Update and improve BUILDING.md

[Korne127]

The building markdown file is outdated (CentOS hasn't been maintained in the last three years), incomplete (there is no tutorial for Arch-based distributions) and misses some packages. It seems like the packages someone needed to install on their system were just written down, but if you run the given commands on a fresh Ubuntu instance, many packages miss, e.g. GPGME, nlohmann json, argagg, boost and many more.

It would be good to update it and improve it to include a complete tutorial on how to build it.

[probonopd]

This project uses Docker to build the binaries, and unfortunately this results in the build process not fully self contained/self documenting in build.yml. I am trying to build it on Ubuntu without Docker. Looks like BUILD.md is not complete indeed.

https://github.com/AppImageCommunity/AppImageUpdate/blob/main/ci/Dockerfile.x86_64 seems to be the key.

(@TheAssassin: For this reason, I always like to have a self-contained .yml file in my projects that build the project, with no other files involved.)

[TheAssassin]

There is no reason to maintain a building README in my opinion. We don't do that elsewhere either. And I certainly don't want to do it.

[Korne127]

Ohhh thank you, that is good to know.
And I can understand not wanting to maintain a building file, but I think if you do, it should be accurate.
If there is no specific building readme file, the main building steps are usually explained in the core README.md file though.

I wouldn't remove these steps from the repository:

git clone --recursive https://github.com/AppImage/AppImageUpdate
cd AppImageUpdate/

mkdir build/
cd build/

cmake -DBUILD_QT_UI=OFF -DCMAKE_INSTALL_PREFIX=/usr ..
make -j$(nproc)

sudo make install

as they're not self-explanatory and pretty important for people without experience building this project to get that done.

[TheAssassin]

And I can understand not wanting to maintain a building file, but I think if you do, it should be accurate.

I agree. I'd rather remove it. In my opinion, the Dockerfile sufficiently documents the necessary requirements for a certain distribution. Some dependencies we build ourselves (e.g., googletest) can be used just fine from the distribution on newer releases.

sudo make install is not an endorsed way to install AppImageUpdate in any way. We do not support distribution-wide installations. I think what would work the easiest is to instruct people how to run ci/build.sh resp. ci/build-in-docker.sh.