feat: implicit return for single expressions using acorn parser

- Parse code with acorn to detect single expression statements
- Auto-wrap expressions with 'return await (...)' for implicit return
- Exclude side-effects: assignments, updates (x++), delete operator
- Update skill.md examples to remove console.log (keep await)
- Add unit tests for shouldAutoReturn function

playwriter/package.json

@@ -46,6 +46,7 @@
     "@hono/node-ws": "^1.2.0",
     "@modelcontextprotocol/sdk": "^1.25.2",
     "@xmorse/cac": "^6.0.7",
+    "acorn": "^8.15.0",
     "async-sema": "^3.1.1",
     "diff": "^8.0.2",
     "dom-accessibility-api": "^0.7.1",

playwriter/src/executor.ts

@@ -12,6 +12,7 @@ import util from 'node:util'
 import { createRequire } from 'node:module'
 import { fileURLToPath } from 'node:url'
 import vm from 'node:vm'
+import * as acorn from 'acorn'
 import { createSmartDiff } from './diff-utils.js'
 import { getCdpUrl } from './utils.js'
 import { waitForPageLoad, WaitForPageLoadOptions, WaitForPageLoadResult } from './wait-for-page-load.js'
@@ -61,6 +62,61 @@ const usefulGlobals = {
   structuredClone,
 } as const
 
+/**
+ * Determines if code should be auto-wrapped with `return await (...)`.
+ * Returns true for single expression statements that aren't assignments.
+ */
+export function shouldAutoReturn(code: string): boolean {
+  try {
+    const ast = acorn.parse(code, {
+      ecmaVersion: 'latest',
+      allowAwaitOutsideFunction: true,
+      allowReturnOutsideFunction: true,
+      sourceType: 'script',
+    })
+
+    // Must be exactly one statement
+    if (ast.body.length !== 1) {
+      return false
+    }
+
+    const stmt = ast.body[0]
+
+    // If it's already a return statement, don't auto-wrap
+    if (stmt.type === 'ReturnStatement') {
+      return false
+    }
+
+    // Must be an ExpressionStatement
+    if (stmt.type !== 'ExpressionStatement') {
+      return false
+    }
+
+    // Don't auto-return side-effect expressions
+    const expr = stmt.expression
+    if (
+      expr.type === 'AssignmentExpression' ||
+      expr.type === 'UpdateExpression' ||
+      (expr.type === 'UnaryExpression' && (expr as acorn.UnaryExpression).operator === 'delete')
+    ) {
+      return false
+    }
+
+    // Don't auto-return sequence expressions that contain assignments
+    if (expr.type === 'SequenceExpression') {
+      const hasAssignment = expr.expressions.some((e: acorn.Expression) => e.type === 'AssignmentExpression')
+      if (hasAssignment) {
+        return false
+      }
+    }
+
+    return true
+  } catch {
+    // Parse failed, don't auto-return
+    return false
+  }
+}
+
 const EXTENSION_NOT_CONNECTED_ERROR = `The Playwriter Chrome extension is not connected. Make sure you have:
 1. Installed the extension: https://chromewebstore.google.com/detail/playwriter-mcp/jfeammnjpkecdekppnclgkkffahnhfhe
 2. Clicked the extension icon on a tab to enable it (or refreshed the page if just installed)`
@@ -721,8 +777,11 @@ export class PlaywrightExecutor {
       }
 
       const vmContext = vm.createContext(vmContextObj)
-      const wrappedCode = `(async () => { ${code} })()`
+      const autoReturn = shouldAutoReturn(code)
-      const hasExplicitReturn = /\breturn\b/.test(code)
+      const wrappedCode = autoReturn
+        ? `(async () => { return await (${code}) })()`
+        : `(async () => { ${code} })()`
+      const hasExplicitReturn = autoReturn || /\breturn\b/.test(code)
 
       const result = await Promise.race([
         vm.runInContext(wrappedCode, vmContext, { timeout, displayErrors: true }),

