Region pointers were considered a scalar type, so compare_scalar_type would
get called to compare region pointers in trans. This would fail, since
compare_scalar_type has no case for region pointers.
Changed type_is_scalar to return false for region pointers. This had the side
effect of breaking casts to types of the form &T. To ameliorate that, I added
library functions ptr::assimilate (taking a &T to a *T) and ptr::to_uint
(taking a &T to a uint), both of which use reinterpret_cast.
While I was at it, I removed ty::type_has_resources, which is dead code.
API is (for now) mostly by value, there are options to use it by
reference if you like. Hash and equality functions must be pure
and by reference (forward looking to the day when something
like send_map becomes the standard map).
What we now do is to create a region variable for each &
expression (and also each borrow). The lifetime of this
variable will be checked by borrowck to ensure it is not greater
than the lifetime of the underlying data. This both leads to
shorter lifetimes in some cases but also longer in others,
such as taking the address to the interior of unique boxes
tht are rooted in region pointers (e.g., returning a pointer
to the interior of a sendable map).
This may lead to issue #2977 if the rvalue is not POD, because
we may drop the data in trans sooner than borrowck expects us
to. Need to work out precisely where that fix ought to occur.
New style is allow(foo), warn(foo), deny(foo) and forbid(foo),
mirrored by -A foo, -W foo, -D foo and -F foo on command line.
These replace -W no-foo, -W foo, -W err-foo, respectively.
Forbid is new, and means "deny, and you can't override it".
It will warn you if you use the default mode for something that
is expensive to copy, and it will warn you if you use any explicit
mode other than copy. So you should migrate over to using the
default mode for most things (and borrowed pointers when you don't
want to copy) and copy mode for things you really wanted to copy.
In order to avoid a confusing use of the tcache, I added an extra
node ID field to trait refs. Now trait refs have a "ref ID" (the one
that resolve3 resolves) and an "impl ID" (the one that you look up
in the tcache to get the self type).
Closes#2434
