Hi, I checked out guix git following instructions in https://github.com/pjotrp/guix-notes/blob/master/INSTALL.org#fetch-repository-with-git
and everything checked out and built fine. the gcc installed is version 10.2.0 ./pre-inst-env gcc --version gcc (GCC) 10.2.0 Copyright (C) 2020 Free Software Foundation, Inc. I tried to update a package definition (vtk) and then tried to build it ./pre-inst-env guix build -k -K vtk and the log file shows gcc 7.5 being used (log fragment) [ 28%] Building CXX object Common/DataModel/CMakeFiles/vtkCommonDataModel.dir/vtkQuadraticLinearWedge.cxx.o cd /tmp/guix-build-vtk-8.2.0.drv-0/build/Common/DataModel && /gnu/store/rn75fm7adgx3pw5j8pg3bczfqq1y17lk-gcc-7.5.0/bin/c++ -DVTK_IN_VTK -DvtkCommonDataModel_EXPORTS -I/tmp/guix-build-vtk-8.2.0.drv-0/build/Common/DataModel -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Common/DataModel -I/tmp/guix-build-vtk-8.2.0.drv-0/build/Common/Core -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Common/Core -I/tmp/guix-build-vtk-8.2.0.drv-0/build/Utilities/KWIML -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Utilities/KWIML -I/tmp/guix-build-vtk-8.2.0.drv-0/build/Utilities/KWSys -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Utilities/KWSys -I/tmp/guix-build-vtk-8.2.0.drv-0/build/ThirdParty/utf8 -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/ThirdParty/utf8 -I/tmp/guix-build-vtk-8.2.0.drv-0/build/Common/Math -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Common/Math -I/tmp/guix-build-vtk-8.2.0.drv-0/build/Common/Misc -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Common/Misc -I/tmp/guix-build-vtk-8.2.0.drv-0/build/Common/System -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Common/System -I/tmp/guix-build-vtk-8.2.0.drv-0/build/Common/Transforms -I/tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Common/Transforms -O3 -DNDEBUG -fPIC -fvisibility=hidden -std=c++11 -o CMakeFiles/vtkCommonDataModel.dir/vtkQuadraticLinearWedge.cxx.o -c /tmp/guix-build-vtk-8.2.0.drv-0/VTK-8.2.0/Common/DataModel/vtkQuadraticLinearWedge.cxx I am not sure why gcc 7.5 is being used; no where in the package definition scm file references explicitly gcc 7.5. I did not install gcc 7.5 explicitly either. (gcc 7.5 has problem compiling the package source so I want to make sure later gcc used) Thanks for any hint on this