a `default impl` need not include all items from the trait
    a `default impl` alone does not mean that a type implements the trait

Rollup of 10 pull requests

- Successful merges: #47613, #47631, #47810, #47883, #47922, #47944, #48014, #48018, #48020, #48028
- Failed merges:

correct E0619 span re method call receivers whose type must be known

Previously, when the type of a method receiver could not be determined,
the error message would, potentially confusingly, highlight the span of
the entire method call.

![unknown_receiver_type](https://user-images.githubusercontent.com/1076988/35838930-a595b17c-0aa2-11e8-9364-6b8e2329f051.png)

Resolves #36598, resolves #42234.

Warn about more ignored bounds in type aliases

It seems that all bounds in type aliases are entirely ignored, not just type bounds. This extends the warning appropriately.

I assume this should be made a hard error with the next epoch? I can't see any reason to accept these programs. (And suddenly enforcing these type bounds would be a breaking change.)

rustc: Add `#[rustc_args_required_const]`

This commit adds a new unstable attribute to the compiler which requires that
arguments to a function are always provided as constants. The primary use case
for this is SIMD intrinsics where arguments are defined by vendors to be
constant and in LLVM they indeed must be constant as well.

For now this is mostly just a semantic guarantee in rustc that an argument is a
constant when invoked, phases like trans don't actually take advantage of it
yet. This means that we'll be able to use this in stdsimd but we won't be able
to remove the `constify_*` macros just yet. Hopefully soon though!

Implement RFC 2052 (Epochs)

This adds -Zepochs and uses it for tyvar_behind_raw_pointer (#46906)

When we move this to --epoch=XXX, we'll need to gate the 2018 epoch on nightly, but not the 2015 one. I can make these changes here itself though it's kinda pointless given that the entire flag is nightly-only.

r? @nikomatsakis @aturon

cc #44581 (epoch tracking)
cc #46906 (tyvar_behind_raw_pointer)

Implement TrustedLen for Take<Repeat> and Take<RangeFrom>

This will allow optimization of simple `repeat(x).take(n).collect()` iterators, which are currently not vectorized and have capacity checks.

This will only support a few aggregates on `Repeat` and `RangeFrom`, which might be enough for simple cases, but doesn't optimize more complex ones. Namely, Cycle, StepBy, Filter, FilterMap, Peekable, SkipWhile, Skip, FlatMap, Fuse and Inspect are not marked `TrustedLen` when the inner iterator is infinite.

Previous discussion can be found in #47082

r? @alexcrichton

correct unused field pattern suggestions

![unused_field_pattern_local](https://user-images.githubusercontent.com/1076988/35662336-7a69488a-06cc-11e8-9901-8d22b5cf924f.png)

r? @estebank

Export wasm source map when debug information is enabled

We use binaryen's linker to produce a wasm file (via s2wasm). The wasm writer has capabilities to export source maps. The pilot support for source maps is added to Firefox.

The produced source map contains references to the original file, that might require additional source map file processing to include / package original files with it.

/cc @alexcrichton

Fix rendering issues on mobile

Fixes #47723

r? @QuietMisdreavus

Add some APIs to ptr::NonNull and fix `since` attributes

This is a follow-up to its stabilization in https://github.com/rust-lang/rust/pull/46952. Tracking issue: https://github.com/rust-lang/rust/issues/27730.

* These trait impls are insta-stable: `Hash`, `PartialEq`, `Eq`, `PartialOrd` and `Ord`.
* The new `cast<U>() -> NonNull<U>`  method is `#[unstable]`. It was proposed in https://github.com/rust-lang/rust/pull/46952#issuecomment-359220010.

Add filtering options to `rustc_on_unimplemented`

- Add filtering options to `rustc_on_unimplemented` for local traits, filtering on `Self` and type arguments.
- Add a way to provide custom notes.
- Tweak binops text.
- Add filter to detect wether `Self` is local or belongs to another crate.
- Add filter to `Iterator` diagnostic for `&str`.

