feat: Use package.links trick for Protobuf compilation (#32)

# What ❔

Propagates Protobuf information via env variables by relying on
[package.links](https://doc.rust-lang.org/cargo/reference/build-scripts.html#the-links-manifest-key).

## Why ❔

This simplifies Protobuf configuration and eliminate misconfiguration
risks.

node/Cargo.toml

@@ -53,9 +53,7 @@ proc-macro2 = "1.0.66"
 prost = "0.12.0"
 prost-build = "0.12.0"
 prost-reflect = { version = "0.12.0", features = ["serde"] }
-prost-types = "0.12.0"
 protox = "0.5.0"
-protox-parse = "0.5.0"
 prettyplease = "0.2.6"
 pretty_assertions = "1.4.0"
 quick-protobuf = "0.8.1"

node/actors/executor/Cargo.toml

@@ -27,4 +27,4 @@ vise.workspace = true
 tokio.workspace = true
 
 [build-dependencies]
-zksync_protobuf.workspace = true
+zksync_protobuf_build.workspace = true

node/actors/executor/build.rs

@@ -1,10 +1,11 @@
 //! Generates rust code from protobufs.
 fn main() {
-    zksync_protobuf::build::Config {
+    zksync_protobuf_build::Config {
         input_root: "src/config/proto".into(),
         proto_root: "zksync/executor/config".into(),
         dependencies: vec![],
         protobuf_crate: "::zksync_protobuf".parse().unwrap(),
+        is_public: false,
     }
     .generate()
     .expect("generate(config)");

node/actors/network/Cargo.toml

@@ -31,5 +31,4 @@ test-casing.workspace = true
 tokio.workspace = true
 
 [build-dependencies]
-zksync_consensus_roles.workspace = true
-zksync_protobuf.workspace = true
+zksync_protobuf_build.workspace = true

node/actors/network/build.rs

@@ -1,28 +1,24 @@
 //! Generates rust code from protobufs.
 fn main() {
-    zksync_protobuf::build::Config {
+    zksync_protobuf_build::Config {
         input_root: "src/proto".into(),
         proto_root: "zksync/network".into(),
         dependencies: vec![
-            (
-                "::zksync_protobuf::proto".parse().unwrap(),
-                &zksync_protobuf::proto::DESCRIPTOR,
-            ),
-            (
-                "::zksync_consensus_roles::proto".parse().unwrap(),
-                &zksync_consensus_roles::proto::DESCRIPTOR,
-            ),
+            "::zksync_protobuf::proto".parse().unwrap(),
+            "::zksync_consensus_roles::proto".parse().unwrap(),
         ],
         protobuf_crate: "::zksync_protobuf".parse().unwrap(),
+        is_public: false,
     }
     .generate()
     .expect("generate()");
 
-    zksync_protobuf::build::Config {
+    zksync_protobuf_build::Config {
         input_root: "src/mux/tests/proto".into(),
         proto_root: "zksync/network/mux/tests".into(),
         dependencies: vec![],
         protobuf_crate: "::zksync_protobuf".parse().unwrap(),
+        is_public: false,
     }
     .generate()
     .expect("generate()");

node/libs/protobuf/Cargo.toml

@@ -6,6 +6,8 @@ authors.workspace = true
 homepage.workspace = true
 license.workspace = true
 
+links = "zksync_protobuf_proto"
+
 [[bin]]
 name = "conformance_test"
 
@@ -28,5 +30,3 @@ tracing-subscriber.workspace = true
 
 [build-dependencies]
 zksync_protobuf_build.workspace = true
-
-anyhow.workspace = true

node/libs/protobuf/build.rs

@@ -5,6 +5,7 @@ fn main() {
         proto_root: "zksync".into(),
         dependencies: vec![],
         protobuf_crate: "crate".parse().expect("protobuf_crate"),
+        is_public: true,
     }
     .generate()
     .expect("generate(std)");
@@ -14,6 +15,7 @@ fn main() {
         proto_root: "zksync/protobuf/tests".into(),
         dependencies: vec![],
         protobuf_crate: "crate".parse().expect("protobuf_crate"),
+        is_public: false,
     }
     .generate()
     .expect("generate(test)");
@@ -23,6 +25,7 @@ fn main() {
         proto_root: "zksync/protobuf/conformance_test".into(),
         dependencies: vec![],
         protobuf_crate: "::zksync_protobuf".parse().expect("protobuf_crate"),
+        is_public: false,
     }
     .generate()
     .expect("generate(conformance)");

