Closes#868. Unfortunately, this causes certain invalid programs to
fail type-checking instead of failing type-state when a type-state
error message would probably be more intuitive. (Although, by any
reasonable interpretation of the static semantics, it technically
ought to be a type error.)
Autoderef on binops is basically unused, kind of silly, and
complicates typechecking. There were only three instances of it in the
compiler and the test drivers, two of which were of the form "*foo =
foo + 1", which should be written as "*foo += 1" anyways.
I tried to pay attention to what was actually being tested so, e.g. when I
test was just using a vec as a boxed thing, I converted to boxed ints, etc.
Haven't converted the macro tests yet. Not sure what to do there.
Previously, typestate was initializing the init constraint for
a declared-but-not-initialized variable (like x in "let x;") to False,
but other constraints to Don't-know. This led to over-lenient results
when a variable was used before declaration (see the included test
case). Now, everything gets initialized to False in the prestate/poststate-
finding phase, and Don't-know should only be used in pre/postconditions.
This aspect of the algorithm really needs formalization (just on paper),
but for now, this closes#700
In the writeback phase, the typechecker now checks that it isn't
replacing a type variable T with a type that contains T. It
also does an occurs check in do_autoderef in order to avoid
getting into an infinite chain of derefs.
I'm a bit worried that there are more places where the occurs
check needs to happen where I'm not doing it now, though.
Closes#768
While it is still technically possible to test stage 0, it is not part of any
of the main testing rules and maintaining xfail-stage0 is a chore. Nobody
should worry about how tests fare in stage0.
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
