JS: Ensure ParseError instead of CastError for malformed patterns

Author: asgerf

javascript/extractor/src/com/semmle/jcorn/Parser.java

@@ -2359,6 +2359,7 @@ protected List<Expression> toAssignableList(List<Expression> exprList, boolean i
       } else if (last != null && last instanceof SpreadElement) {
         Expression arg = ((SpreadElement) last).getArgument();
         arg = (Expression) this.toAssignable(arg, isBinding);
+        if (!(arg instanceof IPattern)) this.unexpected(arg.getLoc().getStart());
         exprList.set(end - 1, last = new RestElement(last.getLoc(), arg));
         --end;
       }

javascript/extractor/test/com/semmle/js/extractor/test/RobustnessTests.java

@@ -1,11 +1,14 @@
 package com.semmle.js.extractor.test;
 
+import com.semmle.jcorn.CustomParser;
 import com.semmle.jcorn.Options;
 import com.semmle.jcorn.Parser;
+import com.semmle.jcorn.SyntaxError;
 import com.semmle.util.io.WholeIO;
 import com.semmle.util.tests.TestPaths;
 import java.io.File;
 import java.nio.charset.StandardCharsets;
+import org.junit.Assert;
 import org.junit.Test;
 
 public class RobustnessTests {
@@ -30,4 +33,15 @@ public void permissiveDestructuringTest() {
             + "({ method(...{ value },) {} });\n";
     new Parser(new Options(), src, 0).parse();
   }
+
+  @Test
+  public void parenthesizedRestParameterTest() {
+    try {
+      new CustomParser(new Options().preserveParens(true), "async(...(x)) => x", 0)
+          .parse();
+      Assert.fail("Expected syntax error, but parsing succeeded.");
+    } catch (SyntaxError expected) {
+      Assert.assertEquals("Unexpected token (1:9)", expected.getMessage());
+    }
+  }
 }