Impl Rand for tuples of arity 11 and 12
rand: Small fix in parameter name

Documentation didn't match with parameter name.
Changes name of parameter in docs and function to 'amount'.
c_str: add `.as_ptr` & `.as_mut_ptr` to replace `.with_[mut_]ref`.

These forms return the pointer directly, rather than the added
indirection, indentation, and inefficiencies of the closures in
`.with_ref` and `.with_mut_ref`. The two closure functions are
deprecated.

Replace

    foo(c_str.with_ref(|p| p))

    c_str.with_ref(|p| {
        foo(p);
        bar(p);
    })

with

    foo(c_str.as_ptr())

    let p = c_str.as_ptr();
    foo(p);
    bar(p);

This change does mean that one has to be careful to avoid writing `let p
= x.to_c_str().as_ptr();` since the `CString` will be freed at the end
of the statement. Previously, `with_ref` was used (and `as_ptr` avoided)
for this reason, but Rust has strongly moved away from closures to more
RAII-style code, and most uses of `.with_ref` where in the form
`.with_ref(|p| p)` anyway, that is, they were exactly `.as_ptr`.

[breaking-change]
c_str: replace .with_ref with .as_ptr throughout the codebase.
c_str: move `.unwrap` & document it more clearly.

This should be called rarely, but it was placed first in the list of
methods, making it very tempting to call.
auto merge of #14904 : huonw/rust/cstr-remove-withref, r=alexcrichton
auto merge of #15249 : aochagavia/rust/rand, r=huonw
rustuv: Don't zero-out data on clones

When cloning a stream, the data is already guaranteed to be in a consistent
state, so there's no need to perform a zeroing. This prevents segfaults as seen
in #15231

Closes #15231
auto merge of #15246 : Sawyer47/rust/rand-doc-fix, r=alexcrichton

Documentation didn't match with parameter name.
Changes name of parameter in docs and function to 'amount'.
Wrap two code examples in backticks

This makes the docs ever-so-slightly easier to read.
librustc: Remove the fallback to `int` for integers and `f64` for
floating point numbers for real.

This will break code that looks like:

    let mut x = 0;
    while ... {
        x += 1;
    }
    println!("{}", x);

Change that code to:

    let mut x = 0i;
    while ... {
        x += 1;
    }
    println!("{}", x);

Closes #15201.

[breaking-change]
collections: minor cleanup
alloc: impl Default for Rc
core: optimize {option,result}::collect

The bug #11084 causes these collect functions to run about
twice as slow as they should because llvm is having trouble
optimizing away the closure for some reason. This patch works
around that performance bug by using a simple adapter iterator
explicitly for capturing if the outer iterator returns an
error.
auto merge of #15234 : pcwalton/rust/integer-fallback-and-casts, r=alexcrichton

This will break code that looks like:

    let mut x = 0;
    while ... {
        x += 1;
    }
    println!("{}", x);

Change that code to:

    let mut x = 0i;
    while ... {
        x += 1;
    }
    println!("{}", x);

Closes #15201.

[breaking-change]

r? @alexcrichton
auto merge of #15252 : alexcrichton/rust/issue-15231, r=pcwalton

When cloning a stream, the data is already guaranteed to be in a consistent
state, so there's no need to perform a zeroing. This prevents segfaults as seen
in #15231

Closes #15231
Extract tests from libcore to a separate crate

Libcore's test infrastructure is complicated by the fact that many lang
items are defined in the crate. The current approach (realcore/realstd
imports) is hacky and hard to work with (tests inside of core::cmp
haven't been run for months!).

Moving tests to a separate crate does mean that they can only test the
public API of libcore, but I don't feel that that is too much of an
issue. The only tests that I had to get rid of were some checking the
various numeric formatters, but those are also exercised through normal
format! calls in other tests.
auto merge of #15245 : sfackler/rust/coretest, r=alexcrichton

Libcore's test infrastructure is complicated by the fact that many lang
items are defined in the crate. The current approach (realcore/realstd
imports) is hacky and hard to work with (tests inside of core::cmp
haven't been run for months!).

Moving tests to a separate crate does mean that they can only test the
public API of libcore, but I don't feel that that is too much of an
issue. The only tests that I had to get rid of were some checking the
various numeric formatters, but those are also exercised through normal
format! calls in other tests.
it -> Cargo

It wasn't clear if we needed to install Hello World or Cargo.
auto merge of #15254 : alex/rust/patch-1, r=alexcrichton

This makes the docs ever-so-slightly easier to read.