repl: add .clearhistory command

doc/api/repl.md

@@ -43,6 +43,8 @@ The following special commands are supported by all REPL instances:
   further input or processing of that expression.
 * `.clear`: Resets the REPL `context` to an empty object and clears any
   multi-line expression being input.
+* `.clearhistory`: Clears the REPL session history, both in memory and in the
+  persistent history file when one is configured.
 * `.exit`: Close the I/O stream, causing the REPL to exit.
 * `.help`: Show this list of special commands.
 * `.save`: Save the current REPL session to a file:

lib/internal/repl/history.js

@@ -418,6 +418,33 @@ class ReplHistory {
     return this[kCloseHandle]();
   }
 
+  /**
+   * Clears the in-memory history and truncates the persisted history file.
+   * @returns {Promise<void>}
+   */
+  async clearHistory() {
+    // Cancel any pending debounced flush so it cannot rewrite the file after
+    // the history has been cleared.
+    if (this[kTimer]) {
+      clearTimeout(this[kTimer]);
+      this[kTimer] = null;
+    }
+    this[kPending] = false;
+    this[kIsFlushing] = false;
+
+    this[kHistory].length = 0;
+    this[kIndex] = -1;
+    this[kContext].emit('history', this[kHistory]);
+
+    if (this[kHistoryHandle] !== null) {
+      try {
+        await this[kHistoryHandle].truncate(0);
+      } catch (err) {
+        debug('Error truncating history file:', err);
+      }
+    }
+  }
+
   [kReplHistoryMessage]() {
     if (this[kHistory].length === 0) {
       ReplHistory[kWriteToOutput](

lib/repl.js

@@ -1370,6 +1370,20 @@ function defineDefaultCommands(repl) {
     },
   });
 
+  repl.defineCommand('clearhistory', {
+    help: 'Clear the REPL session history',
+    action: function() {
+      this.clearBufferedCommand();
+      if (this.historyManager) {
+        this.historyManager.clearHistory();
+        this.output.write('Clearing history...\n');
+      } else {
+        this.output.write('History is not enabled for this REPL session\n');
+      }
+      this.displayPrompt();
+    },
+  });
+
   repl.defineCommand('exit', {
     help: 'Exit the REPL',
     action: function() {

test/parallel/test-repl-clearhistory.js

@@ -0,0 +1,52 @@
+'use strict';
+
+const common = require('../common');
+const { startNewREPLServer } = require('../common/repl');
+const assert = require('node:assert');
+const fs = require('node:fs');
+const path = require('node:path');
+
+const tmpdir = require('../common/tmpdir');
+tmpdir.refresh();
+
+// Tests the `.clearhistory` REPL command, which clears the in-memory history
+// and truncates the persisted history file.
+// Refs: https://github.com/nodejs/node/issues/63905
+
+// The command clears the in-memory history and resets the navigation index.
+{
+  const { replServer, input, output } = startNewREPLServer({ terminal: false });
+
+  replServer.history = ['const a = 1', 'a + 1', 'process.version'];
+  replServer.historyIndex = 2;
+
+  input.run(['.clearhistory']);
+
+  assert.strictEqual(replServer.history.length, 0);
+  assert.strictEqual(replServer.historyIndex, -1);
+  assert.match(output.accumulator, /Clearing history/);
+
+  replServer.close();
+}
+
+// The command truncates the persisted history file.
+{
+  const filePath = path.resolve(tmpdir.path, '.node_repl_history_clear');
+  fs.writeFileSync(filePath, 'const a = 1\na + 1\nprocess.version\n');
+
+  const { replServer, input } = startNewREPLServer({ terminal: false });
+
+  replServer.setupHistory({ filePath }, common.mustSucceed(() => {
+    assert.ok(replServer.history.length > 0);
+    assert.ok(fs.readFileSync(filePath, 'utf8').length > 0);
+
+    input.run(['.clearhistory']);
+    assert.strictEqual(replServer.history.length, 0);
+
+    // File truncation is asynchronous; await it before reading the file back.
+    replServer.historyManager.clearHistory().then(common.mustCall(() => {
+      assert.strictEqual(fs.readFileSync(filePath, 'utf8'), '');
+      replServer.close();
+    }));
+  }));
+}