feat(scala): demonstrate protobuf

scaffold.yaml

@@ -212,5 +212,6 @@ presets:
   scala:
     langs: ['Scala']
     lint: true
+    proto: true
   minimal:
     langs: []

user_stories/scala.md

@@ -52,3 +52,61 @@ output="$(bazel run src:Hello)"
     exit 1
 }
 ~~~
+
+## Using protobuf and gRPC
+
+Let's introduce a small data schema.
+
+~~~sh
+>src/foo.proto cat <<EOF
+syntax = "proto3";
+option java_package = "build.aspect.examples";
+option java_outer_classname = "FooOuterClass";
+message Foo {
+    string message = 1;
+}
+EOF
+~~~
+
+Generate the BUILD rules for protobuf:
+
+~~~sh
+bazel run gazelle
+~~~
+
+There isn't a Gazelle generator for scala_proto_library yet, so add it manually:
+
+~~~sh
+buildozer 'new_load @rules_scala//scala_proto:scala_proto.bzl scala_proto_library' src:__pkg__
+buildozer 'new scala_proto_library foo_scala_proto' src:__pkg__
+buildozer 'add deps :foo_proto' src:foo_scala_proto
+buildozer 'add deps :foo_scala_proto' src:Hello
+~~~
+
+Now overwrite `Hello.scala` to use the generated `Foo` message:
+
+~~~sh
+>src/Hello.scala cat <<EOF
+import build.aspect.examples.FooOuterClass
+
+object Hello {
+  def main(args: Array[String]): Unit = {
+    val foo = FooOuterClass.Foo.newBuilder()
+      .setMessage("Hello from Scala Protobuf!")
+      .build()
+    println(foo)
+  }
+}
+EOF
+~~~
+
+Run the application again:
+
+~~~sh
+output="$(bazel run src:Hello)"
+
+[ "${output}" = "message: \"Hello from Scala Protobuf!\"" ] || {
+    echo >&2 "Wanted output 'Hello from Scala Protobuf' but got '${output}'"
+    exit 1
+}
+~~~

{{ .ProjectSnake }}/MODULE.bazel

@@ -35,10 +35,10 @@ use_repo(multitool, "multitool")
 # Protobuf and gRPC
 bazel_dep(name = "protobuf", version = "33.4")
 bazel_dep(name = "protovalidate", version = "1.0.0")
-{{- if .Computed.java }}
-bazel_dep(name = "grpc-java", version = "1.75.0")
 # Force later resolutions of some transitives to pick up Bazel 9 fixes
 bazel_dep(name = "rules_foreign_cc", version = "0.15.1", repo_name = None)
+{{- if .Computed.java }}
+bazel_dep(name = "grpc-java", version = "1.75.0")
 bazel_dep(name = "bazel_jar_jar", version = "0.1.12", repo_name = None)
 
 {{- end }}
@@ -252,6 +252,15 @@ scala_deps = use_extension(
     "scala_deps",
 )
 scala_deps.scala()
+{{ if .Scaffold.proto -}}
+scala_deps.scala_proto(
+    default_gen_opts = [
+        "grpc",
+        "flat_package",
+        "scala3_sources",
+    ],
+)
+{{- end }}
 {{- end }}
 
 {{- if .Scaffold.oci  }}