From 8b18cd0ab29bb2743aa2d4d7aac0dd59539c43dd Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna.henningsen@mongodb.com>
Date: Tue, 27 Apr 2021 11:54:37 +0200
Subject: [PATCH] fix(history): do not modify empty history MONGOSH-722

---
 packages/cli-repl/src/mongosh-repl.spec.ts | 7 +++++++
 packages/history/src/history.spec.ts       | 6 ++++++
 packages/history/src/history.ts            | 1 +
 3 files changed, 14 insertions(+)

diff --git a/packages/cli-repl/src/mongosh-repl.spec.ts b/packages/cli-repl/src/mongosh-repl.spec.ts
index 1d2a38a883..b59e611c43 100644
--- a/packages/cli-repl/src/mongosh-repl.spec.ts
+++ b/packages/cli-repl/src/mongosh-repl.spec.ts
@@ -415,6 +415,13 @@ describe('MongoshNodeRepl', () => {
               'const a = 20'
             ]);
           });
+
+          it('does not crash if hitting enter and then up', async() => {
+            input.write('\n');
+            await once(mongoshRepl.runtimeState().repl, 'flushHistory');
+            input.write(`${arrowUp}`);
+            await tick();
+          });
         });
       }
     });
diff --git a/packages/history/src/history.spec.ts b/packages/history/src/history.spec.ts
index 1ee98757f6..ffe50a6b58 100644
--- a/packages/history/src/history.spec.ts
+++ b/packages/history/src/history.spec.ts
@@ -33,6 +33,12 @@ describe('changeHistory', () => {
       changeHistory(cloned);
       expect(cloned).to.deep.equal(i);
     });
+
+    it('does not modify an empty history', () => {
+      const i: string[] = [];
+      changeHistory(i);
+      expect(i).to.deep.equal([]);
+    });
   });
 
   context('when redact option is false', () => {
diff --git a/packages/history/src/history.ts b/packages/history/src/history.ts
index b5c258c3a6..e67192533a 100644
--- a/packages/history/src/history.ts
+++ b/packages/history/src/history.ts
@@ -17,6 +17,7 @@ export function removeCommand(history: string, redact = false): string {
  * @param {boolean} redact - Option to redact sensitive info.
  */
 export function changeHistory(history: string[], redact = false): void {
+  if (history.length === 0) return;
   const hiddenCommands = new RegExp(HIDDEN_COMMANDS, 'g');
 
   if (hiddenCommands.test(history[0])) {