jjs> (function x(x){})
Exception in thread "main" java.lang.AssertionError
   at jdk.nashorn.internal.codegen.AssignSymbols.enterFunctionBody(AssignSymbols.java:494)
   at jdk.nashorn.internal.codegen.AssignSymbols.enterBlock(AssignSymbols.java:453)
   at jdk.nashorn.internal.ir.Block.accept(Block.java:177)
   at jdk.nashorn.internal.ir.LexicalContextNode$Acceptor.accept(LexicalContextNode.java:57)
   at jdk.nashorn.internal.ir.Block.accept(Block.java:425)
   at jdk.nashorn.internal.ir.FunctionNode.accept(FunctionNode.java:384)
   at jdk.nashorn.internal.ir.LexicalContextNode$Acceptor.accept(LexicalContextNode.java:57)
   at jdk.nashorn.internal.ir.LexicalContextExpression.accept(LexicalContextExpression.java:47)
   at jdk.nashorn.internal.ir.FunctionNode.accept(FunctionNode.java:59)
   at jdk.nashorn.internal.ir.BinaryNode.accept(BinaryNode.java:347)
   ...