Fix MODULARIZE with sync compilation (#12650)

MODULARIZE + WASM_ASYNC_COMPILATION=0, that is, modularize mode but with
async compilation turned off, so that startup is synchronous, should return the
Module object from the factory function (as it would not make sense to return
a Promise without async startup).

Fixes #12647

ChangeLog.md

@@ -38,6 +38,10 @@ Current Trunk
   modules.  As one side effect of this change it is now required that JavaScript
   functions that are imported by address are now required to have a `__sig`
   specified in the library JavaScript file.
+- `MODULARIZE` + `WASM_ASYNC_COMPILATION=0`, that is, modularize mode but with
+  async compilation turned off, so that startup is synchronous, now returns the
+  Module object from the factory function (as it would not make sense to return
+  a Promise without async startup). See #12647
 
 2.0.8: 10/24/2020
 -----------------

emcc.py

@@ -2835,7 +2835,9 @@ def modularize():
   logger.debug('Modularizing, assigning to var ' + shared.Settings.EXPORT_NAME)
   src = open(final_js).read()
 
-  return_value = shared.Settings.EXPORT_NAME + '.ready'
+  return_value = shared.Settings.EXPORT_NAME
+  if shared.Settings.WASM_ASYNC_COMPILATION:
+    return_value += '.ready'
   if not shared.Settings.EXPORT_READY_PROMISE:
     return_value = '{}'
 

src/settings.js

@@ -954,6 +954,10 @@ var DETERMINISTIC = 0;
 // resolved with the module instance when it is safe to run the compiled code,
 // similar to the `onRuntimeInitialized` callback. You do not need to use the
 // `onRuntimeInitialized` callback when using `MODULARIZE`.
+//
+// (If WASM_ASYNC_COMPILATION is off, that is, if compilation is
+// *synchronous*, then it would not make sense to return a Promise, and instead
+// the Module object itself is returned, which is ready to be used.)
 // 
 // The default name of the function is `Module`, but can be changed using the
 // `EXPORT_NAME` option. We recommend renaming it to a more typical name for a

tests/test_browser.py

@@ -3322,7 +3322,7 @@ def test_modularize(self):
         src = open(path_from_root('tests', 'browser_test_hello_world.c')).read()
         create_test_file('test.c', self.with_report_result(src))
         # this test is synchronous, so avoid async startup due to wasm features
-        self.compile_btest(['test.c', '-s', 'MODULARIZE=1', '-s', 'WASM_ASYNC_COMPILATION=0', '-s', 'SINGLE_FILE=1'] + args + opts)
+        self.compile_btest(['test.c', '-s', 'MODULARIZE=1', '-s', 'SINGLE_FILE=1'] + args + opts)
         create_test_file('a.html', '''
           <script src="a.out.js"></script>
           <script>

tests/test_other.py

@@ -4842,6 +4842,31 @@ def test_EXPORT_NAME_with_html(self):
     self.assertNotEqual(result.returncode, 0)
     self.assertContained('Customizing EXPORT_NAME requires that the HTML be customized to use that name', result.stdout)
 
+  def test_modularize_sync_compilation(self):
+    create_test_file('post.js', r'''
+console.log('before');
+var result = Module();
+// It should be an object.
+console.log(typeof result);
+// And it should have the exports that Module has, showing it is Module in fact.
+console.log(typeof result._main);
+// And it should not be a Promise.
+console.log(typeof result.then);
+console.log('after');
+''')
+    self.run_process([EMCC, path_from_root('tests', 'hello_world.c'),
+                      '-s', 'MODULARIZE=1',
+                      '-s', 'WASM_ASYNC_COMPILATION=0',
+                      '--extern-post-js', 'post.js'])
+    self.assertContained('''\
+before
+hello, world!
+object
+function
+undefined
+after
+''', self.run_js('a.out.js'))
+
   def test_export_all_3142(self):
     create_test_file('src.cpp', r'''
 typedef unsigned int Bit32u;