Add test for TypeIDs diverging between shared library and executable

When the shared library is built with symbol visibility hidden
as the default, the type infos for any type is not available
to anything that links to the library, and the library or
executable will have its own copy of the type info, which
is not merged.

The results in emscripten::internal::TypeID having different
TYPEID values depending on which module does the lookup,
which causes trouble for embind's type registry as that's
indexed on the TYPEIDs.

Context: #16711

Author: torarnv

system/include/emscripten/wire.h

@@ -39,6 +39,10 @@ constexpr bool has_unbound_type_names = false;
 
 namespace internal {
 
+// Note: Neither CanonicalizedID nor the typeid-based approach
+// is guaranteed to produce stable type ids across library
+// boundaries. See core.test_dylink_typeid for more info.
+
 typedef const void* TYPEID;
 
 // We don't need the full std::type_info implementation.  We

test/test_core.py

@@ -5227,6 +5227,40 @@ def test_dylink_tls_export(self):
     self.dylink_testf(test_file('core/test_dylink_tls_export.c'),
                       need_reverse=False)
 
+  @needs_dylink
+  @disabled('TypeID does not currently handle this')
+  def test_dylink_typeid(self):
+    # When the default visibility of the library's symbols is hidden,
+    # the type info is not merged, and we end up with different type
+    # ids in the shared library and the executable.
+    self.emcc_args.append('-fvisibility=hidden')
+    self.dylink_test(header=r'''
+      #include <emscripten/wire.h>
+
+      using namespace emscripten::internal;
+      struct SomeType {};
+      __attribute__((visibility("default"))) TYPEID getSomeTypeId();
+    ''', main=r'''
+      #include "header.h"
+      #include <stdio.h>
+
+      int main() {
+        if (getSomeTypeId() != TypeID<SomeType>::get()) {
+          puts("type ids are not the same");
+          return 1;
+        }
+        puts("success");
+        return 0;
+      }
+    ''', side=r'''
+      #include "header.h"
+      #include <stdio.h>
+
+      TYPEID getSomeTypeId() {
+        return TypeID<SomeType>::get();
+      }
+    ''', expected=['success'], need_reverse=False)
+
   def test_random(self):
     src = r'''#include <stdlib.h>
 #include <stdio.h>