Multiple build configurations?

[stolyaroleh]

I want to try buck2 in a C++ project, and I want to be able to:

• use different compilers (gcc/clang)
• use different build configurations (release/debug/sanitizers)

What's the suggested way to implement this? Multiple toolchains? How does cxx_library or cxx_binary know what toolchain to use?
How would command line look like? Is something like buck2 test //... --debug --asan and buck2 run //:main --release --gcc possible?

I found this page about configurations, and it seems like one should be able to select() things based on config values. Do I write a single toolchain that is parameterized by config values instead? buck2 build -c cpp.compiler=gcc -c cpp.debug=true //...?

I also found this RFC: https://buck2.build/docs/rfcs/drafts/configuration-at-syntax/, but it doesn't specify how to structure the project in order to make buck2 build //foo:bar@release+gcc possible.

[ndmitchell]

There is a single toolchain toolchains//:cxx that is used for all C++ compilations. You can. use either selects or .buckconfig to change what it points at. You could make the toolchains//:cxx an alias with a select statement, or you could call read_config to grab the config and populate the fields from there. Internally we use a select for the outer structure and then read_config for the inner details - but that's not necessarily the recommended approach, where select only would be advised. I'm just not sure if we have all the pieces set up to support that - e.g. the configuration RFC. CC @stepancheg who might know.

[themarwhal]

We have an example where we create a toolchain alias with select that might be of interest to you.

[stolyaroleh]

Thanks, this looks very helpful.
Great podcast episode, by the way :)