Support protobuf format for reports

This migrates to using protobuf to
define the "report" and "changes"
formats in objdiff-cli.

The JSON output now uses the Proto3
"JSON Mapping", which is slightly
incompatible with the existing JSON
format. Mainly, 64-bit numbers are
represented as strings, and addresses
are decimal strings instead of hex.

However, the older JSON format is
still accepted by "report changes"
to ease migration.

objdiff-cli/build.rs

@@ -1,3 +1,5 @@
+use std::path::PathBuf;
+
 fn main() {
     let output = std::process::Command::new("git")
         .args(["rev-parse", "HEAD"])
@@ -6,4 +8,28 @@ fn main() {
     let rev = String::from_utf8(output.stdout).expect("Failed to parse git output");
     println!("cargo:rustc-env=GIT_COMMIT_SHA={rev}");
     println!("cargo:rustc-rerun-if-changed=.git/HEAD");
+
+    let root = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("protos");
+    let proto_files = vec![root.join("report.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());
+    }
+
+    let descriptor_path =
+        PathBuf::from(std::env::var("OUT_DIR").unwrap()).join("proto_descriptor.bin");
+
+    prost_build::Config::new()
+        .file_descriptor_set_path(&descriptor_path)
+        .compile_protos(&proto_files, &[root])
+        .expect("Failed to compile protos");
+
+    let descriptor_set = std::fs::read(descriptor_path).expect("Failed to read descriptor set");
+    pbjson_build::Builder::new()
+        .register_descriptors(&descriptor_set)
+        .expect("Failed to register descriptors")
+        .preserve_proto_field_names()
+        .build(&[".objdiff"])
+        .expect("Failed to build pbjson");
 }