With a lot of work done by Mario Jaun <mario.jaun@zuehlke.com>.

Use the rust-bindgen tool to extract bindings from the Zephyr header files.
The tool is run with the exact configuration of the current build, and
therefore the bindings will match the current target.  The ifdefs and such
are not translated into the Rust code, and this must be generated live for
each build.

Signed-off-by: David Brown <david.brown@linaro.org>

Instead of trying to manually generate the bindings, use those generated by
bindgen in the zephyr-sys crate.

Signed-off-by: David Brown <david.brown@linaro.org>

Remove the manual k_str_out wrapper, and use the one generated by bindgen.

Signed-off-by: David Brown <david.brown@linaro.org>

For CPP builds, a few structs that end up empty in some configurations will
generate compile errors.  With the Rust tools, bindgen ends up producing
empty structsw for these as well.  Although the code compiles, it generates
warnings.  For now, add CONFIG_RUST to the ifdef checks so that these
structs don't end up empty with Rust either.

Signed-off-by: David Brown <david.brown@linaro.org>

When compiling Rust programs, the bindgen utility generates a wrapper file
to expand inline functions, as these otherwise cannot be accessed from
rust.  Pass a consistent name to the cargo build, and add it to our source
build so that this wrapper get compiled.

Signed-off-by: David Brown <david.brown@linaro.org>

Change the header passed into bindgen to be an absolute path.  This will
cause the generated wrapper to refer to this file also using an absolute
path.  As such, remove the explicit include path added as part of the
build.

Signed-off-by: David Brown <david.brown@linaro.org>

Add documentation on the bindings between Rust and C, and the bindgen
tool used to generate them.

Signed-off-by: David Brown <david.brown@linaro.org>

Re-export all of the bindgen generated bindings in the zephyr-sys crate
into `zephyr::raw`.  This keeps things easier, as users of `zephyr` only
need to worry about the single `zephyr` crate.

Signed-off-by: David Brown <david.brown@linaro.org>

Fix `WRAPPER_FiLE` to `WRAPPER_FILE`.

Signed-off-by: David Brown <david.brown@linaro.org>

Zephyr takes advantage of a gcc/clang extension that allows structs that
have no elements.  Rust is perfectly happy with this (it is quite common
in Rust code), but generates a warning when a struct containing no
elements is passed to C code.

For now, suppress this warning on the generated bindings.  This has the
disadvantage of suppressing it entirely, which might possibly detect
other cases of invalid structs.  However, the bindings are
auto-generated from C structs so should always be valid.

Signed-off-by: David Brown <david.brown@linaro.org>

This reverts commit 2046760.

Put these back so we get the zero element structures when using just
rust and not CPP.  A subsequent patch will suppress the warning.

Signed-off-by: David Brown <david.brown@linaro.org>

GCC automatically defines a `__SOFTFP__` define on targets that are
using software floating point.  The clang compiler does not do this by
default, so check this, and define it.

Signed-off-by: David Brown <david.brown@linaro.org>

Rustc for RISCV encodes optional features on the CPU available as part
of the target tuple.  Clang, on the other hand does not.  In order to be
able to use libclang with bindgen on RISCV, we need to simplify the
target tuples a bit.  Do this by just matching 'riscv32' or 'riscv64'
and then passing in a generic tuple.  We aren't generating any code, and
the structs should always match between the targets.

Signed-off-by: David Brown <david.brown@linaro.org>

Although the Cmake rules to build Rust applications keeps the target
directory inside of the build directory, some IDE tools may generate a
target directory while editing the code.  Ignore these so they never get
checked in.

Signed-off-by: David Brown <david.brown@linaro.org>

With bindgen needing to read the headers, make sure CMake knows about
this.

Signed-off-by: David Brown <david.brown@linaro.org>

Minor fixes to the documentation from review feedback.

Signed-off-by: David Brown <david.brown@linaro.org>

Remove a redundant call that does exactly what the previous function
call accomplishes.

Signed-off-by: David Brown <david.brown@linaro.org>

Fix a mispelled word "al" -> "all".

Signed-off-by: David Brown <david.brown@linaro.org>