1 //! Some lints that are built in to the compiler.
3 //! These are the built-in lints that are emitted direct in the main
4 //! compiler code, rather than using their own custom pass. Those
5 //! lints are all available in `rustc_lint::builtin`.
7 use crate::{declare_lint, declare_lint_pass, FutureIncompatibilityReason};
8 use rustc_span::edition::Edition;
9 use rustc_span::symbol::sym;
12 /// The `forbidden_lint_groups` lint detects violations of
13 /// `forbid` applied to a lint group. Due to a bug in the compiler,
14 /// these used to be overlooked entirely. They now generate a warning.
19 /// #![forbid(warnings)]
20 /// #![deny(bad_style)]
27 /// ### Recommended fix
29 /// If your crate is using `#![forbid(warnings)]`,
30 /// we recommend that you change to `#![deny(warnings)]`.
34 /// Due to a compiler bug, applying `forbid` to lint groups
35 /// previously had no effect. The bug is now fixed but instead of
36 /// enforcing `forbid` we issue this future-compatibility warning
37 /// to avoid breaking existing crates.
38 pub FORBIDDEN_LINT_GROUPS,
40 "applying forbid to lint-groups",
41 @future_incompatible = FutureIncompatibleInfo {
42 reference: "issue #81670 <https://github.com/rust-lang/rust/issues/81670>",
47 /// The `ill_formed_attribute_input` lint detects ill-formed attribute
48 /// inputs that were previously accepted and used in practice.
52 /// ```rust,compile_fail
53 /// #[inline = "this is not valid"]
61 /// Previously, inputs for many built-in attributes weren't validated and
62 /// nonsensical attribute inputs were accepted. After validation was
63 /// added, it was determined that some existing projects made use of these
64 /// invalid forms. This is a [future-incompatible] lint to transition this
65 /// to a hard error in the future. See [issue #57571] for more details.
67 /// Check the [attribute reference] for details on the valid inputs for
70 /// [issue #57571]: https://github.com/rust-lang/rust/issues/57571
71 /// [attribute reference]: https://doc.rust-lang.org/nightly/reference/attributes.html
72 /// [future-incompatible]: ../index.md#future-incompatible-lints
73 pub ILL_FORMED_ATTRIBUTE_INPUT,
75 "ill-formed attribute inputs that were previously accepted and used in practice",
76 @future_incompatible = FutureIncompatibleInfo {
77 reference: "issue #57571 <https://github.com/rust-lang/rust/issues/57571>",
83 /// The `conflicting_repr_hints` lint detects [`repr` attributes] with
84 /// conflicting hints.
86 /// [`repr` attributes]: https://doc.rust-lang.org/reference/type-layout.html#representations
90 /// ```rust,compile_fail
101 /// The compiler incorrectly accepted these conflicting representations in
102 /// the past. This is a [future-incompatible] lint to transition this to a
103 /// hard error in the future. See [issue #68585] for more details.
105 /// To correct the issue, remove one of the conflicting hints.
107 /// [issue #68585]: https://github.com/rust-lang/rust/issues/68585
108 /// [future-incompatible]: ../index.md#future-incompatible-lints
109 pub CONFLICTING_REPR_HINTS,
111 "conflicts between `#[repr(..)]` hints that were previously accepted and used in practice",
112 @future_incompatible = FutureIncompatibleInfo {
113 reference: "issue #68585 <https://github.com/rust-lang/rust/issues/68585>",
118 /// The `meta_variable_misuse` lint detects possible meta-variable misuse
119 /// in macro definitions.
123 /// ```rust,compile_fail
124 /// #![deny(meta_variable_misuse)]
126 /// macro_rules! foo {
128 /// ($( $i:ident = $($j:ident),+ );*) => { $( $( $i = $k; )+ )* };
140 /// There are quite a few different ways a [`macro_rules`] macro can be
141 /// improperly defined. Many of these errors were previously only detected
142 /// when the macro was expanded or not at all. This lint is an attempt to
143 /// catch some of these problems when the macro is *defined*.
145 /// This lint is "allow" by default because it may have false positives
146 /// and other issues. See [issue #61053] for more details.
148 /// [`macro_rules`]: https://doc.rust-lang.org/reference/macros-by-example.html
149 /// [issue #61053]: https://github.com/rust-lang/rust/issues/61053
150 pub META_VARIABLE_MISUSE,
152 "possible meta-variable misuse at macro definition"
156 /// The `incomplete_include` lint detects the use of the [`include!`]
157 /// macro with a file that contains more than one expression.
159 /// [`include!`]: https://doc.rust-lang.org/std/macro.include.html
163 /// ```rust,ignore (needs separate file)
165 /// include!("foo.txt");
169 /// where the file `foo.txt` contains:
178 /// error: include macro expected single expression in source
181 /// 1 | println!("1");
184 /// = note: `#[deny(incomplete_include)]` on by default
189 /// The [`include!`] macro is currently only intended to be used to
190 /// include a single [expression] or multiple [items]. Historically it
191 /// would ignore any contents after the first expression, but that can be
192 /// confusing. In the example above, the `println!` expression ends just
193 /// before the semicolon, making the semicolon "extra" information that is
194 /// ignored. Perhaps even more surprising, if the included file had
195 /// multiple print statements, the subsequent ones would be ignored!
197 /// One workaround is to place the contents in braces to create a [block
198 /// expression]. Also consider alternatives, like using functions to
199 /// encapsulate the expressions, or use [proc-macros].
