Clippy wanted features & bugfixes

[ojeda]

Please see as well #350 (i.e. some lints may make sense in Clippy, some in rustdoc).

Features that we would like to see

Required (we almost certainly want them)

• Lint to require // PANIC: ... comments.

  • Issue: // PANIC comment on panic-able calls rust-lang/rust-clippy#15861.
  • Issue (duplicate with more context): Lint to require // PANIC: ... comments rust-lang/rust-clippy#15895.
  • Cc: @blyxyas @hcbarker.

• Lint to detect unneeded // PANIC: ... comments.

  • Issue: Lint to detect unneeded // PANIC: ... comments rust-lang/rust-clippy#15896.
  • The dual to the one that requires it (see above).
  • Cc: @blyxyas @hcbarker.

• Lint to require // CAST: ... comments for as casts.

  • Issue: // CAST: ... comment on as casts rust-lang/rust-clippy#15963.
  • Cc: @blyxyas @hcbarker.

• Lint to require // CAST: ... comments for pointer casts.

  • See the one for as casts.
  • Cc: @blyxyas @hcbarker.

• Lint to detect unneeded // CAST: ... comments.

  • Issue: Lint to detect unneeded // CAST: ... comments rust-lang/rust-clippy#15964.
  • The dual to the one(s) that require it (see above), i.e. as casts and pointer casts.
  • Cc: @blyxyas @hcbarker.

• Lint to catch #[no_mangle] on non-repr(C) pub statics.

  • Issue: Lint against #[no_mangle] for non-repr(C) pub statics rust-lang/rust-clippy#11219.
  • PR: [no_mangle_with_rust_abi]: Check for statics with a non #[repr(Rust)] type rust-lang/rust-clippy#11253.
  • Related (Rust language) PR: Allow explicit #[repr(Rust)] rust-lang/rust#114201 (1.74).

• Support custom dbg!s in the dbg_macro lint.

  • We started using it in Rust 1.60, but it stopped working in 1.61 (but it may be intended).
  • Issue: Custom dbg! macros for dbg_macro lint rust-lang/rust-clippy#11303.

• Lint to catch non-absolute paths in macros, e.g. core::... instead of ::core::....

  • Issue: New lint: relative_path_in_macro_definition rust-lang/rust-clippy#14472.
  • PR: Add relative_path_in_macro_definition lint (#14472) #14645 rust-lang/rust-clippy#14648.
  • PR: Add relative_path_in_macro_definition lint (#14472) rust-lang/rust-clippy#14645.
  • Lore: https://lore.kernel.org/rust-for-linux/D8PDWRH06U1X.3JGHP1311BPPY@proton.me/.

• Lint to catch unnecessary generics like Result<()>.

  • Issue: lint idea: useless_default_generic_parameters rust-lang/rust-clippy#14848.
  • checkpatch.pl issue: Simplify Result<()> uses and implement a checkpatch.pl check for it #1128.
  • Lore: https://lore.kernel.org/rust-for-linux/DA03Y4OQIZ50.157T5EEVHQVMI@kernel.org/.

• Support custom assert*!s for lints like eq_op.

  • Issue: Custom assert_*! macros for eq_op (and possibly others) rust-lang/rust-clippy#14903.
  • Lore: https://lore.kernel.org/rust-for-linux/20250502215133.1923676-2-ojeda@kernel.org/#Z31rust:kernel:kunit.rs.

Nice to have (not critical, we could workaround if needed, etc.)

• Improved shadowing lints.

  • We currently do not enable any of the shadow_* lints. In particular, shadow_reuse would lint on many things that are OK for us, especially "top-level" let ... =s. Please see the details in Lint dangerous uses of shadowing rust-lang/rust-clippy#3433 (comment).
  • It would have already prevented one kernel bug: https://lore.kernel.org/rust-for-linux/20241123-rust-fix-arraylayout-v1-1-197e64c95bd4@asahilina.net/.
  • Issue: Lint dangerous uses of shadowing rust-lang/rust-clippy#3433.
  • Issue: Lint request: warn when variable declared in match pattern shadows other variable rust-lang/rust-clippy#2890.

• Lints that generalize exit, todo, mem_forget, etc.

  • Issue: New lint: generalize exit, todo, mem_forget, etc. rust-lang/rust-clippy#8031.

• disallowed_names support for identifiers.

  • Issue: disallowed_names for identifiers and not just variables rust-lang/rust-clippy#11306.

• Per-path lint levels for DisallowedPath-related lints.

  • Issue: Per-path lint levels in DisallowedPath rust-lang/rust-clippy#11307.

