Return type inference

[Tobias Pankrath]

This does not work and I can see why.

---
auto foo(int x)
{
          if(x < 0)
              return foo(-x);
          return x;
}
----

DMD 2.059 says:
oopsc/compiler/test.d(7): Error: forward reference to foo
oopsc/compiler/test.d(14): Error: forward reference to foo

For the human reader it is easy to see that the return type of
foo should be int. Could the following rule be added to make dmd
see this, too?

> If there are multiple ReturnStatements, the types of them must 
> match exactly. If there are no ReturnStatements, the return 
> type is inferred to be void.
> <new>
> If the function is called recursively the type of the result of 
> this call is inferred in the same way. If the recursive call is 
> part of a return statement >  then this statement is not 
> considered for type inference. If all return statements are 
> discarded in this way, it is an error.