From fdde971ccf9ac81724c9653c30d81aa1043ee87b Mon Sep 17 00:00:00 2001
From: Lucas Sanders <butterflyhug@google.com>
Date: Sat, 18 Mar 2017 22:49:28 -0400
Subject: [PATCH] Fix Duration#isValid after #add or #subtract

Also make the Duration#add and Duration#subtract implementations
internally immutable (so we don't need to wrap them for the
prototype).
---
 src/lib/duration/add-subtract.js    | 18 +++++++++++-------
 src/lib/duration/prototype.js       |  4 ++--
 src/test/moment/duration_invalid.js |  2 +-
 3 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/src/lib/duration/add-subtract.js b/src/lib/duration/add-subtract.js
index 3b44e186f..bfc1a3723 100644
--- a/src/lib/duration/add-subtract.js
+++ b/src/lib/duration/add-subtract.js
@@ -1,13 +1,17 @@
+import { isDuration } from './constructor';
 import { createDuration } from './create';
+import { createInvalid } from './valid';
 
 function addSubtract (duration, input, value, direction) {
-    var other = createDuration(input, value);
-
-    duration._milliseconds += direction * other._milliseconds;
-    duration._days         += direction * other._days;
-    duration._months       += direction * other._months;
-
-    return duration._bubble();
+    var other = isDuration(input) ? input : createDuration(input, value);
+    if (!duration.isValid() || !other.isValid()) {
+        return createInvalid();
+    }
+    return createDuration({
+        ms: duration._milliseconds + direction * other._milliseconds,
+        d:  duration._days         + direction * other._days,
+        M:  duration._months       + direction * other._months
+    });
 }
 
 // supports only 2.0-style add(1, 's') or add(duration)
diff --git a/src/lib/duration/prototype.js b/src/lib/duration/prototype.js
index 7eaca4461..ff6c70ae7 100644
--- a/src/lib/duration/prototype.js
+++ b/src/lib/duration/prototype.js
@@ -15,8 +15,8 @@ import { isValid } from './valid';
 
 proto.isValid        = isValid;
 proto.abs            = abs;
-proto.add            = wrap(Duration, add);
-proto.subtract       = wrap(Duration, subtract);
+proto.add            = add;
+proto.subtract       = subtract;
 proto.as             = as;
 proto.asMilliseconds = asMilliseconds;
 proto.asSeconds      = asSeconds;
diff --git a/src/test/moment/duration_invalid.js b/src/test/moment/duration_invalid.js
index 4b023a880..acfe3c02a 100644
--- a/src/test/moment/duration_invalid.js
+++ b/src/test/moment/duration_invalid.js
@@ -1,7 +1,7 @@
 import { module, test } from '../qunit';
 import moment from '../../moment';
 
-module('invalid');
+module('duration invalid');
 
 test('invalid duration', function (assert) {
     var m = moment.duration.invalid(); // should be invalid
-- 
2.47.2