Upvars are now marked with def_upvar throughout, not just when going
through freevars::lookup_def. This makes things less error-prone. One
thing to watch out for is that def_upvar is used in `for each` bodies
too, when they refer to a local outside the body.
The logic for how the "returns" constraint was handled was always
dodgy, for reasons explained in the comments I added to
auxiliary::fn_info in this commit. Fixed it by adding distinct
"returns" and "diverges" constraints for each function, which
are both handled positively (that is: for a ! function, the
"diverges" constraint must be true on every exit path; for
any other function, the "returns" constraint must be true
on every exit path).
Closes#779
You can now say
let {bcx, val} = some_result_returner();
Similar for loop variables. Assigning to such variables is not safe
yet. Function arguments also remain a TODO.
There are still things not handled properly: relying on other preconditions
of upvars is likely to cause bad things to happen. We probably want to
disallow it.
This adds parser support and most of the machinery for
auto x = 10, y = 20;
However, the above still goes wrong somewhere in typestate, causing
the state checker to believe only the last variable in the list is
initialized after the statement.
Tim, if you have a moment, could you go over the changes to the tstate
code in this patch and see where I'm going wrong?
Multi-var-decls without the typestate extension
Add a loop
Programs with constrained types now parse and typecheck, but
typestate doesn't check them specially, so the one relevant test
case so far is XFAILed.
Also rewrote all of the constraint-related data structures in the
process (again), for some reason. I got rid of a superfluous
data structure in the context that was mapping front-end constraints
to resolved constraints, instead handling constraints in the same
way in which everything else gets resolved.
Assignments and moves with a simple local variable reference on the
RHS now propagate any typestate constraints the RHS was involved
in to the LHS. Swaps where both sides are local variables
exchange the constraints.
This was a pain in the butt and I'm still not proud of the resulting
code. Needs refactoring like whoa.