playwriter/src/executor.unit.test.ts

@@ -0,0 +1,90 @@
+import { describe, it, expect } from 'vitest'
+import { shouldAutoReturn } from './executor.js'
+
+describe('shouldAutoReturn', () => {
+  it('returns true for simple expressions', () => {
+    expect(shouldAutoReturn('1 + 2')).toBe(true)
+    expect(shouldAutoReturn('page.title()')).toBe(true)
+    expect(shouldAutoReturn('await page.title()')).toBe(true)
+    expect(shouldAutoReturn('accessibilitySnapshot({ page })')).toBe(true)
+    expect(shouldAutoReturn('context.pages().map(p => p.url())')).toBe(true)
+  })
+
+  it('returns true for awaited expressions', () => {
+    expect(shouldAutoReturn('await Promise.resolve(42)')).toBe(true)
+    expect(shouldAutoReturn('await page.goto("https://example.com")')).toBe(true)
+  })
+
+  it('returns false for assignment expressions', () => {
+    expect(shouldAutoReturn('state.page = await context.newPage()')).toBe(false)
+    expect(shouldAutoReturn('const x = 1')).toBe(false)
+    expect(shouldAutoReturn('let y = 2')).toBe(false)
+    expect(shouldAutoReturn('x = 5')).toBe(false)
+  })
+
+  it('returns false for update expressions', () => {
+    expect(shouldAutoReturn('x++')).toBe(false)
+    expect(shouldAutoReturn('++x')).toBe(false)
+    expect(shouldAutoReturn('x--')).toBe(false)
+    expect(shouldAutoReturn('--x')).toBe(false)
+  })
+
+  it('returns false for delete expressions', () => {
+    expect(shouldAutoReturn('delete obj.prop')).toBe(false)
+  })
+
+  it('returns false for multiple statements', () => {
+    expect(shouldAutoReturn('const x = 1; x + 1')).toBe(false)
+    expect(shouldAutoReturn('await page.click("button"); await page.title()')).toBe(false)
+    expect(shouldAutoReturn('const a = 1\nconst b = 2')).toBe(false)
+  })
+
+  it('returns false for return statements', () => {
+    expect(shouldAutoReturn('return 5')).toBe(false)
+    expect(shouldAutoReturn('return await page.title()')).toBe(false)
+  })
+
+  it('returns false for non-expression statements', () => {
+    expect(shouldAutoReturn('if (true) { x }')).toBe(false)
+    expect(shouldAutoReturn('for (let i = 0; i < 10; i++) {}')).toBe(false)
+    expect(shouldAutoReturn('function foo() {}')).toBe(false)
+    expect(shouldAutoReturn('class Foo {}')).toBe(false)
+  })
+
+  it('returns false for invalid syntax', () => {
+    expect(shouldAutoReturn('const')).toBe(false)
+    expect(shouldAutoReturn('{')).toBe(false)
+    expect(shouldAutoReturn('await')).toBe(false)
+  })
+
+  it('handles edge cases', () => {
+    // Empty string
+    expect(shouldAutoReturn('')).toBe(false)
+    // Just whitespace
+    expect(shouldAutoReturn('   ')).toBe(false)
+    // Object literal (parsed as block)
+    expect(shouldAutoReturn('{ foo: 1 }')).toBe(false)
+    // Parenthesized object literal (expression)
+    expect(shouldAutoReturn('({ foo: 1 })')).toBe(true)
+    // Array literal
+    expect(shouldAutoReturn('[1, 2, 3]')).toBe(true)
+  })
+
+  it('handles sequence expressions with assignments', () => {
+    // Sequence with assignment should not auto-return
+    expect(shouldAutoReturn('(x = 1, x + 1)')).toBe(false)
+    // Sequence without assignment should auto-return
+    expect(shouldAutoReturn('(1, 2, 3)')).toBe(true)
+  })
+
+  it('handles comments in code', () => {
+    expect(shouldAutoReturn('// comment\npage.title()')).toBe(true)
+    expect(shouldAutoReturn('page.title() // comment')).toBe(true)
+    expect(shouldAutoReturn('/* block */ 42')).toBe(true)
+  })
+
+  it('handles template literals', () => {
+    expect(shouldAutoReturn('`hello`')).toBe(true)
+    expect(shouldAutoReturn('`hello ${name}`')).toBe(true)
+  })
+})

playwriter/src/skill.md

@@ -63,13 +63,13 @@ playwriter -s 1 -e "state.page = await context.newPage(); await state.page.goto(
 playwriter -s 1 -e "await page.click('button')"
 
 # Get page title
-playwriter -s 1 -e "console.log(await page.title())"
+playwriter -s 1 -e "await page.title()"
 
 # Take a screenshot
 playwriter -s 1 -e "await page.screenshot({ path: 'screenshot.png', scale: 'css' })"
 
 # Get accessibility snapshot
-playwriter -s 1 -e "console.log(await accessibilitySnapshot({ page }))"
+playwriter -s 1 -e "await accessibilitySnapshot({ page })"
 ```
 
 **Multiline code:**
@@ -167,7 +167,7 @@ Locators (especially ones with `>> nth=`) can change when the page updates. Alwa
 await page.locator('[id="old-id"]').click();  // element may have changed
 
 // GOOD: get fresh snapshot, then immediately use locators from it
-console.log(await accessibilitySnapshot({ page, showDiffSinceLastCall: true }));
+await accessibilitySnapshot({ page, showDiffSinceLastCall: true })
 // Now use the NEW locators from this output
 ```
 
@@ -229,7 +229,7 @@ await loginPage.waitForURL('**/callback**');
 After any action (click, submit, navigate), verify what happened:
 
 ```js
-console.log('url:', page.url()); console.log(await accessibilitySnapshot({ page }));
+page.url() + '\n' + await accessibilitySnapshot({ page })
 ```
 
 For visually complex pages (grids, galleries, dashboards), use `screenshotWithAccessibilityLabels({ page })` instead to understand spatial layout. Label refs are short `eN` strings (e.g. `e3`).
@@ -366,7 +366,7 @@ state.targetPage = pages[0];
 **List all available pages:**
 
 ```js
-console.log(context.pages().map(p => p.url()));
+context.pages().map(p => p.url())
 ```
 
 ## navigation

pnpm-lock.yaml

@@ -86,6 +86,9 @@ importers:
       '@xmorse/cac':
         specifier: ^6.0.7
         version: 6.0.7
+      acorn:
+        specifier: ^8.15.0
+        version: 8.15.0
       async-sema:
         specifier: ^3.1.1
         version: 3.1.1