201 /// This is a lint instead of a hard error because existing projects were
202 /// found to hit this error. To be cautious, it is a lint for now. The
203 /// future semantics of the `include!` macro are also uncertain, see
206 /// [items]: https://doc.rust-lang.org/reference/items.html
207 /// [expression]: https://doc.rust-lang.org/reference/expressions.html
208 /// [block expression]: https://doc.rust-lang.org/reference/expressions/block-expr.html
209 /// [proc-macros]: https://doc.rust-lang.org/reference/procedural-macros.html
210 /// [issue #35560]: https://github.com/rust-lang/rust/issues/35560
211 pub INCOMPLETE_INCLUDE,
213 "trailing content in included file"
217 /// The `arithmetic_overflow` lint detects that an arithmetic operation
220 /// [overflow]: https://doc.rust-lang.org/reference/expressions/operator-expr.html#overflow
224 /// ```rust,compile_fail
232 /// It is very likely a mistake to perform an arithmetic operation that
233 /// overflows its value. If the compiler is able to detect these kinds of
234 /// overflows at compile-time, it will trigger this lint. Consider
235 /// adjusting the expression to avoid overflow, or use a data type that
236 /// will not overflow.
237 pub ARITHMETIC_OVERFLOW,
239 "arithmetic operation overflows"
243 /// The `unconditional_panic` lint detects an operation that will cause a
244 /// panic at runtime.
248 /// ```rust,compile_fail
249 /// # #![allow(unused)]
257 /// This lint detects code that is very likely incorrect because it will
258 /// always panic, such as division by zero and out-of-bounds array
259 /// accesses. Consider adjusting your code if this is a bug, or using the
260 /// `panic!` or `unreachable!` macro instead in case the panic is intended.
261 pub UNCONDITIONAL_PANIC,
263 "operation will cause a panic at runtime"
267 /// The `const_err` lint detects an erroneous expression while doing
268 /// constant evaluation.
272 /// ```rust,compile_fail
273 /// #![allow(unconditional_panic)]
274 /// const C: i32 = 1/0;
281 /// This lint detects constants that fail to evaluate. Allowing the lint will accept the
282 /// constant declaration, but any use of this constant will still lead to a hard error. This is
283 /// a future incompatibility lint; the plan is to eventually entirely forbid even declaring
284 /// constants that cannot be evaluated. See [issue #71800] for more details.
286 /// [issue #71800]: https://github.com/rust-lang/rust/issues/71800
289 "constant evaluation encountered erroneous expression",
290 @future_incompatible = FutureIncompatibleInfo {
291 reference: "issue #71800 <https://github.com/rust-lang/rust/issues/71800>",
293 report_in_external_macro
297 /// The `unused_imports` lint detects imports that are never used.
302 /// use std::collections::HashMap;
309 /// Unused imports may signal a mistake or unfinished code, and clutter
310 /// the code, and should be removed. If you intended to re-export the item
311 /// to make it available outside of the module, add a visibility modifier
315 "imports that are never used"
319 /// The `must_not_suspend` lint guards against values that shouldn't be held across suspend points
325 /// #![feature(must_not_suspend)]
326 /// #![warn(must_not_suspend)]
328 /// #[must_not_suspend]
329 /// struct SyncThing {}
331 /// async fn yield_now() {}
333 /// pub async fn uhoh() {
334 /// let guard = SyncThing {};
335 /// yield_now().await;
343 /// The `must_not_suspend` lint detects values that are marked with the `#[must_not_suspend]`
344 /// attribute being held across suspend points. A "suspend" point is usually a `.await` in an async
347 /// This attribute can be used to mark values that are semantically incorrect across suspends
348 /// (like certain types of timers), values that have async alternatives, and values that
349 /// regularly cause problems with the `Send`-ness of async fn's returned futures (like
352 pub MUST_NOT_SUSPEND,
354 "use of a `#[must_not_suspend]` value across a yield point",
355 @feature_gate = rustc_span::symbol::sym::must_not_suspend;
359 /// The `unused_extern_crates` lint guards against `extern crate` items
360 /// that are never used.
364 /// ```rust,compile_fail
365 /// #![deny(unused_extern_crates)]
366 /// extern crate proc_macro;
373 /// `extern crate` items that are unused have no effect and should be
374 /// removed. Note that there are some cases where specifying an `extern
375 /// crate` is desired for the side effect of ensuring the given crate is
376 /// linked, even though it is not otherwise directly referenced. The lint
377 /// can be silenced by aliasing the crate to an underscore, such as
378 /// `extern crate foo as _`. Also note that it is no longer idiomatic to
379 /// use `extern crate` in the [2018 edition], as extern crates are now
380 /// automatically added in scope.
382 /// This lint is "allow" by default because it can be noisy, and produce
383 /// false-positives. If a dependency is being removed from a project, it
384 /// is recommended to remove it from the build configuration (such as
385 /// `Cargo.toml`) to ensure stale build entries aren't left behind.
387 /// [2018 edition]: https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-clarity.html#no-more-extern-crate
388 pub UNUSED_EXTERN_CRATES,
390 "extern crates that are never used"
394 /// The `unused_crate_dependencies` lint detects crate dependencies that
399 /// ```rust,ignore (needs extern crate)
400 /// #![deny(unused_crate_dependencies)]
403 /// This will produce:
406 /// error: external crate `regex` unused in `lint_example`: remove the dependency or add `use regex as _;`
408 /// note: the lint level is defined here
409 /// --> src/lib.rs:1:9
411 /// 1 | #![deny(unused_crate_dependencies)]
412 /// | ^^^^^^^^^^^^^^^^^^^^^^^^^
417 /// After removing the code that uses a dependency, this usually also
418 /// requires removing the dependency from the build configuration.
