r? @pcwalton
A month's worth of parser cleanup here. Much of this is new comments and renaming. A number of these commits also remove unneeded code. Probably the biggest refactor here is splitting "parse_item_or_view_item" into two functions; it turns out that the only overlap between items in foreign modules and items in regular modules was macros, so this refactor should make things substantially easier for future maintenance.
I didn't know how to use "use" initially, and an error message like this would
have solved quite a bit of frustration. I think this properly handles cases
where it's not appropriate but I'm not sure.
Closes#3083.
This takes a similar approach to #5797 where a set is present on the `tcx` of used mutable definitions. Everything is by default warned about, and analyses must explicitly add mutable definitions to this set so they're not warned about.
Most of this was pretty straightforward, although there was one caveat that I ran into when implementing it. Apparently when the old modes are used (or maybe `legacy_modes`, I'm not sure) some different code paths are taken to cause spurious warnings to be issued which shouldn't be issued. I'm not really sure how modes even worked, so I was having a lot of trouble tracking this down. I figured that because they're a legacy thing that I'd just de-mode the compiler so that the warnings wouldn't be a problem anymore (or at least for the compiler).
Other than that, the entire compiler compiles without warnings of unused mutable variables. To prevent bad warnings, #5965 should be landed (which in turn is waiting on #5963) before landing this. I figured I'd stick it out for review anyway though.
As the name suggests this replaces many instances of cast::reinterpret_cast by cast::transmute. It's essentially the boring part of fixing #5163, the remaining reinterpret_casts should be more tricky to remove (unless I missed a boring case).
r? @catamorphism
