Since the decl in a for or for-each loop must always be a local
decl, I changed the AST to express this. Fewer potential match
failures and "the impossible happened" error messages = yay!
Generate appropriate constraints for calls to functions with
preconditions, and reject calls where those constraints don't
hold true in the prestate.
...by which I mean that it works for one test case :-)
Before, all aliases were implicitly mutable, and writing
&mutable was the same as writing &. Now, the two are
distinguished, and assignments to regular aliases are
no longer allowed.
Changed function types to include a list of constraints. Added
code for parsing and pretty-printing constraints. This necessitated
splitting pprust into two files (pprust and ppaux) to break a
circulate dependency, as ty_to_str now needs to print out constraints,
which may include literals, but pprust depended on ty.
This litters aberrations like 'alt({foo.bar}) { ... }' and f({*baz})
though the code (mostly in trans.rs). These are a way to explicitly
copy the given value so that it can be safely aliased. At some point
we'll probably want a more explicit copy operator.
Hello from SFO Terminal 3!
unify_fn_common had the expected and actual types reversed in one
place. This was causing the type of an occurence of a function f
with type fn(int) -> T to be set to fn(_|_) -> T at a call site like
f(fail); I think this was also making some of the type error messages
come out backwards, but I haven't checked.
Also: ty_bot does not contain pointers
Previously, block_ty returned the type of the terminating
expression of the block (or nil if said expression was absent).
I changed check_expr to write the type of that expression into
the annotation for the block itself, so now block_ty can use the
block's annotation.
The typechecker had a number of special cases for unifying types
with _|_ (as with checking if and alt). But, a value of type _|_
should be usable in any context, as such a value always diverges,
and will never be used by its immediate context. Changed unify
accordingly, removed special cases.
Change ty_fn to have a controlflow field. A 'controlflow' is
essentially a bit of data that says whether or not this function
never returns to the caller (if it never returns, that means it calls
"fail" or another "never-returns" function on every control path).
Also add syntax for annotating functions that never return:
fn foo() -> ! {
fail;
}
for example. Functions marked with ! implicitly have a result type of
ty_bot, which is a new type that this commit also adds.