419 /// However, sometimes that step can be missed, which leads to time wasted
420 /// building dependencies that are no longer used. This lint can be
421 /// enabled to detect dependencies that are never used (more specifically,
422 /// any dependency passed with the `--extern` command-line flag that is
423 /// never referenced via [`use`], [`extern crate`], or in any [path]).
425 /// This lint is "allow" by default because it can provide false positives
426 /// depending on how the build system is configured. For example, when
427 /// using Cargo, a "package" consists of multiple crates (such as a
428 /// library and a binary), but the dependencies are defined for the
429 /// package as a whole. If there is a dependency that is only used in the
430 /// binary, but not the library, then the lint will be incorrectly issued
433 /// [path]: https://doc.rust-lang.org/reference/paths.html
434 /// [`use`]: https://doc.rust-lang.org/reference/items/use-declarations.html
435 /// [`extern crate`]: https://doc.rust-lang.org/reference/items/extern-crates.html
436 pub UNUSED_CRATE_DEPENDENCIES,
438 "crate dependencies that are never used",
443 /// The `unused_qualifications` lint detects unnecessarily qualified
448 /// ```rust,compile_fail
449 /// #![deny(unused_qualifications)]
464 /// If an item from another module is already brought into scope, then
465 /// there is no need to qualify it in this case. You can call `bar()`
466 /// directly, without the `foo::`.
468 /// This lint is "allow" by default because it is somewhat pedantic, and
469 /// doesn't indicate an actual problem, but rather a stylistic choice, and
470 /// can be noisy when refactoring or moving around code.
471 pub UNUSED_QUALIFICATIONS,
473 "detects unnecessarily qualified names"
477 /// The `unknown_lints` lint detects unrecognized lint attribute.
482 /// #![allow(not_a_real_lint)]
489 /// It is usually a mistake to specify a lint that does not exist. Check
490 /// the spelling, and check the lint listing for the correct name. Also
491 /// consider if you are using an old version of the compiler, and the lint
492 /// is only available in a newer version.
495 "unrecognized lint attribute"
499 /// The `unfulfilled_lint_expectations` lint detects lint trigger expectations
500 /// that have not been fulfilled.
505 /// #![feature(lint_reasons)]
507 /// #[expect(unused_variables)]
509 /// println!("{}", x);
516 /// It was expected that the marked code would emit a lint. This expectation
517 /// has not been fulfilled.
519 /// The `expect` attribute can be removed if this is intended behavior otherwise
520 /// it should be investigated why the expected lint is no longer issued.
522 /// Part of RFC 2383. The progress is being tracked in [#54503]
524 /// [#54503]: https://github.com/rust-lang/rust/issues/54503
525 pub UNFULFILLED_LINT_EXPECTATIONS,
527 "unfulfilled lint expectation",
528 @feature_gate = rustc_span::sym::lint_reasons;
532 /// The `unused_variables` lint detects variables which are not used in
545 /// Unused variables may signal a mistake or unfinished code. To silence
546 /// the warning for the individual variable, prefix it with an underscore
548 pub UNUSED_VARIABLES,
550 "detect variables which are not used in any way"
554 /// The `unused_assignments` lint detects assignments that will never be read.
567 /// Unused assignments may signal a mistake or unfinished code. If the
568 /// variable is never used after being assigned, then the assignment can
569 /// be removed. Variables with an underscore prefix such as `_x` will not
570 /// trigger this lint.
571 pub UNUSED_ASSIGNMENTS,
573 "detect assignments that will never be read"
577 /// The `dead_code` lint detects unused, unexported items.
589 /// Dead code may signal a mistake or unfinished code. To silence the
590 /// warning for individual items, prefix the name with an underscore such
591 /// as `_foo`. If it was intended to expose the item outside of the crate,
592 /// consider adding a visibility modifier like `pub`. Otherwise consider
593 /// removing the unused code.
596 "detect unused, unexported items"
600 /// The `unused_attributes` lint detects attributes that were not used by
613 /// Unused [attributes] may indicate the attribute is placed in the wrong
614 /// position. Consider removing it, or placing it in the correct position.
615 /// Also consider if you intended to use an _inner attribute_ (with a `!`
616 /// such as `#![allow(unused)]`) which applies to the item the attribute
617 /// is within, or an _outer attribute_ (without a `!` such as
618 /// `#[allow(unused)]`) which applies to the item *following* the
621 /// [attributes]: https://doc.rust-lang.org/reference/attributes.html
622 pub UNUSED_ATTRIBUTES,
624 "detects attributes that were not used by the compiler"
628 /// The `unreachable_code` lint detects unreachable code paths.
633 /// panic!("we never go past here!");
642 /// Unreachable code may signal a mistake or unfinished code. If the code
643 /// is no longer in use, consider removing it.
644 pub UNREACHABLE_CODE,
646 "detects unreachable code paths",
647 report_in_external_macro
651 /// The `unreachable_patterns` lint detects unreachable patterns.
667 /// This usually indicates a mistake in how the patterns are specified or
668 /// ordered. In this example, the `y` pattern will always match, so the
669 /// five is impossible to reach. Remember, match arms match in order, you
670 /// probably wanted to put the `5` case above the `y` case.
