rust/protobuf: use prost-build to generate Rust protobuf files

We make a small cli tool, used in CMakeLists, similar to nanopb.

The generated file lands in the source folder and is committed. I
prefer this over generating into the build folder. The advantages are:

- Less reliance on the tool to work when you check out and old commit
- The rust crates do not depend on CMake in this way, which should
make it easier to use standard Rust tooling (though more work is
- needed there).

Author: benma

messages/CMakeLists.txt

@@ -51,6 +51,13 @@ add_custom_command(
     --proto_path=${CMAKE_CURRENT_SOURCE_DIR}
     '--nanopb_out=-I${CMAKE_CURRENT_SOURCE_DIR}:${CMAKE_CURRENT_BINARY_DIR}'
     ${PROTO_FILES_ABSOLUTE}
+  # We build the Rust protobuf files here and put them straight into the crate.
+  # This way, the crate can be compiled and tested without relying on cmake environment vars.
+  # Using prost-build the normal way as part of build.rs does not work due to a cargo bug:
+  # https://github.com/danburkert/prost/issues/344#issuecomment-650721245
+  COMMAND
+  ${CMAKE_COMMAND} -E env
+    cargo run --manifest-path=${CMAKE_SOURCE_DIR}/tools/prost-build/Cargo.toml -- --messages-dir=${CMAKE_CURRENT_SOURCE_DIR} --out-dir=${CMAKE_SOURCE_DIR}/src/rust/bitbox02-rust/src/hww/api/
 )
 
 add_custom_target(