feat: add language examples

.bazelrc

@@ -2,8 +2,9 @@
 # Take care to document any settings that you expect users to apply.
 # Settings that apply only to CI are in .github/workflows/ci.bazelrc
 
-# Required until this is the default; expected in Bazel 7
-common --enable_bzlmod
+# The main ingredient: allow us to register toolchains other than com_google_protobuf targets
+common --incompatible_enable_proto_toolchain_resolution
+common --@aspect_rules_py//py:interpreter_version=3.9.18
 
 # Don’t want to push a rules author to update their deps if not needed.
 # https://bazel.build/reference/command-line-reference#flag--check_direct_dependencies

.github/workflows/ci.yaml

@@ -16,11 +16,14 @@ concurrency:
   group: concurrency-group::${{ github.workflow }}::${{ github.event.pull_request.number > 0 && format('pr-{0}', github.event.pull_request.number) || github.ref_name }}${{ github.ref_name == 'main' && format('::{0}', github.run_id) || ''}}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
 
+env:
+  RULES_PYTHON_ENABLE_PYSTAR: 0
+
 jobs:
   test:
     uses: bazel-contrib/.github/.github/workflows/bazel.yaml@v6
     with:
-      folders: '["e2e/smoke"]'
+      folders: '[".", "e2e/smoke"]'
       exclude: |
         [
           {"bazelversion": "6.4.0"}

.github/workflows/release.yml

@@ -8,6 +8,9 @@ on:
     tags:
       - "v*.*.*"
 
+env:
+  RULES_PYTHON_ENABLE_PYSTAR: 0
+
 jobs:
   release:
     uses: bazel-contrib/.github/.github/workflows/release_ruleset.yaml@v6

MODULE.bazel

@@ -10,11 +10,27 @@ bazel_dep(name = "bazel_skylib", version = "1.4.1")
 bazel_dep(name = "rules_proto", version = "6.0.0-rc2")
 bazel_dep(name = "platforms", version = "0.0.8")
 
-bazel_dep(name = "aspect_bazel_lib", version = "1.32.1", dev_dependency = True)
-bazel_dep(name = "buildifier_prebuilt", version = "6.1.2", dev_dependency = True)
-
 protoc = use_extension("//protoc:extensions.bzl", "protoc")
 protoc.toolchain(version = "v25.3")
 use_repo(protoc, "toolchains_protoc_hub")
 
 register_toolchains("@toolchains_protoc_hub//:all")
+
+bazel_dep(name = "aspect_bazel_lib", version = "1.32.1", dev_dependency = True)
+bazel_dep(name = "buildifier_prebuilt", version = "6.1.2", dev_dependency = True)
+bazel_dep(name = "aspect_rules_py", version = "0.7.1", dev_dependency = True)
+bazel_dep(name = "rules_java", version = "7.4.0", dev_dependency = True)
+bazel_dep(name = "rules_python", version = "0.31.0", dev_dependency = True)
+
+# Update to include
+# https://github.com/bazelbuild/rules_python/pull/1577
+git_override(
+    module_name = "rules_python",
+    commit = "3edcae33dcc43051ca6f200c2d0cb3692df79d03",
+    remote = "https://github.com/bazelbuild/rules_python.git",
+)
+
+register_toolchains(
+    "//examples/lang_toolchains:all",
+    dev_dependency = True,
+)

README.md

@@ -17,8 +17,8 @@ That flag ALSO decouples how each language rule locates the runtime.
 
 This repo simply contains a toolchain that resolves those pre-built binaries.
 
-A full example including several language rules like `py_proto_library` and `java_proto_library` may be found at
-https://github.com/bazelbuild/examples/tree/never_compile_protoc_again/proto
+See `examples` for several language rules like `py_proto_library` and `java_proto_library`.
+There is NO dependency on `@com_google_protobuf` anywhere.
 
