Thoughts on adding Conan support?

[mattyoung101]

I've been doing some experiments recently to try and get OpenROAD building using Conan, a popular C++ package manager.

This started because, as someone who uses a rolling release distro (Arch), the system packages change frequently and break very frequently; particularly for spdlog/fmt.

I'm aware of the Bazel build, and have in fact used it and tinkered with it a lot, but it has issues:

1. Most importantly, there doesn't seem to be a good way to get a compile_commands.json out of it which makes OpenROAD dev really hard. There are a few options available, but they are either broken entirely as a tool, or produce compile_commands that are broken and don't cooperate with clangd.
2. The Bazel build, for whatever reason (I'm not a Bazel expert), does not appear to be hermetic despite its guarantees. There is a requirement to install a system libxml2 in order to compile the GUI. Maybe, perhaps, the GUI build is not hermetic?

Anyway, this is a long-ish project that I'm tinkering away at. I need to upgrade and port a number of packages and get them into the Conan Central repo, mainly: or-tools, coin-cbc and cudd. I'm putting up a PR for coin-cbc soon, and will then have to tackle or-tools next which is quite challenging.

The end result would be just a single file: conanfile.txt, that includes dependency info; and possibly a docs update to indicate it's experimentally supported building with Conan.

Basically, I'm just asking now to see what the likelihood of getting this through a PR would be, and if there's any interest from the community and contributors. thanks!

[maliberty]

Compile commands is identified in #8586 and will be addressed.

The GUI is not as hermetic as I would like but that is also something that can either be solved or a very minimal set of apt commands would be required (much less than the current dependency installer).

I don't see us changing course from bazel to conan. There are a number of benefits to Bazel (caching, remote builds, etc) that are not matched by Conan.

[mattyoung101]

Thanks, good points, makes sense. Good to see #8586 too, I had last played around with Bazel and compile commands several months ago so hadn't seen that.

The only thing that I'd add is that Conan would operate as an alternative/replacement to the dependency installer script and in conjunction with the existing CMake build, not be a replacement for Bazel. Conan is more or less just a way to acquire the dependencies and tell CMake about them, rather than through the system package manager.

That all being said - if the compile commands situation can be cleanly resolved with Bazel, that would resolve my main issue with it.

[maliberty]

The plan is to eventually deprecate and remove cmake. compile commands will have to be solved before that happens.