Improve "unknown key" error message?

[smoelius]

Description

Personally, I find this error message hard to read:

rust-clippy/tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr

Line 1 in c3f3c58

error: error reading Clippy's configuration file `$DIR/clippy.toml`: unknown field `foobar`, expected one of `avoid-breaking-exported-api`, `msrv`, `blacklisted-names`, `cognitive-complexity-threshold`, `cyclomatic-complexity-threshold`, `doc-valid-idents`, `too-many-arguments-threshold`, `type-complexity-threshold`, `single-char-binding-names-threshold`, `too-large-for-stack`, `enum-variant-name-threshold`, `enum-variant-size-threshold`, `verbose-bit-mask-threshold`, `literal-representation-threshold`, `trivial-copy-size-limit`, `pass-by-value-size-limit`, `too-many-lines-threshold`, `array-size-threshold`, `vec-box-size-threshold`, `max-trait-bounds`, `max-struct-bools`, `max-fn-params-bools`, `warn-on-all-wildcard-imports`, `disallowed-methods`, `disallowed-types`, `unreadable-literal-lint-fractions`, `upper-case-acronyms-aggressive`, `cargo-ignore-publish`, `standard-macro-braces`, `enforced-import-renames`, `allowed-scripts`, `enable-raw-pointer-heuristic-for-send`, `max-suggested-slice-pattern-length`, `await-holding-invalid-types`, `max-include-file-size`, `allow-expect-in-tests`, `allow-unwrap-in-tests`, `third-party` at line 5 column 1

I think it would be easier to read if the available keys were sorted and printed one per line.

Would you be open to a PR to improve this error message?

Version

No response

Additional Labels

No response

[Serial-ATA]

@rustbot label +C-enhancement

[xFrednet]

I'm open to it, but this has also been bugging me a bit. Maybe we can have more than one field per line. 🙃