This eliminates an ICE in trans where the scope for a particular
borrow was a statement ID, but the code in trans that does cleanups
wasn't finding the block with that scope. As per #3860
preserve looks at a node ID to see if it's for a statement -- if it
is, it uses the enclosing scope instead when updating the map that
trans looks at later.
I added a comment noting that this is not the best fix (since it may
cause boxes to be frozen for longer than necessary) and referring
to #3511.
r=nmatsakis
- Make `extern fn()` assignable to any closure type, rather than
a subtype.
- Remove unused int_ty_set and float_ty_set
- Refactor variable unification and make it more DRY
- Do fn sub/lub/glb on the level of fn_sig
- Rename infer::to_str::ToStr to infer::to_str::InferStr
- Capitalize names of various types
- Correct hashing of FnMeta
- Convert various records-of-fns into structs-of-fns. This is both
eliminating use of deprecated features and more forwards compatible
with fn reform.
r=pcwalton
