fix(runtime): handle BOM before shebang (#158)

Author: phucnguyen1707

src/runtime.mjs

@@ -23,7 +23,7 @@ export const DEFAULT_MAX = 3;
 
 /** Strip a leading `#!…` shebang line so `#!/usr/bin/env moshscript` files parse. */
 export function stripShebang(src) {
-  return src.startsWith("#!") ? src.replace(/^#![^\n]*\r?\n?/, "") : src;
+  return src.replace(/^\uFEFF?#![^\r\n]*(?:\r?\n|$)/, "");
 }
 
 // The loop governor: owns `alive` truthiness and the iteration budget.

test/runtime.test.mjs

@@ -84,8 +84,15 @@ test("a leading shebang line is stripped, not executed", async () => {
   assert.deepEqual(calls, ["ran"]);
 });
 
+test("a UTF-8 BOM before a shebang is stripped", async () => {
+  const { calls, registry } = recorder();
+  await runScript(`\uFEFF#!/usr/bin/env moshscript\npush("ran");`, { commands: registry });
+  assert.deepEqual(calls, ["ran"]);
+});
+
 test("stripShebang leaves shebang-less source untouched", () => {
   assert.equal(stripShebang('push("x");'), 'push("x");');
+  assert.equal(stripShebang('\uFEFFpush("x");'), '\uFEFFpush("x");');
   assert.equal(stripShebang("#!/usr/bin/env moshscript\npush();"), "push();");
 });