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
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.
src/comp/syntax is currently just a sub-module of rustc, but it will,
in the near future, be its own crate. This includes:
- The AST data structure
- The parser
- The pretty-printer
- Visit, walk, and fold
- The syntax extension system
- Some utility stuff that should be in the stdlib*
*) Stdlib extensions currently require a snapshot before they can be
used, and the win build is very broken right now. This is temporary
and will be cleaned up when one of those problems goes away.
A lot of code was moved by this patch, mostly towards a more organized
layout. Some package paths did get longer, and I guess the new layout
will take some getting used to. Sorry about that!
Please try not to re-introduce any dependencies in syntax/ on any of
the other src/comp/ subdirs.
Modify typestate to check for unused variables and emit warnings
where relevant. This exposed a (previously harmless) bug in
collect_locals where outer functions had bit-vector entries
for init constraints for variables declared in their inner
nested functions. Fixing that required changing collect_locals to
use visit instead of walk -- probably a good thing anyway.
Wrote some small test cases that use while loops and moves, to
make sure the poststate for the loop body gets propagated into the
new prestate and deinitialization gets reflected.
Along with that, rewrite the code for intersecting states. I still
find it dodgy, but I guess I'll continue trying to add more tests.
Also, I'll probably feel better about it once I start formalizing
the algorithm.
typestate now drops constraints correctly in the post-state of
a move expression or a declaration whose op is a move. It doesn't
yet drop constraints mentioning variables that get updated.
To do this, I had to change typestate to use trit-vectors instead
of bit-vectors, because for every constraint, there are three
possible values: known-to-be-false (e.g. after x <- y, init(y) is
known-to-be-false), known-to-be-true, and unknown. Before, we
conflated known-to-be-false with unknown. But move requires them
to be treated differently. Consider:
(program a)
(a1) x = 1;
(a2) y <- x;
(a3) log x;
(program b)
(b1) x = 1;
(b2) y <- z;
(b3) log x;
With only two values, the postcondition of statement a2 for
constraint init(x) is the same as that of b2: 0. But in (a2)'s
postcondition, init(x) *must* be false, but in (b2)'s condition,
it's just whatever it was in the postcondition of the preceding statement.
This reduces some redundancy in the AST data structures and cruft in
the code that works with them. To get a def_id from a node_id, apply
ast::local_def, which adds the local crate_num to the given node_id.
Most code only deals with crate-local node_ids, and won't have to
create def_ids at all.
Revert "rustc: Export only what's needed from middle::ty"
This reverts commit 4255d58aa5db2a05362c4435a0e807205e1b8ed7.
Revert "rustc: Make name resolution errors less fatal"
This reverts commit b8ab9ea89c16c60237e7660804f4321f59ae0435.
Revert "rustc: Make import resolution errors less fatal"
This reverts commit 92a8ae94b971206bf0502da3dc5f416fcb24cc36.
Revert "rustc: Export only what's used from middle::resolve"
This reverts commit 4539a2cf7ad99851a165c98ed2f4e4a475cffd7d.
Revert "rustc: Re-introduce session.span_err, session.err"
This reverts commit 7fe9a88e31ae07f2fd89f6715efedd7e3edf49e6.
Revert "rustc: Rename session.span_err -> span_fatal, err -> fatal"
This reverts commit c394a7f49ac29a099994e243017065de2ff97f2a.
I noticed that typestate was being lazier than it should be,
because it was only checking typestate for statements and
top-level expression (that is, the expression in a stmt_expr, but
not any subexpressions). So I rewrote the checks in tstate/ck.rs
to use walk, which exposed a few bugs in typestate that I fixed.
Also added some more test cases for if-check.
