Stabilizing an inherent method may cause change in behavior instead of
inference error. Updated to use the wording from [varkor's comment].

Closes rust-lang#50232.

[varkor's comment]: rust-lang#50232 (comment)

When looking at any scope in scope chain A, we only need to look for
matches among scopes previously seen in scope chain B, and vice versa.
This halves the number of "seen before?" comparisons, speeding up some
runs of style-servo, clap-rs, and syn by 1--2%.

This reverts commit 05a9acc.

Because they are (a) trivial, and (b) super hot.

This change speeds up most rustc-benchmarks, the best by 5%.

…er-check, r=QuietMisdreavus

Add query search order check

Fixes rust-lang#50180.

r? @QuietMisdreavus

…ion-label, r=estebank

Rename "show type declaration" to "show declaration"

Fixes rust-lang#50347.

r? @QuietMisdreavus

…name-collision, r=nikomatsakis

Clarify wordings of the `unstable_name_collision` lint.

Stabilizing an inherent method may cause change in behavior instead of inference error. Updated to use the wording from [varkor's comment].

Closes rust-lang#50232.

[varkor's comment]: rust-lang#50232 (comment)

…-two-vecs, r=nikomatsakis

Use two vectors in nearest_common_ancestor.

When looking at any scope in scope chain A, we only need to look for
matches among scopes previously seen in scope chain B, and vice versa.
This halves the number of "seen before?" comparisons, speeding up some
runs of style-servo, clap-rs, and syn by 1--2%.

Thanks to @kirillkh for the suggestion.

r? @nikomatsakis

Allow unaligned reads in constants

fixes rust-lang#50356

introduced in rust-lang#49513

…r=sfackler

Revert "Implement FromStr for PathBuf"

This reverts commit 05a9acc.

The libs team was discussing rust-lang#44431 today and the changes originally added in rust-lang#48292 and the conclusion was that we'd like to revert this for now until `!` is stable. This'll provide us maximal flexibility to tweak the error type here in the future, and it looks like `!` is close-ish to stabilization so hopefully this won't be delayed for too long.

…elwoerister

Always inline simple BytePos and CharPos methods.

Because they are (a) trivial, and (b) super hot.

This change speeds up most rustc-perf benchmarks, the best by 5%.

