[llvm] [cmake] Silence GNUInstallDirs warning in LLVMInstallSymlink

[mgorny]

Summary

Set a dummy CMAKE_INSTALL_LIBDIR in order to silence the following CMake
warning when executing LLVMInstallSymlink.cmake script:

CMake Warning (dev) at /usr/share/cmake/Modules/GNUInstallDirs.cmake:243 (message):
  Unable to determine default CMAKE_INSTALL_LIBDIR directory because no
  target architecture is known.  Please enable at least one language before
  including GNUInstallDirs.
Call Stack (most recent call first):
  /usr/lib/llvm/16/lib64/cmake/llvm/LLVMInstallSymlink.cmake:5 (include)
  tools/lld/cmake_install.cmake:66 (include)
  cmake_install.cmake:52 (include)

[MaskRay]

What's the cmake configure command and ninja target to trigger the warning?

[mgorny]

In D136573#3881567, @MaskRay wrote:

What's the cmake configure command and ninja target to trigger the warning?

I've noticed it while installing LLD standalone, so in my case it was:

cmake -G Ninja -DCMAKE_INSTALL_PREFIX=/usr/lib/llvm/16 -DBUILD_SHARED_LIBS=ON -DLLVM_INCLUDE_TESTS=no -DCMAKE_BUILD_TYPE=RelWithDebInfo ../lld
ninja -v -j12
ninja -v -j12 install

[MaskRay]

How to do a standalone build? The lld standalone build is not documented.

% cmake -GNinja -Sllvm -B/tmp/out/custom-llvm custom-llvm -DLLVM_ENABLE_PROJECTS=llvm -DCMAKE_INSTALL_PREFIX=/tmp/opt/llvm
% ninja install
% cmake -GNinja -Slld -B/tmp/out/lld -DLLVM_BUILD_MAIN_SRC_DIR=/tmp/out/custom-llvm/lib/cmake/llvm -DLLVM_DIR=/tmp/out/custom-llvm/lib/cmake/llvm -DLLVM_INCLUDE_TESTS=off
-- Building with -fPIC
-- LLD version: 16.0.0
-- Configuring done
CMake Error at /tmp/out/custom-llvm/lib/cmake/llvm/AddLLVM.cmake:958 (add_executable):
  Cannot find source file:

    /tmp/out/lld/tools/lld/lld-driver.cpp

  Tried extensions .c .C .c++ .cc .cpp .cxx .cu .mpp .m .M .mm .ixx .cppm .h
  .hh .h++ .hm .hpp .hxx .in .txx .f .F .for .f77 .f90 .f95 .f03 .hip .ispc
Call Stack (most recent call first):
  cmake/modules/AddLLD.cmake:35 (add_llvm_executable)
  cmake/modules/AddLLD.cmake:44 (add_lld_executable)
  tools/lld/CMakeLists.txt:5 (add_lld_tool)


CMake Error at /tmp/out/custom-llvm/lib/cmake/llvm/AddLLVM.cmake:958 (add_executable):
  No SOURCES given to target: lld
Call Stack (most recent call first):
  cmake/modules/AddLLD.cmake:35 (add_llvm_executable)
  cmake/modules/AddLLD.cmake:44 (add_lld_executable)
  tools/lld/CMakeLists.txt:5 (add_lld_tool)


CMake Generate step failed.  Build files cannot be regenerated correctly.

[mgorny]

If you don't mind me being busy with other things right now, I've found a simpler reproducer:

$ cmake -GNinja ../llvm  -DCMAKE_INSTALL_PREFIX=$HOME/llvm-install -DCMAKE_BUILD_TYPE=MinSizeRel -DLLVM_DISTRIBUTION_COMPONENTS=llvm-addr2line
[...]
$ ninja install-distribution
[...]
[690/691] cd /home/mgorny/llvm-project/llvm-build/tools/llvm-symbo...2line" -P /home/mgorny/llvm-project/llvm-build/cmake_install.cmake
-- Install configuration: "MinSizeRel"
CMake Warning (dev) at /usr/share/cmake/Modules/GNUInstallDirs.cmake:241 (message):
  Unable to determine default CMAKE_INSTALL_LIBDIR directory because no
  target architecture is known.  Please enable at least one language before
  including GNUInstallDirs.
Call Stack (most recent call first):
  /home/mgorny/llvm-project/llvm/cmake/modules/LLVMInstallSymlink.cmake:5 (include)
  cmake_install.cmake:56 (include)
  /home/mgorny/llvm-project/llvm-build/tools/cmake_install.cmake:119 (include)
  /home/mgorny/llvm-project/llvm-build/cmake_install.cmake:81 (include)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Creating llvm-addr2line

[MaskRay]

Thanks for the instructions. I see the warning and curl -L 'https://reviews.llvm.org/D136573?download=1' | patch -p0 fixes it.

Normally uploaded patches are applied via patch -p1. The patch you uploaded uses

--- llvm/cmake/modules/LLVMInstallSymlink.cmake
+++ llvm/cmake/modules/LLVMInstallSymlink.cmake

instead of a/ b/ (git format-patch -1, git diff 'HEAD^', etc).

[mgorny]

I've uploaded git-format-patch. Phabricator does weird stuff to patches sometimes. Never really figured it out. Can't wait to see it go in favor of GitHub pull requests (or anything else, really).

llvm/cmake/modules/LLVMInstallSymlink.cmake

 # We need to execute this script at installation time because the
 # DESTDIR environment variable may be unset at configuration time.
 # See PR8397.
 
+# Set to an arbitrary directory to silence GNUInstallDirs warnings
+# regarding being unable to determine libdir.
+set(CMAKE_INSTALL_LIBDIR "lib")
 include(GNUInstallDirs)
 
 function(install_symlink name target outdir)
   set(DESTDIR $ENV{DESTDIR})
   if(NOT IS_ABSOLUTE "${outdir}")
     set(outdir "${CMAKE_INSTALL_PREFIX}/${outdir}")
   endif()
   set(outdir "${DESTDIR}${outdir}")