build: setup toolchain for nodejs v12 for integration tests

Sets up another toolchain for the NodeJS v12 version. This allows us
to use Node v12 in integration tests without having to manually manage
the Node version in the integration test which runs usually with the
default Node workspace toolchain.

Note that we need a small patch to `rules_nodejs` as the standalone
node toolchain feature is technically internal (but shipped). Rules
NodeJS is in progress of migrating from their current workspace name
to `@rules_nodejs//`. We temporarily patch the external repository to
work with the workspace name we use with `@build_bazel_rules_nodejs#v4`.

Author: devversion

WORKSPACE

@@ -8,6 +8,7 @@ load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 # Add NodeJS rules
 http_archive(
     name = "build_bazel_rules_nodejs",
+    patches = ["//tools:multiple-node-versions.patch"],
     sha256 = "3635797a96c7bfcd0d265dacd722a07335e64d6ded9834af8d3f1b7ba5a25bba",
     urls = ["https://github.com/bazelbuild/rules_nodejs/releases/download/4.3.0/rules_nodejs-4.3.0.tar.gz"],
 )
@@ -60,6 +61,16 @@ node_repositories(
     package_json = ["//:package.json"],
 )
 
+load("@build_bazel_rules_nodejs//nodejs:repositories.bzl", "nodejs_register_toolchains")
+
+# This call sets up another repository for Node 12.x used in integration tests. This
+# allows us to ensure our schematic code works with NodeJS v12 LTS. The Node v12.x
+# version is not fetched unless explicitly requested by the tests.
+nodejs_register_toolchains(
+    name = "node12",
+    node_version = "12.20.0",
+)
+
 load("//tools:integration.bzl", "create_npm_package_archive_build_file")
 
 yarn_install(

tools/BUILD.bazel

@@ -1,7 +1,7 @@
 package(default_visibility = ["//visibility:public"])
 
 exports_files([
-    "system-config-tmpl.js",
+    "multiple-node-versions.patch",
 ])
 
 # Bazel config setting that matches if the partial compilation flag

tools/defaults.bzl

@@ -347,10 +347,10 @@ def node_integration_test(data = [], tool_mappings = {}, **kwargs):
             # because the `yarn_bin` target is not a self-contained standalone binary.
             "@nodejs//:yarn_files",
         ],
-        tool_mappings = dict(tool_mappings, **{
+        tool_mappings = dict({
             "@nodejs//:yarn_bin": "yarn",
             "@nodejs//:node_bin": "node",
-        }),
+        }, **tool_mappings),
         **kwargs
     )
 

tools/multiple-node-versions.patch

@@ -0,0 +1,44 @@
+diff --git nodejs/private/toolchains_repo.bzl nodejs/private/toolchains_repo.bzl
+index 9dcdc60..4927e75 100644
+--- nodejs/private/toolchains_repo.bzl
++++ nodejs/private/toolchains_repo.bzl
+@@ -70,7 +70,7 @@ def _toolchains_repo_impl(repository_ctx):
+ 
+ # Forward all the providers
+ def _resolved_toolchain_impl(ctx):
+-    toolchain_info = ctx.toolchains["@rules_nodejs//nodejs:toolchain_type"]
++    toolchain_info = ctx.toolchains["@build_bazel_rules_nodejs//nodejs:toolchain_type"]
+     return [
+         toolchain_info,
+         toolchain_info.default,
+@@ -82,7 +82,7 @@ def _resolved_toolchain_impl(ctx):
+ # https://cs.opensource.google/bazel/bazel/+/master:tools/jdk/java_toolchain_alias.bzl
+ resolved_toolchain = rule(
+     implementation = _resolved_toolchain_impl,
+-    toolchains = ["@rules_nodejs//nodejs:toolchain_type"],
++    toolchains = ["@build_bazel_rules_nodejs//nodejs:toolchain_type"],
+     incompatible_use_toolchain_transition = True,
+ )
+ """
+@@ -107,7 +107,7 @@ toolchain(
+     exec_compatible_with = {compatible_with},
+     target_compatible_with = {compatible_with},
+     toolchain = "@{user_node_repository_name}_{platform}//:node_toolchain",
+-    toolchain_type = "@rules_nodejs//nodejs:toolchain_type",
++    toolchain_type = "@build_bazel_rules_nodejs//nodejs:toolchain_type",
+ )
+ """.format(
+             platform = platform,
+diff --git nodejs/repositories.bzl nodejs/repositories.bzl
+index 494217b..6dfb8fb 100644
+--- nodejs/repositories.bzl
++++ nodejs/repositories.bzl
+@@ -690,7 +690,7 @@ filegroup(
+     # the platform attribute is only set when used from this file, not from build_bazel_rules_nodejs
+     if repository_ctx.attr.platform:
+         build_content += """
+-load("@rules_nodejs//nodejs:toolchain.bzl", "node_toolchain")
++load("@build_bazel_rules_nodejs//nodejs:toolchain.bzl", "node_toolchain")
+ node_toolchain(name = "node_toolchain", target_tool = ":node_bin")
+ """
+     repository_ctx.file("BUILD.bazel", content = build_content)