Infinite recursion in macro expansion crashes rustc

[uwap]

Defining macros recursively like so

macro_rules! recursive(
  () => (
    recursive!()
  )
)

fn main() {
  recursive!()
}

will lead rustc to cause a stack overflow.
It would be useful to improve the error message for that problem.
There is currently no error message specified for that issue.

[kmcallister]

We already have a recursion_limit field in Session. We can copy it to libsyntax's ExpansionConfig and then track the recursion depth in ExtCtxt.

[fhahn]

I am looking into this issue. Howerver it seems like the same ExtCtxt and MacroExpander are used for macro expansion, so it seems like recursion depth cannot be tracked naively.

[kmcallister]

The ExtCtxt methods bt_push and bt_pop already maintain a sort of stack of macro invocations. They can also maintain a counter so that we don't have to walk that stack on every check (it's a kind of indirect linked list).

[donkopotamus]

@fhahn Now that recursion depth is limited, is there anyway to configure it from the command line? The current depth setting (64?) is too aggressive for some macro magic I am working on, that recurses heavily.