671 pub UNREACHABLE_PATTERNS,
673 "detects unreachable patterns"
677 /// The `overlapping_range_endpoints` lint detects `match` arms that have [range patterns] that
678 /// overlap on their endpoints.
680 /// [range patterns]: https://doc.rust-lang.org/nightly/reference/patterns.html#range-patterns
687 /// 0..=100 => { println!("small"); }
688 /// 100..=255 => { println!("large"); }
696 /// It is likely a mistake to have range patterns in a match expression that overlap in this
697 /// way. Check that the beginning and end values are what you expect, and keep in mind that
698 /// with `..=` the left and right bounds are inclusive.
699 pub OVERLAPPING_RANGE_ENDPOINTS,
701 "detects range patterns with overlapping endpoints"
705 /// The `bindings_with_variant_name` lint detects pattern bindings with
706 /// the same name as one of the matched variants.
716 /// pub fn foo(x: Enum) {
728 /// It is usually a mistake to specify an enum variant name as an
729 /// [identifier pattern]. In the example above, the `match` arms are
730 /// specifying a variable name to bind the value of `x` to. The second arm
731 /// is ignored because the first one matches *all* values. The likely
732 /// intent is that the arm was intended to match on the enum variant.
734 /// Two possible solutions are:
736 /// * Specify the enum variant using a [path pattern], such as
738 /// * Bring the enum variants into local scope, such as adding `use
739 /// Enum::*;` to the beginning of the `foo` function in the example
742 /// [identifier pattern]: https://doc.rust-lang.org/reference/patterns.html#identifier-patterns
743 /// [path pattern]: https://doc.rust-lang.org/reference/patterns.html#path-patterns
744 pub BINDINGS_WITH_VARIANT_NAME,
746 "detects pattern bindings with the same name as one of the matched variants"
750 /// The `unused_macros` lint detects macros that were not used.
755 /// macro_rules! unused {
767 /// Unused macros may signal a mistake or unfinished code. To silence the
768 /// warning for the individual macro, prefix the name with an underscore
769 /// such as `_my_macro`. If you intended to export the macro to make it
770 /// available outside of the crate, use the [`macro_export` attribute].
772 /// [`macro_export` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
775 "detects macros that were not used"
779 /// The `warnings` lint allows you to change the level of other
780 /// lints which produce warnings.
785 /// #![deny(warnings)]
793 /// The `warnings` lint is a bit special; by changing its level, you
794 /// change every other warning that would produce a warning to whatever
795 /// value you'd like. As such, you won't ever trigger this lint in your
799 "mass-change the level for lints which produce warnings"
803 /// The `unused_features` lint detects unused or unknown features found in
804 /// crate-level [`feature` attributes].
806 /// [`feature` attributes]: https://doc.rust-lang.org/nightly/unstable-book/
808 /// Note: This lint is currently not functional, see [issue #44232] for
811 /// [issue #44232]: https://github.com/rust-lang/rust/issues/44232
814 "unused features found in crate-level `#[feature]` directives"
818 /// The `stable_features` lint detects a [`feature` attribute] that
819 /// has since been made stable.
821 /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
826 /// #![feature(test_accepted_feature)]
834 /// When a feature is stabilized, it is no longer necessary to include a
835 /// `#![feature]` attribute for it. To fix, simply remove the
836 /// `#![feature]` attribute.
839 "stable features found in `#[feature]` directive"
843 /// The `unknown_crate_types` lint detects an unknown crate type found in
844 /// a [`crate_type` attribute].
848 /// ```rust,compile_fail
849 /// #![crate_type="lol"]
857 /// An unknown value give to the `crate_type` attribute is almost
858 /// certainly a mistake.
860 /// [`crate_type` attribute]: https://doc.rust-lang.org/reference/linkage.html
861 pub UNKNOWN_CRATE_TYPES,
863 "unknown crate type found in `#[crate_type]` directive",
868 /// The `trivial_casts` lint detects trivial casts which could be replaced
869 /// with coercion, which may require [type ascription] or a temporary
874 /// ```rust,compile_fail
875 /// #![deny(trivial_casts)]
876 /// let x: &u32 = &42;
877 /// let y = x as *const u32;
884 /// A trivial cast is a cast `e as T` where `e` has type `U` and `U` is a
885 /// subtype of `T`. This type of cast is usually unnecessary, as it can be
886 /// usually be inferred.
888 /// This lint is "allow" by default because there are situations, such as
889 /// with FFI interfaces or complex type aliases, where it triggers
890 /// incorrectly, or in situations where it will be more difficult to
891 /// clearly express the intent. It may be possible that this will become a
892 /// warning in the future, possibly with [type ascription] providing a
893 /// convenient way to work around the current issues. See [RFC 401] for
894 /// historical context.
896 /// [type ascription]: https://github.com/rust-lang/rust/issues/23416
897 /// [RFC 401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
900 "detects trivial casts which could be removed"
904 /// The `trivial_numeric_casts` lint detects trivial numeric casts of types
905 /// which could be removed.
909 /// ```rust,compile_fail
910 /// #![deny(trivial_numeric_casts)]
911 /// let x = 42_i32 as i32;
918 /// A trivial numeric cast is a cast of a numeric type to the same numeric
919 /// type. This type of cast is usually unnecessary.
