Implementation of
rust-lang/rfcs#2799

The Cargo book can be generated the same way as the other books.

This feature adds `X..`, `..X`, and `..=X` patterns.

Add method Result::into_ok

Implementation of rust-lang/rfcs#2799

Tracking issue rust-lang#61695

Introduce `X..`, `..X`, and `..=X` range patterns

Tracking issue: rust-lang#67264
Feature gate: `#![feature(half_open_range_patterns)]`

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In this PR, we introduce range-from (`X..`), range-to (`..X`), and range-to-inclusive (`..=X`) patterns.
These correspond to the `RangeFrom`, `RangeTo`, and `RangeToInclusive` expression forms introduced with the same syntaxes. The correspondence is both syntactic and semantic (in the sense that e.g. a `X..` pattern matching on a scrutinee `s` holds exactly when `(X..).contains(&s)` holds).

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Noteworthy:

- The compiler complexity added with this PR is around 10 lines (discounting new tests, which account for the large PR size).

- `...X` is accepted syntactically with the same meaning as `..=X`. This is done primarily to simplify and unify the implementation & spec. If-and-when we decide to make `X...Y` a hard error on a new edition, we can do the same for `...X` patterns as well.

- `X...` and `X..=` is rejected syntactically just like it is for the expression equivalents. We should perhaps make these into semantic restrictions (cc @petrochenkov).

- In HAIR, these half-open ranges are represented by inserting the max/min values for the approprate types. That is, `X..` where `X: u8` would become `X..=u8::MAX` in HAIR (note the `..=` since `RangeFrom` includes the end).

- Exhaustive integer / char matching does not (yet) allow for e.g. exhaustive matching on `0usize..` or `..5usize | 5..` (same idea for `isize`). This would be a substantially more invasive change, and could be added in some other PR.

- The issues with slice pattern syntax has been resolved as we decided to use `..` to mean a "rest-pattern" and `[xs @ ..]` to bind the rest to a name in a slice pattern.

- Like with rust-lang#35712, which provided `X..Y` range patterns, this is not yet backed up by an RFC. I'm providing this experimental implementation now to have something concrete to discuss. I would be happy to provide an RFC for this PR as well as for rust-lang#35712 to finalize and confirm the ideas with the larger community.

Closes rust-lang/rfcs#947.

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r? @varkor cc @matthewjasper @oli-obk

I would recommend reviewing this (in particular HAIR-lowering and pattern parsing changes) with whitespace changes ignored.

Unify output of "variant not found" errors

Fix rust-lang#49566.

…-Simulacrum

Build compiletest with in-tree libtest

This updates compiletest to build in `Mode::ToolStd`, using the locally-built crates for `std` and especially `test`. This way we're immune to unstable differences in the bootstrap compiler crates, whether that's a prior-release stage0 or a current release local rebuild. Fixes rust-lang#59264.

As a minor cleanup, this also removes the unused `llvm_tools` flag.

remove explicit strip-hidden pass from compiler doc generation

`strip-hidden` is now implied by `--document-private-items` with rust-lang#67875, so there's no need to specify it anymore.

Canonicalize rustc_error imports

r? @Mark-Simulacrum

…xcrichton

Allow specifying LLVM args in target specifications

…ulacrum

rustbuild: Cleanup book generation

The Cargo book can be generated the same way as the other books.