fix: cy.log() inside cy.then() doesn't break subject value in command chain. (#9372)

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

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

@@ -72,6 +72,18 @@ describe('src/cy/commands/misc', () => {
           })
         })
       })
+
+      // https://github.com/cypress-io/cypress/issues/8084
+      it('log does not corrupt the stack and returns subject correctly', () => {
+        cy.wrap({ a: 42 }).then(async (data) => {
+          cy.log('count', Object.keys(data).length)
+          cy.log('another log')
+
+          return await Object.keys(data).length
+        }).then((test) => {
+          expect(test).to.eq(1)
+        })
+      })
     })
   })
 

packages/driver/src/cy/commands/misc.js

@@ -4,7 +4,7 @@ const Promise = require('bluebird')
 const $dom = require('../../dom')
 const $errUtils = require('../../cypress/error_utils')
 
-module.exports = (Commands, Cypress, cy) => {
+module.exports = (Commands, Cypress, cy, state) => {
   Commands.addAll({ prevSubject: 'optional' }, {
     end () {
       return null
@@ -17,6 +17,22 @@ module.exports = (Commands, Cypress, cy) => {
     },
 
     log (msg, args) {
+      // https://github.com/cypress-io/cypress/issues/8084
+      // The return value of cy.log() corrupts the command stack, so cy.then() returned the wrong value
+      // when cy.log() is used inside it.
+      // The code below restore the stack when cy.log() is injected in cy.then().
+      if (state('current').get('injected')) {
+        const restoreCmdIndex = state('index') + 1
+
+        cy.queue.splice(restoreCmdIndex, 0, {
+          args: [state('subject')],
+          name: 'log-restore',
+          fn: (subject) => subject,
+        })
+
+        state('index', restoreCmdIndex)
+      }
+
       Cypress.log({
         end: true,
         snapshot: true,

packages/driver/src/cypress/cy.js

@@ -1099,8 +1099,9 @@ const create = function (specWindow, Cypress, Cookies, state, config, log) {
         // dont enqueue / inject any new commands if
         // onInjectCommand returns false
         const onInjectCommand = state('onInjectCommand')
+        const injected = _.isFunction(onInjectCommand)
 
-        if (_.isFunction(onInjectCommand)) {
+        if (injected) {
           if (onInjectCommand.call(cy, name, ...args) === false) {
             return
           }
@@ -1112,6 +1113,7 @@ const create = function (specWindow, Cypress, Cookies, state, config, log) {
           type,
           chainerId,
           userInvocationStack,
+          injected,
           fn: wrap(firstCall),
         })