• Have a lint against usize-to-u64 casts (or, against all integer casts).

  • Issue: Have a lint against usize-to-u64 casts (or, against *all* integer casts) rust-lang/rust-clippy#9231.

• Make unnecessary_cast cover some core::ffi::c_* cases.

  • Issue: unnecessary_cast: core::ffi::c_* cases rust-lang/rust-clippy#13494.

• unnecessary_cast does not trigger with a local but it does with a parameter.

  • Issue: unnecessary_cast false negative: parameter vs. local rust-lang/rust-clippy#13495.

• Ignoring lints added after a given Rust version.

  • Issue: Ignoring lints added after a given Rust version rust-lang/rust-clippy#11227.
  • Related: New lints are not backwards compatible rust-lang/cargo#12495 (about ignoring unknown lints, explicitly passed, when compiling with an older compiler, rather than a new compiler introducing new lints).
  • If we had something like this, then we could consider using -D for some lint groups or leaving Clippy's default for some lints in clippy::all.

• Unsafe attributes support.

  • Issue: Unsafe attributes support (undocumented_unsafe_blocks) rust-lang/rust-clippy#13316.
  • Issue: Unsafe attributes support (unnecessary_safety_comment) rust-lang/rust-clippy#13317.

• Avoid inherent methods on generic smart pointers.

  • Issue: New lint suggestion: Avoid inherent methods on generic smart pointers rust-lang/rust-clippy#11820.
  • Zulip: https://rust-for-linux.zulipchat.com/#narrow/stream/288089-General/topic/.60self.60.20receiver.20vs.20associated.20function.20for.20.60Arc.60/near/472175254.

• Split needless_lifetimes.

  • One "major addition" to the lint added in 1.86.
  • Currently it is the only clippy::all lint that we allow.
  • Issue: Consider splitting needless_lifetimes into cases that do and do not require '_ rust-lang/rust-clippy#13514.
  • Lore: https://lore.kernel.org/rust-for-linux/20241012231300.397010-1-ojeda@kernel.org/.
  • Lore: https://lore.kernel.org/rust-for-linux/20241116181538.369355-1-ojeda@kernel.org/.

• Support for --fix without Cargo (e.g. inside clippy-driver).

  • Using cargo (the binary) would be fine if needed, but not if it requires a Cargo-based structure.

• unsafe extern support.

  • Issue: unsafe extern support (undocumented_unsafe_blocks?) rust-lang/rust-clippy#13560.

• Unneeded rust as language in rustdoc's documentation examples.

  • Issue: Unneeded rust as language in rustdoc's documentation examples rust-lang/rust-clippy#13604.

• manual_div_ceil suggests change that could alter behaviour.

  • Issue: manual_div_ceil suggests change that could alter behaviour rust-lang/rust-clippy#14333.

• Lint to catch docs using /// instead of //!.

  • Issue: Documentation mistakenly using /// instead of //! rust-lang/rust-clippy#14402.
  • Example: 8d9b095 ("samples: rust_misc_device: Provide an example C program to exercise functionality").

• Support msrv with a list of unstable features to assume (or perhaps a list of lints that ignore the msrv field).

  • Issue: feature request: #[feature] awareness in MSRV-gated lints rust-lang/rust-clippy#14477.

• Lint to catch links in normal comments (i.e. //) that are not formatted as Markdown autolinks (i.e. <https://...>).

  • Should lints like these be part of rustdoc in general, like the wish for intra-doc links there?
  • Rust for Linux example issue to clean instances of these: Use Markdown autolinks in normal comments #1153.

• Lint to detect unindented triple backquotes in the end of examples.

  • Issue: Detect code block marker in docs without "base indentation" rust-lang/rust-clippy#15023.
  • Example: https://lore.kernel.org/rust-for-linux/20250609-topics-tyr-regulator-v4-1-b4fdcf1385a7@collabora.com/.

• Lint to detect code block contents without "base indentation" in docs.

  • Issue: Detect code block contents without "base indentation" in docs rust-lang/rust-clippy#15024.

• Lint to detect extra "base indentation" in Rust code blocks.

  • Issue: Detect extra "base indentation" in Rust code blocks in docs rust-lang/rust-clippy#15025.

• Lint to detect inconsistent "style" for safety-related docs/comments.

  • Issue: Detect inconsistent "style" for safety-related docs/comments rust-lang/rust-clippy#15033.
  • Related: unnecessary_safety_comment inconsistency with wrong-style safety section rust-lang/rust-clippy#15034.
  • Example: https://lore.kernel.org/rust-for-linux/4823a58093c6dfa20df62b5c18da613621b9716e.1749554599.git.viresh.kumar@linaro.org/.

