More iter().last() -> last(), iter().next() -> first()

[compiler-errors]

r? @estebank

Follow-up to #145401, which was missing some cases. Also change .iter().next() -> .first() when applicable.

[rustbot]

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

rustc_errors::emitter was changed

cc @Muscraft

rustc_macros::diagnostics was changed

cc @davidtwco, @compiler-errors, @TaKO8Ki

[estebank]

r=me

[estebank]

also filed rust-lang/rust-clippy#15487

[rust-log-analyzer]

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    Checking rustc_codegen_cranelift v0.1.0 (/checkout/compiler/rustc_codegen_cranelift)
error[E0599]: no method named `first` found for struct `SwitchTargetsIter` in the current scope
   --> compiler/rustc_codegen_cranelift/src/base.rs:442:71
    |
442 |                     || (targets.iter().count() == 1 && targets.iter().first().unwrap().0 == 0);
    |                                                                       ^^^^^ method not found in `SwitchTargetsIter<'_>`

error[E0599]: no method named `first` found for struct `SwitchTargetsIter` in the current scope
   --> compiler/rustc_codegen_cranelift/src/base.rs:445:67
    |
445 |                     let (then_value, then_block) = targets.iter().first().unwrap();
    |                                                                   ^^^^^ method not found in `SwitchTargetsIter<'_>`

For more information about this error, try `rustc --explain E0599`.
[RUSTC-TIMING] rustc_codegen_cranelift test:false 1.081
error: could not compile `rustc_codegen_cranelift` (lib) due to 2 previous errors
Build completed unsuccessfully in 0:02:25

[bjorn3]

Can this be done in the cg_clif repo instead?