Allow execution of the peggy binary on Windows.

Handle node runtime flags manually, executing a sub-instance of node to actually run `peggy`.

Fixes #514.

CHANGELOG.md

@@ -22,6 +22,9 @@ Released: TBD
 
 - [#531](https://github.com/peggyjs/peggy/issues/531) Clean up rollup hacks
   from CLI code.
+- [#514](https://github.com/peggyjs/peggy/issues/514) Allow execution of
+  the `peggy` binary on Windows by handling node runtime flags manually,
+  executing a sub-instance of node to actually run `peggy`.
 
 ### Documentation
 

bin/peggy.js

@@ -1,7 +1,28 @@
-#!/usr/bin/env -S node --experimental-vm-modules --no-warnings
+#!/usr/bin/env node
 
 "use strict";
 
+// Since Windows can't handle `env -S`, exec once to get permission
+// to use the vm module in its modern form.
+const execArgv = new Set(process.execArgv);
+if (!execArgv.has("--experimental-vm-modules")) {
+  execArgv.add("--experimental-vm-modules");
+  execArgv.add("--no-warnings");
+  const { spawnSync } = require("child_process");
+  // NOTE: Does not replace process.  Node can't do that, apparently.
+  const { status, signal, error } = spawnSync(process.argv[0], [
+    ...execArgv,
+    ...process.argv.slice(1),
+  ], { stdio: "inherit" });
+  if (error) {
+    throw error;
+  }
+  if (signal) {
+    process.kill(process.pid, signal);
+  }
+  process.exit(status);
+}
+
 const {
   CommanderError, InvalidArgumentError, PeggyCLI,
 } = require("./peggy-cli.js");