`enable_language` option for Rust/Cargo

Development
21

A bit of update. Got the above problems fixed. Now, linking to Rust executables works fine as well. Going to create a PR after ensuring that tests run as part of Cmake test suite instead of individually.

22

Well, this error showed up again. After some digging, I found that the normal rustc path is just a symlink to rustup:
```
lrwxrwxrwx. 1 ayush ayush 6 May 20 23:18 /home/ayush/.cargo/bin/rustc → rustup
```
If I hardcode the path to rustc, things work fine. So I guess I somehow need to resolve this path to actual rustc path for all cases.

23

Or CMake needs to determine the version used and use the +VERSION syntax to select the implementation version. It isn’t dissimilar to /usr/bin/clang on macOS with xcode-select and the DEVELOPER_DIR environment.

24

I did a bit more digging into what env looks like inside ctest:

SHELL=/usr/bin/zsh
COLORTERM=truecolor
HISTCONTROL=ignoredups
HISTSIZE=10000
HOSTNAME=192.168.1.10
DESKTOP_SESSION=sway
XDG_SEAT=seat0
PWD=/home/ayush/Documents/Programming/Rust/cmake/build
XDG_SESSION_DESKTOP=sway
XDG_SESSION_TYPE=wayland
TOOLBOX_PATH=/usr/bin/toolbox
container=oci
HOME=/home/ayush/Documents/Programming/Rust/cmake/build/Tests/CMakeFiles/TestHome
LANG=en_US.UTF-8
XDG_CURRENT_DESKTOP=sway
WAYLAND_DISPLAY=wayland-1
XDG_SESSION_CLASS=user
TERM=foot
USER=ayush
P11_KIT_SERVER_ADDRESS=unix:path=/run/user/1000/toolbox/pkcs11
DISPLAY=:0
SHLVL=1
XDG_VTNR=2
XDG_SESSION_ID=2
XDG_RUNTIME_DIR=/run/user/1000
XDG_DATA_DIRS=/home/ayush/.local/share/flatpak/exports/share:/var/lib/flatpak/exports/share:/usr/local/share:/usr/share
PATH=/home/ayush/.cargo/bin:/usr/local/bin:/usr/bin:/home/ayush/.local/bin
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
LOGNAME=ayush
OLDPWD=/home/ayush/Documents/Programming/Rust/cmake
MAIL=/var/spool/mail/ayush
LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=01;37;41:su=37;41:sg=30;43:ca=00:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.7z=01;31:*.ace=01;31:*.alz=01;31:*.apk=01;31:*.arc=01;31:*.arj=01;31:*.bz=01;31:*.bz2=01;31:*.cab=01;31:*.cpio=01;31:*.crate=01;31:*.deb=01;31:*.drpm=01;31:*.dwm=01;31:*.dz=01;31:*.ear=01;31:*.egg=01;31:*.esd=01;31:*.gz=01;31:*.jar=01;31:*.lha=01;31:*.lrz=01;31:*.lz=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.lzo=01;31:*.pyz=01;31:*.rar=01;31:*.rpm=01;31:*.rz=01;31:*.sar=01;31:*.swm=01;31:*.t7z=01;31:*.tar=01;31:*.taz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tgz=01;31:*.tlz=01;31:*.txz=01;31:*.tz=01;31:*.tzo=01;31:*.tzst=01;31:*.udeb=01;31:*.war=01;31:*.whl=01;31:*.wim=01;31:*.xz=01;31:*.z=01;31:*.zip=01;31:*.zoo=01;31:*.zst=01;31:*.avif=01;35:*.jpg=01;35:*.jpeg=01;35:*.mjpg=01;35:*.mjpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.webp=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=01;36:*.au=01;36:*.flac=01;36:*.m4a=01;36:*.mid=01;36:*.midi=01;36:*.mka=01;36:*.mp3=01;36:*.mpc=01;36:*.ogg=01;36:*.ra=01;36:*.wav=01;36:*.oga=01;36:*.opus=01;36:*.spx=01;36:*.xspf=01;36:*~=00;90:*#=00;90:*.bak=00;90:*.crdownload=00;90:*.dpkg-dist=00;90:*.dpkg-new=00;90:*.dpkg-old=00;90:*.dpkg-tmp=00;90:*.old=00;90:*.orig=00;90:*.part=00;90:*.rej=00;90:*.rpmnew=00;90:*.rpmorig=00;90:*.rpmsave=00;90:*.swp=00;90:*.tmp=00;90:*.ucf-dist=00;90:*.ucf-new=00;90:*.ucf-old=00;90:
DEBUGINFOD_URLS=https://debuginfod.fedoraproject.org/ 
DEBUGINFOD_IMA_CERT_PATH=/etc/keys/ima:
GPG_TTY=/dev/pts/3
LESSOPEN=||/usr/bin/lesspipe.sh %s
EDITOR=nvim
P9K_TTY=old
_P9K_TTY=/dev/pts/3
VISUAL=nvim
AUTOSWITCH_VERSION=3.7.1
AUTOSWITCH_FILE=.venv
P9K_SSH=0
_P9K_SSH_TTY=/dev/pts/3
_=/usr/bin/ctest
CTEST_INTERACTIVE_DEBUG_MODE=1
CMAKE_MAXIMUM_RECURSION_DEPTH=100
CMAKE_CONFIG_DIR=/home/ayush/Documents/Programming/Rust/cmake/build/Tests/CMakeFiles/TestHome/.config/cmake
CTEST_REAL_HOME=/home/ayush

I also got rustup show to run inside ctest:

rustup show Default host: x86_64-unknown-linux-gnu
rustup home:  /home/ayush/Documents/Programming/Rust/cmake/build/Tests/CMakeFiles/TestHome/.rustup

As can be seen rustup home is incorrect.

I think the HOME variable inside ctest is the problem.

25

Ok, I am now forcing rusthome to be $CTEST_REAL_HOME/.rustup if rustup is being used and $CTEST_REAL_HOME is defined. With that tweak, tests run fine now.

26

I have created the PR: https://gitlab.kitware.com/cmake/cmake/-/merge_requests/11389
Feel free to help review and improve it.