PR rust-lang#69562, which fixed a bug that was causing clippy to ICE, passed the
place for the *result* of `Rvalue::Discriminant` instead of the
*operand* to `apply_discriminant_switch_effect`. As a result, no effect
was applied at all, and we lost the perf benefits from marking
inactive enum variants as uninitialized.

For all of the methods that pick off the first or last element, we can
use subslice patterns to implement them directly, rather than relying on
deeper indexing function calls. At a minimum, this means the generated
code will rely less on inlining for performance, but in some cases it
also optimizes better.

…'tcx

Use .next() instead of .nth(0) on iterators.

Rename DefKind::Method and TraitItemKind::Method

r? @eddyb, @Centril, or @matthewjasper

cc rust-lang#69498 rust-lang#60163

…t, r=oli-obk

Pass correct place to `discriminant_switch_effect`

PR rust-lang#69562, which fixed a bug that was causing clippy to ICE, mistakenly passed the place holding the *result* of `Rvalue::Discriminant` instead of the place holding its *operand* to `apply_discriminant_switch_effect` as the enum place. As a result, no effect was applied at all, and we lost the perf benefits from marking inactive enum variants as uninitialized.

**edit:** The regression test has been split into rust-lang#69744.

r? @oli-obk

Use subslice patterns in slice methods

For all of the methods that pick off the first or last element, we can
use subslice patterns to implement them directly, rather than relying on
deeper indexing function calls. At a minimum, this means the generated
code will rely less on inlining for performance, but in some cases it
also optimizes better.

…i-obk

Make PlaceRef take just one lifetime

r? @eddyb

Avoid using `unwrap()` in suggestions

Addresses rust-lang#69725, still need a regression test.

r? @estebank