Remove USE_ES6_IMPORT_META setting

This setting was added (IIUC) as a temporary workaround for the lack or
support for `import.meta` in browser and tooling.

However `import.meta` has been at stage 4 for almost 5 years now:
tc39/proposal-import-meta#21

Webback (released in 2020) also has builtin support for `import.meta`,
so I would hope the use case for disabling this setting no longer
exists.

See emscripten-core#9234 and emscripten-core#8729

Author: sbc100

ChangeLog.md

@@ -27,6 +27,10 @@ See docs/process.md for more on how version tagging works.
   (#20735)
 - Added Lua contrib port (`--use-port=contrib.lua`) to easily embed the Lua
   scripting language in any C/C++ Emscripten project (#23682)
+- The `USE_ES6_IMPORT_META` settings was removed.  This setting was always
+  on by default, but now it cannot be disabled.  This setting was originally
+  added in 2019 as a temporary measure while engines and bundlers learned to
+  deal with `import.meta`. (#23171)
 
 4.0.3 - 02/07/25
 ----------------

site/source/docs/tools_reference/settings_reference.rst

@@ -1978,18 +1978,6 @@ This is implicitly enabled if the output suffix is set to 'mjs'.
 
 Default value: false
 
-.. _use_es6_import_meta:
-
-USE_ES6_IMPORT_META
-===================
-
-Use the ES6 Module relative import feature 'import.meta.url'
-to auto-detect WASM Module path.
-It might not be supported on old browsers / toolchains. This setting
-may not be disabled when Node.js is targeted (-sENVIRONMENT=*node*).
-
-Default value: true
-
 .. _export_name:
 
 EXPORT_NAME

src/lib/libpthread.js

@@ -418,7 +418,7 @@ var LibraryPThread = {
     // Creates a new web Worker and places it in the unused worker pool to wait for its use.
     allocateUnusedWorker() {
       var worker;
-#if EXPORT_ES6 && USE_ES6_IMPORT_META
+#if EXPORT_ES6
       // If we're using module output, use bundler-friendly pattern.
 #if PTHREADS_DEBUG
       dbg(`Allocating a new web worker from ${import.meta.url}`);
@@ -440,7 +440,7 @@ var LibraryPThread = {
       // the first case in their bundling step. The latter ends up producing an invalid
       // URL to import from the server (e.g., for webpack the file:// path).
       worker = new Worker(new URL('{{{ TARGET_JS_NAME }}}', import.meta.url), {{{ pthreadWorkerOptions }}});
-#else
+#else // EXPORT_ES6
       var pthreadMainJs = _scriptName;
 #if expectToReceiveOnModule('mainScriptUrlOrBlob')
       // We can't use makeModuleReceiveWithVar here since we want to also
@@ -463,7 +463,7 @@ var LibraryPThread = {
       } else
 #endif
       worker = new Worker(pthreadMainJs, {{{ pthreadWorkerOptions }}});
-#endif // EXPORT_ES6 && USE_ES6_IMPORT_META
+#endif // EXPORT_ES6
       PThread.unusedWorkers.push(worker);
     },
 

src/parseTools.mjs

@@ -65,7 +65,7 @@ function findIncludeFile(filename, currentDir) {
 // Also handles #include x.js (similar to C #include <file>)
 export function preprocess(filename) {
   let text = readFile(filename);
-  if (EXPORT_ES6 && USE_ES6_IMPORT_META) {
+  if (EXPORT_ES6) {
     // `eval`, Terser and Closure don't support module syntax; to allow it,
     // we need to temporarily replace `import.meta` and `await import` usages
     // with placeholders during preprocess phase, and back after all the other ops.

src/preamble.js

@@ -564,11 +564,11 @@ var wasmBinaryFile = '{{{ WASM_BINARY_FILE }}}';
 #else
 var wasmBinaryFile;
 function findWasmBinary() {
-#if EXPORT_ES6 && USE_ES6_IMPORT_META && !AUDIO_WORKLET
+#if EXPORT_ES6 && !AUDIO_WORKLET
   if (Module['locateFile']) {
 #endif
     return locateFile('{{{ WASM_BINARY_FILE }}}');
-#if EXPORT_ES6 && USE_ES6_IMPORT_META && !AUDIO_WORKLET // For an Audio Worklet, we cannot use `new URL()`.
+#if EXPORT_ES6 && !AUDIO_WORKLET // For an Audio Worklet, we cannot use `new URL()`.
   }
 #if ENVIRONMENT_MAY_BE_SHELL
   if (ENVIRONMENT_IS_SHELL) {

src/settings.js

@@ -1353,13 +1353,6 @@ var MODULARIZE = false;
 // [link]
 var EXPORT_ES6 = false;
 
