Hook to run command after node_modules installed (#55)

internal/npm_install/npm_install.bzl

@@ -315,6 +315,13 @@ data attribute.
             First argument must be an exectuable, CWD will be that of package directory.
         """,
     ),
+    "postinstall_cmd": attr.string_list(
+        doc = """
+            Command to run after installing `node_modules`.
+
+            First argument must be an exectuable, CWD will be that of package directory.
+        """,
+    ),
     "_inputs": attr.label_list(
         default = [
             "//internal/npm_install:pre_process_package_json.js",
@@ -353,6 +360,19 @@ def _run_preinstall_cmd(repository_ctx, env):
         if result.return_code:
             fail("preinstall command failed: %s (%s)" % (result.stdout, result.stderr))
 
+def _run_postinstall_cmd(repository_ctx, env):
+    if len(repository_ctx.attr.preinstall_cmd) > 0:
+        repository_ctx.report_progress("Running postinstall command")
+        result = repository_ctx.execute(
+            repository_ctx.attr.postinstall_cmd,
+            timeout = repository_ctx.attr.timeout,
+            quiet = repository_ctx.attr.quiet,
+            environment = env,
+            working_directory = str(repository_ctx.path(_rerooted_workspace_package_json_dir(repository_ctx))),
+        )
+        if result.return_code:
+            fail("postinstall command failed: %s (%s)" % (result.stdout, result.stderr))
+
 def _apply_pre_install_patches(repository_ctx):
     if len(repository_ctx.attr.pre_install_patches) == 0:
         return
@@ -721,6 +741,8 @@ cd /D "{root}" && "{npm}" {npm_args}
     if result.return_code:
         fail("npm_install failed: %s (%s)" % (result.stdout, result.stderr))
 
+    _run_postinstall_cmd(repository_ctx, env)
+
     # removeNPMAbsolutePaths is run on node_modules after npm install as the package.json files
     # generated by npm are non-deterministic. They contain absolute install paths and other private
     # information fields starting with "_". removeNPMAbsolutePaths removes all fields starting with "_".
@@ -886,6 +908,8 @@ cd /D "{root}" && "{yarn}" {yarn_args}
     if result.return_code:
         fail("yarn_install failed: %s (%s)" % (result.stdout, result.stderr))
 
+    _run_postinstall_cmd(repository_ctx, env)
+
     _symlink_node_modules(repository_ctx)
     _apply_post_install_patches(repository_ctx)