chore: address @aorinevo's code review so that we can land

docs/advanced.md

@@ -478,6 +478,9 @@ const normalizeCredentials = (argv) => {
   }
   return {}
 }
+
+// Add normalizeCredentials to yargs
+yargs.middleware(normalizeCredentials)
 ```
 
 ### Example Async Credentials Middleware
@@ -496,6 +499,9 @@ const normalizeCredentials = (argv) => {
   }
   return {}
 }
+
+// Add normalizeCredentials to yargs
+yargs.middleware(normalizeCredentials)
 ```
 
 #### yargs parsing configuration
@@ -508,7 +514,7 @@ var argv = require('yargs')
                     .option('password')
       } ,(argv) => {
         authenticateUser(argv.username, argv.password)
-      }, 
+      },
       [normalizeCredentials]
      )
   .argv;

lib/command.js

@@ -1,6 +1,8 @@
 'use strict'
 
 const inspect = require('util').inspect
+const isPromise = require('./is-promise')
+const {applyMiddleware} = require('./middleware')
 const path = require('path')
 const Parser = require('yargs-parser')
 
@@ -232,24 +234,7 @@ module.exports = function command (yargs, usage, validation, globalMiddleware) {
 
       const middlewares = commandHandler.middlewares || []
 
-      innerArgv = middlewares
-        .reduce((accumulation, middleware) => {
-          if (isPromise(accumulation)) {
-            return accumulation
-              .then(initialObj =>
-                Promise.all([initialObj, middleware(initialObj)])
-              )
-              .then(([initialObj, middlewareObj]) =>
-                Object.assign(initialObj, middlewareObj)
-              )
-          } else {
-            const result = middleware(innerArgv)
-
-            return isPromise(result)
-              ? result.then(middlewareObj => Object.assign(accumulation, middlewareObj))
-              : Object.assign(accumulation, result)
-          }
-        }, innerArgv)
+      innerArgv = applyMiddleware(innerArgv, middlewares)
 
       const handlerResult = isPromise(innerArgv)
         ? innerArgv.then(argv => commandHandler.handler(argv))
@@ -449,7 +434,3 @@ module.exports = function command (yargs, usage, validation, globalMiddleware) {
 
   return self
 }
-
-function isPromise(maybePromise) {
-  return maybePromise instanceof Promise
-}

lib/is-promise.js

@@ -0,0 +1,3 @@
+module.exports = function isPromise (maybePromise) {
+  return maybePromise instanceof Promise
+}

lib/middleware.js

@@ -1,3 +1,5 @@
+const isPromise = require('./is-promise')
+
 module.exports = function (globalMiddleware, context) {
   return function (callback) {
     if (Array.isArray(callback)) {
@@ -8,3 +10,24 @@ module.exports = function (globalMiddleware, context) {
     return context
   }
 }
+
+module.exports.applyMiddleware = function (argv, middlewares) {
+  return middlewares
+    .reduce((accumulation, middleware) => {
+      if (isPromise(accumulation)) {
+        return accumulation
+          .then(initialObj =>
+            Promise.all([initialObj, middleware(initialObj)])
+          )
+          .then(([initialObj, middlewareObj]) =>
+            Object.assign(initialObj, middlewareObj)
+          )
+      } else {
+        const result = middleware(argv)
+
+        return isPromise(result)
+          ? result.then(middlewareObj => Object.assign(accumulation, middlewareObj))
+          : Object.assign(accumulation, result)
+      }
+    }, argv)
+}

test/command.js

@@ -1458,36 +1458,4 @@ describe('Command', () => {
       return done()
     })
   })
-
-  // addresses https://github.com/yargs/yargs/issues/1237
-  it('fails when the promise returned by the middleware rejects', (done) => {
-    const error = new Error()
-    const handlerErr = new Error('should not have been called')
-    yargs('foo')
-      .command('foo', 'foo command', noop, (yargs) => done(handlerErr), [ (yargs) => Promise.reject(error) ])
-      .fail((msg, err) => {
-        expect(msg).to.equal(null)
-        expect(err).to.equal(error)
-        done()
-      })
-      .argv
-  })
-
-  it('calls the command handler when all middleware promises resolve', (done) => {
-    const middleware = (key, value) => () => new Promise((resolve, reject) => {
-      setTimeout(() => {
-        return resolve({ [key]: value })
-      }, 5)
-    })
-    yargs('foo hello')
-      .command('foo <pos>', 'foo command', () => {}, (yargs) => {
-        yargs.hello.should.equal('world')
-        yargs.foo.should.equal('bar')
-        done()
-      }, [ middleware('hello', 'world'), middleware('foo', 'bar') ])
-      .fail((msg, err) => {
-        return done(Error('should not have been called'))
-      })
-      .argv
-  })
 })

test/middleware.js

@@ -1,6 +1,7 @@
 'use strict'
 /* global describe, it, beforeEach, afterEach */
 
+const {expect} = require('chai')
 const middlewareFactory = require('../lib/middleware')
 let yargs
 require('chai').should()
@@ -105,4 +106,38 @@ describe('middleware', () => {
       .exitProcess(false) // defaults to true.
       .parse()
   })
+
+  // addresses https://github.com/yargs/yargs/issues/1237
+  describe('async', () => {
+    it('fails when the promise returned by the middleware rejects', (done) => {
+      const error = new Error()
+      const handlerErr = new Error('should not have been called')
+      yargs('foo')
+        .command('foo', 'foo command', () => {}, (argv) => done(handlerErr), [ (argv) => Promise.reject(error) ])
+        .fail((msg, err) => {
+          expect(msg).to.equal(null)
+          expect(err).to.equal(error)
+          done()
+        })
+        .parse()
+    })
+
+    it('calls the command handler when all middleware promises resolve', (done) => {
+      const middleware = (key, value) => () => new Promise((resolve, reject) => {
+        setTimeout(() => {
+          return resolve({ [key]: value })
+        }, 5)
+      })
+      yargs('foo hello')
+        .command('foo <pos>', 'foo command', () => {}, (argv) => {
+          argv.hello.should.equal('world')
+          argv.foo.should.equal('bar')
+          done()
+        }, [ middleware('hello', 'world'), middleware('foo', 'bar') ])
+        .fail((msg, err) => {
+          return done(Error('should not have been called'))
+        })
+        .parse()
+    })
+  })
 })