• Lint to detect // within /// (only when the empty comment is empty).

  • Issue: Lint to detect empty comments within docs ("// within ///") rust-lang/rust-clippy#15245.
  • PR: Add new comment_within_doc lint rust-lang/rust-clippy#15260.
  • Lore: https://lore.kernel.org/rust-for-linux/CANiq72nh71s9to5v1KHJWN79bEFv97zN6jcGJyEQkaJZ5UuJfg@mail.gmail.com/.

• Lint to disallow imports of certain items (to force users to write e.g. ordering::Any).

  • Issue: Lint to disallow imports of certain items rust-lang/rust-clippy#15244.
  • Lore: "[PATCH v6 3/9] rust: sync: atomic: Add ordering annotation types".

• wildcard_imports's allowed-wildcard-imports with several path segments.

  • Issue: wildcard_imports's allowed-wildcard-imports with several path segments rust-lang/rust-clippy#15246.

• manual_is_multiple_of suggests change that could alter behaviour.

  • Issue: manual_is_multiple_of suggests change that could alter behaviour rust-lang/rust-clippy#15335.

• Providing information about integer type aliases with multiple sizes.

  • Issue: Providing information about integer type aliases with multiple sizes rust-lang/rust-clippy#15337.
  • Lore: https://lore.kernel.org/rust-for-linux/CANiq72ktx9JsTXN_HTfjGWHxpBh430tkxHE2xL_1BQB2yb16rA@mail.gmail.com/.

Low priority (we will likely not use them in the end)

• Conditional compilation for clippy.toml?

  • No concrete use cases from our side yet; and if needed, we could always handle it on our side generating .clippy.toml on the fly (and using CLIPPY_CONF_DIR to find it in the objtree instead of the srctree).
  • Issue: Conditional compilation for configuration file? rust-lang/rust-clippy#11433.

• Fine-grained check-private-items (https://doc.rust-lang.org/clippy/lint_configuration.html#check-private-items).

  • So far, we have check-private-items enabled, but we do not have all the lints covered enabled, and in the future we might want to enable them, thus check-private-items may make it harder to start.
  • Issue: Separate check-private-items configuration for different lints rust-lang/rust-clippy#13074.

Done (stabilized, fixed, not needed anymore, etc.)

• Overindented lines lint (similar to doc_lazy_continuation).

  • We had a case in https://lore.kernel.org/rust-for-linux/ZxkcU5yTFCagg_lX@ohnotp/.
  • Issue: Overindented lines lint (similar to doc_lazy_continuation) rust-lang/rust-clippy#13601.
  • PR: Add new lint doc_overindented_list_items rust-lang/rust-clippy#13711 (1.86).

• Support/document running Clippy as a rustc wrapper.

  • PR: README: Add subsection on running Clippy as a rustc wrapper rust-lang/rust-clippy#6782.

• Configuring lint levels when using clippy-driver.

  • Issue: Configuring lint levels when using clippy-driver rust-lang/rust-clippy#6799.

• Normalize semicolon inside/outside blocks for () returning expressions (semicolon_outside_block and semicolon_inside_block, 1.68.0).

  • Issue: Normalize semicolon inside/outside blocks for () returning expressions rust-lang/rust-clippy#7322.
  • PR: Add semicolon-outside/inside-block lints rust-lang/rust-clippy#9826.

• Lint to warn about missing // SAFETY: explanations (undocumented_unsafe_blocks, 1.58.0).

  • Issue: Enforce unsafe blocks to have comments explaining why the required invariants hold rust-lang/rust-clippy#9330.
  • PR: Add undocumented_unsafe_blocks lint rust-lang/rust-clippy#7748.

• Lint to warn about unexpected # Safety contracts (i.e. the reverse of the missing_safety_doc lint) (unnecessary_safety_doc, 1.67.0).

  • Issue: Lint request: Safety comment on safe code rust-lang/rust-clippy#6880.
  • PR: Add unnecessary_safety_doc lint rust-lang/rust-clippy#9822.

• Lint to warn about unexpected // SAFETY: comments (i.e. the reverse of the undocumented_unsafe_blocks lint) (unnecessary_safety_comment, 1.67.0).

  • Issue: New lint (unnecessary_safety_comment): reverse of undocumented_unsafe_blocks rust-lang/rust-clippy#7954.
  • PR: Lint unnecessary safety comments  rust-lang/rust-clippy#9851.
  • Unclear if we will use // SAFETY: comments also for explaining why safe code makes other unsafe code sound, though.

