[macos] Missing cmath.h definitions

[csparker247]

Description
I've recently been getting build errors on a C++ project in the macos-10.15 image. A compiler error is thrown because multiple things from cmath.h aren't found, like ::signbit, ::isless, and ::isgreater. These are compiler errors from deep inside a dependency, in this case ITK, and not my code.

In file included from /Users/runner/work/cpp-build-action/cpp-build-action/main.cpp:1:
In file included from /usr/local/include/ITK-5.1/itkMesh.h:32:
In file included from /usr/local/include/ITK-5.1/itkPointSet.h:32:
In file included from /usr/local/include/ITK-5.1/itkDefaultStaticMeshTraits.h:21:
In file included from /usr/local/include/ITK-5.1/itkCellInterface.h:24:
In file included from /usr/local/include/ITK-5.1/itkArray.h:24:
In file included from /usr/local/include/ITK-5.1/vnl/vnl_vector.h:23:
In file included from /usr/local/include/ITK-5.1/vnl/vnl_c_vector.h:24:
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cmath:317:9: error: no member named 'signbit' in the global namespace
using ::signbit;

I've seen this before on my personal machine, and it's almost always caused by something weird in the SDK configuration. My solution in those cases has been to make sure Xcode.app is uninstalled and only rely on the Command Line Tools. I first noticed this in Github Actions on 12/2/20 when a job failed for a commit, but then another job succeeded on a tagged version of the same commit. Prior to this, the job ran successfully. The timing implies that this has something to do with the change to a default Xcode 12.2.

I've setup a minimal project to explore the issue here. Thus far, I have observed the problem in both macos-10.15 and macos-11.0 when using the default Xcode. I do not have the problem on macos-11.0 when I use:

sudo xcode-select -s "/Library/Developer/CommandLineTools/"

but this does not work on macos-10.15. On that environment, I've tried using Xcode_12.app, Xcode_12.1.1.app, and /Library/Developer/CommandLineTools/, none of which work. I've also tried doing export SDKROOT=[full SDK path] along with xcode-select, since CMake pulls from that variable when determining the SDK to use.

I have already referred to #2056, #2211 (comment), and #2218 for possible solutions.

Area for Triage:

Apple, C/C++

Question, Bug, or Feature?:
Bug

Virtual environments affected

• Ubuntu 16.04
• Ubuntu 18.04
• Ubuntu 20.04
• macOS 10.15
• macOS 11.0
• Windows Server 2016 R2
• Windows Server 2019

Expected behavior
Project builds successfully.

Actual behavior
Compiler error due to missing definitions.

Repro steps
I've setup a minimal example project here. It contains one action which performs all of the requisite steps. In brief, those steps are:

1. (optional) Set the Xcode version and/or SDKROOT
2. Run brew install itk
3. Setup a CMake executable project that includes itkMesh.h and links against ITKCommon
4. Try to compile.

[MaksimZhukov]

Hello @csparker247 !

We've reproduced this issue, but unfortunately we have not found the root cause yet. As a temporary solution you can define the CPLUS_INCLUDE_PATH environment variable for your entire workflow:

env:
  CPLUS_INCLUDE_PATH: /usr/local/opt/llvm/include/c++/v1:/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include

We will continue to investigate the issue, I will keep you posted.

[MaksimZhukov]

Xcode Command Line Tools (12.2) installed on the macOS-10.15 include both MacOSX10.15.sdk and MacOSX11.0.sdk. The MacOSX.sdk symlink points to the MacOSX11.0.sdk. Here is the output of the ls -la /Library/Developer/CommandLineTools/SDKs command:

total 0
drwxr-xr-x  5 root  wheel  160 Dec 12 21:15 .
drwxr-xr-x  5 root  wheel  160 Dec 12 21:14 ..
lrwxr-xr-x  1 root  wheel   14 Dec 12 21:15 MacOSX.sdk -> MacOSX11.0.sdk
drwxr-xr-x  8 root  wheel  256 Jul  9 16:33 MacOSX10.15.sdk
drwxr-xr-x  7 root  wheel  224 Oct 19 20:39 MacOSX11.0.sdk

To fix this issue you can override the MacOSX.sdk symlink and remove the MacOSX11.0.sdk from the CommandLineTools/SDKs:

- name: Override the MacOSX.sdk symLink
  run: |
    sudo rm /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
    sudo rm -rf /Library/Developer/CommandLineTools/SDKs/MacOSX11.0.sdk
    sudo ln -sf MacOSX10.15.sdk /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk 

[csparker247]

Confirmed that this works on macos-10.15 using CLT. I assume something similar would need to be done for those on 10.15 using Xcode_12.app.

I am confused as to why it wouldn't work outright on macos-11.0 by default. Assumably MacOSX.sdk in Xcode_12.2.app is symlinked to MacOSX11.0.sdk.

Anyway, this hints to me that maybe there's something broken in CMake or ITK for resolving the correct SDK. If MacOSX.sdk is a moving target based on the tooling version, it seems like it should always try to find the SDK named MacOSX10.15.sdk if the target platform is 10.15.

[MaksimZhukov]

In this case, I am going to close this issue, but feel free to contact us if you have any concerns!