From e778e36221a7d5a974db1c7cfff343bc0a0c21e5 Mon Sep 17 00:00:00 2001
From: Unknown <captain@mikeddavidson.com>
Date: Wed, 6 Sep 2017 18:09:34 -0400
Subject: [PATCH] fix: only run coercion functions once, despite aliases. (#76)

---
 index.js             | 20 ++++++++++++++------
 test/yargs-parser.js | 19 +++++++++++++++++++
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/index.js b/index.js
index 2ab9c2cc..6e5daff0 100644
--- a/index.js
+++ b/index.js
@@ -513,13 +513,21 @@ function parse (args, opts) {
 
   function applyCoercions (argv) {
     var coerce
+    var applied = {}
     Object.keys(argv).forEach(function (key) {
-      coerce = checkAllAliases(key, flags.coercions)
-      if (typeof coerce === 'function') {
-        try {
-          argv[key] = coerce(argv[key])
-        } catch (err) {
-          error = err
+      if (applied.hasOwnProperty(key)) { // If we already coerced this option via one of its aliases
+        argv[key] = applied[key]
+      } else {
+        coerce = checkAllAliases(key, flags.coercions)
+        if (typeof coerce === 'function') {
+          try {
+            var value = coerce(argv[key])
+            ;([].concat(flags.aliases[key] || [], key)).forEach(ali => {
+              applied[ali] = argv[ali] = value
+            })
+          } catch (err) {
+            error = err
+          }
         }
       }
     })
diff --git a/test/yargs-parser.js b/test/yargs-parser.js
index fa296b6c..79b52377 100644
--- a/test/yargs-parser.js
+++ b/test/yargs-parser.js
@@ -2429,6 +2429,25 @@ describe('yargs-parser', function () {
       })
       parsed.error.message.should.equal('foo is array: true')
     })
+
+    // see: https://github.com/yargs/yargs-parser/issues/76
+    it('only runs coercion functions once, even with aliases', function () {
+      var runcount = 0
+      var func = (arg) => {
+        runcount++
+        return undefined
+      }
+      parser([ '--foo', 'bar' ], {
+        alias: {
+          foo: ['f', 'foo-bar', 'bar'],
+          b: ['bar']
+        },
+        coerce: {
+          bar: func
+        }
+      })
+      runcount.should.equal(1)
+    })
   })
 
   // see: https://github.com/yargs/yargs-parser/issues/37