fix: remove dependency on protoc in pbjson-types

This change moves pbjson-type's code generation to a manual executable
instead of build.rs. Now the generated files are checked into the repo,
and users do not need `protoc` to build the pbjson-types crate.

This has a slight drawback in that pbjson developers will need to invoke
the generator manually after any relevant code-gen changes. This should
generally be a worthwhile tradeoff, as several users have encountered
trouble with requiring protoc (see influxdata#62).

That drawback could potentially be averted with some CI steps to run the
generator and check-in the code automatically; this change does not
include such automation however.

Cargo.toml

@@ -4,4 +4,5 @@ members = [
   "pbjson-build",
   "pbjson-test",
   "pbjson-types",
+  "pbjson-types/code-gen",
 ]

pbjson-types/Cargo.toml

@@ -18,7 +18,3 @@ serde = { version = "1.0", features = ["derive"] }
 
 [dev-dependencies]
 serde_json = "1.0"
-
-[build-dependencies] # In alphabetical order
-prost-build = "0.11"
-pbjson-build = { path = "../pbjson-build", version = "0.5" }

pbjson-types/code-gen/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "code_gen"
+version = "0.1.0"
+edition = "2021"
+license = "MIT"
+publish = false
+
+[dependencies]
+clap = { version = "3", features = ["derive"] }
+prost-build = "0.11"
+pbjson-build = { path = "../../pbjson-build", version = "0.5" }
+tempfile = "3.3.0"

pbjson-types/build.rs → pbjson-types/code-gen/src/main.rs

@@ -1,28 +1,46 @@
 //! Compiles Protocol Buffers and FlatBuffers schema definitions into
 //! native Rust types.
+//!
+//! This is kept as a separate binary to generate code for manual check-in, instead of running at
+//! compile time as `build.rs` -- that way downstream consumers do not require the build
+//! dependencies (espeically protoc) and can import rust sources directly.
 
 use std::env;
 use std::path::PathBuf;
 
+use clap::Parser;
+
 type Error = Box<dyn std::error::Error>;
 type Result<T, E = Error> = std::result::Result<T, E>;
 
+#[derive(Parser)]
+struct Args {
+    /// The path of the directory containing the protobuf sources.
+    #[clap(short, long, default_value = concat!(env!("CARGO_MANIFEST_DIR"), "/../protos"))]
+    input_proto_dir: PathBuf,
+
+    /// The destination directory for generated code.
+    #[clap(short, long, default_value = concat!(env!("CARGO_MANIFEST_DIR"), "/../src/pb/"))]
+    output_dir: PathBuf,
+}
+
 fn main() -> Result<()> {
-    let root = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("protos");
+    let args = Args::parse();
+    let root = args.input_proto_dir;
+    let out_dir = &args.output_dir;
 
     let proto_files = vec![root.join("google/protobuf/types.proto")];
 
-    // Tell cargo to recompile if any of these proto files are changed
-    for proto_file in &proto_files {
-        println!("cargo:rerun-if-changed={}", proto_file.display());
-    }
+    std::fs::create_dir_all(out_dir)?;
 
-    let descriptor_path = PathBuf::from(env::var("OUT_DIR").unwrap()).join("proto_descriptor.bin");
+    let temp_dir = tempfile::tempdir()?;
+    let descriptor_path = temp_dir.path().join("proto_descriptor.bin");
     prost_build::Config::new()
         .file_descriptor_set_path(&descriptor_path)
         .compile_well_known_types()
         .disable_comments(&["."])
         .bytes(&[".google"])
+        .out_dir(out_dir)
         .compile_protos(&proto_files, &[root])?;
 
     let descriptor_set = std::fs::read(descriptor_path)?;
@@ -45,6 +63,7 @@ fn main() -> Result<()> {
             ".google.protobuf.UInt32Value",
             ".google.protobuf.UInt64Value",
         ])
+        .out_dir(out_dir)
         .build(&[".google"])?;
 
     Ok(())

pbjson-types/src/lib.rs

@@ -27,14 +27,7 @@
     clippy::enum_variant_names,
     clippy::use_self
 )]
-mod pb {
-    pub mod google {
-        pub mod protobuf {
-            include!(concat!(env!("OUT_DIR"), "/google.protobuf.rs"));
-            include!(concat!(env!("OUT_DIR"), "/google.protobuf.serde.rs"));
-        }
-    }
-}
+mod pb;
 
 mod duration;
 mod list_value;