allow custom wasm binary name

Author: PgBiel

godot-core/src/init/mod.rs

@@ -244,6 +244,38 @@ fn gdext_on_level_deinit(level: InitLevel) {
 /// Note that this only changes the name. You cannot provide your own function -- use the [`on_level_init()`][ExtensionLibrary::on_level_init]
 /// hook for custom startup logic.
 ///
+/// # Custom Wasm binary filename
+/// Upon exporting a game to the web, the library has to know at runtime the exact name of the `.wasm` binary file being used to load
+/// each GDExtension. By default, Rust exports the binary as `cratename.wasm`, so that is the name checked by godot-rust by default.
+///
+/// However, if you need to rename that binary, you can make the library aware of the new binary name with
+/// `#[gdextension(wasm_binary = "newname.wasm")]` (don't forget to include the `.wasm` extension).
+///
+/// For example, to have two simultaneous versions, one supporting multi-threading and the other not, you could add a suffix to the
+/// filename of the Wasm binary of the multi-threaded version in your build process. If you choose the suffix `.threads.wasm`, you're
+/// in luck as godot-rust already accepts this suffix by default. But let's say you want to use a different suffix, such as
+/// `-with-threads.wasm`. For this, you can have a `"nothreads"` feature which, when absent, should produce a suffixed binary, which
+/// can be informed to gdext as follows:
+///
+/// ```no_run
+/// # use godot::init::*;
+/// struct MyExtension;
+///
+/// // Tell gdext we add a custom suffix to the binary with thread support
+/// // Please note that this is not needed if "mycrate.threads.wasm" is used
+/// #[cfg(not(feature = "nothreads"))]
+/// #[gdextension(wasm_binary = "mycrate-with-threads.wasm")]
+/// unsafe impl ExtensionLibrary for MyExtension {}
+///
+/// // Binary name unchanged (mycrate.wasm) without thread support
+/// #[cfg(feature = "nothreads")]
+/// #[gdextension]
+/// unsafe impl ExtensionLibrary for MyExtension {}
+/// ```
+/// Note that simply specifying that option won't change the name of the Wasm binary produced by Rust automatically: you'll still have
+/// to rename it by yourself in your build process, as well as specify the updated binary name in your `.gdextension` file. This is
+/// just to ensure gdext is aware of the new name given to the binary, avoiding runtime errors.
+///
 /// # Safety
 /// The library cannot enforce any safety guarantees outside Rust code, which means that **you as a user** are
 /// responsible to uphold them: namely in GDScript code or other GDExtension bindings loaded by the engine.

godot-macros/src/gdextension.rs

@@ -29,6 +29,7 @@ pub fn attribute_gdextension(item: venial::Item) -> ParseResult<TokenStream> {
     let mut parser = KvParser::parse_required(&drained_attributes, "gdextension", &impl_decl)?;
     let entry_point = parser.handle_ident("entry_point")?;
     let entry_symbol = parser.handle_ident("entry_symbol")?;
+    let wasm_binary = parser.handle_expr("wasm_binary")?;
     parser.finish()?;
 
     if entry_point.is_some() && entry_symbol.is_some() {
@@ -48,6 +49,19 @@ pub fn attribute_gdextension(item: venial::Item) -> ParseResult<TokenStream> {
         .or(entry_point)
         .unwrap_or_else(|| ident("gdext_rust_init"));
 
+    let wasm_binary = match wasm_binary {
+        Some(wasm_binary) => {
+            quote! {
+                {
+                    // Ensure a string-like expression is passed
+                    let wasm_binary: &str = &#wasm_binary;
+                    format!("'{}'", wasm_binary.replace("\\", "\\\\").replace("'", "\\'"))
+                }
+            }
+        }
+        None => quote! { "snakePkgName + '.wasm'" },
+    };
+
     let impl_ty = &impl_decl.self_ty;
 
     Ok(quote! {
@@ -58,6 +72,9 @@ pub fn attribute_gdextension(item: venial::Item) -> ParseResult<TokenStream> {
         // host. See: https://github.com/rust-lang/rust/issues/42587
         #[cfg(target_os = "emscripten")]
         fn emscripten_preregistration() {
+            let pkg_name = env!("CARGO_PKG_NAME");
+            let wasm_binary = #wasm_binary;
+
             // Module is documented here[1] by emscripten, so perhaps we can consider it a part
             // of its public API? In any case for now we mutate global state directly in order
             // to get things working.
@@ -69,34 +86,37 @@ pub fn attribute_gdextension(item: venial::Item) -> ParseResult<TokenStream> {
             // involved, but I don't know what guarantees we have here.
             //
             // We should keep an eye out for these sorts of failures!
-            let script = std::ffi::CString::new(concat!(
-                "var pkgName = '", env!("CARGO_PKG_NAME"), "';", r#"
-                var libName = pkgName.replaceAll('-', '_') + '.wasm';
-                if (!(libName in LDSO.loadedLibsByName)) {
+            let script = format!(
+                r#"var pkgName = '{pkg_name}';
+                var snakePkgName = pkgName.replaceAll('-', '_');
+                var libName = {wasm_binary};
+                if (!(libName in LDSO.loadedLibsByName)) {{
                     // Always print to console, even if the error is suppressed.
-                    console.error(`godot-rust could not find the Wasm module '${libName}', needed to load the '${pkgName}' crate. Please ensure a file named '${libName}' exists in the game's web export files. This may require updating Wasm paths in the crate's corresponding '.gdextension' file, or just renaming the Wasm file to the correct name otherwise.`);
-                    throw new Error(`Wasm module '${libName}' not found. Check the console for more information.`);
-                }
+                    console.error(`godot-rust could not find the Wasm module '${{libName}}', needed to load the '${{pkgName}}' crate. Please ensure a file named '${{libName}}' exists in the game's web export files. This may require updating Wasm paths in the crate's corresponding '.gdextension' file, or just renaming the Wasm file to the correct name otherwise.`);
+                    throw new Error(`Wasm module '${{libName}}' not found. Check the console for more information.`);
+                }}
                 var dso = LDSO.loadedLibsByName[libName];
                 // This property was renamed as of emscripten 3.1.34
                 var dso_exports = "module" in dso ? dso["module"] : dso["exports"];
                 var registrants = [];
-                for (sym in dso_exports) {
-                    if (sym.startsWith("dynCall_")) {
-                        if (!(sym in Module)) {
-                            console.log(`Patching Module with ${sym}`);
+                for (sym in dso_exports) {{
+                    if (sym.startsWith("dynCall_")) {{
+                        if (!(sym in Module)) {{
+                            console.log(`Patching Module with ${{sym}}`);
                             Module[sym] = dso_exports[sym];
-                        }
-                    } else if (sym.startsWith("__godot_rust_registrant_")) {
+                        }}
+                    }} else if (sym.startsWith("__godot_rust_registrant_")) {{
                         registrants.push(sym);
-                    }
-                }
-                for (sym of registrants) {
-                    console.log(`Running registrant ${sym}`);
+                    }}
+                }}
+                for (sym of registrants) {{
+                    console.log(`Running registrant ${{sym}}`);
                     dso_exports[sym]();
-                }
+                }}
                 console.log("Added",  registrants.length, "plugins to registry!");
-            "#)).expect("Unable to create CString from script");
+            "#);
+
+            let script = std::ffi::CString::new(script).expect("Unable to create CString from script");
 
             extern "C" { fn emscripten_run_script(script: *const std::ffi::c_char); }
             unsafe { emscripten_run_script(script.as_ptr()); }