921 /// This lint is "allow" by default because there are situations, such as
922 /// with FFI interfaces or complex type aliases, where it triggers
923 /// incorrectly, or in situations where it will be more difficult to
924 /// clearly express the intent. It may be possible that this will become a
925 /// warning in the future, possibly with [type ascription] providing a
926 /// convenient way to work around the current issues. See [RFC 401] for
927 /// historical context.
929 /// [type ascription]: https://github.com/rust-lang/rust/issues/23416
930 /// [RFC 401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
931 pub TRIVIAL_NUMERIC_CASTS,
933 "detects trivial casts of numeric types which could be removed"
937 /// The `private_in_public` lint detects private items in public
938 /// interfaces not caught by the old implementation.
943 /// # #![allow(unused)]
948 /// impl super::SemiPriv {
949 /// pub fn f(_: Priv) {}
959 /// The visibility rules are intended to prevent exposing private items in
960 /// public interfaces. This is a [future-incompatible] lint to transition
961 /// this to a hard error in the future. See [issue #34537] for more
964 /// [issue #34537]: https://github.com/rust-lang/rust/issues/34537
965 /// [future-incompatible]: ../index.md#future-incompatible-lints
966 pub PRIVATE_IN_PUBLIC,
968 "detect private items in public interfaces not caught by the old implementation",
969 @future_incompatible = FutureIncompatibleInfo {
970 reference: "issue #34537 <https://github.com/rust-lang/rust/issues/34537>",
975 /// The `exported_private_dependencies` lint detects private dependencies
976 /// that are exposed in a public interface.
980 /// ```rust,ignore (needs-dependency)
981 /// pub fn foo() -> Option<some_private_dependency::Thing> {
986 /// This will produce:
989 /// warning: type `bar::Thing` from private dependency 'bar' in public interface
990 /// --> src/lib.rs:3:1
992 /// 3 | pub fn foo() -> Option<bar::Thing> {
993 /// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
995 /// = note: `#[warn(exported_private_dependencies)]` on by default
1000 /// Dependencies can be marked as "private" to indicate that they are not
1001 /// exposed in the public interface of a crate. This can be used by Cargo
1002 /// to independently resolve those dependencies because it can assume it
1003 /// does not need to unify them with other packages using that same
1004 /// dependency. This lint is an indication of a violation of that
1007 /// To fix this, avoid exposing the dependency in your public interface.
1008 /// Or, switch the dependency to a public dependency.
1010 /// Note that support for this is only available on the nightly channel.
1011 /// See [RFC 1977] for more details, as well as the [Cargo documentation].
1013 /// [RFC 1977]: https://github.com/rust-lang/rfcs/blob/master/text/1977-public-private-dependencies.md
1014 /// [Cargo documentation]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#public-dependency
1015 pub EXPORTED_PRIVATE_DEPENDENCIES,
1017 "public interface leaks type from a private dependency"
1021 /// The `pub_use_of_private_extern_crate` lint detects a specific
1022 /// situation of re-exporting a private `extern crate`.
1026 /// ```rust,compile_fail
1027 /// extern crate core;
1028 /// pub use core as reexported_core;
1035 /// A public `use` declaration should not be used to publicly re-export a
1036 /// private `extern crate`. `pub extern crate` should be used instead.
1038 /// This was historically allowed, but is not the intended behavior
1039 /// according to the visibility rules. This is a [future-incompatible]
1040 /// lint to transition this to a hard error in the future. See [issue
1041 /// #34537] for more details.
1043 /// [issue #34537]: https://github.com/rust-lang/rust/issues/34537
1044 /// [future-incompatible]: ../index.md#future-incompatible-lints
1045 pub PUB_USE_OF_PRIVATE_EXTERN_CRATE,
1047 "detect public re-exports of private extern crates",
1048 @future_incompatible = FutureIncompatibleInfo {
1049 reference: "issue #34537 <https://github.com/rust-lang/rust/issues/34537>",
1054 /// The `invalid_type_param_default` lint detects type parameter defaults
1055 /// erroneously allowed in an invalid location.
1059 /// ```rust,compile_fail
1060 /// fn foo<T=i32>(t: T) {}
1067 /// Default type parameters were only intended to be allowed in certain
1068 /// situations, but historically the compiler allowed them everywhere.
1069 /// This is a [future-incompatible] lint to transition this to a hard
1070 /// error in the future. See [issue #36887] for more details.
1072 /// [issue #36887]: https://github.com/rust-lang/rust/issues/36887
1073 /// [future-incompatible]: ../index.md#future-incompatible-lints
1074 pub INVALID_TYPE_PARAM_DEFAULT,
1076 "type parameter default erroneously allowed in invalid location",
1077 @future_incompatible = FutureIncompatibleInfo {
1078 reference: "issue #36887 <https://github.com/rust-lang/rust/issues/36887>",
1083 /// The `renamed_and_removed_lints` lint detects lints that have been
1084 /// renamed or removed.
1089 /// #![deny(raw_pointer_derive)]
1096 /// To fix this, either remove the lint or use the new name. This can help
1097 /// avoid confusion about lints that are no longer valid, and help
1098 /// maintain consistency for renamed lints.
1099 pub RENAMED_AND_REMOVED_LINTS,
1101 "lints that have been renamed or removed"
1105 /// The `unaligned_references` lint detects unaligned references to fields
1106 /// of [packed] structs.
1108 /// [packed]: https://doc.rust-lang.org/reference/type-layout.html#the-alignment-modifiers
1112 /// ```rust,compile_fail
1114 /// pub struct Foo {
1121 /// let foo = Foo { field1: 0, field2: 0 };
1122 /// let _ = &foo.field1;
1123 /// println!("{}", foo.field1); // An implicit `&` is added here, triggering the lint.
