D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082
We now pass the current subproject to every FeatureNew and
FeatureDeprecated call. This requires a bunch of rework to:
1. Ensure that we have access to the subproject in the list of
arguments when used as a decorator (see _get_callee_args).
2. Pass the subproject to .use() when it's called manually.
3. We also can't do feature checks for new features in
meson_options.txt because that's parsed before we know the
meson_version from project()
Jussi Pakkanen
Dylan Baker
Xavier Claessens
Nirbheek Chauhan
Jon Turney