feat: throw error on unused args

src/cac.ts

@@ -349,6 +349,8 @@ export class CAC extends EventTarget {
 
     command.checkRequiredArgs()
 
+    command.checkUnusedArgs()
+
     const actionArgs: any[] = []
     command.args.forEach((arg, index) => {
       if (arg.variadic) {

src/command.ts

@@ -307,6 +307,22 @@ export class Command {
       }
     }
   }
+
+  /**
+   * Check if the number of args is more than expected
+   */
+  checkUnusedArgs(): void {
+    const hasVariadicArg = this.args.some((arg) => arg.variadic)
+    const maximumArgsCount = hasVariadicArg ? Infinity : this.args.length
+
+    if (maximumArgsCount < this.cli.args.length) {
+      const argsString = this.cli.args
+        .slice(maximumArgsCount)
+        .map((arg) => `\`${arg}\``)
+        .join(', ')
+      throw new CACError(`Unused args: ${argsString}`)
+    }
+  }
 }
 
 export class GlobalCommand extends Command {

tests/index.test.ts

@@ -165,6 +165,16 @@ test('throw on unknown options', () => {
   }).toThrowError('Unknown option `--xx`')
 })
 
+test('throw on unused args', () => {
+  const cli = cac()
+
+  cli.command('build [entry]', 'Build your app').action(() => {})
+
+  expect(() => {
+    cli.parse(`node bin build app.js foo bar`.split(' '))
+  }).toThrowError('Unused args: `foo`, `bar`')
+})
+
 describe('--version in help message', () => {
   test('sub command', async () => {
     const output = await getOutput('help.ts', ['lint', '--help'])