fix: cy.task() can pass undefined as default argument. (#8600)

Co-authored-by: Gleb Bahmutov <gleb.bahmutov@gmail.com>

packages/driver/cypress/integration/commands/task_spec.js

@@ -38,6 +38,10 @@ describe('src/cy/commands/task', () => {
       cy.task('return:arg', 'works').should('eq', 'works')
     })
 
+    it('returns the default value when no argument is given', () => {
+      cy.task('arg:is:undefined').should('eq', 'arg was undefined')
+    })
+
     describe('.log', () => {
       beforeEach(function () {
         this.logs = []
@@ -205,7 +209,7 @@ describe('src/cy/commands/task', () => {
           expect(lastLog.get('error')).to.eq(err)
           expect(lastLog.get('state')).to.eq('failed')
 
-          expect(err.message).to.eq(`\`cy.task('bar')\` failed with the following error:\n\nThe task 'bar' was not handled in the plugins file. The following tasks are registered: return:arg, wait, create:long:file\n\nFix this in your plugins file here:\n${Cypress.config('pluginsFile')}\n\nhttps://on.cypress.io/api/task`)
+          expect(err.message).to.eq(`\`cy.task('bar')\` failed with the following error:\n\nThe task 'bar' was not handled in the plugins file. The following tasks are registered: return:arg, arg:is:undefined, wait, create:long:file\n\nFix this in your plugins file here:\n${Cypress.config('pluginsFile')}\n\nhttps://on.cypress.io/api/task`)
 
           done()
         })

packages/driver/cypress/plugins/index.js

@@ -38,6 +38,13 @@ module.exports = (on) => {
     'return:arg' (arg) {
       return arg
     },
+    'arg:is:undefined' (arg) {
+      if (arg === undefined) {
+        return 'arg was undefined'
+      }
+
+      throw new Error(`Expected arg to be undefined, but it was ${arg}`)
+    },
     'wait' () {
       return Promise.delay(2000)
     },

packages/server/lib/plugins/child/task.js

@@ -32,7 +32,13 @@ const merge = (prevEvents, events) => {
 
 const wrap = (ipc, events, ids, args) => {
   const task = args[0]
-  const arg = args[1]
+  let arg = args[1]
+
+  // ipc converts undefined to null.
+  // we're restoring it.
+  if (arg && arg.__cypress_task_no_argument__) {
+    arg = undefined
+  }
 
   const invoke = (eventId, args = []) => {
     const handler = _.get(events, `${eventId}.handler.${task}`)

packages/server/lib/plugins/index.js

@@ -119,6 +119,14 @@ const init = (config, options) => {
               invocationId,
             }
 
+            // no argument is passed for cy.task()
+            // This is necessary because undefined becomes null when it is sent through ipc.
+            if (args[1] === undefined) {
+              args[1] = {
+                __cypress_task_no_argument__: true,
+              }
+            }
+
             ipc.send('execute', registration.event, ids, args)
           })
         })