1132 /// Creating a reference to an insufficiently aligned packed field is [undefined behavior] and
1133 /// should be disallowed. Using an `unsafe` block does not change anything about this. Instead,
1134 /// the code should do a copy of the data in the packed field or use raw pointers and unaligned
1135 /// accesses. See [issue #82523] for more information.
1137 /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1138 /// [issue #82523]: https://github.com/rust-lang/rust/issues/82523
1139 pub UNALIGNED_REFERENCES,
1141 "detects unaligned references to fields of packed structs",
1142 @future_incompatible = FutureIncompatibleInfo {
1143 reference: "issue #82523 <https://github.com/rust-lang/rust/issues/82523>",
1144 reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
1146 report_in_external_macro
1150 /// The `const_item_mutation` lint detects attempts to mutate a `const`
1156 /// const FOO: [i32; 1] = [0];
1160 /// // This will print "[0]".
1161 /// println!("{:?}", FOO);
1169 /// Trying to directly mutate a `const` item is almost always a mistake.
1170 /// What is happening in the example above is that a temporary copy of the
1171 /// `const` is mutated, but the original `const` is not. Each time you
1172 /// refer to the `const` by name (such as `FOO` in the example above), a
1173 /// separate copy of the value is inlined at that location.
1175 /// This lint checks for writing directly to a field (`FOO.field =
1176 /// some_value`) or array entry (`FOO[0] = val`), or taking a mutable
1177 /// reference to the const item (`&mut FOO`), including through an
1178 /// autoderef (`FOO.some_mut_self_method()`).
1180 /// There are various alternatives depending on what you are trying to
1183 /// * First, always reconsider using mutable globals, as they can be
1184 /// difficult to use correctly, and can make the code more difficult to
1185 /// use or understand.
1186 /// * If you are trying to perform a one-time initialization of a global:
1187 /// * If the value can be computed at compile-time, consider using
1188 /// const-compatible values (see [Constant Evaluation]).
1189 /// * For more complex single-initialization cases, consider using a
1190 /// third-party crate, such as [`lazy_static`] or [`once_cell`].
1191 /// * If you are using the [nightly channel], consider the new
1192 /// [`lazy`] module in the standard library.
1193 /// * If you truly need a mutable global, consider using a [`static`],
1194 /// which has a variety of options:
1195 /// * Simple data types can be directly defined and mutated with an
1196 /// [`atomic`] type.
1197 /// * More complex types can be placed in a synchronization primitive
1198 /// like a [`Mutex`], which can be initialized with one of the options
1200 /// * A [mutable `static`] is a low-level primitive, requiring unsafe.
1201 /// Typically This should be avoided in preference of something
1202 /// higher-level like one of the above.
1204 /// [Constant Evaluation]: https://doc.rust-lang.org/reference/const_eval.html
1205 /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
1206 /// [mutable `static`]: https://doc.rust-lang.org/reference/items/static-items.html#mutable-statics
1207 /// [`lazy`]: https://doc.rust-lang.org/nightly/std/lazy/index.html
1208 /// [`lazy_static`]: https://crates.io/crates/lazy_static
1209 /// [`once_cell`]: https://crates.io/crates/once_cell
1210 /// [`atomic`]: https://doc.rust-lang.org/std/sync/atomic/index.html
1211 /// [`Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
1212 pub CONST_ITEM_MUTATION,
1214 "detects attempts to mutate a `const` item",
1218 /// The `patterns_in_fns_without_body` lint detects `mut` identifier
1219 /// patterns as a parameter in functions without a body.
1223 /// ```rust,compile_fail
1225 /// fn foo(mut arg: u8);
1233 /// To fix this, remove `mut` from the parameter in the trait definition;
1234 /// it can be used in the implementation. That is, the following is OK:
1238 /// fn foo(arg: u8); // Removed `mut` here
1241 /// impl Trait for i32 {
1242 /// fn foo(mut arg: u8) { // `mut` here is OK
1248 /// Trait definitions can define functions without a body to specify a
1249 /// function that implementors must define. The parameter names in the
1250 /// body-less functions are only allowed to be `_` or an [identifier] for
1251 /// documentation purposes (only the type is relevant). Previous versions
1252 /// of the compiler erroneously allowed [identifier patterns] with the
1253 /// `mut` keyword, but this was not intended to be allowed. This is a
1254 /// [future-incompatible] lint to transition this to a hard error in the
1255 /// future. See [issue #35203] for more details.
1257 /// [identifier]: https://doc.rust-lang.org/reference/identifiers.html
1258 /// [identifier patterns]: https://doc.rust-lang.org/reference/patterns.html#identifier-patterns
1259 /// [issue #35203]: https://github.com/rust-lang/rust/issues/35203
1260 /// [future-incompatible]: ../index.md#future-incompatible-lints
1261 pub PATTERNS_IN_FNS_WITHOUT_BODY,
1263 "patterns in functions without body were erroneously allowed",
1264 @future_incompatible = FutureIncompatibleInfo {
1265 reference: "issue #35203 <https://github.com/rust-lang/rust/issues/35203>",
1270 /// The `missing_fragment_specifier` lint is issued when an unused pattern in a
1271 /// `macro_rules!` macro definition has a meta-variable (e.g. `$e`) that is not
1272 /// followed by a fragment specifier (e.g. `:expr`).
