fix: help always displayed for the first command parsed having an asy…

…nc handler (#1535)

lib/command.js

@@ -256,6 +256,9 @@ module.exports = function command (yargs, usage, validation, globalMiddleware) {
             // fail's throwing would cause an unhandled rejection.
             }
           })
+          .then(() => {
+            yargs.getUsageInstance().clearCachedHelpMessage()
+          })
       } else {
         if (handlerFinishCommand) {
           handlerFinishCommand(handlerResult)

lib/usage.js

@@ -411,6 +411,12 @@ module.exports = function usage (yargs, y18n) {
     cachedHelpMessage = this.help()
   }
 
+  // however this snapshot must be cleared afterwards
+  // not to be be used by next calls to parse
+  self.clearCachedHelpMessage = function () {
+    cachedHelpMessage = undefined
+  }
+
   // given a set of keys, place any keys that are
   // ungrouped under the 'Options:' grouping.
   function addUngroupedKeys (keys, aliases, groups) {

test/helpers/utils.js

@@ -34,8 +34,7 @@ exports.checkOutput = function checkOutput (f, argv, cb) {
     }
     process.emit = function emit (ev, value) {
       if (ev === 'uncaughtException') {
-        done()
-        cb(value)
+        cb(value, done())
         return true
       }
 

test/usage.js

@@ -8,7 +8,7 @@ const yargs = require('../')
 const rebase = require('../yargs').rebase
 const YError = require('../lib/yerror')
 
-require('chai').should()
+const should = require('chai').should()
 
 const noop = () => {}
 
@@ -3430,4 +3430,76 @@ describe('usage tests', () => {
       ])
     })
   })
+
+  describe('help message caching', () => {
+    it('should display proper usage when an async handler fails', (done) => {
+      const y = yargs()
+        .command('cmd', 'test command', {}, () => {
+          return new Promise((resolve, reject) =>
+            setTimeout(reject, 10)
+          )
+        })
+        .exitProcess(false)
+
+      checkUsage(
+        () => {
+          y.parse('cmd')
+          setTimeout(() => process.exit(1), 100)
+        },
+        undefined,
+        (err, r) => {
+          should.not.exist(err)
+          should.exist(r.errors[0])
+          r.errors[0].split('\n').should.deep.equal([
+            '_mocha cmd',
+            '',
+            'test command',
+            '',
+            'Options:',
+            '  --help     Show help                                                 [boolean]',
+            '  --version  Show version number                                       [boolean]'
+          ])
+          done()
+        }
+      )
+    })
+
+    it('should not display a cached help message for the next parsing', (done) => {
+      const y = yargs()
+        .command('cmd', 'test command', {}, () => {
+          return new Promise((resolve, reject) =>
+            setTimeout(resolve, 10)
+          )
+        })
+        .demandCommand(1, 'You need at least one command before moving on')
+        .exitProcess(false)
+
+      checkUsage(
+        () => {
+          y.parse('cmd')
+          setTimeout(() => {
+            y.parse('')
+            setTimeout(() => process.exit(1), 100)
+          }, 100)
+        },
+        undefined,
+        (err, r) => {
+          should.exist(err)
+          err.message.should.equal('You need at least one command before moving on')
+          should.exist(r.errors[0])
+          r.errors[0].split('\n').should.deep.equal([
+            '_mocha <command>',
+            '',
+            'Commands:',
+            '  _mocha cmd  test command',
+            '',
+            'Options:',
+            '  --help     Show help                                                 [boolean]',
+            '  --version  Show version number                                       [boolean]'
+          ])
+          done()
+        }
+      )
+    })
+  })
 })