How easy is it to extend Meson for languages that it doesn't ship support for by default? That always seemed to be one of the strong points of SCons/something many modern build systems don't support so well.
Meson developers are highly opinionated regarding what "should" and "should not" be supported, and aggressively block anything that might be considered, or even lead to "badness". Sometimes this is justified, but it makes one's job very difficult if one disagrees with them. For example, they insist on completely integrating Rust into the build framework, but also (apparently) don't have the manpower to actually implement that, so, coupled with the fact that extending the language is impossible from within the language, practical Rust (i.e. any dependencies, any Cargo use at all) is difficult to impossible.
It's not possible in the way it's possible in SCons. You can basically use custom_target, but its usefulness is limited since there are no user-defined functions in Meson's subset of Python. CMake is a little better in this regard here, since it at least offers macros and functions.
