This destabilises all the implementation details of `thread_local!`,
since they do not *need* to be stable with the new attribute.

Unstable items used in a macro expansion will now always trigger
stability warnings, *unless* the unstable items are directly inside a
macro marked with `#[allow_internal_unstable]`. IOW, the compiler warns
unless the span of the unstable item is a subspan of the definition of a
macro marked with that attribute.

E.g.

    #[allow_internal_unstable]
    macro_rules! foo {
        ($e: expr) => {{
            $e;
            unstable(); // no warning
            only_called_by_foo!();
        }}
    }

    macro_rules! only_called_by_foo {
        () => { unstable() } // warning
    }

    foo!(unstable()) // warning

The unstable inside `foo` is fine, due to the attribute. But the
`unstable` inside `only_called_by_foo` is not, since that macro doesn't
have the attribute, and the `unstable` passed into `foo` is also not
fine since it isn't contained in the macro itself (that is, even though
it is only used directly in the macro).

In the process this makes the stability tracking much more precise,
e.g. previously `println!("{}", unstable())` got no warning, but now it
does. As such, this is a bug fix that may cause [breaking-change]s.

The attribute is definitely feature gated, since it explicitly allows
side-stepping the feature gating system.

Fixes #19674
Fixes #17396 (already closed, yeah)

cc @kmcallister , @cmr

This commit deprecates the majority of std::old_io::fs in favor of std::fs and
its new functionality. Some functions remain non-deprecated but are now behind a
feature gate called `old_fs`. These functions will be deprecated once
suitable replacements have been implemented.

The compiler has been migrated to new `std::fs` and `std::path` APIs where
appropriate as part of this change.

[breaking-change]

This commit deprecates the majority of std::old_io::fs in favor of std::fs and
its new functionality. Some functions remain non-deprecated but are now behind a
feature gate called `old_fs`. These functions will be deprecated once
suitable replacements have been implemented.

The compiler has been migrated to new `std::fs` and `std::path` APIs where
appropriate as part of this change.

This allows to create proper debuginfo line information for items inlined from other crates (e.g. instantiations of generics). Only the codemap's 'metadata' is stored in a crate's metadata. That is, just filename, positions of line-beginnings, etc. but not the actual source code itself.

Crate metadata size is increased by this change because spans in the encoded ASTs take up space now:
```
                BEFORE    AFTER
libcore         36 MiB    39.6 MiB    +10%
libsyntax       51.1 MiB  60.5 MiB    +18.4%
libcollections  11.2 MiB  12.8 MiB    +14.3%
```
This only affects binaries containing metadata (rlibs and dylibs), executables should not be affected in size. 

Fixes #19228 and probably #22226.

Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>

This allows to create proper debuginfo line information for items inlined from other crates (e.g. instantiations of generics).
Only the codemap's 'metadata' is stored in a crate's metadata. That is, just filename, line-beginnings, etc. but not the actual source code itself. We are thus missing the opportunity of making Rust the first "open-source-only" programming language out there. Pity.

Runway for RFC 809 (overloaded box/placement-in) by adding type annotations or explicit calls to `Box::new` where I found it necessary on PR #22086.

I have broken this up into more than one PR because the entire commit chain (see PR #22086) is long, widespread and unwieldy to rebase frequently.

To my knowledge this is not a breaking change.  Also, there is in principle nothing stopping someone from reverting some/all of these annotations, since without the rest of the commit chain in #22086, the associated code would continue to compile.

All I can do is ask: Try to discourage others from removing seemingly "unnecessary" uses of the `Box` type or the `Box::new()` function, until the rest of RFC 809 lands.

Many of the modifications putting in `Box::new` calls also include a
pointer to Issue 22405, which tracks going back to `box <expr>` if
possible in the future.

(Still tried to use `Box<_>` where it sufficed; thus some tests still
have `box_syntax` enabled, as they use a mix of `box` and `Box::new`.)

Precursor for overloaded-`box` and placement-`in`; see Issue 22181.

(You shouldn't use it, but it is a semi-reasonable way to annotate
types when necessary.)

This is the kind of change that one is expected to need to make to
accommodate overloaded-`box`.

----

Note that this is not *all* of the changes necessary to accommodate
Issue 22181.  It is merely the subset of those cases where there was
already a let-binding in place that made it easy to add the necesasry
type ascription.

(For unnamed intermediate `Box` values, one must go down a different
route; `Box::new` is the option that maximizes portability, but has
potential inefficiency depending on whether the call is inlined.)

----

There is one place worth note, `run-pass/coerce-match.rs`, where I
used an ugly form of `Box<_>` type ascription where I would have
preferred to use `Box::new` to accommodate overloaded-`box`.  I
deliberately did not use `Box::new` here, because that is already done
in coerce-match-calls.rs.

----

Precursor for overloaded-`box` and placement-`in`; see Issue 22181.

Make build timestamp files robust in face of concurrent source modification.

Strategy: If the end goal is to touch e.g. `stamp.std`, then we first touch `stamp.std.start_time` before doing anything else.  Then when the receipe finishes, we touch `stamp.std` using the timestamp from `stamp.std.start_time` as the reference time, and remove `stamp.std.start_time`.

