The alias checker works by ensuring that any value to which an alias
is created is rooted in some way that ensures it outlives the alias.
It is now disallowed to create an alias to the content of a mutable
box, or to a box hanging off a mutable field. There is also machinery
in place to prevent assignment to local variables whenever they are
the root of a live alias.
Changed the typechecker to correctly typecheck the declared variable
type in a for or for-each loop against the vector element type (for
a for loop) or the iterator type (for a for-each loop). Added a
test case.
The error message for (for example) "import vec;" without "use std;"
was "cyclic import", which was misleading because there were no
cycles. I changed it to "cyclic import or nonexistent module",
which doesn't break existing tests.
Previously, if you wrote
let @vec[int] foo = @[];
that would be a type error. That didn't seem right, so I changed
pushdown to unify the inner type in an unop application with the
argument type of the operator type.
This required quite a bit of tiresome plumbing about of spans.
On the bright side, now other errors can be converted to span_err too.
Includes test cases.
* Reorganized typestate into several modules.
* Made typestate check that any function with a non-nil return type
returns a value. For now, the check is a warning and not an error
(see next item).
* Added a "bot" type (prettyprinted as _|_), for constructs like be, ret, break, cont, and
fail that don't locally return a value that can be inspected. "bot"
is distinct from "nil". There is no concrete syntax for _|_, while
the concrete syntax for the nil type is ().
* Added support to the parser for a ! annotation on functions whose
result type is _|_. Such a function is required to have either a
fail or a call to another ! function that is reached in all control
flow paths. The point of this annotation is to mark functions like
unimpl() and span_err(), so that an alt with a call to err() in one
case isn't a false positive for the return-value checker. I haven't
actually annotated anything with it yet.
* Random bugfixes:
* * Fixed bug in trans::trans_binary that was throwing away the
cleanups for nested subexpressions of an and or or
(tests: box-inside-if and box-inside-if2).
** In typeck, unify the expected type arguments of a tag with the
actual specified arguments.
Ping me if you disagree, but I think that in a language that's as
in-flux as rust currently is, it is silly to try and enforce a single
future-compatibility. The reserved words didn't work well with the
parser refactor, so I dropped them for the time being. We can,
eventually, bring them back as type-only reserved words.
Module names no longer clash with type and value names. The
tokenizer/parser still needs to be taught to be more careful in
identifying keywords, so that we can use 'str' and 'vec' and so as
module names.
