Add a rollup plugin for tree shaking Emscripten output.

.gitignore

@@ -25,6 +25,8 @@ tools/coverage/
 htmlcov/
 coverage.xml
 
+/tools/rollup-plugin-emscripten/node_modules
+
 .DS_Store
 
 # Test output

bootstrap.py

@@ -24,6 +24,10 @@
      'package.json',
      'package-lock.json'
    ], ['npm', 'ci']),
+  ('npm rollup plugin packages', [
+     'tools/rollup-plugin-emscripten/package.json',
+     'tools/rollup-plugin-emscripten/package-lock.json'
+   ], ['npm', 'ci', '--prefix', 'tools/rollup-plugin-emscripten']),
   ('create entry points', [
      'tools/maint/create_entry_points.py',
      'tools/maint/run_python.bat',

test/rollup_plugin/index.mjs

@@ -0,0 +1,6 @@
+import init, { _used_externally } from './library.mjs';
+
+await init();
+
+console.log(_used_externally());
+console.log('done');

test/rollup_plugin/library.c

@@ -0,0 +1,16 @@
+#include <emscripten.h>
+
+// Should NOT be removed (used by index.mjs).
+EMSCRIPTEN_KEEPALIVE int used_externally() {
+  return 42;
+}
+
+// Should NOT be removed (used by library.js).
+EMSCRIPTEN_KEEPALIVE int used_internally() {
+  return 99;
+}
+
+// Should be removed.
+EMSCRIPTEN_KEEPALIVE int unused() {
+  return 0xDEAD;
+}

test/rollup_plugin/library.js

@@ -0,0 +1,9 @@
+
+addToLibrary({
+  $placeHolder__deps: ['used_internally'],
+  $placeHolder: function() {
+    _used_internally();
+  }
+});
+
+extraLibraryFuncs.push('$placeHolder');

test/rollup_plugin/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "test-rollup-plugin",
+  "type": "module"
+}

test/rollup_plugin/rollup.config.mjs

@@ -0,0 +1,15 @@
+import emscriptenPlugin from 'rollup-plugin-emscripten';
+
+export default {
+  input: 'index.mjs',
+  output: {
+    dir: 'dist',
+    format: 'es'
+  },
+  plugins: [
+    emscriptenPlugin({
+      'input': 'library.mjs',
+      'wasmMetaDCE': 'BINARYEN_PATH'
+    })
+  ]
+};

test/test_other.py

@@ -15860,6 +15860,39 @@ def test_rollup(self):
     shutil.copy('hello.wasm', 'dist/')
     self.assertContained('hello, world!', self.run_js('dist/bundle.mjs'))
 
+  @parameterized({
+    '': ('',),
+    'O1': ('-O1',),
+    'O2': ('-O2',),
+    'O3': ('-O3',),
+  })
+  def test_rollup_plugin(self, opt):
+    def get_exports(path):
+      with webassembly.Module(path) as module:
+        return [export.name for export in module.get_exports()]
+
+    # Pass the path to wasm-metadce into the plugin.
+    copytree(test_file('rollup_plugin'), '.')
+    rollup_config_file = 'rollup.config.mjs'
+    replacement_path = str(Path(building.get_binaryen_bin(), 'wasm-metadce'))
+    modified_content = read_file(rollup_config_file).replace("BINARYEN_PATH", replacement_path)
+    write_file(rollup_config_file, modified_content)
+
+    self.run_process([EMCC, 'library.c', opt, '--no-entry', '-sMODULARIZE=instance', '-sENVIRONMENT=node', '--js-library', 'library.js', '-o', 'library.mjs'])
+    self.run_process(['npm', 'install', path_from_root('tools/rollup-plugin-emscripten')])
+    self.run_process(shared.get_npm_cmd('rollup') + ['--config'])
+    exports_pre_rollup = get_exports('library.wasm')
+    self.assertContained('42\ndone\n', self.run_js('dist/index.js'))
+    exports = get_exports('dist/library.wasm')
+    self.assertTrue(len(exports) < len(exports_pre_rollup))
+    if opt != '-O3':
+      # In O3 wasm export names are minified.
+      self.assertTrue('used_externally' in exports)
+      self.assertTrue('used_internally' in exports)
+      self.assertTrue('unused' not in exports)
+
+
+
   def test_rlimit(self):
     self.do_other_test('test_rlimit.c', emcc_args=['-O1'])
 

tools/rollup-plugin-emscripten/package.json

@@ -0,0 +1,10 @@
+{
+  "name": "rollup-plugin-emscripten",
+  "version": "0.0.1",
+  "description": "Rollup plugin for Emscripten output with tree shaking.",
+  "main": "src/index.mjs",
+  "dependencies": {
+    "tmp": "^0.2.3",
+    "which": "^5.0.0"
+  }
+}