Link flags with clang-cl vs clang

[loriab]

EDIT: I just realized that the issue I described below (specifying clang-cl through cbc.yaml) in a pure C/C++ recipe on staged-recipes produces the same error about /link flag and fails to configure. Filtering out the flag via set "LDFLAGS=%LDFLAGS:/link=%" works fine (effectively same solution as I came to below). So flang has nothing to do with it. Perhaps I'm utterly using the compiler wrong or this issue should be moved to https://github.com/conda-forge/clang-win-activation-feedstock .

2025-04-14T19:26:56.2056605Z (%PREFIX%) %SRC_DIR%\tests>cmake -S. -Bbuild -GNinja -DCMAKE_PREFIX_PATH="%PREFIX%\Library" -DCMAKE_CXX_COMPILER=clang-cl -DCMAKE_BUILD_TYPE=Release" 
2025-04-14T19:26:57.5879410Z -- The CXX compiler identification is Clang 20.1.2 with MSVC-like command-line
2025-04-14T19:26:57.7719227Z -- Detecting CXX compiler ABI info
2025-04-14T19:26:58.1244659Z -- Detecting CXX compiler ABI info - failed
2025-04-14T19:26:58.1246495Z -- Check for working CXX compiler: D:/bld/openorbitaloptimizer-split_1744658708593/_test_env/Library/bin/clang-cl.exe
2025-04-14T19:26:58.4495009Z CMake Error at D:/bld/openorbitaloptimizer-split_1744658708593/_test_env/Library/share/cmake-4.0/Modules/CMakeTestCXXCompiler.cmake:73 (message):
2025-04-14T19:26:58.4496319Z -- Check for working CXX compiler: D:/bld/openorbitaloptimizer-split_1744658708593/_test_env/Library/bin/clang-cl.exe - broken
2025-04-14T19:26:58.4501830Z -- Configuring incomplete, errors occurred!
2025-04-14T19:26:58.4502819Z   The C++ compiler
2025-04-14T19:26:58.4503372Z 
2025-04-14T19:26:58.4504023Z     "D:/bld/openorbitaloptimizer-split_1744658708593/_test_env/Library/bin/clang-cl.exe"
2025-04-14T19:26:58.4504503Z 
2025-04-14T19:26:58.4505065Z   is not able to compile a simple test program.
2025-04-14T19:26:58.4505518Z 
2025-04-14T19:26:58.4506060Z   It fails with the following output:
2025-04-14T19:26:58.4506484Z 
2025-04-14T19:26:58.4507109Z     Change Dir: 'D:/bld/openorbitaloptimizer-split_1744658708593/test_tmp/tests/build/CMakeFiles/CMakeScratch/TryCompile-1tz29h'
2025-04-14T19:26:58.4507740Z     
2025-04-14T19:26:58.4508351Z     Run Build Command(s): D:/bld/openorbitaloptimizer-split_1744658708593/_test_env/Library/bin/ninja.exe -v cmTC_b7a0a
2025-04-14T19:26:58.4509370Z     [1/2] D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\Library\bin\clang-cl.exe  /nologo -TP   /Oi /O2 /GS /Gy /MD -march=nocona -mtune=haswell -fuse-ld=lld /std:c++17 -D_CRT_SECURE_NO_WARNINGS -fms-runtime-lib=dll -fuse-ld=lld  /DWIN32 /D_WINDOWS /GR /EHsc  /Zi /Ob0 /Od /RTC1 -MDd /showIncludes /FoCMakeFiles\cmTC_b7a0a.dir\testCXXCompiler.cxx.obj /FdCMakeFiles\cmTC_b7a0a.dir\ -c -- D:\bld\openorbitaloptimizer-split_1744658708593\test_tmp\tests\build\CMakeFiles\CMakeScratch\TryCompile-1tz29h\testCXXCompiler.cxx
2025-04-14T19:26:58.4511090Z     [2/2] C:\Windows\system32\cmd.exe /C "cd . && D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\Library\bin\cmake.exe -E vs_link_exe --msvc-ver=1929 --intdir=CMakeFiles\cmTC_b7a0a.dir --rc=C:\PROGRA~2\WI3CF2~1\10\bin\100261~1.0\x64\rc.exe --mt=D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\Library\bin\llvm-mt.exe --manifests  -- D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\Library\bin\lld-link.exe /nologo CMakeFiles\cmTC_b7a0a.dir\testCXXCompiler.cxx.obj  /out:cmTC_b7a0a.exe /implib:cmTC_b7a0a.lib /pdb:cmTC_b7a0a.pdb /version:0.0 /machine:x64 /link /DEFAULTLIB:D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\lib\clang\20\lib\windows\clang_rt.builtins-x86_64.lib  /debug /INCREMENTAL /subsystem:console  kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib && cd ."
2025-04-14T19:26:58.4512737Z     FAILED: cmTC_b7a0a.exe 
2025-04-14T19:26:58.4513993Z     C:\Windows\system32\cmd.exe /C "cd . && D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\Library\bin\cmake.exe -E vs_link_exe --msvc-ver=1929 --intdir=CMakeFiles\cmTC_b7a0a.dir --rc=C:\PROGRA~2\WI3CF2~1\10\bin\100261~1.0\x64\rc.exe --mt=D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\Library\bin\llvm-mt.exe --manifests  -- D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\Library\bin\lld-link.exe /nologo CMakeFiles\cmTC_b7a0a.dir\testCXXCompiler.cxx.obj  /out:cmTC_b7a0a.exe /implib:cmTC_b7a0a.lib /pdb:cmTC_b7a0a.pdb /version:0.0 /machine:x64 /link /DEFAULTLIB:D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\lib\clang\20\lib\windows\clang_rt.builtins-x86_64.lib  /debug /INCREMENTAL /subsystem:console  kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib && cd ."
2025-04-14T19:26:58.4516185Z     LINK Pass 1: command "D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\Library\bin\lld-link.exe /nologo CMakeFiles\cmTC_b7a0a.dir\testCXXCompiler.cxx.obj /out:cmTC_b7a0a.exe /implib:cmTC_b7a0a.lib /pdb:cmTC_b7a0a.pdb /version:0.0 /machine:x64 /link /DEFAULTLIB:D:\bld\openorbitaloptimizer-split_1744658708593\_test_env\lib\clang\20\lib\windows\clang_rt.builtins-x86_64.lib /debug /INCREMENTAL /subsystem:console kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib /MANIFEST /MANIFESTFILE:CMakeFiles\cmTC_b7a0a.dir/intermediate.manifest CMakeFiles\cmTC_b7a0a.dir/manifest.res" failed (exit code 1) with the following output:
2025-04-14T19:26:58.4517398Z     lld-link: error: could not open '/link': no such file or directory

