Fix executable JavaScript scripts running in arbitrary directories

It was working inside a Node project with type: module in its
package.json (e.g. Ursa), but not elsewhere.

Also add a test for both types of executable script.

src/testutil.ts

@@ -23,15 +23,15 @@ import {compile as ursaCompile} from './ursa/compiler.js'
 import {format} from './ursa/fmt.js'
 import version from './version.js'
 
-const command = process.env.NODE_ENV === 'coverage' ? './bin/test-run.sh' : './bin/run.js'
+export const ursaCommand = process.env.NODE_ENV === 'coverage' ? './bin/test-run.sh' : './bin/run.js'
 
 const arkTargets = new Set(['ark', 'js'])
 
 export function run(args: string[], options: ExecaOptions) {
   if (process.env.DEBUG) {
-    console.log(`run ${command} ${args} ${options.inputFile}`)
+    console.log(`run ${ursaCommand} ${args} ${options.inputFile}`)
   }
-  return execa(command, args, options)
+  return execa(ursaCommand, args, options)
 }
 
 function arkCompile(source: string) {

src/ursa/cli.ts

@@ -304,7 +304,7 @@ async function compileCommand(args: Args) {
     output += serializeVal(exp)
   } else {
     if (args.executable) {
-      output += '#!/usr/bin/env -S node --no-warnings --\n'
+      output += '#!/usr/bin/env -S node --experimental-default-type=module --\n'
       output += await buildRuntime()
       // Read prelude but elide the "use strict" line.
       const prelude = preludeJs.slice(preludeJs.indexOf('\n') + 1)

src/ursa/examples.test.ts

@@ -4,9 +4,14 @@
 
 import assert from 'assert'
 import test from 'ava'
+import {execa} from 'execa'
+import fs from 'fs'
 import kill from 'tree-kill'
+import tmp from 'tmp'
 
-import {ursaTest, ursaDirTest, run} from '../testutil.js'
+import {
+  ursaTest, ursaDirTest, ursaCommand, run,
+} from '../testutil.js'
 
 [
   ['Increment a variable in a loop', 'test/increment-variable-in-loop'],
@@ -69,6 +74,21 @@ ursaDirTest('fs', 'test/fs', 'test/fs.result')
 // Rosetta code examples with command-line arguments
 ursaTest('Anagrams', 'rosettacode/Anagrams', ['rosettacode/unixdict.txt'])
 
+// Test executable script generation
+test('Executable scripts', async (t) => {
+  for (const target of ['ark', 'js']) {
+    const tempExecFile = tmp.fileSync({discardDescriptor: true})
+    // t.teardown(() => tempExecFile.removeCallback())
+    await execa(ursaCommand, [
+      `--target=${target}`,
+      'compile', '--executable', 'test/advent-of-code-2023-day-25.ursa',
+      `--output=${tempExecFile.name}`,
+    ])
+    const {stdout} = await execa(tempExecFile.name, ['test/advent-of-code-2023-day-25-input.txt'])
+    t.deepEqual(stdout, fs.readFileSync('test/advent-of-code-2023-day-25.stdout', {encoding: 'utf-8'}))
+  }
+})
+
 // Complex tests
 test('Web server', async (t) => {
   const proc = run(['./test/web-server.ursa'], {