Make sure to pass C++ version to preprocessor as well.

.github/workflows/test-osx.yml

@@ -32,17 +32,19 @@ jobs:
         faber -v
         sed -e "s/\$PYTHON/python/g" .ci/faber > ~/.faber
         faber \
-          --with-boost-include=/opt/homebrew/Cellar/boost/1.86.0/include \
+          --with-boost-include=$(brew --prefix boost)/include \
           --builddir=build \
           cxx.name=${{ matrix.cxx }} \
           cxxflags=-std=${{ matrix.std }} \
+          cppflags=-std=${{ matrix.std }} \
           -j`sysctl -n hw.ncpu`
     - name: test
       run: |
         faber \
-          --with-boost-include=/opt/homebrew/Cellar/boost/1.86.0/include \
+          --with-boost-include=$(brew --prefix boost)/include \
           --builddir=build\
           cxx.name=${{ matrix.cxx }} \
           cxxflags=-std=${{ matrix.std }} \
+          cppflags=-std=${{ matrix.std }} \
           -j`sysctl -n hw.ncpu` \
           test.report

.github/workflows/test-ubuntu.yml

@@ -39,6 +39,7 @@ jobs:
           --builddir=build \
           cxx.name=${{ matrix.cxx }} \
           cxxflags=-std=${{ matrix.std }} \
+          cppflags=-std=${{ matrix.std }} \
           -j`nproc`
     - name: test
       run: |
@@ -47,5 +48,6 @@ jobs:
           --builddir=build \
           cxx.name=${{ matrix.cxx }} \
           cxxflags=-std=${{ matrix.std }} \
+          cppflags=-std=${{ matrix.std }} \
           -j`nproc` \
           test.report