Create symbolic link during install

[nischild]

Summary

Setting the install directory in the CMake install step gives an error in the creation of the symlink for libamrex.a.
The proposed fix creates the path for the symlink during the install step, allowing to change CMAKE_INSTALL_PREFIX in the install step.

Basically the fix moves the creation of the path-variable into cmake_install.cmake.
The previous version created the path in CMake configure step and the link during the CMake install step.

Reproducer

git clone https://github.com/AMReX-Codes/amrex.git
cmake -S . -B build
cmake --build build
cmake --install build --prefix install

Gives the error

CMake Error at build/cmake_install.cmake:420 (file):                                                                                                                                                                                                         
  file Copy failed: No such file or directory     

[WeiqunZhang]

See also #4775 Are the two related?

[nischild]

Thanks for pointing out the MR.
Yes, it will also solve the above bug.
Are there any plans to merge #4775 for the coming releases of AMReX?

[ax3l]

After a quick test: Your patch fixes the cmake --install --prefix ... failure.

I added one more fix for staged installs, which are commonly used by package builders and installers. I was not super aware of that workflow either and found it as an issue w/ Codex: DESTDIR is used where the install is written into a temporary root first instead of directly into the final location. For example:

DESTDIR=/tmp/amrex-stage cmake --install build --prefix /usr/local

That should place everything under: /tmp/amrex-stage/usr/local/...

Before the follow-up, the normal AMReX install rules did that correctly, but the legacy libamrex.a symlink step still tried to create the link under /usr/local/... instead of inside the staged tree. So packaging installs could fail, or produce an incomplete staged install.

The follow-up makes the legacy symlink behave like the rest of the install, and it also records that link in install_manifest.txt.