node/libs/protobuf/src/build.rs

@@ -0,0 +1,85 @@
+//! Build-related functionality. This should only be used by the code generated by the `protobuf_build` crate.
+
+pub use once_cell::sync::Lazy;
+pub use prost;
+use prost::Message as _;
+pub use prost_reflect;
+use prost_reflect::prost_types;
+use std::sync::RwLock;
+
+/// Global descriptor pool.
+static POOL: Lazy<RwLock<prost_reflect::DescriptorPool>> = Lazy::new(RwLock::default);
+
+/// Protobuf descriptor + info about the mapping to rust code.
+#[derive(Debug)]
+pub struct Descriptor(());
+
+impl Descriptor {
+    /// Constructs a descriptor and adds it to the global pool.
+    pub fn new(_dependencies: &[&'static Self], descriptor_bytes: &[u8]) -> Self {
+        let descriptor = prost_types::FileDescriptorSet::decode(descriptor_bytes).unwrap();
+        let pool = &mut POOL.write().unwrap();
+
+        // Dependencies are already loaded to the global pool on their initialization.
+        // The fact that we have their refs is sufficient to prove that they are already in the global pool.
+        Self::load(pool, descriptor).expect("failed loading descriptor into global pool");
+        Self(())
+    }
+
+    /// Loads the descriptor to the pool, if not already loaded.
+    fn load(
+        pool: &mut prost_reflect::DescriptorPool,
+        descriptor: prost_types::FileDescriptorSet,
+    ) -> anyhow::Result<()> {
+        let pool_has_all_files = descriptor
+            .file
+            .iter()
+            .all(|file| pool.get_file_by_name(file.name()).is_some());
+        if pool_has_all_files {
+            return Ok(());
+        }
+        pool.add_file_descriptor_set(descriptor)?;
+        Ok(())
+    }
+
+    /// Returns a descriptor by a fully qualified message name.
+    pub fn get_message_by_name(&self, name: &str) -> Option<prost_reflect::MessageDescriptor> {
+        POOL.read().unwrap().get_message_by_name(name)
+        // ^ This works because this descriptor must have been loaded into the global pool
+        // when the instance was constructed.
+    }
+}
+
+/// Expands to a descriptor declaration.
+#[macro_export]
+macro_rules! declare_descriptor {
+    ($name:ident => $descriptor_path:expr, $($rust_deps:path),*) => {
+        pub static $name: $crate::build::Lazy<$crate::build::Descriptor> =
+            $crate::build::Lazy::new(|| {
+                $crate::build::Descriptor::new(
+                    &[$({ use $rust_deps as dep; &dep::DESCRIPTOR }),*],
+                    ::std::include_bytes!($descriptor_path),
+                )
+            });
+    }
+}
+
+/// Implements `ReflectMessage` for a type based on a provided `Descriptor`.
+#[macro_export]
+macro_rules! impl_reflect_message {
+    ($ty:ty, $descriptor:expr, $proto_name:expr) => {
+        impl $crate::build::prost_reflect::ReflectMessage for $ty {
+            fn descriptor(&self) -> $crate::build::prost_reflect::MessageDescriptor {
+                static INIT: $crate::build::Lazy<$crate::build::prost_reflect::MessageDescriptor> =
+                    $crate::build::Lazy::new(|| {
+                        $crate::build::Descriptor::get_message_by_name($descriptor, $proto_name)
+                            .unwrap()
+                    });
+                INIT.clone()
+            }
+        }
+    };
+}
+
+pub use declare_descriptor;
+pub use impl_reflect_message;

node/libs/protobuf/src/lib.rs

@@ -1,13 +1,14 @@
 //! Code generated from protobuf schema files and
 //! utilities for serialization.
 
+#[doc(hidden)] // should only be used by code generated by `protobuf_build` crate
+pub mod build;
 pub mod proto;
 mod proto_fmt;
 mod std_conv;
 pub mod testonly;
 
-pub use proto_fmt::*;
-pub use zksync_protobuf_build as build;
+pub use self::proto_fmt::*;
 
 #[cfg(test)]
 mod tests;

node/libs/protobuf_build/Cargo.toml

@@ -9,16 +9,10 @@ license.workspace = true
 [dependencies]
 anyhow.workspace = true
 heck.workspace = true
-once_cell.workspace = true
 prettyplease.workspace = true
 proc-macro2.workspace = true
-prost.workspace = true
 prost-build.workspace = true
-prost-types.workspace = true
 prost-reflect.workspace = true
 protox.workspace = true
-protox-parse.workspace = true
 quote.workspace = true
-rand.workspace = true
 syn.workspace = true
-

node/libs/protobuf_build/src/canonical.rs

@@ -1,6 +1,8 @@
 //! Checks whether messages in the given file descriptor set support canonical encoding.
+
 use crate::syntax::extract_message_names;
 use anyhow::Context as _;
+use prost_reflect::{self, prost_types};
 use std::collections::HashSet;
 
 #[derive(Default)]