Open Radar

 
Summary:
It looks like the CLANG_ENABLE_MODULES build setting doesn't enable the -fmodules flag in Obj-C++ files. This is problematic because it means I can't import my "ModuleName-Swift.h" bridging header in Obj-C++ as the header generated by Swift requires modules if I'm pulling in any external frameworks (which I am).

As best as I can tell, the -fmodules flag doesn't actually enable the experimental C++ modules feature anyway, that uses a separate -fcxx-modules flag, so it's unclear to me why Xcode doesn't pass -fmodules to Obj-C++ files.

Steps to Reproduce:
1. Set up an Xcode project with CLANG_ENABLE_MODULES set to Yes
2. Add an Obj-C++ file to the project
3. In the Obj-C++ file try to use an @import statement.

Expected Results:
It should compile.

Actual Results:
It complains that modules are disabled.

Version/Build:
Xcode 9.2 (9C40b)

Notes:
If there's backwards compatibility concerns you could change CLANG_ENABLE_MODULES into a trinary build setting (like some of the warning settings are), so that way people still have to opt in to it.