 ## Design
 

WORKSPACE.bazel

@@ -1 +1,19 @@
 # Marker that this is the root of a Bazel workspace.
+
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_file", "http_jar")
+
+# Fetch the runtime package that applications need to marshal proto files.
+# This does NOT do any code generation of .pb2.py files, we still use protoc for that.
+# From https://pypi.org/project/protobuf/4.25.3/
+http_file(
+    name = "protobuf_4_25_3",
+    downloaded_file_path = "protobuf-4.25.3-py3-none-any.whl",
+    sha256 = "f0700d54bcf45424477e46a9f0944155b46fb0639d69728739c0e47bab83f2b9",
+    urls = ["https://files.pythonhosted.org/packages/f4/d5/db585a5e8d64af6b384c7b3a63da13df2ff86933e486ba78431736c67c25/protobuf-4.25.3-py3-none-any.whl"],
+)
+
+http_jar(
+    name = "protobuf-java_3_25_3",
+    sha256 = "e90d8ddb963b20a972a6a59b5093ade2b07cbe546cab3279aaf4383260385f58",
+    urls = ["https://repo1.maven.org/maven2/com/google/protobuf/protobuf-java/3.25.3/protobuf-java-3.25.3.jar"],
+)

examples/BUILD

@@ -0,0 +1,19 @@
+load("@rules_proto//proto:defs.bzl", "proto_library")
+load("@rules_python//python:proto.bzl", "py_proto_library")
+
+package(default_visibility = ["//visibility:public"])
+
+proto_library(
+    name = "foo_proto",
+    srcs = ["foo.proto"],
+)
+
+py_proto_library(
+    name = "foo_py_proto",
+    deps = [":foo_proto"],
+)
+
+java_proto_library(
+    name = "foo_java_proto",
+    deps = [":foo_proto"],
+)

examples/foo.proto

@@ -0,0 +1,7 @@
+syntax = "proto3";
+
+option java_package = "proto";
+
+message Foo {
+    string msg = 1;
+}

examples/java/BUILD

@@ -0,0 +1,9 @@
+java_binary(
+    name = "java",
+    srcs = ["Main.java"],
+    main_class = "Main",
+    deps = [
+        "//examples:foo_java_proto",
+        "@protobuf-java_3_25_3//jar",
+    ],
+)

examples/java/Main.java

@@ -0,0 +1,14 @@
+import com.google.protobuf.InvalidProtocolBufferException;
+import static proto.FooOuterClass.Foo;
+
+public class Main {
+  public static void main(String[] args) throws InvalidProtocolBufferException {
+    System.out.println(makeMessage("Hello World!"));
+  }
+
+  public static Foo makeMessage(String msg) {
+    Foo.Builder person = Foo.newBuilder();
+    person.setMsg(msg);
+    return person.build();
+  }
+}

examples/lang_toolchains/BUILD

@@ -0,0 +1,39 @@
+load("@aspect_rules_py//py:defs.bzl", "py_unpacked_wheel")
+load("@rules_proto//proto:defs.bzl", "proto_lang_toolchain")
+
+# See WORKSPACE.bazel for fetch instructions of "protobuf_4_25_3".
+# Turn the downloaded .whl file into a py_library-shape (provides PyInfo)
+# Avoids the need for any pip, requirements files, python interpreter for wheel unpacking, etc
+py_unpacked_wheel(
+    name = "protobuf_wheel",
+    src = "@protobuf_4_25_3//file",
+    py_package_name = "protobuf",
+)
+
+# Configure protoc to have the right arguments for generating Python stubs.
+proto_lang_toolchain(
+    name = "protoc_py_toolchain",
+    command_line = "--python_out=%s",
+    progress_message = "Generating Python proto_library %{label}",
+    runtime = ":protobuf_wheel",
+)
+
+proto_lang_toolchain(
+    name = "protoc_java_toolchain",
+    command_line = "--java_out=%s",
+    progress_message = "Generating Java proto_library %{label}",
+    runtime = "@protobuf-java_3_25_3//jar",
+)
+
+# Adapters to the register_toolchains call, adding the toolchain_type to above
+toolchain(
+    name = "protoc_py_toolchain.registration",
+    toolchain = ":protoc_py_toolchain",
+    toolchain_type = "@rules_python//python/proto:toolchain_type",
+)
+
+toolchain(
+    name = "protoc_java_toolchain.registration",
+    toolchain = ":protoc_java_toolchain",
+    toolchain_type = "@rules_java//java/proto:toolchain_type",
+)

examples/python/BUILD

@@ -0,0 +1,5 @@
+py_test(
+    name = "message_test",
+    srcs = ["message_test.py"],
+    deps = ["//examples:foo_py_proto"],
+)

examples/python/message_test.py

@@ -0,0 +1,15 @@
+import sys
+import unittest
+
+from examples import foo_pb2
+
+class TestCase(unittest.TestCase):
+    def test_message(self):
+        got = foo_pb2.Foo(
+            msg = "hello world",
+        )
+        self.assertIsNotNone(got)
+
+
+if __name__ == "__main__":
+  sys.exit(unittest.main())