-// Use the ES6 Module relative import feature 'import.meta.url'
-// to auto-detect WASM Module path.
-// It might not be supported on old browsers / toolchains. This setting
-// may not be disabled when Node.js is targeted (-sENVIRONMENT=*node*).
-// [link]
-var USE_ES6_IMPORT_META = true;
-
 // Global variable to export the module as for environments without a
 // standardized module loading system (e.g. the browser and SM shell).
 // [link]
@@ -2270,4 +2263,5 @@ var LEGACY_SETTINGS = [
   ['MIN_IE_VERSION', [0x7FFFFFFF], 'No longer supported'],
   ['WORKAROUND_OLD_WEBGL_UNIFORM_UPLOAD_IGNORED_OFFSET_BUG', [0], 'No longer supported'],
   ['AUTO_ARCHIVE_INDEXES', [0, 1], 'No longer needed'],
+  ['USE_ES6_IMPORT_META', [1], 'Disabling is no longer supported'],
 ];

test/test_other.py

@@ -402,16 +402,6 @@ def test_emcc_output_mjs_closure(self):
     self.assertContained('new URL("hello_world.wasm", import.meta.url)', src)
     self.assertContained('hello, world!', self.run_js('hello_world.mjs'))
 
-  def test_emcc_output_mjs_web_no_import_meta(self):
-    # Ensure we don't emit import.meta.url at all for:
-    # ENVIRONMENT=web + EXPORT_ES6 + USE_ES6_IMPORT_META=0
-    self.run_process([EMCC, '-o', 'hello_world.mjs',
-                      test_file('hello_world.c'),
-                      '-sENVIRONMENT=web', '-sUSE_ES6_IMPORT_META=0'])
-    src = read_file('hello_world.mjs')
-    self.assertNotContained('import.meta.url', src)
-    self.assertContained('export default Module;', src)
-
   def test_export_es6_implies_modularize(self):
     self.run_process([EMCC, test_file('hello_world.c'), '-sEXPORT_ES6'])
     src = read_file('a.out.js')
@@ -421,11 +411,6 @@ def test_export_es6_requires_modularize(self):
     err = self.expect_fail([EMCC, test_file('hello_world.c'), '-sEXPORT_ES6', '-sMODULARIZE=0'])
     self.assertContained('EXPORT_ES6 requires MODULARIZE to be set', err)
 
-  def test_export_es6_node_requires_import_meta(self):
-    err = self.expect_fail([EMCC, test_file('hello_world.c'),
-                            '-sENVIRONMENT=node', '-sEXPORT_ES6', '-sUSE_ES6_IMPORT_META=0'])
-    self.assertContained('EXPORT_ES6 and ENVIRONMENT=*node* requires USE_ES6_IMPORT_META to be set', err)
-
   @parameterized({
     '': ([],),
     # load a worker before startup to check ES6 modules there as well

tools/link.py

@@ -1432,11 +1432,11 @@ def phase_linker_setup(options, linker_args):  # noqa: C901, PLR0912, PLR0915
 
   set_initial_memory()
 
-  if settings.EXPORT_ES6 and settings.ENVIRONMENT_MAY_BE_NODE and not settings.USE_ES6_IMPORT_META:
-    # EXPORT_ES6 + ENVIRONMENT=*node* requires the use of import.meta.url
-    if 'USE_ES6_IMPORT_META' in user_settings:
-      exit_with_error('EXPORT_ES6 and ENVIRONMENT=*node* requires USE_ES6_IMPORT_META to be set')
-    settings.USE_ES6_IMPORT_META = 1
+  if settings.EXPORT_ES6 and not settings.MODULARIZE:
+    # EXPORT_ES6 requires output to be a module
+    if 'MODULARIZE' in user_settings:
+      exit_with_error('EXPORT_ES6 requires MODULARIZE to be set')
+    settings.MODULARIZE = 1
 
   if settings.MODULARIZE and not settings.DECLARE_ASM_MODULE_EXPORTS:
     # When MODULARIZE option is used, currently requires declaring all module exports
@@ -2065,7 +2065,7 @@ def phase_source_transforms(options):
 # both main code and libraries.
 # See also: `preprocess` in parseTools.js.
 def fix_es6_import_statements(js_file):
-  if not settings.EXPORT_ES6 or not settings.USE_ES6_IMPORT_META:
+  if not settings.EXPORT_ES6:
     return
 
   src = read_file(js_file)
@@ -2415,7 +2415,7 @@ def modularize():
     # In EXPORT_ES6 + PTHREADS the 'thread' is actually an ES6 module
     # webworker running in strict mode, so doesn't have access to 'document'.
     # In this case use 'import.meta' instead.
-    if settings.EXPORT_ES6 and settings.USE_ES6_IMPORT_META:
+    if settings.EXPORT_ES6:
       script_url = 'import.meta.url'
     else:
       script_url = "typeof document != 'undefined' ? document.currentScript?.src : undefined"

tools/settings.py

@@ -68,7 +68,6 @@
     'HEADLESS',
     'MODULARIZE',
     'EXPORT_ES6',
-    'USE_ES6_IMPORT_META',
     'EXPORT_NAME',
     'DYNAMIC_EXECUTION',
     'PTHREAD_POOL_SIZE',