Move to protobuf 3.x

This also adds rules to not unnecessarily run the build script
(build.rs) if the input has not changed. This also moves the protobuf
generation in its own library/subdirectory to avoid errors on docs.rs
which mounts the src/ directory as read-only.

Signed-off-by: Adrian Reber <areber@redhat.com>

Cargo.toml

@@ -9,11 +9,9 @@ license-file = "LICENSE"
 
 [dependencies]
 libc = "0.2"
-protobuf = "2.27.1"
 anyhow = "1.0.56"
-
-[build-dependencies]
-protobuf-codegen-pure = "2.25.2"
+protobuf = "3.2.0"
+rust-criu-protobuf = { path = "rust-criu-protobuf" }
 
 [lib]
 name = "rust_criu"

build.rs

@@ -1,15 +1,7 @@
-extern crate protobuf_codegen_pure;
-
 fn main() {
-    protobuf_codegen_pure::Codegen::new()
-        .out_dir("src/proto")
-        .inputs(["proto/rpc.proto"])
-        .include("proto")
-        .run()
-        .expect("Codegen failed.");
-
     std::process::Command::new("gcc")
         .args(["test/piggie.c", "-o", "test/piggie"])
         .status()
         .unwrap();
+    println!("cargo:rerun-if-changed=test/piggie.c");
 }

rust-criu-protobuf/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "rust-criu-protobuf"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+protobuf = "3.2.0"
+
+[build-dependencies]
+protobuf-codegen = "3.2.0"
+
+[lib]
+name = "rust_criu_protobuf"
+path = "src/mod.rs"

rust-criu-protobuf/build.rs

@@ -0,0 +1,11 @@
+extern crate protobuf_codegen;
+
+fn main() {
+    protobuf_codegen::Codegen::new()
+        .includes(["proto"])
+        .input("proto/rpc.proto")
+        .out_dir("src")
+        .run_from_script();
+
+    println!("cargo:rerun-if-changed=proto/rpc.proto");
+}

rust-criu-protobuf/src/mod.rs

@@ -0,0 +1,3 @@
+// @generated
+
+pub mod rpc;