Repro PeepholeDeadCode + @closureUnaware crash

PiperOrigin-RevId: 856792483

Author: lauraharker

test/com/google/javascript/jscomp/TranspileAndOptimizeClosureUnawareTest.java

@@ -121,6 +121,30 @@ public void testFoldConstants_multipleClosureUnawareBlocksInFile() {
             expectedClosureUnaware("console.log(3);", "console.log(33);", "console.log(333);")));
   }
 
+  @Test
+  public void testFoldConstants_regressionTest_crashInNodeUtilAddFeatureToScript() {
+    setLanguageOut(CompilerOptions.LanguageMode.ECMASCRIPT_NEXT);
+
+    // TODO: b/421970620 - fix this crash.
+    assertThrows(
+        RuntimeException.class,
+        () ->
+            testSame(
+                closureUnaware(
+                    """
+                    return function f() {
+                      function referenceX() { return x; }
+
+                      return 1;
+
+                      // Regression test for a crash in PeepholeRemoveDeadCode.
+                      let x = 0;
+                      referenceX();
+                      x++;
+                    }
+                    """)));
+  }
+
   @Test
   public void testInlineLocalObject() {
     test(