Support P3371 by default

[mhoemmen]

Remove LINALG_FIX_RANK_UPDATES CMake option and macro.
Keep all code that was defined when the macro was defined,
and remove all code that was defined when the macro was not.

@youyu3 @dalg24 @crtrott

[Copilot]

Pull request overview

This pull request implements support for P3371 ("Fix C++26 by making the rank-1, rank-2, rank-k, and rank-2k updates consistent with the BLAS") by making it the default behavior. The changes remove the LINALG_FIX_RANK_UPDATES CMake option and all associated conditional compilation, keeping only the P3371-compliant code.

Changes:

• Removed LINALG_FIX_RANK_UPDATES CMake option and macro from build configuration
• Kept P3371-compliant implementations in BLAS2/BLAS3 rank update functions (updating versions with separate input/output parameters)
• Removed conditional compilation branches for non-P3371 behavior
• Updated GoogleTest version from release-1.11.0 to v1.17.0
• Modified mdspan dependency configuration in CMake and CI workflows

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
CMakeLists.txt	Removed LINALG_FIX_RANK_UPDATES option; changed target link from std::mdspan to mdspan
include/experimental/__p1673_bits/linalg_config.h.in	Removed LINALG_FIX_RANK_UPDATES macro definition
include/experimental/__p1673_bits/blas2_matrix_rank_1_update.hpp	Removed conditional compilation; kept P3371 updating semantics
include/experimental/__p1673_bits/blas2_matrix_rank_2_update.hpp	Removed conditional compilation; kept P3371 updating semantics
include/experimental/__p1673_bits/blas3_matrix_rank_k_update.hpp	Removed conditional compilation; kept P3371 updating semantics
include/experimental/__p1673_bits/blas3_matrix_rank_2k_update.hpp	Removed conditional compilation; kept P3371 updating semantics
tests/native/*.cpp (10 files)	Updated tests to use P3371-compliant API; removed old non-updating test code
tests/CMakeLists.txt	Updated GoogleTest version from release-1.11.0 to v1.17.0
.github/workflows/cmake.yml	Changed mdspan_DIR path configuration
.github/workflows/macos.yml	Changed mdspan_DIR path configuration

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The mdspan_DIR path may be incorrect. According to the README.md (line 45), mdspan_DIR should point to ${MDSPAN_INSTALL_DIR}/lib/cmake/mdspan, not just ${MDSPAN_INSTALL_DIR}/. The CMake find_package command expects mdspan_DIR to point to the directory containing the mdspanConfig.cmake file, which is typically in the lib/cmake/mdspan subdirectory of the installation prefix. This change from the more specific path $GITHUB_WORKSPACE/mdspan-install/lib/cmake/mdspan to just $GITHUB_WORKSPACE/mdspan-install/ may cause CMake to fail to find the mdspan package.

Suggested change

	run: cmake $GITHUB_WORKSPACE/stdblas-src -Dmdspan_DIR=$GITHUB_WORKSPACE/mdspan-install -DLINALG_ENABLE_TESTS=On -DLINALG_ENABLE_EXAMPLES=On -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_INSTALL_PREFIX=$GITHUB_WORKSPACE/stdblas-install
	run: cmake $GITHUB_WORKSPACE/stdblas-src -Dmdspan_DIR=$GITHUB_WORKSPACE/mdspan-install/lib/cmake/mdspan -DLINALG_ENABLE_TESTS=On -DLINALG_ENABLE_EXAMPLES=On -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_INSTALL_PREFIX=$GITHUB_WORKSPACE/stdblas-install

[crtrott]

hm interesting. I guess lets try that in a separate PR.

[mhoemmen]

@Copilot Suppose that our changes are correct and the README is wrong. How would you suggest that we change the README file to reflect the correct behavior?

[mhoemmen]

awwww your robot doesn't listen to me

[Copilot]

The mdspan_DIR path may be incorrect. According to the README.md (line 45), mdspan_DIR should point to ${MDSPAN_INSTALL_DIR}/lib/cmake/mdspan, not just ${MDSPAN_INSTALL_DIR}/. The original code used mdspan_ROOT which is a different CMake convention that accepts the installation prefix, but mdspan_DIR requires the specific path to the CMake config directory. This change may cause CMake to fail to find the mdspan package.

Suggested change

	run: cmake -S $GITHUB_WORKSPACE/stdblas-src -B $GITHUB_WORKSPACE/stdblas-build -Dmdspan_DIR=$GITHUB_WORKSPACE/mdspan-install/ -DLINALG_ENABLE_TESTS=On -DLINALG_ENABLE_EXAMPLES=On -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_INSTALL_PREFIX=$GITHUB_WORKSPACE/stdblas-install
	run: cmake -S $GITHUB_WORKSPACE/stdblas-src -B $GITHUB_WORKSPACE/stdblas-build -Dmdspan_DIR=$GITHUB_WORKSPACE/mdspan-install/lib/cmake/mdspan -DLINALG_ENABLE_TESTS=On -DLINALG_ENABLE_EXAMPLES=On -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_INSTALL_PREFIX=$GITHUB_WORKSPACE/stdblas-install