`Box<[T]>` is created by allocating `Box<[T, ..n]>` and coercing it so
this code path is never used. It's also broken because it clamps the
capacity of the memory allocations to 4 elements and that's incompatible
with sized deallocation. This dates back to when `~[T]` was a growable
vector type implemented as:

*{ { tydesc, ref_count, prev, next }, { length, capacity, data[] } }

Since even empty vectors had to allocate, it started off the capacity of
all vectors at 4 as a heuristic. It's not possible to grow `Box<[T]>`
and there is no need for a memory allocation when it's empty, so it
would be a terrible heuristic today even if it worked.

This PR fixes debuginfo tests on Windows.

Updates the callbacks section to refer to the right function name and fixes a couple of minor whitespace issues in the examples.

Fixes #17120.

This can break code like:

    fn call_rec(f: |uint| -> uint) -> uint {
        (|x| f(x))(call_rec(f))
    }

Change this code to use a temporary instead of violating the borrow
rules:

    fn call_rec(f: |uint| -> uint) -> uint {
        let tmp = call_rec(|x| f(x)); f(tmp)
    }

Closes #17144.

[breaking-change]

r? @huonw

The other extension types already worked this way and it can be useful to track some state along with the extension.

I also removed the `BasicMacroExpander` and `BasicIdentMacroExpander` since the span inside of them was never used. The expander function types now directly implement the relevant trait.

Fixing more suggestions from @dherman . I made them individual commits in case we want to discuss any of them further.

This PR creates a new lint : ``unused_extern_crate``, which do pretty much the same thing as ``unused_import``, but for ``extern crate`` statements. It is related to feature request #10385.

I adapted the code tracking used imports so that it tracks extern crates usage as well. This was mainly trial and error and while I believe all cases are covered, there might be some code I added that is useless (long compile times didn't give me the opportunity to check this in detail).

Also, I removed some unused ``extern crate`` statements from the libs, that where spotted by this new lint.

Few visitors used the context passing feature and it can be easily emulated.
The added lifetime threading allows a visitor to keep safe references to AST
nodes it visits, making a non-owning ast_map design possible, for #13316.

This switches win64 hosts to bootstrap from win64 snaps.

`Box<[T]>` is created by allocating `Box<[T, ..n]>` and coercing it so
this code path is never used. It's also broken because it clamps the
capacity of the memory allocations to 4 elements and that's incompatible
with sized deallocation. This dates back to when `~[T]` was a growable
vector type implemented as:

*{ { tydesc, ref_count, prev, next }, { length, capacity, data[] } }

Since even empty vectors had to allocate, it started off the capacity of
all vectors at 4 as a heuristic. It's not possible to grow `Box<[T]>`
and there is no need for a memory allocation when it's empty, so it
would be a terrible heuristic today even if it worked.

https://github.com/rust-lang/rust-guidelines/blob/master/style/whitespace.md

closes #16977 

r? @nikomatsakis 

The Guide isn't 100% perfect, but it's basically complete. It's
certainly better than the tutorial is. Time to start pointing more
people its way.

I also just made it consistent to call all things 'guides' rather than
tutorials.

Fixes #9874. This is the big one.

And two bugs that just go away.

Fixes #14503.
Fixes #15009.

Package rustc's mingw dependencies into Windows installer to avoid requiring a separate mingw install.

Closes #11782

closes #16977

The Guide isn't 100% perfect, but it's basically complete. It's
certainly better than the tutorial is. Time to start pointing more
people its way.

I also just made it consistent to call all things 'guides' rather than
tutorials.

Fixes #9874. This is the big one.

And two bugs that just go away.

Fixes #14503.
Fixes #15009.

This can break code like:

    fn call_rec(f: |uint| -> uint) -> uint {
        (|x| f(x))(call_rec(f))
    }

Change this code to use a temporary instead of violating the borrow
rules:

    fn call_rec(f: |uint| -> uint) -> uint {
        let tmp = call_rec(|x| f(x)); f(tmp)
    }

Closes #17144.

[breaking-change]

fixes #17148

gcc, ld, ar, dlltool, windres go into $(RUST)/bin/rustlib/<triple>/bin/
platform libraries and startup objects got into $(RUST)/bin/rustlib/<triple>/lib/

so that rustc can invoke them.

whoops

Fixes https://github.com/rust-lang/rust/pull/16827#issuecomment-55160273

Avoid ever constructing cyclic types in the first place, rather than detecting them in resolve. This simplifies logic elsewhere in the compiler, in particular on the trait reform branch.

r? @pnkfelix or @pcwalton 

cc #5527

Bugs in pdflatex (#12804) are preventing the guide from landing (https://github.com/rust-lang/rust/pull/16657). This solves the immediate problem by changing the build system to prefer lualatex, xelatex to pdflatex (which is apparently obsolete). Because the xelatex on the snapshot bot seems to completely ignore the `-output-directory` option, I also had to frob the makefiles a bit for that case.