Full measurements:
```
coercions-check
	avg: -3.0%	min: -5.4%	max: -1.3%
helloworld-check
	avg: -3.9%	min: -4.1%	max: -3.6%
unify-linearly-check
	avg: -3.1%	min: -3.7%	max: -2.5%
deeply-nested-check
	avg: -2.6%	min: -3.6%	max: -2.1%
coercions-opt
	avg: -2.1%	min: -3.6%	max: -1.3%
coercions
	avg: -2.0%	min: -3.5%	max: -1.0%
issue-46449-check
	avg: -2.8%	min: -3.1%	max: -2.6%
parser-check
	avg: -2.6%	min: -3.1%	max: -2.0%
deeply-nested-opt
	avg: -1.5%	min: -3.0%	max: -0.8%
deeply-nested
	avg: -1.8%	min: -2.9%	max: -1.1%
issue-46449
	avg: -1.4%	min: -2.7%	max: -1.1%
issue-46449-opt
	avg: -1.0%	min: -2.7%	max: -0.5%
regression-31157-check
	avg: -1.7%	min: -2.3%	max: -1.1%
tuple-stress-opt
	avg: -1.0%	min: -2.2%	max: -0.5%
tokio-webpush-simple-check
	avg: -1.6%	min: -2.1%	max: -1.2%
tuple-stress-check
	avg: -1.2%	min: -2.1%	max: -0.8%
unused-warnings-check
	avg: -1.6%	min: -2.0%	max: -1.4%
encoding-check
	avg: -1.4%	min: -1.8%	max: -1.0%
tuple-stress
	avg: -1.0%	min: -1.7%	max: -0.6%
encoding-opt
	avg: -0.9%	min: -1.6%	max: -0.3%
unused-warnings
	avg: -1.3%	min: -1.6%	max: -1.2%
unused-warnings-opt
	avg: -1.3%	min: -1.5%	max: -1.2%
encoding
	avg: -1.0%	min: -1.5%	max: -0.4%
html5ever-opt
	avg: -0.7%	min: -1.5%	max: -0.3%
futures
	avg: -1.0%	min: -1.5%	max: -0.5%
futures-check
	avg: -1.0%	min: -1.5%	max: -0.5%
futures-opt
	avg: -0.8%	min: -1.4%	max: -0.3%
regression-31157-opt
	avg: -0.5%	min: -1.4%	max: -0.0%
unify-linearly-opt
	avg: -1.2%	min: -1.4%	max: -1.0%
parser-opt
	avg: -1.2%	min: -1.4%	max: -1.0%
helloworld
	avg: -1.3%	min: -1.4%	max: -1.3%
helloworld-opt
	avg: -1.3%	min: -1.3%	max: -1.3%
parser
	avg: -1.2%	min: -1.3%	max: -1.0%
regex-check
	avg: -1.1%	min: -1.3%	max: -0.7%
unify-linearly
	avg: -1.1%	min: -1.3%	max: -1.0%
syn-check
	avg: -0.8%	min: -1.3%	max: -0.3%
piston-image-check
	avg: -0.7%	min: -1.2%	max: -0.4%
regex-opt
	avg: -0.5%	min: -1.2%	max: -0.0%
syn
	avg: -0.6%	min: -1.2%	max: -0.3%
hyper
	avg: -0.8%	min: -1.2%	max: -0.4%
syn-opt
	avg: -0.5%	min: -1.2%	max: -0.1%
regex
	avg: -0.7%	min: -1.2%	max: -0.3%
regression-31157
	avg: -0.7%	min: -1.2%	max: -0.3%
clap-rs-check
	avg: -0.6%	min: -1.1%	max: -0.2%
hyper-check
	avg: -0.8%	min: -1.1%	max: -0.5%
piston-image-opt
	avg: -0.4%	min: -1.1%	max: -0.0%
hyper-opt
	avg: -0.6%	min: -1.0%	max: 0.0%
inflate
	avg: -0.4%	min: -1.0%	max: -0.2%
html5ever
	avg: -0.5%	min: -1.0%	max: -0.2%
inflate-opt
	avg: -0.3%	min: -1.0%	max: 0.3%
deep-vector-check
	avg: -0.6%	min: -1.0%	max: -0.3%
style-servo-check
	avg: -0.7%	min: -1.0%	max: -0.5%
tokio-webpush-simple-opt
	avg: -0.3%	min: -0.9%	max: 0.0%
inflate-check
	avg: -0.3%	min: -0.9%	max: -0.1%
piston-image
	avg: -0.4%	min: -0.8%	max: -0.2%
deep-vector
	avg: -0.4%	min: -0.8%	max: -0.1%
clap-rs
	avg: -0.4%	min: -0.7%	max: -0.2%
deep-vector-opt
	avg: -0.2%	min: -0.7%	max: 0.2%
style-servo
	avg: -0.3%	min: -0.7%	max: 0.1%
crates.io
	avg: -0.4%	min: -0.6%	max: -0.2%
crates.io-opt
	avg: -0.3%	min: -0.6%	max: -0.1%
tokio-webpush-simple
	avg: -0.4%	min: -0.6%	max: -0.3%
crates.io-check
	avg: -0.4%	min: -0.6%	max: -0.3%
html5ever-check
	avg: -0.4%	min: -0.6%	max: -0.2%
serde
	avg: -0.1%	min: -0.6%	max: 0.2%
serde-check
	avg: -0.1%	min: -0.5%	max: 0.4%
serde-opt
	avg: -0.2%	min: -0.5%	max: -0.1%
style-servo-opt
	avg: -0.2%	min: -0.4%	max: -0.0%
clap-rs-opt
	avg: -0.1%	min: -0.3%	max: 0.0%

Update Cargo

This should fix RLS

cc rust-lang#50379, rust-lang/cargo#5465

…g-range-inclusive-from-closure, r=michaelwoerister

Fix ICE when using a..=b in a closure.

Fix rust-lang#50415.

Forbid constructing empty identifiers from concat_idents

The empty identifier is a [reserved identifier](https://github.com/rust-lang/rust/blob/8a37c75a3a661385cc607d934c70e86a9eaf5fd7/src/libsyntax_pos/symbol.rs#L300-L305) in rust, apparently used for black magicks like representing the crate root or somesuch... and therefore, being able to construct it is Ungood.  Presumably.

...even if the macro that lets you construct it is so useless that you can't actually do any damage with it. (and believe me, I tried)

Fixes rust-lang#50403.

**Note:** I noticed that when you try to do something similar with `proc_macro::Term`, the compiler actually catches it and flags the identifier as reserved.  Perhaps a better solution would be to somehow have that same check applied here.

check if the token is a lifetime before parsing

Fixes rust-lang#50381.

…ration, r=QuietMisdreavus

Fix invalid path generation in rustdoc search

Fixes rust-lang#50311.