• Lint to catch #[no_mangle] but non-extern "C" (no_mangle_with_rust_abi, 1.69.0).

  • From: rust: kernel: Mark rust_fmt_argument as extern "C" #967.
  • Issue: Lint against #[no_mangle] with the rust ABI rust-lang/rust-clippy#10347.
  • PR: Add new lint no_mangle_with_rust_abi rust-lang/rust-clippy#10369.

• Lint to catch printing/formatting pointers (including :p and :?).

  • In Linux, ideally, there would be a way to customize all pointer printing, i.e. including :p and :?, so that we can get them hashed as expected, and thus at that point we wouldn't need to lint for it. Meanwhile, this lint can be useful (and may be for other projects that do not want any printing whatsoever, too).
  • PR: new restriction lint: pointer_format rust-lang/rust-clippy#14792 (1.89).
  • Zulip: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Clippy.20lint.20for.20detecting.20pointer.20printing/near/517813625.

• Macros wrapping expressions in unsafe blocks when using unsafe_op_in_unsafe_fn.

  • This was eventually handled by clippy::macro_metavars_in_unsafe, which is in suspicious already, so we are already using it and e.g. writing a "bad" container_of! (and using it) does lint for us.
  • Issue: Macros wrapping expressions in unsafe blocks when using unsafe_op_in_unsafe_fn rust-lang/rust-clippy#7323.
  • Unfinished PR: Add new lint macros_hiding_unsafe_code rust-lang/rust-clippy#7469.
  • PR: new lint: macro_metavars_in_unsafe rust-lang/rust-clippy#12107 (1.80).

• Lint to suggest cast_signed and cast_unsigned (added suggestion to cast_possible_wrap and cast_sign_loss).

  • Stable since Rust 1.87, unstable since 1.80 (i.e. we would need to wait until we bump the minimum).
  • Issue: Suggest cast_signed and cast_unsigned instead of as rust-lang/rust-clippy#14974.
  • PR: Add suggestion to cast_sign_loss and cast_possible_wrap using the cast_{un,}signed() methods rust-lang/rust-clippy#15384 (1.92).

---

Bugs that we would like to see fixed

Required (we almost certainly want them)

• disallowed_macros false negatives.

  • For dbg_macro emulation purposes.
  • Issue: disallowed_macros false negatives rust-lang/rust-clippy#11431.
  • PR (for the $t + $t case): Check binary operators and attributes in disallowed_macros rust-lang/rust-clippy#11439 (1.74).

• cast_lossless false negative on char as u32.

  • Issue: cast_lossless not triggered by char as u32 rust-lang/rust-clippy#14469.
  • PR: cast_lossless: lint when converting usize, isize, char and float as well rust-lang/rust-clippy#14470.
  • Lore: https://lore.kernel.org/rust-for-linux/D8PAQXHJDVQE.36QKQGBVVL4QU@proton.me/.

Nice to have (probably not critical, we could workaround if needed, etc.)

• unnecessary_safety_comment does not lint for "orphan" comments.

  • Issue: unnecessary_safety_comment does not lint for "orphan" comments rust-lang/rust-clippy#14556.

• unnecessary_safety_comment inconsistency with wrong-style safety section.

  • Issue: unnecessary_safety_comment inconsistency with wrong-style safety section rust-lang/rust-clippy#15034.

• Feedback on needless_continue in Rust 1.86.0 (which we will probably disable globally).

  • Lore: https://lore.kernel.org/rust-for-linux/20250401221205.52381-1-ojeda@kernel.org/.
  • Lore: https://lore.kernel.org/rust-for-linux/20250403163805.67770-1-ojeda@kernel.org/.
  • Issue: Feedback on needless_continue in Rust 1.86 rust-lang/rust-clippy#14536.

Low priority (we will likely not use them in the end)

Done (stabilized, fixed, or not needed anymore, etc.)

• README: document that Clippy may change codegen.

  • Issue: Can clippy-driver be always used as replacement of rustc? rust-lang/rust-clippy#8035.
  • PR: README: document that Clippy may change codegen rust-lang/rust-clippy#8037 (1.60).

• new_ret_no_self false positive when returning impl Trait<Self>.

  • For pin-init usage.
  • Issue: new_ret_no_self false positive when returning impl Trait<Self> rust-lang/rust-clippy#7344.
  • PR: Ensure new_ret_no_self is not fired if impl Trait<Self> is returned. rust-lang/rust-clippy#9733 (1.67).

• macro_metavars_in_unsafe false negative without statement.

