Pure ESM library builds

[maxholman]

I recently switched one of our pure ESM javascript libraries to Bazel.

As a pure ESM lib with a top level package.json of type: "module", the rules_nodejs code which is targeting commonjs throws an ERR_REQUIRE_ESM error during builds.

I came up with a patch (love this feature btw) that introduces a package.json into the rules_nodejs source tree so that it avoids consuming my own.

Here's the patch:

diff --git a/internal/node/BUILD.bazel b/internal/node/BUILD.bazel
index 684a60df..50a04c80 100644
--- a/internal/node/BUILD.bazel
+++ b/internal/node/BUILD.bazel
@@ -18,6 +18,7 @@ load("@build_bazel_rules_nodejs//:index.bzl", "generated_file_test")
 package(default_visibility = ["//visibility:public"])

 exports_files([
+    "package.json",
     "node_patches.js",
     "require_patch.js",
     "loader.js",
diff --git a/internal/node/node.bzl b/internal/node/node.bzl
index be59fcce..b5389ef6 100644
--- a/internal/node/node.bzl
+++ b/internal/node/node.bzl
@@ -251,6 +251,7 @@ fi
     node_tool_files = ctx.files._node[:]
     node_tool_files.extend(ctx.toolchains["@build_bazel_rules_nodejs//toolchains/node:toolchain_type"].nodeinfo.tool_files)

+    node_tool_files.append(ctx.file._package_json)
     node_tool_files.append(ctx.file._link_modules_script)
     node_tool_files.append(ctx.file._runfile_helpers_bundle)
     node_tool_files.append(ctx.file._runfile_helpers_main)
@@ -595,6 +596,10 @@ Predefined genrule variables are not supported in this context.
         default = Label("@nodejs//:node_bin"),
         allow_single_file = True,
     ),
+    "_package_json": attr.label(
+        default = Label("//internal/node:package.json"),
+        allow_single_file = True,
+    ),
     "_node_patches_script": attr.label(
         default = Label("//internal/node:node_patches.js"),
         allow_single_file = True,
diff --git a/internal/node/package.json b/internal/node/package.json
new file mode 100644
index 00000000..5bbefffb
--- /dev/null
+++ b/internal/node/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}
diff --git a/internal/pkg_npm/BUILD.bazel b/internal/pkg_npm/BUILD.bazel
index 0c89f44e..edcd4a55 100644
--- a/internal/pkg_npm/BUILD.bazel
+++ b/internal/pkg_npm/BUILD.bazel
@@ -10,11 +10,11 @@ bzl_library(
 )

 # Exported to be consumed for generating stardoc.
-exports_files(["pkg_npm.bzl"])
+exports_files(["pkg_npm.bzl", "package.json"])

 nodejs_binary(
     name = "packager",
-    data = ["//third_party/github.com/gjtorikian/isBinaryFile"],
+    data = ["//third_party/github.com/gjtorikian/isBinaryFile", "package.json"],
     entry_point = ":packager.js",
     # TODO: figure out why isbinaryfile is not linked in a way this can resolve
     templated_args = ["--bazel_patch_module_resolver"],
diff --git a/internal/pkg_npm/package.json b/internal/pkg_npm/package.json
new file mode 100644
index 00000000..5bbefffb
--- /dev/null
+++ b/internal/pkg_npm/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}

I am way out of my depth when it comes to Bazel, so I thought it best to avoid going for a PR and post a discussion instead. I'm sure I have missed some edge cases which I am not currently using.

If the above is useful/correct I'd be happy to contribute!