Partly addresses #44755 with a different syntax, as a first approach. Fixes #46216, fixes #37522, CC #34297, #46806.

[NLL] Improve DefiningTy::Const

Fixes #47590 by fixing the way DefiningTy represents constants. Previously, constants were represented using just the type of the variable. However, this will fail to capture early-bound regions as NLL inference vars, resulting in an ICE when we try to compute region VIDs a little bit later in the universal
region resolution process. (ref #47590)

Fixes #47590 by fixing the way DefiningTy represents constants. Previously,
constants were represented using just the type of the variable. However, this
will fail to capture early-bound regions as NLL inference vars, resulting in an
ICE when we try to compute region VIDs a little bit later in the universal
region resolution process.

MIR-borrowck: augmented assignment causes duplicate errors

Fixes #45697. This PR resolves the error duplication. I attempted to replace the existing sets since there were quite a few but only managed to replace two of them.

r? @nikomatsakis

Rollup of 7 pull requests

- Successful merges: #46962, #47986, #48012, #48013, #48026, #48031, #48036
- Failed merges:

proc_macro: don't panic parsing ..= (fix #47950)

config.toml.example: fix typos.

Most of them were found by codespell: https://github.com/lucasdemarchi/codespell

Document that associated constants prevent a trait from being made into an object

Fixes https://github.com/rust-lang/rust/issues/47952

Add a short mention of associated constants to E0038

Use time crate in bootstrap dist instead of date

`bootstrap dist` command is trying to run *NIX specific `date` command to get current month and year. This command keep failing when it's called on a Windows command prompt. This patch is making it use time crate.

Closes: #47908

Override try_[r]fold for RangeInclusive

Because the last item needs special handling, it seems that LLVM has trouble canonicalizing the loops in external iteration.  With the override, it becomes obvious that the start==end case exits the loop (as opposed to the one *after* that exiting the loop in external iteration).

Demo adapted from https://github.com/rust-lang/rust/issues/45222
```rust
#[no_mangle]
pub fn foo3r(n: u64) -> u64 {
    let mut count = 0;
    (0..n).for_each(|_| {
        (0 ..= n).rev().for_each(|j| {
            count += j;
        })
    });
    count
}
```

<details>
 <summary>Current nightly ASM, 100 lines (https://play.rust-lang.org/?gist=f5674c702c6e2045c3aab5d03763e5f6&version=nightly&mode=release)</summary>

```asm
foo3r:
	pushq	%rbx
.Lcfi0:
.Lcfi1:
	testq	%rdi, %rdi
	je	.LBB0_1
	testb	$1, %dil
	jne	.LBB0_4
	xorl	%eax, %eax
	xorl	%r8d, %r8d
	cmpq	$1, %rdi
	jne	.LBB0_11
	jmp	.LBB0_23
.LBB0_1:
	xorl	%eax, %eax
	popq	%rbx
	retq
.LBB0_4:
	xorl	%r8d, %r8d
	movq	$-1, %r9
	xorl	%eax, %eax
	movq	%rdi, %r11
	xorl	%r10d, %r10d
	jmp	.LBB0_5
.LBB0_8:
	addq	%r11, %rax
	movq	%rsi, %r11
	movq	%rdx, %r10
.LBB0_5:
	cmpq	%r11, %r10
	movl	$1, %ecx
	cmovbq	%r9, %rcx
	cmoveq	%r8, %rcx
	testq	%rcx, %rcx
	movl	$0, %esi
	movl	$1, %edx
	je	.LBB0_8
	cmpq	$-1, %rcx
	jne	.LBB0_9
	leaq	-1(%r11), %rsi
	movq	%r10, %rdx
	jmp	.LBB0_8
.LBB0_9:
	movl	$1, %r8d
	cmpq	$1, %rdi
	je	.LBB0_23
.LBB0_11:
	xorl	%r9d, %r9d
	movq	$-1, %r10
.LBB0_12:
	movq	%rdi, %rsi
	xorl	%r11d, %r11d
	jmp	.LBB0_13
.LBB0_16:
	addq	%rsi, %rax
	movq	%rcx, %rsi
	movq	%rbx, %r11
.LBB0_13:
	cmpq	%rsi, %r11
	movl	$1, %edx
	cmovbq	%r10, %rdx
	cmoveq	%r9, %rdx
	testq	%rdx, %rdx
	movl	$0, %ecx
	movl	$1, %ebx
	je	.LBB0_16
	cmpq	$-1, %rdx
	jne	.LBB0_17
	leaq	-1(%rsi), %rcx
	movq	%r11, %rbx
	jmp	.LBB0_16
.LBB0_17:
	movq	%rdi, %rcx
	xorl	%r11d, %r11d
	jmp	.LBB0_18
.LBB0_21:
	addq	%rcx, %rax
	movq	%rsi, %rcx
	movq	%rbx, %r11
.LBB0_18:
	cmpq	%rcx, %r11
	movl	$1, %edx
	cmovbq	%r10, %rdx
	cmoveq	%r9, %rdx
	testq	%rdx, %rdx
	movl	$0, %esi
	movl	$1, %ebx
	je	.LBB0_21
	cmpq	$-1, %rdx
	jne	.LBB0_22
	leaq	-1(%rcx), %rsi
	movq	%r11, %rbx
	jmp	.LBB0_21
.LBB0_22:
	addq	$2, %r8
	cmpq	%rdi, %r8
	jne	.LBB0_12
.LBB0_23:
	popq	%rbx
	retq
.Lfunc_end0:
```
</details><br>

