Generates rust code from the proto files.
Protobuf files are collected recursively from $CARGO_MANIFEST_DIR/<input_root>/ directory. Corresponding "cargo:rerun-if-changed=..." line is printed to stdout, so that the build script running this function is rerun whenever proto files change. A single rust file is generated and stored at $OUT_DIR/<input_root>/gen.rs file.
Protobuf files are compiled to a protobuf descriptor stored at $OUT_DIR/<input_root>/gen.binpb. Additionally a "PROTOBUF_DESCRIPTOR=" line is printed to stdout. This can be used to collect all the descriptors across the build as follows:
- Checkout the repo to a fresh directory and then run "cargo build --all-targets" We need it fresh so that every crate containing protobufs has only one build in the cargo cache.
- grep through all target/debug/build/*/output files to find all "PROTOBUF_DESCRIPTOR=..." lines and merge the descriptor files by simply concatenating them.
Note that you can run this procedure for 2 revisions of the repo and look for breaking changes by running "buf breaking <after.binpb> --against <before.binpb>" where before.binpb and after.binpb are the concatenated descriptors from those 2 revisions.
The proto files are not expected to be self-contained - to import proto files from different crates you need to specify them as dependencies in the Config.dependencies. It is not possible to depend on a different proto bundle within the same crate (because these are being built simultaneously from the same build script).