From 5fcc6ece9eb15a451283c84f9d79f1b64fd82644 Mon Sep 17 00:00:00 2001
From: James Diefenderfer <james.diefenderfer@salesforce.com>
Date: Thu, 13 Aug 2020 15:17:11 -0700
Subject: [PATCH] fix: correctly handle arrays in snapshot deep merge

---
 CHANGELOG.md                                  |  1 +
 .../jest-snapshot/src/__tests__/utils.test.ts | 44 +++++++++++++++++++
 packages/jest-snapshot/src/utils.ts           | 10 ++++-
 3 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9a56057e52a0..dd0ebbcf853a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Fixes
 
 - `[jest-reporters]` Fixes notify reporter on Linux (using notify-send) ([#10393](https://github.com/facebook/jest/pull/10400))
+- `[jest-snapshot]` Correctly handles arrays and property matchers in snapshots ([#10404](https://github.com/facebook/jest/pull/10404))
 
 ### Chore & Maintenance
 
diff --git a/packages/jest-snapshot/src/__tests__/utils.test.ts b/packages/jest-snapshot/src/__tests__/utils.test.ts
index 573b8cb54308..49f6c005a3fc 100644
--- a/packages/jest-snapshot/src/__tests__/utils.test.ts
+++ b/packages/jest-snapshot/src/__tests__/utils.test.ts
@@ -419,6 +419,50 @@ describe('DeepMerge with property matchers', () => {
         },
       },
     ],
+
+    [
+      'an array of objects',
+      // Target
+      [
+        {name: 'one'},
+        {name: 'two'},
+        {name: 'three'},
+      ],
+      // Matchers
+      [
+        {name: 'one'},
+        {name: matcher},
+        {name: matcher},
+      ],
+      // Expected
+      [
+        {name: 'one'},
+        {name: matcher},
+        {name: matcher},
+      ],
+    ],
+
+    [
+      'an array of arrays',
+      // Target
+      [
+        ['one'],
+        ['two'],
+        ['three'],
+      ],
+      // Matchers
+      [
+        ['one'],
+        [matcher],
+        [matcher],
+      ],
+      // Expected
+      [
+        ['one'],
+        [matcher],
+        [matcher],
+      ],
+    ],
   ];
   /* eslint-enable sort-keys */
 
diff --git a/packages/jest-snapshot/src/utils.ts b/packages/jest-snapshot/src/utils.ts
index a0ddb4e33268..da5867ce2121 100644
--- a/packages/jest-snapshot/src/utils.ts
+++ b/packages/jest-snapshot/src/utils.ts
@@ -231,8 +231,9 @@ const deepMergeArray = (target: Array<any>, source: Array<any>) => {
 
 // eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export const deepMerge = (target: any, source: any): any => {
-  const mergedOutput = {...target};
   if (isObject(target) && isObject(source)) {
+    const mergedOutput = {...target};
+
     Object.keys(source).forEach(key => {
       if (isObject(source[key]) && !source[key].$$typeof) {
         if (!(key in target)) Object.assign(mergedOutput, {[key]: source[key]});
@@ -243,6 +244,11 @@ export const deepMerge = (target: any, source: any): any => {
         Object.assign(mergedOutput, {[key]: source[key]});
       }
     });
+
+    return mergedOutput;
+  } else if (Array.isArray(target) && Array.isArray(source)) {
+    return deepMergeArray(target, source);
   }
-  return mergedOutput;
+
+  return target;
 };