Blocks (or statements involving blocks) that end in a semicolon are no
longer considered the block-expression of their outer block. This used
to be an expression block, but now is a statement block:
{ if foo { ret 1; } else { ret 10; } }
This helps clear up some ambiguities in our grammar.
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.)
* 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.
