feat: Add DEC mode 2026 support (Synchronized Output) to Jest (#15008)

This commit introduces support for DEC private mode 2026, also known as Synchronized Output, to DefaultReporter. The Synchronized Output mode is a terminal feature that helps mitigate screen tearing effects that can occur when the terminal is rendering output while the application is still writing to the screen.

Two new methods have been added to the DefaultReporter:

- `__beginSynchronizedUpdate`: This method sends the control sequence to enable Synchronized Output mode to the terminal.
- `__endSynchronizedUpdate`: This method sends the control sequence to disable Synchronized Output mode to the terminal.

These methods are called before and after the reporter updates the status, respectively. By doing this, we ensure that the terminal renders a consistent state of the screen for each status update, even if we're writing to the screen frequently.

Read more: https://gist.github.com/christianparpart/d8a62cc1ab659194337d73e399004036

CHANGELOG.md

@@ -22,6 +22,7 @@
 - `[@jest/fake-timers]` Exposing new modern timers function `advanceTimersToFrame()` which advances all timers by the needed milliseconds to execute callbacks currently scheduled with `requestAnimationFrame` ([#14598](https://github.com/jestjs/jest/pull/14598))
 - `[jest-matcher-utils]` Add `SERIALIZABLE_PROPERTIES` to allow custom serialization of objects ([#14893](https://github.com/jestjs/jest/pull/14893))
 - `[jest-mock]` Add support for the Explicit Resource Management proposal to use the `using` keyword with `jest.spyOn(object, methodName)` ([#14895](https://github.com/jestjs/jest/pull/14895))
+- `[jest-reporters]` Add support for [DEC mode 2026](https://gist.github.com/christianparpart/d8a62cc1ab659194337d73e399004036)
 - `[jest-runtime]` Exposing new modern timers function `jest.advanceTimersToFrame()` from `@jest/fake-timers` ([#14598](https://github.com/jestjs/jest/pull/14598))
 - `[jest-runtime]` Support `import.meta.filename` and `import.meta.dirname` (available from [Node 20.11](https://nodejs.org/en/blog/release/v20.11.0)) ([#14854](https://github.com/jestjs/jest/pull/14854))
 - `[jest-runtime]` Support `import.meta.resolve` ([#14930](https://github.com/jestjs/jest/pull/14930))

packages/jest-reporters/src/BaseReporter.ts

@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import type {WriteStream} from 'tty';
 import type {
   AggregatedResult,
   Test,
@@ -12,7 +13,7 @@ import type {
   TestContext,
   TestResult,
 } from '@jest/test-result';
-import {preRunMessage} from 'jest-util';
+import {isInteractive, preRunMessage} from 'jest-util';
 import type {Reporter, ReporterOnStartOptions} from './types';
 
 const {remove: preRunMessageRemove} = preRunMessage;
@@ -57,4 +58,16 @@ export default class BaseReporter implements Reporter {
   getLastError(): Error | undefined {
     return this._error;
   }
+
+  protected __beginSynchronizedUpdate(write: WriteStream['write']): void {
+    if (isInteractive) {
+      write('\u001B[?2026h');
+    }
+  }
+
+  protected __endSynchronizedUpdate(write: WriteStream['write']): void {
+    if (isInteractive) {
+      write('\u001B[?2026l');
+    }
+  }
 }

packages/jest-reporters/src/DefaultReporter.ts

@@ -53,8 +53,14 @@ export default class DefaultReporter extends BaseReporter {
     this.__wrapStdio(process.stdout);
     this.__wrapStdio(process.stderr);
     this._status.onChange(() => {
+      this.__beginSynchronizedUpdate(
+        this._globalConfig.useStderr ? this._err : this._out,
+      );
       this.__clearStatus();
       this.__printStatus();
+      this.__endSynchronizedUpdate(
+        this._globalConfig.useStderr ? this._err : this._out,
+      );
     });
   }
 
@@ -69,11 +75,17 @@ export default class DefaultReporter extends BaseReporter {
       buffer = [];
 
       // This is to avoid conflicts between random output and status text
+      this.__beginSynchronizedUpdate(
+        this._globalConfig.useStderr ? this._err : this._out,
+      );
       this.__clearStatus();
       if (string) {
         write(string);
       }
       this.__printStatus();
+      this.__endSynchronizedUpdate(
+        this._globalConfig.useStderr ? this._err : this._out,
+      );
 
       this._bufferedOutput.delete(flushBufferedOutput);
     };
@@ -194,9 +206,7 @@ export default class DefaultReporter extends BaseReporter {
       const testRetryReasons = testResult.retryReasons;
       if (testRetryReasons && testRetryReasons.length > 0) {
         this.log(
-          `${chalk.reset.inverse.bold.yellow(
-            ' LOGGING RETRY ERRORS ',
-          )} ${chalk.bold(testResult.fullName)}`,
+          `${chalk.reset.inverse.bold.yellow(' LOGGING RETRY ERRORS ')} ${chalk.bold(testResult.fullName)}`,
         );
         for (const [index, retryReasons] of testRetryReasons.entries()) {
           let {message, stack} = separateMessageFromStack(retryReasons);
@@ -219,11 +229,7 @@ export default class DefaultReporter extends BaseReporter {
     this.log(getResultHeader(result, this._globalConfig, config));
     if (result.console) {
       this.log(
-        `  ${TITLE_BULLET}Console\n\n${getConsoleOutput(
-          result.console,
-          config,
-          this._globalConfig,
-        )}`,
+        `  ${TITLE_BULLET}Console\n\n${getConsoleOutput(result.console, config, this._globalConfig)}`,
       );
     }
   }