Error message now makes clear that mutable borrow conflicts on a single
value in a loop body is caused by the borrow outlasting a single pass of
the loop.
Loop conflicts are detected by seeing when two borrow locations are the
same - which indicates the same code being run more than once.

rustbuild: Fix the --build argument to bootstrap.py

This makes the --build argument also apply for the downloading of the stage0 toolchain and building rustbuild.

Fixes #42116

Fix overflowing_literals lint for large f32s

Float literals need to be parsed as the correct type so they can be
rounded correctly.

improve the TryFrom implementations

This removes the need for a 128 bit storage by making use of the fact that there can be either no over/underflow, either one or both, and each time the target type suffices to hold the limit for comparison. This also means that the implementation will work in targets without 128bit support (unless it's for 128bit types, of course).

The downside is that the code looks a bit more complex.

This removes the need for a 128 bit storage by making use of the fact that
there can be either no over/underflow, either one or both, and each time
the target type suffices to hold the limit for comparison.

The downside is that the code looks a bit more complex.

This test code included in this commit is from @oyvindln 's PR. They also
greatly helped fixing a number of errors I made along the way. Thanks a lot!

Rollup of 11 pull requests

- Successful merges: #43297, #43322, #43342, #43361, #43366, #43374, #43379, #43401, #43421, #43428, #43446
- Failed merges:

Rustbuild regression fixes

I believe this will fix https://github.com/rust-lang/rust/issues/43427.

This PR also avoids running pretty tests by-default.

r? @alexcrichton

rustdoc: add unions to whitelist of sidebar types

This resolves #43405.

Fix some doc/comment typos.

rustc: Add some build scripts for librustc crates

This commit adds some "boilerplate" build scripts to librustc/libsyntax crates
to declare dependencies on various environment variables that are configured
throughout the build. Cargo recently gained the ability to depend on environment
variables in build scripts which can help trigger recompilation of a crate.

This should fix weird bugs where after you make a commit or a few days later
you'll get weird "not built with the same compiler" errors hopefully.

Correct the spelling of "homogeneous"

None

Add a missing verb to the description of std::process::ExitStatus::success()

"Signal termination not considered" -> "Signal termination **is** not considered"

The first line of the description was rewrapped so it fits into 80 characters.

Clarify that sort_unstable is deterministic

@frankmcsherry complained that the documentation said "it is randomized but deterministic", which is a contradictory statement.

This PR uses a different and clearer wording.

Fix docs: BufReader/File doesn't need to be mut

Neither `BufReader` nor `File` need to be declared `mut` for most of these examples. The cookbook example using `BufReader` doesn't declare them as `mut` either (https://brson.github.io/rust-cookbook/basics.html#ex-std-read-lines).

Remove unused DefPathTable::retrace_path()

`DefPathTable::retrace_path()` is not used anymore for a while now and removing it also removes the need to build the costly `DefPathTable::key_to_index` map for every upstream crate.

cc #43300

r? @EddyB

Document use of `compiler_builtins` with `no_std` binaries

See discussion in #43264.

The docs for the `compiler_builtins_lib` feature were removed in
PR #42899. But, though the `compiler_builtins` library has been
migrated out-of-tree, the language feature remains, and is needed to
use the stand-alone crate. So, we reintroduce the docs for the
feature, and add a reference to them when describing how to create a
`no_std` executable.

Update liblibc

This updates liblibc to the latest master and fixes #43305

configure: allow distros to disable debuginfo-only-std

This allows builders to generate debugging information for everything, even in a stable release build. This is useful for distros like Fedora (already carrying a [similar patch](https://src.fedoraproject.org/cgit/rpms/rust.git/tree/rust-1.16.0-configure-no-override.patch)) and Debian that automatically put all debuginfo in separate "debug symbol" packages.

This commit preserves the default behaviour of switching these on when a non-dev channel is selected, but allows the user to override this via the `./configure` command line.

In theory, one could also do this via `bootstrap/config.toml` but it doesn't work currently due to #43295.

rustdoc: fix layout of Fields section in documentation for unions

Previously, the union fields would all render on the same line with
hideous spacing; comparison to the analogous section for structs makes
it undoubtable that `display: block` is the true intent.

Concisely and definitively resolves #43404 and its perfidious
malignancy.

Use a config struct for save-analysis

Replaces some existing customisation options, including removing the -Zsave-analysis-api flag

r? @EddyB

And cargo update

Add #[derive(Clone)] to TokenTreeIter

I've found this useful for writing backtracking parsers.

The underlying `Cursor` implements `Clone` already, so it's just a matter of adding `#[derive(Clone)]` to the type.

r? @jseyfried

Add generic example of std::ops::Sub in doc comments

This PR adds an example of using generics with std::ops::Sub and is a follow up of PR #41612 and is related to issue #29365. I also wanted to add examples to Mul and Div, but I think these two traits are already loaded with examples.

This resolves #43405.

Point at `:` when using it instead of `;`

When triggering type ascription in such a way that we can infer a
statement end was intended, add a suggestion for the change. Always
point out the reason for the expectation of a type is due to type
ascription.

Fix #42057, #41928.

Previously, the union fields would all render on the same line with
hideous spacing; comparison to the analogous section for structs makes
it undoubtable that `display: block` is the true intent.

Concisely and definitively resolves #43404 and its perfidious
malignancy.

Adjust new suggestions to the suggestion guidelines

Addresses https://github.com/rust-lang/rust/pull/42033#discussion_r127694915

guidelines are https://github.com/rust-lang/rust/blob/master//src/librustc_errors/diagnostic.rs#L212-L224

doc: provide an actual equivalent to filter_map

Improve panic docs for Instant::duration_since

The docs for Instant::duration_since has a confusing section on panicking. It's
much more clear without the second two sentences of description.

This commit adds some "boilerplate" build scripts to librustc/libsyntax crates
to declare dependencies on various environment variables that are configured
throughout the build. Cargo recently gained the ability to depend on environment
variables in build scripts which can help trigger recompilation of a crate.

This should fix weird bugs where after you make a commit or a few days later
you'll get weird "not built with the same compiler" errors hopefully.

Add missing `!: Clone` impl

Fixes #43296

(untested because I'm having computer troubles, but a one-liner can't break anything right?)

Update Rust LLVM bindings for LLVM 5.0

This is the initial set of changes to update the rust llvm bindings for 5.0. The llvm commits necessitating these changes are linked from the tracking issue, #43370.

Ignore stack probe tests on AArch64

Stack probes are only implemented for x86, and as such currently fail on AArch64. This patch ignores those tests on this architecture.

Fixes #43356.

r? @alexcrichton