…ator docs.

example:
    let s: String = format!("hello").into();

Fail on multiple declarations of `main`.

Closes rust-lang#67946.

Previously, when inserting the entry function, we only checked for
duplicate _definitions_ of `main`.  However, it's possible to cause
problems even only having a duplicate _declaration_. For example,
shadowing `main` using an extern block isn't caught by the current
check, and causes an assertion failure down the line in in LLVM code.

r? @pnkfelix

librustc_typeck: remove loop that never actually loops

…mulacrum

Do not ping PR reviewers in toolstate breakage

As per rust-lang#69419 (comment)

We should also remove author part?

…acrum

rustc_span: Add `Symbol::to_ident_string` for use in diagnostic messages

Covers the same error reporting use case (rust-lang#69387 (comment)) as the `Display` impl for `Ident`.
cc rust-lang#69053

Follow-up to rust-lang#69387.
r? @Mark-Simulacrum

don't take redundant references to operands

…c-morse

use find(x) instead of filter(x).next()

…morse

note that find(f) is equivalent to filter(f).next() in the docs.

r? @ecstatic-morse

…mt-on-untracked-paths, r=Mark-Simulacrum

Ignore untracked paths when running `rustfmt` on repository.

This is a step towards resolving rust-lang#69291

(It might be the only step necessary at the moment; I'm not yet sure.)

…sion, r=Mark-Simulacrum

don't use .into() to convert types into identical types.

This removes redundant `.into()` calls.

example: `let s: String = format!("hello").into();`