Support cross-compiling in the libmagic vcpkg port overlay, attempt 2.

[teo-tsirpanis]

TYPE: NO_HISTORY

[teo-tsirpanis]

We move this block before the configure and install steps, so that libmagic's build system can find the file command in the path we built it for the host.

[dudoslav]

Well, not quite sure what this does, but have you tested this with cross compilation? (If it works for x86_64 and crosscompilation x86_64->aarch64)

[teo-tsirpanis]

It's tested as outlined in #5338 (comment).

As for what this does, in libmagic's CMakeLists.txt we have this command:

add_custom_command(OUTPUT magic.mgc
  COMMAND file -C -m magic
  COMMENT "Compiling magic file"
)

When not cross-compiling, CMake resolves file to the file executable we built, but when cross-compiling file will be passed to the shell as-is and resolved from PATH. The vcpkg_add_to_path command ensures the host's file we built gets found.

The elseif part makes sure libmagic.dll gets found on Windows if we are using dynamic linkage for the dependencies (which we don't currently do).

This block exists in the upstream port BTW.

https://github.com/microsoft/vcpkg/blob/b8d688b979bd54f0269ea1c6101e6a977613175f/ports/libmagic/portfile.cmake#L61-L67

[dudoslav]

Thanks a lot for the explanation!

[teo-tsirpanis]

Conda nightlies and Release workflow succeed. This is ready to review.

I tried locally to cross-compile to arm64-windows, but it failed due to reasons related to the Windows command line¹. Let's not try to fix that too, the upstream port works and we don't officially support this platform.

Footnotes

1. If you have an incompatible foo.exe in your working directory and a compatible foo.exe in PATH, running foo will use the former executable in cmd but the latter in Powershell. At this point this is an issue for CMake. ↩

[dudoslav]

LGTM