Allow Drop types in const's too, with #![feature(drop_types_in_const)].

Implements the remaining amendment, see #33156. cc @SergioBenitez

r? @nikomatsakis

Revert clamp

Revert clamp per https://github.com/rust-lang/rust/issues/44095#issuecomment-328218316 while we take time to assess the potential backwards compatibility damage done by it.

Avoid hashing when creating a DepNode from a HirId

Instead, combine the already-present DefPathHash with the 32-bit
ItemLocalIndex.

Should fix #44323.

r? @alexcrichton

limit and clear cache obligations opportunistically

Keeping **all** the obligations for every projection is wasteful of
memory and compilation time. We only really care about those
subobligations that may inform the result of the projection (i.e., may
help to resolve any inference variables that appear within).
Therefore, we can clear the subobligations from the cache that don't
potentially affect the result of the projection. On every cache hit,
we also take the opportunity to check if the type variables have been
resolved *yet* and, if so, clear out the pending obligations.

Fixes #43613.

r? @arielb1

NB -- not sure how to test for this. Probably we should add the #43613 test case to perf.

This reverts commit c589f867.

This reverts commit f74c5d2e.

This reverts commit 61f20f8d.

This reverts commit 576426a0.

This reverts commit 2e34ff76.

This reverts commit b762283e.

Migrate a slew of metadata methods to queries

This PR intends to make more progress on #41417, knocking off some low-hanging fruit.

Closes #44190
cc #44137

pprust: fix parenthesization of exprs

The pretty printer in `syntax::print::pprust` currently relies on the presence of `ExprKind::Paren` hints in order to correctly parenthesize expressions in its output.  If `Paren` nodes are missing, it sometimes produces wrong output, such as printing `1 - (2 - 3)` as `1 - 2 - 3`.  This PR fixes `pprust` to correctly print expressions regardless of the presence or absence of `Paren` nodes.  This should make `pprust` easier to use with programmatically constructed ASTs.

A few notes:

 * I added a function for assigning precedence values to exprs in `syntax::util::parser`, since there is already code there for assigning precedence values to binops.  Let me know if I should move this somewhere more `pprust`-specific.

 * I also moved the `contains_exterior_struct_lit` function from `rustc_lint::unused::UnusedParens` into `syntax::util::parser`, since it's needed for determining the correct parenthesization of `if`/`while` conditional expressions.

 * I couldn't find a good way to compare two exprs for equivalence while ignoring semantically-irrelevant details like spans.  So the test for the new behavior relies on a slight hack: it adds `Paren` nodes everywhere, so that the pretty-printed version exactly reflects the structure of the AST, and then compares the printed strings.  This works, but let me know if there's a better way.

travis: Downgrade to previous images temporarily

Travis is in the process of [rolling out an update][update] but looks like our
tests are breaking, let's temporarily roll back to get the queue moving again.

[update]: https://blog.travis-ci.com/2017-08-29-trusty-image-updates

Travis is in the process of [rolling out an update][update] but looks like our
tests are breaking, let's temporarily roll back to get the queue moving again.

[update]: https://blog.travis-ci.com/2017-08-29-trusty-image-updates

This commit moves the `crates` method to a query and then migrates all callers
to use a query instead of the now-renamed `crates_untracked` method where
possible.

Closes #41417

Debugflag: -Z emit-end-regions

 Skip EndRegion emission by default. Use `-Z emit-end-regions` to reenable it.

The main intent is to fix cases where `EndRegion` emission is believed to be causing excess peak memory pressure.

It may also be a welcome change to people inspecting the MIR output who find the EndRegions to be a distraction.

(In later follow-up PR's I will put in safe-guards against using the current mir-borrowck without enabling `EndRegion` emission. But I wanted this PR to be minimal, in part because we may wish to backport it to the beta channel if we find that it reduces peak memory usage significantly.)

Make the LocalKey facade of thread_local! inlineable cross-crate.

Fixes (almost*) #25088 by changing the `LocalKey` `static` `thread_local!` generates to a `const`.
This can be done because a `LocalKey` value holds no actual TLS data, only function pointers to get at said data, and it could even be made `Copy` without any negative consequences.
The recent stabilization of rvalue promotion to `'static` allows doing this without changing the API.
r? @alexcrichton

*almost because we can't yet inline `__getit` because it breaks on MSVC, see https://github.com/rust-lang/rust/pull/43931#issuecomment-323534214

rustc: Attempt to handle super long linker invocations

This commit adds logic to the compiler to attempt to handle super long linker
invocations by falling back to the `@`-file syntax if the invoked command is too
large. Each OS has a limit on how many arguments and how large the arguments can
be when spawning a new process, and linkers tend to be one of those programs
that can hit the limit!

The logic implemented here is to unconditionally attempt to spawn a linker and
then if it fails to spawn with an error from the OS that indicates the command
line is too big we attempt a fallback. The fallback is roughly the same for all
linkers where an argument pointing to a file, prepended with `@`, is passed.
This file then contains all the various arguments that we want to pass to the
linker.

Closes #41190

Rollup of 23 pull requests

- Successful merges: #44097, #44206, #44218, #44276, #44277, #44296, #44303, #44313, #44315, #44317, #44319, #44321, #44325, #44326, #44327, #44328, #44330, #44351, #44353, #44354, #44361, #44362, #44377
- Failed merges:

config.toml.example: fix some typos

Fix a bug in the inliner

r? @EddyB

Suggest changing literals instead of calling methods (fixes #44307)

bootstrap: openssl for NetBSD/sparc64 in extended build

r? @Mark-Simulacrum

Include rustc in the default `./x.py install`

The default install used to include rustc, rust-std, and rust-docs, but
the refactoring in commit 6b3413d8 make rustc only default in
extended builds.  This commit makes rustc installed by default again.

More PowerPC Altivec intrinsics

Fix link typo in 1.20.0 release notes

Should have been included in https://github.com/rust-lang/rust/pull/44230

Removed the incorrect documentation for from_str

Fixes #44242.

#12808 is closed remove the FIXME

let's see if this can be cleaned up.

https://github.com/rust-lang/rust/issues/12808#issuecomment-326852052

#33490 is closed remove the FIXME

let's see if this can be cleaned up.

https://github.com/rust-lang/rust/issues/33490#issuecomment-326851930

Make slice::split_at_mut example demonstrate mutability

Moved the examples from split_at_mut to split_at so the example at
split_at_mut can just demonstrate mutability.

See #44314

r? @steveklabnik

bootstrap: only include docs in extended distribution if enabled

Fixes #44163

Improve DefIndex formatting to be more semantic

Fixes #44318

r? @EddyB

Add test for #22706

Closes #22706

std/time: Give an example to get UNIX_EPOCH in seconds

rustbook: remove dead test functions

There is no "test" subcommand added to the `clap::App`, so this is all dead code.

Cc @steveklabnik -- your [commit](https://github.com/RalfJung/rust/commit/a076961fd0e3d8a68f8b047460b8f5191d203b08) introducing this stated the intention of having both commands, but it seems nobody has missed the `test` command since February.

impl Debug for SplitWhitespace.

This one got missed because `libstd_unicode` doesn't have a `deny(missing_debug_implementations)` like `libstd` and `libcore`. I think that perhaps this lint should check for items exported from other crates too.

Minor documentation improvements for StmtKind

Documentation for Semi and Marco StmtKinds.

Wasn't obvious to me what these were when writing a lint recently.