From d70fe1dd5a839211d01705fc178c15d170aa27c5 Mon Sep 17 00:00:00 2001
From: Aditya Jain <adityaj0714@gmail.com>
Date: Tue, 25 Aug 2026 01:19:30 -0700
Subject: [PATCH] fix(cli): --yes mode requires a TTY when a request's default
 is falsy
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CliIoHost.resolveRequest's auto-respond path checked `if (msg.defaultResponse)`
before returning the default in --yes/autoRespond mode. A falsy-but-defined
default (empty string '', or 0) fails that truthy check, so the code falls
through past the auto-respond block to the isTTY check and throws
TtyNotAttached instead of returning the default — even though --yes was
passed specifically to avoid needing a TTY.

This is user-visible today: the resource-import prompt (importer.ts) and the
SDK MFA-token prompt (awscli-compatible.ts) both pass an empty-string
defaultResponse, so `cdk import --yes` (or any non-interactive/CI run hitting
these prompts) aborts with TtyNotAttached instead of silently taking the
default, unlike NonInteractiveIoHost's equivalent codepath which returns the
default unconditionally.

Fixes #1891
---
 .../aws-cdk/lib/cli/io-host/cli-io-host.ts    |  2 +-
 .../test/cli/io-host/cli-io-host.test.ts      | 31 +++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/packages/aws-cdk/lib/cli/io-host/cli-io-host.ts b/packages/aws-cdk/lib/cli/io-host/cli-io-host.ts
index 768c76c7d..90c13b796 100644
--- a/packages/aws-cdk/lib/cli/io-host/cli-io-host.ts
+++ b/packages/aws-cdk/lib/cli/io-host/cli-io-host.ts
@@ -1003,7 +1003,7 @@ export class CliIoHost implements IIoHost, ObservableIoHost {
         }
 
         // respond with the default for all other messages
-        if (msg.defaultResponse) {
+        if (msg.defaultResponse !== undefined) {
           await this.writeMessage({
             ...msg,
             message: `${chalk.cyan(msg.message)} (auto-responded with default: ${util.format(msg.defaultResponse)})`,
diff --git a/packages/aws-cdk/test/cli/io-host/cli-io-host.test.ts b/packages/aws-cdk/test/cli/io-host/cli-io-host.test.ts
index d03d1af2a..087468280 100644
--- a/packages/aws-cdk/test/cli/io-host/cli-io-host.test.ts
+++ b/packages/aws-cdk/test/cli/io-host/cli-io-host.test.ts
@@ -1336,6 +1336,37 @@ describe('CliIoHost', () => {
         }));
         expect(response).toBe('foobar');
       });
+
+      test('falsy defaults (empty string, zero) are auto-responded instead of requiring a TTY', async () => {
+        const nonTtyAutoRespondingIoHost = CliIoHost.instance({
+          logLevel: 'trace',
+          autoRespond: true,
+          isCI: false,
+          isTTY: false,
+        }, true);
+
+        // empty string default
+        const stringResponse = await nonTtyAutoRespondingIoHost.requestResponse(plainMessage({
+          time: new Date(),
+          level: 'info',
+          action: 'synth',
+          code: 'CDK_TOOLKIT_I5060',
+          message: 'test message',
+          defaultResponse: '',
+        }));
+        expect(stringResponse).toBe('');
+
+        // zero default
+        const numberResponse = await nonTtyAutoRespondingIoHost.requestResponse(plainMessage({
+          time: new Date(),
+          level: 'info',
+          action: 'synth',
+          code: 'CDK_TOOLKIT_I0001',
+          message: 'test message',
+          defaultResponse: 0,
+        }));
+        expect(numberResponse).toBe(0);
+      });
     });
 
     describe('non-promptable data', () => {