feat(builtin): allow bundling ESM output with the pkg_npm rule

internal/pkg_npm/pkg_npm.bzl

@@ -6,7 +6,7 @@ If all users of your library code use Bazel, they should just add your library
 to the `deps` of one of their targets.
 """
 
-load("//:providers.bzl", "DeclarationInfo", "JSModuleInfo", "LinkablePackageInfo", "NODE_CONTEXT_ATTRS", "NodeContextInfo")
+load("//:providers.bzl", "DeclarationInfo", "JSEcmaScriptModuleInfo", "JSNamedModuleInfo", "LinkablePackageInfo", "NODE_CONTEXT_ATTRS", "NodeContextInfo")
 
 _DOC = """The pkg_npm rule creates a directory containing a publishable npm artifact.
 
@@ -98,6 +98,10 @@ PKG_NPM_ATTRS = dict(NODE_CONTEXT_ATTRS, **{
         doc = """Other targets which produce files that should be included in the package, such as `rollup_bundle`""",
         allow_files = True,
     ),
+    "include_esm": attr.bool(
+        doc = """Whether generated ESM files should also be included in the package, in addition to CommonJS modules.""",
+        default = False,
+    ),
     "nested_packages": attr.label_list(
         doc = """Other pkg_npm rules whose content is copied into this package.""",
         allow_files = True,
@@ -295,11 +299,15 @@ def _pkg_npm(ctx):
         # Only collect DefaultInfo files (not transitive)
         deps_files_depsets.append(dep.files)
 
-        # All direct & transitive JavaScript-producing deps
-        if JSModuleInfo in dep:
-            deps_files_depsets.append(dep[JSModuleInfo].sources)
+        # All direct and transitive deps that produce CommonJS modules
+        if JSNamedModuleInfo in dep:
+            deps_files_depsets.append(dep[JSNamedModuleInfo].sources)
+
+        # All direct and transitive deps that produce ES6 modules
+        if JSEcmaScriptModuleInfo in dep and ctx.attr.include_esm:
+            deps_files_depsets.append(dep[JSEcmaScriptModuleInfo].sources)
 
-        # Include all transitive declerations
+        # Include all transitive declarations
         if DeclarationInfo in dep:
             deps_files_depsets.append(dep[DeclarationInfo].transitive_declarations)
 

internal/pkg_npm/test/BUILD.bazel

@@ -63,6 +63,15 @@ pkg_npm(
     ],
 )
 
+pkg_npm(
+    name = "test_esm_pkg",
+    srcs = [],
+    include_esm = True,
+    deps = [
+        ":ts_library",
+    ],
+)
+
 pkg_npm(
     name = "test_noop_pkg",
     # Special case where these is a single dep that is a directory artifact
@@ -109,12 +118,14 @@ jasmine_node_test(
     name = "test",
     srcs = ["pkg_npm.spec.js"],
     data = [
+        ":test_esm_pkg",
         ":test_noop2_pkg",
         ":test_noop_pkg",
         ":test_pkg",
     ],
     templated_args = [
         "$(rootpath :test_pkg)",
+        "$(rootpath :test_esm_pkg)",
         "$(rootpath :test_noop_pkg)",
         "$(rootpath :test_noop2_pkg)",
     ],

internal/pkg_npm/test/pkg_npm.spec.js

@@ -2,16 +2,22 @@ const fs = require('fs');
 const runfiles = require(process.env['BAZEL_NODE_RUNFILES_HELPER']);
 const args = process.argv.slice(2);
 const testPkgRootpath = args[0];
-const testNoopPkgRootpath = args[1];
-const testNoop2PkgRootpath = args[2];
+const testEsmPkgRootpath = args[1];
+const testNoopPkgRootpath = args[2];
+const testNoop2PkgRootpath = args[3];
 const testPkgPath = runfiles.resolveWorkspaceRelative(testPkgRootpath);
+const testEsmPkgPath = runfiles.resolveWorkspaceRelative(testEsmPkgRootpath);
 const testNoopPkgPath = runfiles.resolveWorkspaceRelative(testNoopPkgRootpath);
 const testNoop2PkgPath = runfiles.resolveWorkspaceRelative(testNoop2PkgRootpath);
 
 function readFromPkg(p) {
   return fs.readFileSync(`${testPkgPath}/${p}`, {encoding: 'utf-8'}).trim();
 }
 
+function readFromEsmPkg(p) {
+  return fs.readFileSync(`${testEsmPkgPath}/${p}`, {encoding: 'utf-8'}).trim();
+}
+
 function readFromNoopPkg(p) {
   return fs.readFileSync(`${testNoopPkgPath}/${p}`, {encoding: 'utf-8'}).trim();
 }
@@ -39,6 +45,12 @@ describe('pkg_npm', () => {
   it('copies declaration files from ts_library', () => {
     expect(readFromPkg('foo.d.ts')).toContain('export declare const a: string;');
   });
+  it('copies ESM files from ts_library if include_esm is True', () => {
+    expect(readFromEsmPkg('foo.mjs')).toContain('export const a = \'\';');
+  });
+  it('does not copy ESM files if include_esm is False', () => {
+    expect(() => readFromPkg('foo.mjs')).toThrow();
+  });
   it('copies data dependencies', () => {
     expect(readFromPkg('data.json')).toEqual('[]');
   });