Add initial integration with wasm-bindgen (#23493)

When `-sWASM_BINDGEN` is set, Emscripten will now call out to `wasm-bindgen` in the users's `PATH` and integrate the wasm-bindgen JS with the normal Emscripten JS. 

Some wasm-bindgen features may not yet be fully supported.

Author: walkingeyerobot

.circleci/config.yml

@@ -72,6 +72,7 @@ commands:
             curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
             export PATH=${HOME}/.cargo/bin:${PATH}
             rustup target add wasm32-unknown-emscripten
+            cargo install wasm-bindgen-cli
             echo "export PATH=\"\$HOME/.cargo/bin:\$PATH\"" >> $BASH_ENV
   install-node-version:
     description: "install a specific version of node"

ChangeLog.md

@@ -22,6 +22,10 @@ See docs/process.md for more on how version tagging works.
 ----------------------
 - The `-sUSE_PTHREADS` and `-sMEMORY64` flags have been deprecated in favor of the
   more standard `-pthread` and `-m64` (or `--target=wasm64`) flags. (#27025)
+- Adds wasm-bindgen support. When `-sWASM_BINDGEN` is set, Emscripten will call
+  out to `wasm-bindgen` in the users's path and integrate the wasm-bindgen JS
+  with the normal Emscripten JS. Some wasm-bindgen features may not yet be fully
+  supported. (#23493)
 
 6.0.0 - 06/04/26
 ----------------

emcc.py

@@ -578,7 +578,7 @@ def compile_source_file(input_file):
       # Default to assuming the inputs are object files and pass them to the linker
       pass
 
-  return [f.value for f in linker_args]
+  return linker_args
 
 
 if __name__ == '__main__':

site/source/docs/tools_reference/settings_reference.rst

@@ -3288,6 +3288,15 @@ Example use ``-sSIGNATURE_CONVERSIONS=someFunction:_p,anotherFunction:p``
 
 Default value: []
 
+.. _wasm_bindgen:
+
+WASM_BINDGEN
+============
+
+Run wasm-bindgen and integrate the rust-exported symbols into the rest of Emscripten's JS output.
+
+Default value: 0
+
 .. _source_phase_imports:
 
 SOURCE_PHASE_IMPORTS

src/settings.js

@@ -2167,6 +2167,10 @@ var LEGACY_RUNTIME = false;
 // [link]
 var SIGNATURE_CONVERSIONS = [];
 
+// Run wasm-bindgen and integrate the rust-exported symbols into the rest of Emscripten's JS output.
+// [link]
+var WASM_BINDGEN = 0;
+
 // Experimental support for wasm source phase imports.
 // This is only currently implemented in the pre-release/nightly version of
 // node, and not yet supported by browsers.

test/rust/basics/.cargo/config.toml

@@ -0,0 +1,2 @@
+[build]
+target = "wasm32-unknown-emscripten"

test/rust/bindgen_integration/.cargo/config.toml

@@ -0,0 +1,7 @@
+[build]
+target = "wasm32-unknown-emscripten"
+rustflags = [
+    "-Cllvm-args=-enable-emscripten-cxx-exceptions=0",
+    "-Cpanic=abort",
+    "-Crelocation-model=static",
+]

test/rust/bindgen_integration/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "bindgen_integration"
+edition = "2021"
+
+[lib]
+crate-type = ["staticlib"]
+
+[dependencies]

test/rust/bindgen_integration/src/lib.rs

@@ -0,0 +1,6 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+pub fn rs_add(a: i32, b: i32) -> i32 {
+    return a + b;
+}

test/test_other.py

@@ -14830,6 +14830,22 @@ def test_rust_integration_basics(self):
     }''')
     self.do_runf('main.cpp', 'Hello from rust!', cflags=[lib])
 
+  @requires_rust
+  def test_wasm_bindgen_integration(self):
+    copytree(test_file('rust/bindgen_integration'), '.')
+    self.run_process(['cargo', 'add', 'wasm-bindgen'])
+    self.run_process(['cargo', 'build'])
+    lib = 'target/wasm32-unknown-emscripten/debug/libbindgen_integration.a'
+    self.assertExists(lib)
+
+    create_file('empty.c', '')
+    create_file('post.js', '''
+      Module.onRuntimeInitialized = () => out(Module.rs_add(17, 25));
+    ''')
+    emcc_args = [lib, '-sWASM_BINDGEN', '--post-js=post.js', '-lexports.js']
+
+    self.do_runf('empty.c', '42', cflags=emcc_args)
+
   def test_relative_em_cache(self):
     with env_modify({'EM_CACHE': 'foo'}):
       self.assert_fail([EMCC, '-c', test_file('hello_world.c')], 'emcc: error: environment variable EM_CACHE must be an absolute path: foo')