[CMake] Odd Behavior in macOS Mojave

[Steven Stallion]

On Wed, Nov 14, 2018 at 8:19 AM Sean McBride <sean at rogue-research.com> wrote:

> Could you elaborate?  What odd behaviour are you seeing?  Any error message to share?  What 'workaround package' are you speaking of?  What version of Xcode?

We first noticed that some sources would fail to find certain system
headers (stddef.h in this case) when using Xcode 10 (also seen on
Xcode 10.1). It looks like Apple decided to relocate system include
paths under /Library /Developer and did away with /usr/include. After
some spelunking, it looks like this was tucked away in the release
notes for Xcode:
https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes

"The Command Line Tools package installs the macOS system headers
inside the macOS SDK. Software that compiles with the installed tools
will search for headers within the macOS SDK provided by either Xcode
at:

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk

or the Command Line Tools at:

/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk

depending on which is selected using xcode-select.

The command line tools will search the SDK for system headers by
default. However, some software may fail to build correctly against
the SDK and require macOS headers to be installed in the base system
under /usr/include. If you are the maintainer of such software, we
encourage you to update your project to work with the SDK or file a
bug report for issues that are preventing you from doing so. As a
workaround, an extra package is provided which will install the
headers to the base system. In a future release, this package will no
longer be provided. You can find this package at:

/Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg


To make sure that you're using the intended version of the command
line tools, run xcode-select -s <path to Xcode> or xcode select -s
/Library/Developer/CommandLineTools after installing."

Installing the package seemed to resolve the issues we had building
with AppleClang, which made me wonder if something is needed in the
platform modules to account for this change.

HTH,
Steve