(no_mangle)]` functions that will become the component are created
+/// with the generated `export!` macro.
 ///
 /// Each call to `generate!` will itself generate a macro called `export!`.
 /// The macro's first argument is the name of a type that implements the traits

crates/rust/src/interface.rs

@@ -332,7 +332,7 @@ macro_rules! {macro_name} {{
                 r#"
                 const _: () = {{
                     #[doc(hidden)]
-                    #[export_name = "{export_prefix}{module}#[dtor]{name}"]
+                    #[unsafe(export_name = "{export_prefix}{module}#[dtor]{name}")]
                     #[allow(non_snake_case)]
                     unsafe extern "C" fn dtor(rep: *mut u8) {{
                         $($path_to_types)*::{camel}::dtor::<
@@ -575,7 +575,7 @@ pub mod vtable{ordinal} {{
             struct Buffer([::core::mem::MaybeUninit::<u8>; {size}]);
             let mut buffer = Buffer([::core::mem::MaybeUninit::uninit(); {size}]);
             let address = buffer.0.as_mut_ptr() as *mut u8;
-        
+
             #[link(wasm_import_module = "{module}")]
             extern "C" {{
                 #[link_name = "[async][future-read-{index}]{func_name}"]
@@ -1145,7 +1145,7 @@ pub mod vtable{ordinal} {{
         uwrite!(
             self.src,
             "\
-                #[export_name = \"{export_prefix}{export_name}\"]
+                #[unsafe(export_name = \"{export_prefix}{export_name}\")]
                 unsafe extern \"C\" fn export_{name_snake}\
 ",
         );
@@ -1164,7 +1164,7 @@ pub mod vtable{ordinal} {{
             uwrite!(
                 self.src,
                 "\
-                    #[export_name = \"{export_prefix}[callback]{export_name}\"]
+                    #[unsafe(export_name = \"{export_prefix}[callback]{export_name}\")]
                     unsafe extern \"C\" fn _callback_{name_snake}(ctx: *mut u8, event0: i32, event1: i32, event2: i32) -> i32 {{
                         {path_to_self}::__callback_{name_snake}(ctx, event0, event1, event2)
                     }}
@@ -1174,7 +1174,7 @@ pub mod vtable{ordinal} {{
             uwrite!(
                 self.src,
                 "\
-                    #[export_name = \"{export_prefix}cabi_post_{export_name}\"]
+                    #[unsafe(export_name = \"{export_prefix}cabi_post_{export_name}\")]
                     unsafe extern \"C\" fn _post_return_{name_snake}\
 "
             );

crates/rust/src/lib.rs

@@ -826,8 +826,8 @@ impl As{upcase} for {to_convert} {{
         uwriteln!(
             self.src,
             r#"
-/// Generates `#[no_mangle]` functions to export the specified type as the
-/// root implementation of all generated traits.
+/// Generates `#[unsafe(no_mangle)]` functions to export the specified type as
+/// the root implementation of all generated traits.
 ///
 /// For more information see the documentation of `wit_bindgen::generate!`.
 ///
@@ -907,8 +907,8 @@ macro_rules! __export_{world_name}_impl {{
         let pkg = &resolve.packages[world.package.unwrap()].name;
         let version = env!("CARGO_PKG_VERSION");
         self.src.push_str(&format!(
-            "#[link_section = \"component-type:wit-bindgen:{version}:\
-             {pkg}:{world_name}:{section_suffix}{opts_suffix}\"]\n"
+            "#[unsafe(link_section = \"component-type:wit-bindgen:{version}:\
+             {pkg}:{world_name}:{section_suffix}{opts_suffix}\")]\n"
         ));
 
         let mut producers = wasm_metadata::Producers::empty();