resolving it as a dependency.

Fixes rust-lang#46816

A problem caused by not doing so in Chrome has been reported here:
https://randomascii.wordpress.com/2018/02/25/compiler-bug-linker-bug-windows-kernel-bug/amp/

File::sync_all() calls FlushFileBuffers() down the line,
causing potentially unflushed buffers on high I/O-load systems to flush
and prevent nasty non-reproducible bugs.

The force-flush is only done on Windows and if the linker exited successfully

Closes rust-lang#48545

This should be enough and shouldn't require append(true) since we're not
explicitly writing anything so we're not flushing it so we've no risk of
overwriting it

the rust-std component only contains the core and compiler-builtins (+c +mem) crates

cc rust-lang#49382

vec![0; n], via implementations of SpecFromElem, has an optimization
that uses with_capacity_zeroed instead of with_capacity, which will use
calloc instead of malloc, and avoid an extra memset.

This adds the same optimization for vec![ptr::null(); n] and
vec![ptr::null_mut(); n], assuming their bit value is 0 (which is true
on all currently supported platforms).

This does so by adding an intermediate trait IsZero, which looks very
much like nonzero::Zeroable, but that one is on the way out, and doesn't
apply to pointers anyways.

Adding such a trait allows to avoid repeating the logic using
with_capacity_zeroed or with_capacity, or making the macro more complex
to support generics.

Similarly to vec![ptr::null{,_mut}(); n] in previous change, this adds
the optimization for vec!['\0'; n].

This commit applies a few code size optimizations for the wasm target to
the standard library, namely around panics. We notably know that in most
configurations it's impossible for us to print anything in
wasm32-unknown-unknown so we can skip larger portions of panicking that
are otherwise simply informative. This allows us to get quite a nice
size reduction.

Finally we can also tweak where the allocation happens for the
`Box<Any>` that we panic with. By only allocating once unwinding starts
we can reduce the size of a panicking wasm module from 44k to 350 bytes.

So we can cut some params by using stuff from the environment.

the goal is to build, in a single Cargo invocation, several no-std crates that we want to put in the
rust-std component of no-std targets. The nostd crate builds these crates:

- core
- compiler-builtin (with the "c" and "mem" features enabled)
- alloc
- std_unicode

This reverts commit 14768f9.

remove erroneous error message when checking impl trait params

fixes rust-lang#48703

…akis

Stabilize attributes on generic parameters

Closes rust-lang#48848

AST: Give spans to all identifiers

Change representation of `ast::Ident` from `{ name: Symbol, ctxt: SyntaxContext }` to `{ name: Symbol, span: Span }`.
Syntax contexts still can be extracted from spans (`span.ctxt()`).

Why this should not require more memory:
- `Span` is `u32` just like `SyntaxContext`.
- Despite keeping more spans in AST we don't actually *create* more spans, so the number of "outlined" spans kept in span interner shouldn't become larger.

Why this may be slightly slower:
- When we need to extract ctxt from an identifier instead of just field read we need to do bit field extraction possibly followed by and access by index into span interner's vector. Both operations should be fast (unless the span interner is under some synchronization) and we already do ctxt extraction from spans all the time during macro expansion, so the difference should be lost in noise.

cc rust-lang#48842 (comment)

…chton

Take the original extra-filename passed to a crate into account when resolving it as a dependency

resolving it as a dependency.

Fixes rust-lang#46816

RFC 2008: Finishing Touches

Part of rust-lang#44109.

r? @nikomatsakis
(not sure who was best for this PR).

…gs, r=nikomatsakis

Small typeck refactorings

Some code improvements I noticed while reading the code.

…rister

Flush executables to disk after linkage

A problem caused by not doing so in Chrome has been reported [here](https://randomascii.wordpress.com/2018/02/25/compiler-bug-linker-bug-windows-kernel-bug/amp/).

`File::sync_all()` calls `FlushFileBuffers()` down the line, causing potentially unflushed buffers on high I/O-load systems to flush and preventing nasty non-reproducible bugs.

Closes rust-lang#48545

…ackler

std: Minimize size of panicking on wasm

This commit applies a few code size optimizations for the wasm target to
the standard library, namely around panics. We notably know that in most
configurations it's impossible for us to print anything in
wasm32-unknown-unknown so we can skip larger portions of panicking that
are otherwise simply informative. This allows us to get quite a nice
size reduction.

Finally we can also tweak where the allocation happens for the
`Box<Any>` that we panic with. By only allocating once unwinding starts
we can reduce the size of a panicking wasm module from 44k to 350 bytes.

Add more vec![... ; n] optimizations

vec![0; n], via implementations of SpecFromElem, has an optimization that uses with_capacity_zeroed instead of with_capacity, which will use calloc instead of malloc, and avoid an extra memset.

This PR adds the same optimization for ptr::null, ptr::null_mut, and None, when their in-memory representation is zeroes.

add a dist builder to build rust-std components for the THUMB targets

the rust-std component only contains the core and compiler-builtins (+c +mem) crates

cc rust-lang#49382

- I'm not entirely sure if this PR alone will produce rust-std components installable by rustup or if something else needs to be changed
- I could have done the THUMB builds in an existing builder / image; I wasn't sure if that was a good idea so I added a new image
- I could build other crates like alloc into the rust-std component but, AFAICT, that would require calling Cargo a second time (one for alloc and one for compiler-builtins), or have alloc depend on compiler-builtins (rust-lang#49503 will perform that change) *and* have alloc resurface the "c" and "mem" Cargo features.

r? @alexcrichton