[docs] Update README/docs with clippy.toml limitations

[nyurik]

UPDATE Turns out this is not a bug but missing feature and unclear documentation, so converting to a docs improvement ticket.

Please clarify what lints/features are available in clippy.toml, and that most regular lints cannot be enabled/disabled in it. Relevant docs locations (might be more?):

• README.md
• book/src/configuration.md
• book/src/development/adding_lints.md

---

Original post

Summary

I was unable to configure clippy.toml to include some pedantic lints as described in the main readme. It seems clippy.toml only supports a subset of the all available clippy lints.

Reproducer

I created a clippy.toml in the root of the crate with this content (I also tried it with - instead of the _ to make sure)

default_trait_access = true

I expected to see this happen:

cargo clippy should have produced some lint suggestions.

Instead, this happened:

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

Version

rustc 1.64.0-nightly (9067d5277 2022-07-28)
binary: rustc
commit-hash: 9067d5277d10f0f32a49ec9c125a33828e26a32b
commit-date: 2022-07-28
host: x86_64-unknown-linux-gnu
release: 1.64.0-nightly
LLVM version: 14.0.6

Additional Labels

No response

[xFrednet]

Hey 👋, the config file is only for config values and not lints themselves. There is an issue #6625 for having a config file which allows the configuration of lint levels.

[nyurik]

Oh, thx @xFrednet , that's really confusing, I think we should update the readme (and wherever else the clippy.toml is mentiond)

[nyurik]

I updated this ticket to be a docs improvement ticket instead. Hopefully others won't get so confused :)