Future of vendored libraries

[lonvia]

Some libraries we depend on are included in the osm2pgsql repository in the contrib directory. This kind of vendoring is usually not a good idea because it makes packaging more difficult. There was a good reason to add the libraries anyway, usually because we needed very new features not available in the distributions. Many of the reasons have now gone away and it is time to review the vendoring decision. This issue is to track the state of these libraries.

Protozero

Used by Libosmium. Widely available in versions that are okay for us.

• Debian: Buster has a version that's too old, buster has reached EOL already.
• macOS: Homebrew doesn't have Protozero as its own library but ships it with libosmium.
• Windows: Available with vcpkg.

After Trixie is released (expected in summer 2025) at the latest we can remove support for Buster at which point we can remove our copy.

Libosmium

Used all over for basic OSM code. Widely available in versions that are okay for us.

• Debian: Same as with Protozero.
• macOS: Current versions are in homebrew.
• Windows: Available with vcpkg.

CLI11

Used for parsing command line arguments. Included because it is missing in Debian versions before Bookworm.

• Debian: Version 2.1.2 available in Bookworm, not available in Bullseye or before.
• Fedora: Available since Fedora 30 from 2019, long EOL. Current Fedora versions still in support have version 2.
• macOS: Available in homebrew.
• Windows: Available with vcpkg.

We can probably remove our copy once Bullseye reached EOL.

fmt

Used all over the code for string formatting. Although widely available in distributions we have our own copy because fmt doesn't provide backwards compatibility between major versions and they are releasing a new major version about once a year.

Long-term this library should be replaced by using the equivalent functions from the C++ library introduced in C++20. But support in C++ libraries is lagging a bit, so it will be some time until we can switch.

Catch2

Used for unit tests. We are currently stuck at version 2, because version 3 is not available in Debian yet.

Note the confusing version numbering: "Catch" is version 1 from long ago, "Catch2" is version 2 and above. Version 1 and 2 are header only, "Catch 2 v3" is a proper library. Versions 1 and 2 are not maintained any more.

• Debian: Debian catch2 is version 2 in Bookworm, Trixie will have version 3.
• Fedora: Package catch2 is version 2, package catch seems always to be the "current" version, currently 2. Version 3 available since Fedora 38.
• macOS: Packages of version 2 are available as catch, version 3 as catch2.
• Windows: catch2 in vcpkg is version 3.

Catch2 is only a development dependency. That means we can be less strict regarding compatibility with Linux distributions. Compatibility with latest distros should be sufficient as long as we find a solution for the CI. We should start experimenting with Catch2-v3 once Debian Trixie is out and then decide about the future. We need in particular figure out how catch2v3 handles compatibility between minor versions or if we'd be stuck with the latest version.