Ruby Bazel Starter

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set -o errexit -o nounset -o xtrace
alias ~~~=":<<'~~~sh'";:<<'~~~sh'

This repo includes:

• 🧱 Latest version of Bazel and dependencies
• 📦 Curated bazelrc flags via [bazelrc-preset.bzl]
• 🧰 Developer environment setup with [bazel_env.bzl]
• 🎨 rubocop and standard, using rules_lint
• ✅ Pre-commit hooks for automatic linting and formatting

Note

You can customize languages and features with the interactive wizard in the aspect init command. init is an alternative to this starter repo, which was generated using the 'ruby' preset. See https://docs.aspect.build/cli/overview

Setup dev environment

First, we recommend you setup a Bazel-based developer environment with direnv.

1. install https://direnv.net/docs/installation.html
2. run direnv allow and follow the prompts to bazel run //tools:bazel_env

This isn't strictly required, but the commands which follow assume that needed tools are on the PATH, so skipping direnv means you're responsible for installing them yourself.

Try it out

Write a simple Ruby application:

mkdir app
>app/hello.rb cat <<'EOF'
# frozen_string_literal: true

require 'faker'
puts "Hello, #{Faker::Name.name} from Bazel + Ruby!"
EOF

Declare the dependency to the package manager:

bundle config set path 'vendor/bundle'
bundle add faker
bundle lock --add-checksums --normalize-platforms

There isn't a Gazelle extension yet, so write a BUILD file by hand:

>app/BUILD cat <<EOF
load("@rules_ruby//ruby:defs.bzl", "rb_binary")

rb_binary(
    name = "hello",
    srcs = ["hello.rb"],
    main = "hello.rb",
    deps = ["@bundle"],
)
EOF

Run it to see the result:

(Note that Bundle will spam the stdout with install information, so we just want the last line)

output=$(bazel run //app:hello | tail -1)

Let's verify the application output matches expectation:

echo "${output}" | grep -qE "^Hello, .+ from Bazel \\+ Ruby!$" || {
    echo >&2 "Wanted output matching 'Hello, <name> from Bazel + Ruby!' but got '${output}'"
    exit 1
}

Linting

We can lint the code with rubocop, by running the Aspect CLI:

aspect lint

Proto & gRPC

Create the message and service definition:

mkdir proto
>proto/foo.proto cat <<EOF
syntax = "proto3";

package foo;
import "google/protobuf/empty.proto";

service FooService {
  rpc GetFoo(GetFooRequest) returns (GetFooResponse);
}

message GetFooRequest {
  google.protobuf.Empty empty = 1;
}

message GetFooResponse {
  string name = 1;
}
EOF

And create the BUILD file:

bazel run gazelle

Update the application code to start a server:

>app/hello.rb cat <<'EOF'
# TODO: is there a ruby runfiles helper?
runfiles_dir = ENV["RUNFILES_DIR"]
if runfiles_dir
  main_root = File.join(runfiles_dir, "_main")
  $LOAD_PATH.unshift(main_root) if Dir.exist?(main_root) && !$LOAD_PATH.include?(main_root)
end

require "grpc"
require "proto/foo_pb"
require "proto/foo_services_pb"

class FooServer < Foo::FooService::Service
  def get_foo(_req, _call)
    Foo::GetFooResponse.new(name: "Hello from Bazel + Ruby gRPC server!")
  end
end

server = GRPC::RpcServer.new
server.add_http2_port("0.0.0.0:50051", :this_port_is_insecure)
server.handle(FooServer.new)
puts "gRPC server listening on 0.0.0.0:50051"
server.run_till_terminated
EOF

Declare a dependency on the proto_library target:

buildozer "add deps //proto:foo_proto" app:hello

Finally run it, verify the gRPC service responds, then shut it down:

cleanup() {
    kill $server_pid 2>/dev/null
    wait $server_pid 2>/dev/null || true
}
trap cleanup EXIT

bazel run app:hello &
server_pid=$!

# Wait for the gRPC server to be ready (timeout after 30 seconds)
for i in $(seq 1 6); do
    if response=$(buf curl --schema proto --protocol grpc --http2-prior-knowledge \
        -d '{"empty":{}}' \
        http://localhost:50051/foo.FooService/GetFoo 2>/dev/null); then
        echo "Server responded: $response"
        break
    fi
    if [ $i -eq 6 ]; then
        echo >&2 "Timed out waiting for server to start"
        exit 1
    fi
    sleep 5
done

# Verify the response
echo "$response" | grep -q "Hello from Bazel + Ruby gRPC server!" || {
    echo >&2 "Unexpected response: $response"
    exit 1
}