feat: add js_rpc_library and js_rpc_toolchain for ConnectRPC support (#2797)

Adds a new `js_rpc_library` rule and `js_rpc_toolchain` macro to support
protoc-based RPC code generators such as `protoc-gen-connect-query`.

- `js_rpc_library`: a rule that runs a protoc plugin on its immediate
proto_library deps and exposes the output as JsInfo.
- `js_rpc_toolchain`: a macro wrapping `_js_proto_toolchain` but with a
new `//js/toolchains:protoc_rpc_plugin` toolchain type.
- Updates to `e2e/protobuf-es` showing how to use Connect and
Connect-Query
 - Updates to `e2/protobuf-google` showing how to use grpc-js
    
Support for Connect-Query seems to be the only thing in the deprecated
`ts_proto_library` rule that was lacking in `rules_js`. Hopefully now
that we have support for it, we can start recommending that everyone
migrate away from `ts_proto_library`.

---

### Changes are visible to end-users: yes

- Searched for relevant documentation and updated as needed: no
- Breaking change (forces users to change their own code or config): no
- Suggested release notes appear below: yes

A `js_rpc_library` rule is now available and can generate RPC bindings
for any RPC system that is built on a protoc plugin. The plugin just
needs to be registered with the `js_rpc_toolchain` macro.

### Test plan

- New test cases added

---------

Co-authored-by: Claude Sonnet 4.6 <[email protected]>

Author: acozzette

MODULE.bazel

@@ -88,6 +88,12 @@ use_repo(
 
 ####### Dev dependencies ########
 
+register_toolchains(
+    "//js/private/test/proto:proto_toolchain_for_tests_toolchain",
+    "//js/private/test/proto:rpc_toolchain_for_tests_toolchain",
+    dev_dependency = True,
+)
+
 # Dev-only pnpm used for local testing
 pnpm10 = use_extension("@aspect_rules_js//npm:extensions.bzl", "pnpm", dev_dependency = True)
 pnpm10.pnpm(

e2e/protobuf-es/.bazelversion

@@ -1 +1 @@
-../../../.bazelversion
+../../.bazelversion

e2e/protobuf-es/BUILD.bazel

@@ -1,4 +1,5 @@
 load("@aspect_rules_js//js:defs.bzl", "js_library", "js_test")
+load("@aspect_rules_js//js:rpc.bzl", "js_rpc_library")
 load("@npm//:defs.bzl", "npm_link_all_packages")
 load("@protobuf//bazel:proto_library.bzl", "proto_library")
 
@@ -38,3 +39,50 @@ js_test(
     data = [":test_lib"],
     entry_point = "test_proto.js",
 )
+
+js_library(
+    name = "test_connect_lib",
+    srcs = ["test_connect.js"],
+    deps = [
+        ":node_modules/@connectrpc/connect",
+        ":user_proto",
+    ],
+)
+
+js_test(
+    name = "test_connect",
+    data = [":test_connect_lib"],
+    entry_point = "test_connect.js",
+)
+
+proto_library(
+    name = "eliza_proto",
+    srcs = ["eliza.proto"],
+)
+
+js_rpc_library(
+    name = "eliza_rpc",
+    outs = [
+        "eliza-ElizaService_connectquery.d.ts",
+        "eliza-ElizaService_connectquery.js",
+    ],
+    deps = [":eliza_proto"],
+)
+
+js_library(
+    name = "test_connect_query_lib",
+    srcs = ["test_connect_query.js"],
+    deps = [
+        ":eliza_proto",
+        ":eliza_rpc",
+        ":node_modules/@bufbuild/protobuf",
+        ":node_modules/@connectrpc/connect",
+        ":node_modules/@connectrpc/connect-query-core",
+    ],
+)
+
+js_test(
+    name = "test_connect_query",
+    data = [":test_connect_query_lib"],
+    entry_point = "test_connect_query.js",
+)

e2e/protobuf-es/MODULE.bazel

@@ -1,6 +1,5 @@
 bazel_dep(name = "aspect_rules_js")
 bazel_dep(name = "bazel_skylib", version = "1.8.2")
-bazel_dep(name = "diff.bzl", version = "0.4.3")
 bazel_dep(name = "protobuf", version = "33.4")  # Works with Bazel 7-9
 bazel_dep(name = "rules_nodejs", version = "6.7.3")
 

e2e/protobuf-es/README.md

@@ -1,8 +1,9 @@
 # Buf.build protobuf-es example
 
 This directory contains an example of how to set up and use the Buf.build
-protobuf-es implementation. See also e2e/protobuf-google/ for an example of how
-to use Google's protobuf implementation.
+protobuf-es implementation, along with Connect and Connect-Query. See also
+e2e/protobuf-google/ for an example of how to use Google's protobuf
+implementation.
 
 Ideally we would like to support every JavaScript or TypeScript implementation
 for which Buf [provides](https://buf.build/bazel/bazel/sdks/main:protobuf) an

e2e/protobuf-es/eliza.proto

@@ -0,0 +1,16 @@
+syntax = "proto3";
+
+package eliza.v1;
+
+message SayRequest {
+    string sentence = 1;
+}
+
+message SayResponse {
+    string sentence = 1;
+}
+
+service ElizaService {
+    // Say returns the input message back.
+    rpc Say(SayRequest) returns (SayResponse) {}
+}

e2e/protobuf-es/package.json

@@ -2,7 +2,9 @@
     "private": true,
     "packageManager": "[email protected]",
     "dependencies": {
-        "@bufbuild/protobuf": "catalog:"
+        "@bufbuild/protobuf": "catalog:",
+        "@connectrpc/connect": "catalog:",
+        "@connectrpc/connect-query-core": "catalog:"
     },
     "type": "module"
 }

e2e/protobuf-es/pnpm-lock.yaml

@@ -3,5 +3,7 @@ packages:
 
 catalog:
     '@bufbuild/protobuf': '2.7.0'
+    '@connectrpc/connect': '2.1.1'
+    '@connectrpc/connect-query-core': '2.2.0'
 
 onlyBuiltDependencies: []

e2e/protobuf-es/pnpm-workspace.yaml

@@ -0,0 +1,23 @@
+import { GetUserRequestSchema, UserSchema, UserService } from './user_pb.js'
+import { createClient, createRouterTransport } from '@connectrpc/connect'
+import { create } from '@bufbuild/protobuf'
+import assert from 'node:assert'
+
+// In protobuf-es v2, service descriptors are embedded in the _pb.js file
+// alongside message schemas, so no separate codegen step is needed.
+assert.ok(UserService, 'UserService should be defined')
+assert.ok(UserService.method.getUser, 'getUser method should be defined')
+
+const transport = createRouterTransport((router) => {
+    router.service(UserService, {
+        getUser(req) {
+            return create(UserSchema, { name: req.name })
+        },
+    })
+})
+
+const client = createClient(UserService, transport)
+const response = await client.getUser(
+    create(GetUserRequestSchema, { name: 'alice' })
+)
+assert.equal(response.name, 'alice')