Always return a value for public methods

[Tommo-L]

apply neo-project/neo#1706

• When create a public void method, compiler may return a Null.
• When call a void method, compiler need to drop the top value on the stack.

We may need to know the ABI of the invoked contract.

[erikzhang]

When create a public void method, compiler may return a Null.

This is wrong.

[Tommo-L]

Has already returned a null value in neo-core?

// neo.SmartContract.ApplicationEngine.cs
protected override void ContextUnloaded(ExecutionContext context)
{
      base.ContextUnloaded(context);
      if (CurrentContext != null && context.EvaluationStack != CurrentContext.EvaluationStack)
          if (context.EvaluationStack.Count == 0)
              Push(StackItem.Null);
}

[shargon]

Yes, we already return a null item with void

[ShawnYun]

But how does the compiler know the return type of the calling contract.

[erikzhang]

See neo-project/neo#1680 (comment)