Fix REPL crash when V8 emits warnings during preview mode (Issue #63473)

src/node_errors.cc

@@ -1064,7 +1064,18 @@ void PerIsolateMessageListener(Local<Message> message, Local<Value> error) {
                   filename,
                   message->GetLineNumber(env->context()).FromMaybe(-1),
                   msg);
-      USE(ProcessEmitWarningGeneric(env, warning, "V8"));
+      // If we're inside a DisallowJavascriptExecutionScope (e.g., REPL preview),
+      // defer the warning to the next event loop iteration when JS execution is
+      // allowed. This prevents crashes when V8 emits warnings during code
+      // evaluation with throwOnSideEffect.
+      if (!env->can_call_into_js()) {
+        std::string warning_str = warning;
+        env->SetImmediate([warning_str](Environment* env) {
+          ProcessEmitWarningGeneric(env, warning_str, "V8");
+        });
+      } else {
+        USE(ProcessEmitWarningGeneric(env, warning, "V8"));
+      }
       break;
     }
     case Isolate::MessageErrorLevel::kMessageError:

test/parallel/test-repl-asm-warning-no-crash.js

@@ -0,0 +1,67 @@
+'use strict';
+
+// Regression test for issue #63473:
+// When asm.js code is evaluated in the Node.js REPL with previews enabled,
+// V8 emits a deprecation warning inside a DisallowJavascriptExecutionScope.
+// This test verifies that the warning is deferred and the process does not crash.
+
+const common = require('../common');
+const assert = require('assert');
+const spawn = require('child_process').spawn;
+
+// asm.js code that may trigger a deprecation warning in V8
+const asmCode = `
+function asm(stdlib, foreign, heap) {
+  "use asm";
+  function f() { return 1; }
+  return { f: f };
+}
+asm(this, null, new ArrayBuffer(1024));
+`;
+
+const child = spawn(process.execPath, ['-i'], {
+  stdio: ['pipe', 'pipe', 'pipe'],
+});
+
+let stdout = '';
+let stderr = '';
+let crashed = false;
+
+child.stdout.setEncoding('utf8');
+child.stdout.on('data', (chunk) => {
+  stdout += chunk;
+  process.stdout.write(chunk);
+});
+
+child.stderr.setEncoding('utf8');
+child.stderr.on('data', (chunk) => {
+  stderr += chunk;
+  process.stderr.write(chunk);
+  // Check for crash indicators
+  if (chunk.includes('FATAL ERROR') || chunk.includes('Segmentation fault')) {
+    crashed = true;
+  }
+});
+
+// Feed the asm.js code to REPL via stdin
+child.stdout.once('data', function() {
+  child.stdin.write(asmCode);
+  child.stdin.write('\n');
+  setTimeout(() => {
+    child.stdin.end();
+  }, 500);
+});
+
+child.on('close', common.mustCall((exitCode) => {
+  // Most important: process should not crash (exit code 0 or normal termination)
+  assert.strictEqual(crashed, false, 'Process should not crash');
+  // In Node.js, exit code 0 is normal, but we also allow the process to exit
+  // naturally without a crash (which would have exit code 0)
+  // The main assertion is that it doesn't crash with FATAL ERROR or segfault
+  if (exitCode !== 0 && exitCode !== null) {
+    // Note: We only fail if there's clear evidence of a crash in stderr
+    if (stderr.includes('FATAL ERROR') || stderr.includes('Segmentation')) {
+      assert.fail(`Process crashed with exit code ${exitCode}\nstderr: ${stderr}`);
+    }
+  }
+}));