Comment:

Hi, I've been playing around with the flang19 migration PRs on a few feedstocks, in particular conda-forge/gdma-feedstock#10 . Whenever I tried to switch the C/C++ compiler to clang-cl officially (through cbc.yaml) rather than through CMAKE_C_COMPILER=clang-cl, the compiler fails CMake configuration (clang-cl.exe" is not able to compile a simple test program.). I looked into the linker lines added by the various compiler activation feedstocks and tried resetting LDFLAGS in the recipe bld.bat according to their patterns, and I found a variation on the clang-cl one that worked. Comparison of activate LDFLAGS lines and their effect in a flang20 recipe below.

I suspect that the general solution is that the flang activation script in this feedstock needs to choose how to set LDFLAGS depending on whether clang or clang-cl is the target C/C++ compiler.

clang-win-activation-feedstock/.../activate-clang-cl_win-64.bat

::set "LDFLAGS=/link /DEFAULTLIB:%CONDA_PREFIX%\lib\clang\@MAJOR_VER@\lib\windows\clang_rt.builtins-x86_64.lib"
::set "LDFLAGS=/DEFAULTLIB:%CONDA_PREFIX%\lib\clang\@MAJOR_VER@\lib\windows\clang_rt.builtins-x86_64.lib"
set "LDFLAGS=/DEFAULTLIB:%CONDA_PREFIX%\lib\clang\20\lib\windows\clang_rt.builtins-x86_64.lib"

:: outcome
:: WORKS! (after removing /LINK and hard-coding v20)

flang-activation-feedstock/.../activate.bat

set "LDFLAGS=%LDFLAGS% -Wl,-defaultlib:%CONDA_PREFIX:\=/%/lib/clang/@MAJOR_VER@/lib/windows/clang_rt.builtins-x86_64.lib"

:: outcome
:: FAILS: "D:/bld/gdma-split_1744384002874/_build_env/Library/bin/clang-cl.exe" is not able to compile a simple test program.

clang-win-activation-feedstock/.../activate-clang_win-64.bat

set "LDFLAGS=-nostdlib -Wl,-defaultlib:%CONDA_PREFIX:\=/%/lib/clang/@MAJOR_VER@/lib/windows/clang_rt.builtins-x86_64.lib"

:: outcome
:: ALLOWS compiler and library link. on exe: LINK: command "D:\bld\gdma-split_1744384917393\_build_env\Library\bin\lld-link.exe /nologo CMakeFiles\gdmaexe.dir\src\exe.f90.obj /out:gdma.exe /implib:gdma.lib /pdb:gdma.pdb /version:0.0 /machine:x64 -nostdlib -Wl,-defaultlib:D:/bld/gdma-split_1744384917393/_build_env/lib/clang/@MAJOR_VER@/lib/windows/clang_rt.builtins-x86_64.lib /INCREMENTAL:NO /subsystem:console libgdma.lib -libpath:D:/bld/gdma-split_1744384917393/_build_env/Library/lib -libpath:D:/bld/gdma-split_1744384917393/_build_env/Library/lib/clang/20/lib/windows /MANIFEST:EMBED,ID=1" failed (exit code 1) with the following output:
::lld-link: warning: ignoring unknown argument '-nostdlib'
::lld-link: warning: ignoring unknown argument '-Wl,-defaultlib:D:/bld/gdma-split_1744384917393/_build_env/lib/clang/@MAJOR_VER@/lib/windows/clang_rt.builtins-x86_64.lib'

[lucascolley]

lld-link: warning: ignoring unknown argument '-Wl,-defaultlib

this one should be fixed by gh-51

[lucascolley]

I think your other issues should have been fixed by conda-forge/clang-win-activation-feedstock#66. scipy/scipy#24839 successfully builds SciPy just using Pixi's

[workspace.target.win.build-variants]
c_compiler = ["clang-cl"] 
cxx_compiler = ["clang-cl"]
fortran_compiler = ["flang"]

So this issue can probably be closed with the merge of gh-51