1274 /// This warning can always be fixed by removing the unused pattern in the
1275 /// `macro_rules!` macro definition.
1279 /// ```rust,compile_fail
1280 /// macro_rules! foo {
1294 /// To fix this, remove the unused pattern from the `macro_rules!` macro definition:
1297 /// macro_rules! foo {
1304 pub MISSING_FRAGMENT_SPECIFIER,
1306 "detects missing fragment specifiers in unused `macro_rules!` patterns",
1307 @future_incompatible = FutureIncompatibleInfo {
1308 reference: "issue #40107 <https://github.com/rust-lang/rust/issues/40107>",
1313 /// The `late_bound_lifetime_arguments` lint detects generic lifetime
1314 /// arguments in path segments with late bound lifetime parameters.
1322 /// fn late<'a, 'b>(self, _: &'a u8, _: &'b u8) {}
1326 /// S.late::<'static>(&0, &0);
1334 /// It is not clear how to provide arguments for early-bound lifetime
1335 /// parameters if they are intermixed with late-bound parameters in the
1336 /// same list. For now, providing any explicit arguments will trigger this
1337 /// lint if late-bound parameters are present, so in the future a solution
1338 /// can be adopted without hitting backward compatibility issues. This is
1339 /// a [future-incompatible] lint to transition this to a hard error in the
1340 /// future. See [issue #42868] for more details, along with a description
1341 /// of the difference between early and late-bound parameters.
1343 /// [issue #42868]: https://github.com/rust-lang/rust/issues/42868
1344 /// [future-incompatible]: ../index.md#future-incompatible-lints
1345 pub LATE_BOUND_LIFETIME_ARGUMENTS,
1347 "detects generic lifetime arguments in path segments with late bound lifetime parameters",
1348 @future_incompatible = FutureIncompatibleInfo {
1349 reference: "issue #42868 <https://github.com/rust-lang/rust/issues/42868>",
1354 /// The `order_dependent_trait_objects` lint detects a trait coherency
1355 /// violation that would allow creating two trait impls for the same
1356 /// dynamic trait object involving marker traits.
1360 /// ```rust,compile_fail
1361 /// pub trait Trait {}
1363 /// impl Trait for dyn Send + Sync { }
1364 /// impl Trait for dyn Sync + Send { }
1371 /// A previous bug caused the compiler to interpret traits with different
1372 /// orders (such as `Send + Sync` and `Sync + Send`) as distinct types
1373 /// when they were intended to be treated the same. This allowed code to
1374 /// define separate trait implementations when there should be a coherence
1375 /// error. This is a [future-incompatible] lint to transition this to a
1376 /// hard error in the future. See [issue #56484] for more details.
1378 /// [issue #56484]: https://github.com/rust-lang/rust/issues/56484
1379 /// [future-incompatible]: ../index.md#future-incompatible-lints
1380 pub ORDER_DEPENDENT_TRAIT_OBJECTS,
1382 "trait-object types were treated as different depending on marker-trait order",
1383 @future_incompatible = FutureIncompatibleInfo {
1384 reference: "issue #56484 <https://github.com/rust-lang/rust/issues/56484>",
1389 /// The `coherence_leak_check` lint detects conflicting implementations of
1390 /// a trait that are only distinguished by the old leak-check code.
1395 /// trait SomeTrait { }
1396 /// impl SomeTrait for for<'a> fn(&'a u8) { }
1397 /// impl<'a> SomeTrait for fn(&'a u8) { }
1404 /// In the past, the compiler would accept trait implementations for
1405 /// identical functions that differed only in where the lifetime binder
1406 /// appeared. Due to a change in the borrow checker implementation to fix
1407 /// several bugs, this is no longer allowed. However, since this affects
1408 /// existing code, this is a [future-incompatible] lint to transition this
1409 /// to a hard error in the future.
1411 /// Code relying on this pattern should introduce "[newtypes]",
1412 /// like `struct Foo(for<'a> fn(&'a u8))`.
1414 /// See [issue #56105] for more details.
1416 /// [issue #56105]: https://github.com/rust-lang/rust/issues/56105
1417 /// [newtypes]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#using-the-newtype-pattern-for-type-safety-and-abstraction
1418 /// [future-incompatible]: ../index.md#future-incompatible-lints
1419 pub COHERENCE_LEAK_CHECK,
1421 "distinct impls distinguished only by the leak-check code",
1422 @future_incompatible = FutureIncompatibleInfo {
1423 reference: "issue #56105 <https://github.com/rust-lang/rust/issues/56105>",
1428 /// The `deprecated` lint detects use of deprecated items.
1445 /// Items may be marked "deprecated" with the [`deprecated` attribute] to
1446 /// indicate that they should no longer be used. Usually the attribute
1447 /// should include a note on what to use instead, or check the
1450 /// [`deprecated` attribute]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute
1453 "detects use of deprecated items",
1454 report_in_external_macro
1458 /// The `unused_unsafe` lint detects unnecessary use of an `unsafe` block.
1470 /// If nothing within the block requires `unsafe`, then remove the
1471 /// `unsafe` marker because it is not required and may cause confusion.
1474 "unnecessary use of an `unsafe` block"
1478 /// The `unused_mut` lint detects mut variables which don't need to be
1491 /// The preferred style is to only mark variables as `mut` if it is
1495 "detect mut variables which don't need to be mutable"
1499 /// The `unconditional_recursion` lint detects functions that cannot
1500 /// return without calling themselves.
