google.protobuf.rs becomes bigger after each build

[Chaoses-Ib]

I ran into a problem where add_serde() will append trait impls to google.protobuf.rs after each build, but neither prost nor prost-wkt would clear it, so it only becomes bigger and bigger.

prost-wkt/wkt-build/src/lib.rs

Lines 12 to 41 in bedabbb

	pub fn add_serde(out: PathBuf, descriptor: FileDescriptorSet) {
	for fd in &descriptor.file {
	let package_name = match fd.package {
	Some(ref pkg) => pkg,
	None => continue,
	};
	let rust_path = out
	.join(Module::from_protobuf_package_name(package_name).to_file_name_or(package_name));
	// In some cases the generated file would be in empty. These files are no longer created by Prost, so
	// we'll create here. Otherwise we append.
	let mut rust_file = OpenOptions::new()
	.create(true)
	.append(true)
	.open(rust_path)
	.unwrap();
	for msg in &fd.message_type {
	let message_name = match msg.name {
	Some(ref name) => name,
	None => continue,
	};
	let type_url = format!("type.googleapis.com/{package_name}.{message_name}");
	gen_trait_impl(&mut rust_file, package_name, message_name, &type_url);
	}
	}
	}

And I found the generated google.protobuf.rs isn't actually used, so the duplicated code won't break the build. But if anyone includes the generated files in VCS, there will be a problem. A simple workaround I currently use is to remove google.protobuf.rs after add_serde():

_ = fs::remove_file(out.join("google.protobuf.rs"));

[fdeantoni]

Thanks for raising this! Indeed not good if the file keeps growing. I will dig a little deeper to see what the best solution is.

[wtzhang23]

I played around with creating a derive proc-macro which could help in this case.