  • Issue: macro_metavars_in_unsafe does not lint "without a statement". rust-lang/rust-clippy#13219.
  • PR: [macro_metavars_in_unsafe]: recognize metavariables in tail expressions rust-lang/rust-clippy#13220 (1.82?).

• single_match difference in 1.85.0 -- is it intended?

  • We cannot use expect in https://lore.kernel.org/rust-for-linux/20250122054719.595878-1-dirk.behme@de.bosch.com/.
  • Issue: clippy::single_match does not report if a comment is on top of an arm rust-lang/rust-clippy#14418.
  • PR: Reinstate single_match/single_match_else lints with comments rust-lang/rust-clippy#14420 (1.87?).

• Diagnostic for unexpected paths in configuration file.

  • For instance, for disallowed_macros's paths.
  • Issue: Diagnostic for unexpected paths in configuration file rust-lang/rust-clippy#11432.
  • PR: Validate paths in disallowed_* configurations rust-lang/rust-clippy#14397 (1.87?).

• Reduce or split ptr_eq.

  • One "major addition" to the lint (linting all pointer comparisons) added in 1.87.
  • We may need to allow it globally otherwise, like needless_continue.
  • Issue: Feedback on needless_continue in Rust 1.86 rust-lang/rust-clippy#14536.
  • Issue: clippy beta 1.87 lints all pointer comparisons, possibly too much? rust-lang/rust-clippy#14525.
  • PR: Restrict the cases where ptr_eq triggers rust-lang/rust-clippy#14526.
  • Backport PR (for Rust 1.87): [beta] Clippy beta backport rust-lang/rust#140810, [stable] Prepare the 1.87.0 release rust-lang/rust#140859.
  • Patch that allowed a few of them (when applied): https://lore.kernel.org/rust-for-linux/20250502140237.1659624-3-ojeda@kernel.org/.

• undocumented_unsafe_blocks false positives around attributes.

  • Workaround: moving the attribute on top always fixes it.
  • Workaround: where it makes sense, moving the comment inside the expression, also works.
  • Issue: undocumented_unsafe_blocks false positives around attributes rust-lang/rust-clippy#13189.
  • PR: Propagate accept-comment-above-attributes to statements rust-lang/rust-clippy#15213 (1.90).

• Fix false positives around undocumented_unsafe_blocks's accept-comment-above-statement.

  • i.e. that trigger when long statements are split into several lines by e.g. rustfmt.
  • Originally Clippy didn't support the config option, but eventually it was implemented and then made the default later on. However, there have been false positives around it.
  • When we introduced the lint in Linux (commit db4f72c ("rust: enable clippy::undocumented_unsafe_blocks lint")), we just put the // SAFETY comment on the previous line, even if it is in the middle of the statement, to workaround it, e.g. see do_unlocked in the commit.
  • Starting with Rust 1.87.0, false positives like those we triggered in the kernel seem to be fixed, e.g. https://lore.kernel.org/rust-for-linux/87msbw1s9e.fsf@kernel.org/ and https://lore.kernel.org/rust-for-linux/DBG25OQZJ18V.1W13FEOPX8MOH@kernel.org/.
  • Issue: undocumented_unsafe_blocks can be broken by rustfmt rust-lang/rust-clippy#13024.
  • PR: fix: undocumented_unsafe_blocks FP on trait/impl items rust-lang/rust-clippy#13888 (1.87).

• unnecessary_safety_comment does not lint for the first line.

  • Issue: unnecessary_safety_comment does not lint for the first line rust-lang/rust-clippy#14553.
  • PR: Fixunnecessary_safety_comment does not lint for the first line rust-lang/rust-clippy#15354 (1.91).

• unnecessary_safety_comment does not lint the first item of a module without a body.

  • Issue: unnecessary_safety_comment does not lint the first item of a module without a body rust-lang/rust-clippy#14554.
  • PR: Fixunnecessary_safety_comment does not lint for the first line rust-lang/rust-clippy#15354 (1.91).
  • Lore: https://lore.kernel.org/rust-for-linux/20250405060154.1550858-3-andrewjballance@gmail.com/.

• unnecessary_safety_comment does not lint for a doc(hidden) item.

  • Issue: unnecessary_safety_comment does not lint for a doc(hidden) item rust-lang/rust-clippy#14555.
  • PR: [unnecessary_safety_comment] Some fixes regarding comments above attributes rust-lang/rust-clippy#15678 (1.92).

[tgross35]

I am working on enabling some of these. I will exclude unnecessary_safety_comment for now because it has a false positive in macros rust-lang/rust-clippy#10084