Fix libomp installation for MacOS CI Builds

build/ci/job-template.yml

@@ -50,7 +50,7 @@ jobs:
 
     steps:
     - ${{ if eq(parameters.pool.name, 'Hosted macOS') }}:
-      - script: brew update && brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/f5b1ac99a7fba27c19cee0bc4f036775c889b359/Formula/libomp.rb && brew unlink python@2 && brew install mono-libgdiplus gettext && brew link gettext --force && brew link libomp --force
+      - script: brew update && brew install $(Build.SourcesDirectory)/build/libomp.rb && brew unlink python@2 && brew install mono-libgdiplus gettext && brew link gettext --force && brew link libomp --force
         displayName: Install build dependencies
     - ${{ if and( eq(parameters.nightlyBuild, 'true'), eq(parameters.pool.name, 'Hosted Ubuntu 1604')) }}:
       - bash: echo "##vso[task.setvariable variable=LD_LIBRARY_PATH]$(nightlyBuildRunPath):$LD_LIBRARY_PATH"

build/libomp.rb

@@ -0,0 +1,62 @@
+class Libomp < Formula
+  desc "LLVM's OpenMP runtime library"
+  homepage "https://openmp.llvm.org/"
+  url "https://releases.llvm.org/7.0.0/openmp-7.0.0.src.tar.xz"
+  sha256 "30662b632f5556c59ee9215c1309f61de50b3ea8e89dcc28ba9a9494bba238ff"
+
+  bottle do
+    cellar :any
+    sha256 "c8788028105e9ec32e29bcdba8c7b550c2afd96b3f0a7bd0d6b6136a8729174a" => :mojave
+    sha256 "046f659ad8a2cc336049a1e7f7be0dac2f2e28ce322409f10396f9582b94b660" => :high_sierra
+    sha256 "ba1b9a78326c671fb864a95d93f2fcf47f3af2ef8f12f6c7ee54a7c0cf7802b4" => :sierra
+    sha256 "0ea5b6ae3e9e0b32a2b49a7430fb0f653430107164089b067a7b0039e91ce527" => :el_capitan
+  end
+
+  depends_on "cmake" => :build
+  depends_on :macos => :yosemite
+
+  def install
+    system "cmake", ".", *std_cmake_args
+    system "make", "install"
+    system "cmake", ".", "-DLIBOMP_ENABLE_SHARED=OFF", *std_cmake_args
+    system "make", "install"
+  end
+
+  def caveats; <<~EOS
+    On Apple Clang, you need to add several options to use OpenMP's front end
+    instead of the standard driver option. This usually looks like
+      -Xpreprocessor -fopenmp -lomp
+
+    You might need to make sure the lib and include directories are discoverable
+    if #{HOMEBREW_PREFIX} is not searched:
+
+      -L#{opt_lib} -I#{opt_include}
+
+    For CMake, the following flags will cause the OpenMP::OpenMP_CXX target to
+    be set up correctly:
+      -DOpenMP_CXX_FLAGS="-Xpreprocessor -fopenmp -I#{opt_include}" -DOpenMP_CXX_LIB_NAMES="omp" -DOpenMP_omp_LIBRARY=#{opt_lib}/libomp.dylib
+  EOS
+  end
+
+  test do
+    (testpath/"test.cpp").write <<~EOS
+      #include <omp.h>
+      #include <array>
+      int main (int argc, char** argv) {
+        std::array<size_t,2> arr = {0,0};
+        #pragma omp parallel num_threads(2)
+        {
+            size_t tid = omp_get_thread_num();
+            arr.at(tid) = tid + 1;
+        }
+        if(arr.at(0) == 1 && arr.at(1) == 2)
+            return 0;
+        else
+            return 1;
+      }
+    EOS
+    system ENV.cxx, "-Werror", "-Xpreprocessor", "-fopenmp", "test.cpp",
+                    "-L#{lib}", "-lomp", "-o", "test"
+    system "./test"
+  end
+end