Fix #6518.

Rebase and follow-through on work done by @cmr and @aatch.

Implements most of rust-lang/rfcs#560. Errors encountered from the checks during building were fixed.

The checks for division, remainder and bit-shifting have not been implemented yet.

See also PR #20795

cc @Aatch ; cc @nikomatsakis

Strategy: If the end goal is to touch e.g. `stamp.std`, then we first
touch `stamp.std.start_time` before doing anything else.  Then when
the receipe finishes, we touch `stamp.std` using the timestamp from
`stamp.std.start_time` as the reference time, and remove
`stamp.std.start_time`.

Fix #6518.

See buildlog here for evidence of such occurring:
  http://buildbot.rust-lang.org/builders/auto-linux-32-opt/builds/3910/steps/test/logs/stdio

r? @Manishearth

 Fixes #15778.

r? @sfackler

Conflicts:
	src/libstd/thread.rs

 Reverts a small part of c74d49c8 because compilation pukes with warnings now.

 Make `test/run-pass/backtrace.rs` more robust about own host environment

Namely, I have been annoyed in the past when I have done `RUST_BACKTRACE=1 make check` only to discover (again) that such a trick causes this test to fail, because it assumes that the `RUST_BACKTRACE` environment variable is not set.

Fix #22870

 aarch64-linux-android build has been broken since #22839.
Aarch64 android has _Unwind_GetIPInfo, so re-define this only for arm32 android.
r? @alexcrichton

 Unstable is the conservative choice.

cc #22950.

 `#[derive(Clone)]` unnecessarily requires the element type to also be
`Clone`.

 This changes the type of some public constants/statics in libunicode.
Notably some `&'static &'static [(char, char)]` have changed
to `&'static [(char, char)]`. The regexp crate seems to be the
sole user of these, yet this is technically a [breaking-change]

 Associated types are now treated as part of the public API by the privacy checker.

If you were exposing a private type in your public API via an associated type, make that type public:

``` diff
  pub struct PublicType { .. }

- struct Struct { .. }
+ pub struct Struct { .. }

  pub trait PublicTrait {
      type Output;

      fn foo(&self) -> Self::Output;
  }

  impl PublicTrait for PublicType {
      type Output = Struct;

      fn foo(&self) -> Struct {  // `Struct` is part of the public API, it must be marked as `pub`lic
          ..
      }
  }
```

[breaking-change]

---

r? @nikomatsakis
closes #22912

 Fix the return type in the comments.

An old commit 082bfde4 (\"Fallout of std::str stabilization\") removed
the example of FromStr::from_str(), this commit adds it back. But
the example of StrExt::parse() is still kept with an additinal note.
Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>

 Its only user was lvalue_scratch_datum which is called with zero=true
anymore, so it's effectively unused.

 The API this exposes is a little strange (being attached to `static`s),
so it makes sense to conservatively feature gate it. If it is highly
popular, it is possible to reverse this gating.

 * The lint visitor's visit_ty method did not recurse, and had a
  reference to the now closed #10894
* The newly enabled recursion has only affected the `deprectated` lint
  which now detects uses of deprecated items in trait impls and
  function return types
* Renamed some references to `CowString` and `CowVec` to `Cow<str>` and
  `Cow<[T]>`, respectively, which appear outside of the crate which
  defines them
* Replaced a few instances of `InvariantType<T>` with
  `PhantomData<Cell<T>>`
* Disabled the `deprecated` lint in several places that
  reference/implement traits on deprecated items which will get cleaned
  up in the future
* Unfortunately, this means that if a library declares
  `#![deny(deprecated)]` and marks anything as deprecated, it will have
  to disable the lint for any uses of said item, e.g. any impl the now
  deprecated item

For any library that denies deprecated items but has deprecated items
of its own, this is a [breaking-change]

I had originally intended for the lint to ignore uses of deprecated items that are declared in the same crate, but this goes against some previous test cases that expect the lint to capture *all* uses of deprecated items, so I maintained the previous approach to avoid changing the expected behavior of the lint.

Tested locally on OS X, so hopefully there aren't any deprecated item uses behind a `cfg` that I may have missed.

  * Make num::UpperHex private.  I was unable to determine why this struct
   is public.  The num module itself is not public, and the UpperHex struct
   is not referenced anywhere in the core::fmt module.  (Only the UpperHex
   trait is reference.)  num::LowerHex is not public.

 * Remove the suffix parameters from the macros that generate integral
   display traits.

   The code to print the Debug::fmt suffixes was removed when Show was
   renamed to Debug.  It was an intentional change.  From RFC 0565:

    * Focus on the *runtime* aspects of a type; repeating information such
      as suffixes for integer literals is not generally useful since that
      data is readily available from the type definition.

 * Because Show was renamed to Debug, rename show! to debug!.

Suggestion was here:

  https://github.com/rust-lang/rust/pull/22532#discussion_r25505609

Added pair of regression tests that I should have made when I thought
of doing this in the first place.