feat: make usage of references to mutable static safe (#32)

Author: Gurgel100

msfs/src/msfs.rs

@@ -35,6 +35,14 @@ pub enum MSFSEvent<'a> {
     SimConnect(SimConnectRecv<'a>),
 }
 
+/// Internal helper function to allow usage of mutable globals.
+/// # Safety
+/// Only call this function if you know what you're doing! This function is only safe
+/// to be used if one is **absolutely sure** that there is only 1 reference to it at all times!
+pub unsafe fn wrap_executor<E, T>(executor: *mut E, handle: impl FnOnce(&mut E) -> T) -> T {
+    handle(&mut *executor)
+}
+
 /// Gauge
 pub struct Gauge {
     executor: *mut GaugeExecutor,

msfs_derive/src/lib.rs

@@ -29,6 +29,8 @@ pub fn standalone_module(_args: TokenStream, item: TokenStream) -> TokenStream {
     let output = quote! {
         #input
 
+        // SAFETY: it is safe to create references of this static since all WASM modules are single threaded
+        // and there is only 1 reference in use at all times
         #[allow(non_upper_case_globals)]
         static mut #executor_name: ::msfs::StandaloneModuleExecutor = ::msfs::StandaloneModuleExecutor {
             executor: ::msfs::executor::Executor {
@@ -41,14 +43,14 @@ pub fn standalone_module(_args: TokenStream, item: TokenStream) -> TokenStream {
         #[no_mangle]
         pub extern "C" fn module_init() {
             unsafe {
-                #executor_name.handle_init();
+                ::msfs::wrap_executor(&raw mut #executor_name, |e| e.handle_init());
             }
         }
 
         #[no_mangle]
         pub extern "C" fn module_deinit() {
             unsafe {
-                #executor_name.handle_deinit();
+                ::msfs::wrap_executor(&raw mut #executor_name, |e| e.handle_deinit());
             }
         }
     };
@@ -110,6 +112,8 @@ pub fn gauge(args: TokenStream, item: TokenStream) -> TokenStream {
     let output = quote! {
         #input
 
+        // SAFETY: it is safe to create references of this static since all WASM modules are single threaded
+        // and there is only 1 reference in use at all times
         #[allow(non_upper_case_globals)]
         static mut #executor_name: ::msfs::GaugeExecutor = ::msfs::GaugeExecutor {
             fs_ctx: None,
@@ -128,7 +132,7 @@ pub fn gauge(args: TokenStream, item: TokenStream) -> TokenStream {
             p_data: *mut std::os::raw::c_void,
         ) -> bool {
             unsafe {
-                #executor_name.handle_gauge(ctx, service_id, p_data)
+                ::msfs::wrap_executor(&raw mut #executor_name, |e| e.handle_gauge(ctx, service_id, p_data))
             }
         }
 
@@ -139,9 +143,9 @@ pub fn gauge(args: TokenStream, item: TokenStream) -> TokenStream {
             fy: std::os::raw::c_float,
             i_flags: std::os::raw::c_uint,
         ) {
-             unsafe {
-                #executor_name.handle_mouse(fx, fy, i_flags);
-             }
+            unsafe {
+                ::msfs::wrap_executor(&raw mut #executor_name, |e| e.handle_mouse(fx, fy, i_flags));
+            }
          }
     };