Previously, we would emit a "compiler doesn't understand error" since we would
detect the escape and fail. That is the correct behavior here if the
partial_apply is not already identified as escaping by an earlier pass. But in
the case where we see that the partial_apply's callee was marked with
semantics::NO_MOVEONLY_DIAGNOSTICS, then we:
1. Suppress the "compiler doesn't understand error" for this specific
mark_must_check.
2. Suppress function wide the "copy of noncopyable type" error. Since we stopped
processing the mark_must_check that was passed to the partial_apply, we may
have left copies of noncopyable types on that mark_must_check value. This is
ok since the user will get the error, will recompile, and if any further show
up after they fix the inout escaping issue, they will be emitted
appropriately.
This is the first slice of bringing up escaping closure support. The support is
based around introducing a new type of SILGen VarLoc: a VarLoc with a box and
without a value. Because the VarLoc only has a box, we have to in SILGen always
eagerly reproject out the address from the box. The reason why I am doing this
is that it makes it easy for the move checker to distinguish in between
different accesses to the box that we want to check separately. As such every
time that we open the box, we insert a mark_must_check
[assignable_but_not_consumable] on that project. If allocbox_to_stack manages to
determine that the box can be stack allocated, we eliminate all of the
mark_must_check and place a new mark_must_check [consumable_and_assignable] on
the alloc_stack. The end result is that we get the old model that we had before
and also can support escaping closures.
Otherwise, sometimes when the object checker emits a diagnostic and cleans up
the IR, some of the cleaned up copies are copies that should have been handled
by the address checker. The end result is that the address checker does not emit
diagnostics for that IR. I found this problem was exascerbated when writing code
for escaping closures.
This commit also cleans up the passes in preparation for at a future time moving
some of the transformations into the utils folder.
