From 7ba00683715457fa26575c34bf34168900c055d5 Mon Sep 17 00:00:00 2001
From: Matteo Pagliazzi <matteopagliazzi@gmail.com>
Date: Sat, 12 May 2018 19:02:36 +0200
Subject: [PATCH 1/2] feat(error): add modified paths to VersionError

backport #6464 to 4.x
---
 lib/error/version.js    | 6 ++++--
 lib/model.js            | 5 ++++-
 test/versioning.test.js | 1 +
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/lib/error/version.js b/lib/error/version.js
index 33d1bd88e66..8386aefb474 100644
--- a/lib/error/version.js
+++ b/lib/error/version.js
@@ -13,11 +13,13 @@ var MongooseError = require('./');
  * @api private
  */
 
-function VersionError(doc, currentVersion) {
+function VersionError(doc, currentVersion, modifiedPaths) {
+  var modifiedPathsStr = modifiedPaths.join(', ');
   MongooseError.call(this, 'No matching document found for id "' + doc._id +
-    '" version ' + currentVersion);
+    '" version ' + currentVersion + 'modifiedPaths "' + modifiedPathsStr + '"');
   this.name = 'VersionError';
   this.version = currentVersion;
+  this.modifiedPaths = modifiedPaths;
 }
 
 /*!
diff --git a/lib/model.js b/lib/model.js
index e502bc8479f..f0ba6eb4324 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -229,6 +229,9 @@ Model.prototype.$__save = function(options, callback) {
       });
     }
 
+    // store the modified paths before the document is reset
+    var modifiedPaths = _this.modifiedPaths();
+
     _this.$__reset();
 
     var numAffected = 0;
@@ -263,7 +266,7 @@ Model.prototype.$__save = function(options, callback) {
 
       if (numAffected <= 0) {
         // the update failed. pass an error back
-        var err = new VersionError(_this, version);
+        var err = new VersionError(_this, version, modifiedPaths);
         return callback(err);
       }
 
diff --git a/test/versioning.test.js b/test/versioning.test.js
index 4e6856c8b08..4fa34acd7c9 100644
--- a/test/versioning.test.js
+++ b/test/versioning.test.js
@@ -266,6 +266,7 @@ describe('versioning', function() {
       assert.ok(/No matching document/.test(err), err);
       assert.equal(a._doc.__v, 5);
       assert.equal(err.version, b._doc.__v - 1);
+      assert.deepEqual(err.modifiedPaths, ['numbers', 'numbers.2']);
       a.set('arr.0.0', 'updated');
       var d = a.$__delta();
       assert.equal(a._doc.__v, d[0].__v, 'version should be added to where clause');

From 5046cef4393b3a705ab36ddfdf08569a232aaddd Mon Sep 17 00:00:00 2001
From: Sean Lavine <freewil@users.noreply.github.com>
Date: Mon, 20 Aug 2018 11:57:38 -0700
Subject: [PATCH 2/2] fix str spacing

---
 lib/error/version.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/error/version.js b/lib/error/version.js
index 8386aefb474..eed37fd5888 100644
--- a/lib/error/version.js
+++ b/lib/error/version.js
@@ -16,7 +16,7 @@ var MongooseError = require('./');
 function VersionError(doc, currentVersion, modifiedPaths) {
   var modifiedPathsStr = modifiedPaths.join(', ');
   MongooseError.call(this, 'No matching document found for id "' + doc._id +
-    '" version ' + currentVersion + 'modifiedPaths "' + modifiedPathsStr + '"');
+    '" version ' + currentVersion + ' modifiedPaths "' + modifiedPathsStr + '"');
   this.name = 'VersionError';
   this.version = currentVersion;
   this.modifiedPaths = modifiedPaths;