Fix webidl_binder so it can't handle missing assert function

This can happen when ASSERTIONS is not set and we are in STRICT
mode or MINIMAL_RUNTIME mode.

See emscripten-core#20592

Author: sbc100

test/test_core.py

@@ -7637,6 +7637,7 @@ def test_embind_no_rtti_followed_by_rtti(self):
   def test_webidl(self, mode, allow_memory_growth):
     self.uses_es6 = True
     self.set_setting('WASM_ASYNC_COMPILATION', 0)
+    self.set_setting('STRICT')
     if self.maybe_closure():
       # avoid closure minified names competing with our test code in the global name space
       self.set_setting('MODULARIZE')
@@ -7670,7 +7671,7 @@ def test_webidl(self, mode, allow_memory_growth):
 
     # Export things on "TheModule". This matches the typical use pattern of the bound library
     # being used as Box2D.* or Ammo.*, and we cannot rely on "Module" being always present (closure may remove it).
-    self.emcc_args += ['--post-js=glue.js', '--extern-post-js=extern-post.js']
+    self.emcc_args += ['--no-entry', '--post-js=glue.js', '--extern-post-js=extern-post.js']
     if mode == 'ALL':
       self.emcc_args += ['-sASSERTIONS']
     if allow_memory_growth:

tools/webidl_binder.py

@@ -133,6 +133,15 @@ def build_constructor(name):
 mid_js += build_constructor('WrapperObject')
 
 mid_js += ['''
+/*
+ * For now, the webidl-generated code unconditionally depends on the `assert` function,
+ * but there are certain build modes where emscripten does not define this.
+ * TODO(sbc): Make the usage of assert conditional.
+ */
+if (typeof assert == "undefined") {
+  assert = (cond) => {}
+}
+
 /** @suppress {duplicate} (TODO: avoid emitting this multiple times, it is redundant)
     @param {*=} __class__ */
 function getCache(__class__) {