From 5d7ad989a851398587a0349cdd15344769b4cd79 Mon Sep 17 00:00:00 2001
From: Peter Hedenskog <peter@soulgalore.com>
Date: Fri, 6 Sep 2019 21:41:09 +0200
Subject: [PATCH] feat: make it possible to merge configurations when extending
 other config. (#1411)

---
 docs/advanced.md                       |  3 +-
 lib/apply-extends.js                   | 18 ++++++++--
 test/fixtures/extends/config_deep.json | 12 +++++++
 test/yargs.js                          | 50 ++++++++++++++++++++++++++
 yargs.js                               |  4 +--
 5 files changed, 82 insertions(+), 5 deletions(-)
 create mode 100644 test/fixtures/extends/config_deep.json

diff --git a/docs/advanced.md b/docs/advanced.md
index 9605cc576..8a0bb2a1a 100644
--- a/docs/advanced.md
+++ b/docs/advanced.md
@@ -439,7 +439,8 @@ yargs.parserConfiguration({
   "camel-case-expansion": true,
   "dot-notation": true,
   "parse-numbers": true,
-  "boolean-negation": true
+  "boolean-negation": true,
+  "deep-merge-config": false
 })
 ```
 
diff --git a/lib/apply-extends.js b/lib/apply-extends.js
index 864567a61..20ded5e07 100644
--- a/lib/apply-extends.js
+++ b/lib/apply-extends.js
@@ -16,7 +16,21 @@ function getPathToDefaultConfig (cwd, pathToExtend) {
   return path.resolve(cwd, pathToExtend)
 }
 
-function applyExtends (config, cwd) {
+function mergeDeep (config1, config2) {
+  const target = {}
+  const isObject = obj => obj && typeof obj === 'object' && !Array.isArray(obj)
+  Object.assign(target, config1)
+  for (let key of Object.keys(config2)) {
+    if (isObject(config2[key]) && isObject(target[key])) {
+      target[key] = mergeDeep(config1[key], config2[key])
+    } else {
+      target[key] = config2[key]
+    }
+  }
+  return target
+}
+
+function applyExtends (config, cwd, mergeExtends) {
   let defaultConfig = {}
 
   if (Object.prototype.hasOwnProperty.call(config, 'extends')) {
@@ -47,7 +61,7 @@ function applyExtends (config, cwd) {
 
   previouslyVisitedConfigs = []
 
-  return Object.assign({}, defaultConfig, config)
+  return mergeExtends ? mergeDeep(defaultConfig, config) : Object.assign({}, defaultConfig, config)
 }
 
 module.exports = applyExtends
diff --git a/test/fixtures/extends/config_deep.json b/test/fixtures/extends/config_deep.json
new file mode 100644
index 000000000..d4e1bdbbf
--- /dev/null
+++ b/test/fixtures/extends/config_deep.json
@@ -0,0 +1,12 @@
+{
+  "a": {
+    "b": 15,
+    "c": 12,
+    "d": [1,2,3],
+    "e": [1],
+    "f": "yes"
+  },
+  "test": {
+    "yes": 1
+  }
+}
diff --git a/test/yargs.js b/test/yargs.js
index 29ba21454..8be9e7a28 100644
--- a/test/yargs.js
+++ b/test/yargs.js
@@ -1374,6 +1374,56 @@ describe('yargs dsl tests', () => {
         argv.c.should.equal(201)
         argv.z.should.equal(15)
       })
+
+      it('deep merge objects when extending when configured', () => {
+        const argv = yargs()
+          .parserConfiguration({ 'deep-merge-config': true })
+          .config({
+            extends: './test/fixtures/extends/config_deep.json',
+            a: {
+              b: 11,
+              d: [5, 2],
+              f: 'no',
+              g: {
+                h: 122
+              },
+              i: [1, 2]
+            }
+          })
+          .parse()
+
+        argv.a.b.should.equal(11)
+        argv.a.c.should.equal(12)
+        argv.a.d.should.deep.equal([5, 2])
+        argv.a.e.should.equal(1)
+        argv.a.f.should.equal('no')
+        argv.a.g.h.should.equal(122)
+        argv.a.i.should.deep.equal([1, 2])
+        argv.test.yes.should.equal(1)
+      })
+
+      it('do not merge objects by default when extending', () => {
+        const argv = yargs()
+          .config({
+            extends: './test/fixtures/extends/config_deep.json',
+            a: {
+              b: 11,
+              d: [5, 2],
+              f: 'no',
+              g: {
+                h: 122
+              }
+            }
+          })
+          .parse()
+
+        argv.a.b.should.equal(11)
+        argv.a.should.not.have.property('c')
+        argv.a.d.should.deep.equal([5, 2])
+        argv.a.should.not.have.property('e')
+        argv.a.f.should.equal('no')
+        argv.a.g.h.should.equal(122)
+      })
     })
   })
 
diff --git a/yargs.js b/yargs.js
index 794cf0255..a4ed28e5a 100644
--- a/yargs.js
+++ b/yargs.js
@@ -330,7 +330,7 @@ function Yargs (processArgs, cwd, parentRequire) {
     argsert('[object|string] [string|function] [function]', [key, msg, parseFn], arguments.length)
     // allow a config object to be provided directly.
     if (typeof key === 'object') {
-      key = applyExtends(key, cwd)
+      key = applyExtends(key, cwd, self.getParserConfiguration()['deep-merge-config'])
       options.configObjects = (options.configObjects || []).concat(key)
       return self
     }
@@ -504,7 +504,7 @@ function Yargs (processArgs, cwd, parentRequire) {
 
     // If an object exists in the key, add it to options.configObjects
     if (obj[key] && typeof obj[key] === 'object') {
-      conf = applyExtends(obj[key], rootPath || cwd)
+      conf = applyExtends(obj[key], rootPath || cwd, self.getParserConfiguration()['deep-merge-config'])
       options.configObjects = (options.configObjects || []).concat(conf)
     }