[embind] Using EMSCRIPTEN_HAS_UNBOUND_TYPE_NAMES=0 fails with polymorphic types

[sbc100]

The EMSCRIPTEN_HAS_UNBOUND_TYPE_NAMES=0 feature seems to not work with polymorphic types.

Adding a flavor of other.test_embind that builds with EMSCRIPTEN_HAS_UNBOUND_TYPE_NAMES=0 causes the test to fail with:

Error: expected: PolyDerived, actual: PolyBase
    at Object.assert.equal (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:6055:18)
    at Object.<anonymous> (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:6688:20)
    at runTest (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:5887:23)
    at run_all (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:5907:26)
    at run_all_tests (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:6410:5)
    at Object.<anonymous> (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:9366:5)
    at Module._compile (node:internal/modules/cjs/loader:1196:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1250:10)
    at Module.load (node:internal/modules/cjs/loader:1074:32)
    at Function.Module._load (node:internal/modules/cjs/loader:909:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:22:47
error: Error: expected: PolyDerived, actual: PolyBase
    at Object.assert.equal (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:6055:18)
    at Object.<anonymous> (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:6688:20)
    at runTest (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:5887:23)
    at run_all (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:5907:26)
    at run_all_tests (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:6410:5)
    at Object.<anonymous> (/usr/local/google/home/sbc/dev/wasm/emscripten/out/test/embind_test.js:9366:5)
    at Module._compile (node:internal/modules/cjs/loader:1196:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1250:10)
    at Module.load (node:internal/modules/cjs/loader:1074:32)
    at Function.Module._load (node:internal/modules/cjs/loader:909:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:22:47 {
  info: { Expected: 'PolyDerived', Actual: 'PolyBase' }
}

I believe this is because getLightTypeID() is able to inspect the type of a value when EMSCRIPTEN_HAS_UNBOUND_TYPE_NAMES is enabled but other wise it only looks at the type T and not the value:

emscripten/system/include/emscripten/wire.h

Lines 85 to 95 in d99707c

	if (has_unbound_type_names) {
	#if __has_feature(cxx_rtti)
	return &typeid(value);
	#else
	static_assert(!has_unbound_type_names,
	"Unbound type names are illegal with RTTI disabled. "
	"Either add -DEMSCRIPTEN_HAS_UNBOUND_TYPE_NAMES=0 to or remove -fno-rtti "
	"from the compiler arguments");
	#endif
	}
	return LightTypeID<T>::get();

[sbc100]

It looks like when this feature was first added we only used the LightTypeID when the type was not polymorphic: 2bbdb0c

However this check was removed in #10914

[sbc100]

@brendandahl

[sbc100]

@dnfield it seems like the assumption of #10914 is that all cases should work find without RTTI. If that is true why do we have the rtti mode still? Why not default to not -DEMSCRIPTEN_HAS_UNBOUND_TYPE_NAMES=0 and no rtti usage.

However, based on the above failure, I'm not sure this assumption is true.

[sbc100]

CC @chadaustin