added rustc_const_unstable attribute

extended tests

added conversion test

fixed tidy test

added feature attribute

Generate an IO error if the offset is out of bounds for the system call.

The Higher Intermediate Representation doesn't have spans for visibility
keywords, so we were assuming that the first whitespace-delimited token
in the item span was the `pub` to be weakened. This doesn't work for
brace-grouped `use`s, which get lowered as if they were several
individual `use` statements, but with spans that only cover the braced
path-segments. Constructing a correct suggestion here presents some
challenges—until someone works those out, we can at least protect the
dignity of our compiler marking the suggestion for `use` items as
potentially incorrect.

This resolves rust-lang#50455 (but again, it would be desirable in the future to
make a correct suggestion instead of copping out like this).

This commit fixes a hard error where the `#![feature(rust_2018_preview)]`
feature was forbidden to be mentioned when the `--edition 2018` flag was passed.
This instead silently accepts that feature gate despite it not being necessary.
It's intended that this will help ease the transition into the 2018 edition as
users will, for the time being, start off with the `rust_2018_preview` feature
and no longer immediately need to remove it.

Closes rust-lang#50662

This commit fixes recommending the `crate` prefix when migrating to 2018 for
paths that look like `use foo;` or `use {bar, baz}`

Closes rust-lang#50660

…gestion, r=Manishearth

don't make crazy suggestion for unreachable braced pub-use

The Higher Intermediate Representation doesn't have spans for visibility
keywords, so we were assuming that the first whitespace-delimited token
in the item span was the `pub` to be weakened. This doesn't work for
brace-grouped `use`s, which get lowered as if they were several
individual `use` statements, but with spans that only cover the braced
path-segments. Constructing a correct suggestion here presents some
challenges—until someone works those out, we can at least protect the
dignity of our compiler by not offering any suggestion at all for `use` items.

This resolves rust-lang#50455 (but again, it would be desirable in the future to
make a correct suggestion instead of copping out like this).

r? @Manishearth

Made some functions in time module const

They may be const, or i missed something?

use fmt::Result where applicable

This is a quite boring PR, but I think the type alias improves readability, so why not use it?

…ster

Remove all reference to DepGraph::work_products

This is an attempt at fixing rust-lang#50500. It will remove the `work_products` key from `DepGraphData` completely, in favour of just passing the relevant data around. I went in a little blindly; everything appears to work just fine but I'd appreciate any additional advice people.

I didn't want to remove too much of what was already there, so I kept the structure pretty much the same (aside from some naming tweaks) - if anyone has suggestions on how to streamline it a little better, happy to follow up.

r? @michaelwoerister

…cs, r=cramertj

Update canonicalize docs

I was recently working with file-paths in Rust, and I felt let down by the `std::fs::canonicalize` docs, so I figured I should submit a PR with some suggestions.

I was looking for a method to turn a relative path into an absolute path. The `canonicalize` docs didn't mention the words "relative" or "absolute", but they did mention resolving symlinks (which is a kind of canonicalisation and does not imply converting to absolute), so I assumed that's all it did. To remedy this, I've added the word "absolute" to the description of both `std::fs::canonicalize` and `std::path::Path::canonicalize`.

After calling `canonicalize` on Windows, I ran into a bunch of other problems I would not have expected from the function's behaviour on Linux. Specifically, if you call `canonicalize` on a path:

  - it's allowed to be much longer than it otherwise would
  - `.join("a/slash/delimited/path")` gives you a broken path that Windows can't use, where the same operation would have worked perfectly without `canonicalize` (if the path were short enough)
  - the resulting path may confuse other Windows programs if you pass it to them on the command-line, or write it to a config file that they read, etc.

...so I tried to summarize those behaviours too.

If I understand correctly, those behaviours are a side-effect of calling `GetFinalPathNameByHandle`, and the documentation says `canonicalize` might not call that function in future, so maybe those side-effects shouldn't be part of the function's documentation. However, I bet there's a lot of applications deliberately calling `canonicalize` just for the path-length-extension alone, so that particular side-effect is de-facto part of the `canonicalize` interface.

…veklabnik

fs::write: Add example writing a &str

This adds an example to the documentation for `fs::write` that demonstrates the use of the `AsRef<[u8]>` implementation for &str. Experienced users should already recognize the possibility from the type signature, but new users may not recognize the significance.

…nnytm

Do not silently truncate offsets for `read_at`/`write_at` on emscripten

Generate an IO error if the offset is out of bounds for the system call.

…richton

AppVeyor: Read back trace from crash dump on failure.

This is an attempt to debug spurious access violations on Windows (rust-lang#33434, rust-lang#50604). Thanks to rust-lang#50276, there should be minidumps to read when rustc segfault.

(The implementation is based on <https://github.com/springmeyer/travis-coredump/blob/master/test.bat>.)

…nishearth

rustc: Allow an edition's feature on that edition

This commit fixes a hard error where the `#![feature(rust_2018_preview)]`
feature was forbidden to be mentioned when the `--edition 2018` flag was passed.
This instead silently accepts that feature gate despite it not being necessary.
It's intended that this will help ease the transition into the 2018 edition as
users will, for the time being, start off with the `rust_2018_preview` feature
and no longer immediately need to remove it.

Closes rust-lang#50662

…arnings, r=Manishearth

rustc: Fix `crate` lint for single-item paths

This commit fixes recommending the `crate` prefix when migrating to 2018 for
paths that look like `use foo;` or `use {bar, baz}`

Closes rust-lang#50660