With this PR:
```asm
foo3r:
	test	rcx, rcx
	je	.LBB3_1
	lea	r8, [rcx - 1]
	lea	rdx, [rcx - 2]
	mov	rax, r8
	mul	rdx
	shld	rdx, rax, 63
	imul	r8, r8
	add	r8, rcx
	sub	r8, rdx
	imul	r8, rcx
	mov	rax, r8
	ret
.LBB3_1:
	xor	r8d, r8d
	mov	rax, r8
	ret
```

libtest: Replace panics with error messages

This replaces explicit panics on failures in libtest with prints to stderr.
Where "failures" == CLI argument parsing and such

Before:
```
$ ./foo-stable --not-an-option
thread 'main' panicked at '"Unrecognized option: \'not-an-option\'"', libtest/lib.rs:251:27
note: Run with `RUST_BACKTRACE=1` for a backtrace.
```

After:
```
$ ./foo-nightly --not-an-option
error: Unrecognized option: 'not-an-option'
```

Document std::os::raw.

This adds a brief explanation to each type and its definition according to C. This also helps clarify that the definitions of the types, as described by rustdoc, are not necessarily the same from platform to platform.

Most of them were found by codespell: https://github.com/lucasdemarchi/codespell

Warn when rustc output conflicts with existing directories

When the compiled executable would conflict with a directory, display a
rustc error instead of a verbose and potentially-confusing linker
error. This is a usability improvement, and doesn’t actually change
behaviour with regards to compilation success. This addresses the
concern in #35887. Fixes #13098.

Rollup of 10 pull requests

- Successful merges: #46030, #47496, #47543, #47704, #47753, #47807, #47948, #47959, #48003, #48007
- Failed merges:

Previously, when the type of a method receiver could not be determined,
the error message would, potentially confusingly, highlight the span of
the entire method call.

Resolves #36598, resolves #42234.

Swapped order of left/right visits to ensure consistency in read/write pass ordering when -O is passed.

This commit adds a new unstable attribute to the compiler which requires that
arguments to a function are always provided as constants. The primary use case
for this is SIMD intrinsics where arguments are defined by vendors to be
constant and in LLVM they indeed must be constant as well.

For now this is mostly just a semantic guarantee in rustc that an argument is a
constant when invoked, phases like trans don't actually take advantage of it
yet. This means that we'll be able to use this in stdsimd but we won't be able
to remove the `constify_*` macros just yet. Hopefully soon though!