I think I have an inference algorithm that works. It can infer
the required scope levels for local variables given the
constraints of function parameters, and it can even infer the
annotations for the parameters (in template functions). It can
also cope with local variables that are explicitly declared as
`scope`, though these are mostly unnecessary.
Interestingly, the rvalue/lvalue problem deadalnix found is only
relevant during assignment checking, but not during inference.
That's because we are free to widen the scope of variables that
are to be inferred as needed.
It's based on two principles:
* We start with the minimum possible scope a variable may have,
which is empty for local variables, and its own lifetime for
parameters.
* When a scoped value is stored somewhere, it is then reachable
through the destination. Therefore, assuming the source's scope
is fixed, the destination's scope must be widened to accommodate
the source's scope.
* From the opposite viewpoint, a value that is to be stored
somewhere must have at least the destination's scope. Therefore,
assuming the destination's scope is fixed, the source's scope
needs to be widened accordingly.
I haven't formalized it yet, but I posted a very detailed
step-by-step demonstration on my wiki talk page (nicer to read
because it has syntax highlighting):
http://wiki.dlang.org/User_talk:Schuetzm/scope2
I will also add examples how return and static annotations are
handled.
