This is more complicated than it needs to be thanks to the presence of CMake and
the C++ ffi in the picture. rsconf can correctly detect the required libraries
and instruct rustc to link against them, but since we generate a static rust
library and have CMake link it against the C++ binaries, we are still at the
mercy of CMake picking up the symbols we want.
Unfortunately, we could detect the gettext symbols but discover at runtime that
they weren't linked in because CMake was compiled with `-DWITH_GETTEXT=0` or
similar (as the macOS CI runner does). This means we also need to pass state
between CMake and our build script to communicate which CMake options were
enabled.
This wasn't providing a lot of value, and the license compatibility is iffy.
There's a bit of weirdness in that this now uses a `Box<dyn Error>`,
but since currently nothing actually errors out let's punt that for
later.
Most of it is duplicated, hence untested.
Functions like mbrtowc are not exposed by the libc crate, so declare them
ourselves.
Since we don't know the definition of C macros, add two big hacks to make
this work:
1. Replace MB_LEN_MAX and mbstate_t with values (resp types) that should
be large enough for any implementation.
2. Detect the definition of MB_CUR_MAX in the build script. This requires
more changes for each new libc. We could also use this approach for 1.
Additionally, this commit brings a small behavior change to
read_unquoted_escape(): we cannot decode surrogate code points like \UDE01
into a Rust char, so use � (\UFFFD, replacement character) instead.
Previously, we added such code points to a wcstring; looks like they were
ignored when printed.
lazy_static has better ergonomics at the call/access sites (it returns a
reference to the type directly, whereas with once_cell we get a static Lazy<T>
that we must dereference instead) but the once_cell api is slated for
integration into the standard library [0] and has been the "preferred" way to
declare static global variables w/ deferred initialization. It's also less
opaque and easier to comprehend how it works, I guess?
(Both `once_cell` and `lazy_static` are already in our dependency tree, so this
should have no detrimental effect on build times. It actually negligibly
*improves* build times by not using macros, reducing the amount of expansion the
compiler has to do by a miniscule amount.)
[0]: https://github.com/rust-lang/rust/issues/74465
The nix crate had all its default features enabled, which included features that
are not present under BSD. We should only enable the select subset of crate
features that we know are available cross-platform (or else use conditional
targeting in Cargo.toml to only enable Linux-only features when compiling for
Linux targets).
For now, it seems we can just use the nix crate with all features disabled as it
still builds under Linux and FreeBSD in this state.