1514 /// It is usually a mistake to have a recursive call that does not have
1515 /// some condition to cause it to terminate. If you really intend to have
1516 /// an infinite loop, using a `loop` expression is recommended.
1517 pub UNCONDITIONAL_RECURSION,
1519 "functions that cannot return without calling themselves"
1523 /// The `single_use_lifetimes` lint detects lifetimes that are only used
1528 /// ```rust,compile_fail
1529 /// #![deny(single_use_lifetimes)]
1531 /// fn foo<'a>(x: &'a u32) {}
1538 /// Specifying an explicit lifetime like `'a` in a function or `impl`
1539 /// should only be used to link together two things. Otherwise, you should
1540 /// just use `'_` to indicate that the lifetime is not linked to anything,
1541 /// or elide the lifetime altogether if possible.
1543 /// This lint is "allow" by default because it was introduced at a time
1544 /// when `'_` and elided lifetimes were first being introduced, and this
1545 /// lint would be too noisy. Also, there are some known false positives
1546 /// that it produces. See [RFC 2115] for historical context, and [issue
1547 /// #44752] for more details.
1549 /// [RFC 2115]: https://github.com/rust-lang/rfcs/blob/master/text/2115-argument-lifetimes.md
1550 /// [issue #44752]: https://github.com/rust-lang/rust/issues/44752
1551 pub SINGLE_USE_LIFETIMES,
1553 "detects lifetime parameters that are only used once"
1557 /// The `unused_lifetimes` lint detects lifetime parameters that are never
1562 /// ```rust,compile_fail
1563 /// #[deny(unused_lifetimes)]
1565 /// pub fn foo<'a>() {}
1572 /// Unused lifetime parameters may signal a mistake or unfinished code.
1573 /// Consider removing the parameter.
1574 pub UNUSED_LIFETIMES,
1576 "detects lifetime parameters that are never used"
1580 /// The `tyvar_behind_raw_pointer` lint detects raw pointer to an
1581 /// inference variable.
1585 /// ```rust,edition2015
1587 /// let data = std::ptr::null();
1588 /// let _ = &data as *const *const ();
1590 /// if data.is_null() {}
1597 /// This kind of inference was previously allowed, but with the future
1598 /// arrival of [arbitrary self types], this can introduce ambiguity. To
1599 /// resolve this, use an explicit type instead of relying on type
1602 /// This is a [future-incompatible] lint to transition this to a hard
1603 /// error in the 2018 edition. See [issue #46906] for more details. This
1604 /// is currently a hard-error on the 2018 edition, and is "warn" by
1605 /// default in the 2015 edition.
1607 /// [arbitrary self types]: https://github.com/rust-lang/rust/issues/44874
1608 /// [issue #46906]: https://github.com/rust-lang/rust/issues/46906
1609 /// [future-incompatible]: ../index.md#future-incompatible-lints
1610 pub TYVAR_BEHIND_RAW_POINTER,
1612 "raw pointer to an inference variable",
1613 @future_incompatible = FutureIncompatibleInfo {
1614 reference: "issue #46906 <https://github.com/rust-lang/rust/issues/46906>",
1615 reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1620 /// The `elided_lifetimes_in_paths` lint detects the use of hidden
1621 /// lifetime parameters.
1625 /// ```rust,compile_fail
1626 /// #![deny(elided_lifetimes_in_paths)]
1627 /// struct Foo<'a> {
1631 /// fn foo(x: &Foo) {
1639 /// Elided lifetime parameters can make it difficult to see at a glance
1640 /// that borrowing is occurring. This lint ensures that lifetime
1641 /// parameters are always explicitly stated, even if it is the `'_`
1642 /// [placeholder lifetime].
1644 /// This lint is "allow" by default because it has some known issues, and
1645 /// may require a significant transition for old code.
1647 /// [placeholder lifetime]: https://doc.rust-lang.org/reference/lifetime-elision.html#lifetime-elision-in-functions
1648 pub ELIDED_LIFETIMES_IN_PATHS,
1650 "hidden lifetime parameters in types are deprecated",
1655 /// The `bare_trait_objects` lint suggests using `dyn Trait` for trait
1660 /// ```rust,edition2018
1663 /// fn takes_trait_object(_: Box<Trait>) {
1671 /// Without the `dyn` indicator, it can be ambiguous or confusing when
1672 /// reading code as to whether or not you are looking at a trait object.
1673 /// The `dyn` keyword makes it explicit, and adds a symmetry to contrast
1674 /// with [`impl Trait`].
1676 /// [`impl Trait`]: https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
1677 pub BARE_TRAIT_OBJECTS,
1679 "suggest using `dyn Trait` for trait objects",
1680 @future_incompatible = FutureIncompatibleInfo {
1681 reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
1682 reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
1687 /// The `absolute_paths_not_starting_with_crate` lint detects fully
1688 /// qualified paths that start with a module name instead of `crate`,
1689 /// `self`, or an extern crate name
1693 /// ```rust,edition2015,compile_fail
1694 /// #![deny(absolute_paths_not_starting_with_crate)]
1709 /// Rust [editions] allow the language to evolve without breaking
1710 /// backwards compatibility. This lint catches code that uses absolute
1711 /// paths in the style of the 2015 edition. In the 2015 edition, absolute
1712 /// paths (those starting with `::`) refer to either the crate root or an
1713 /// external crate. In the 2018 edition it was changed so that they only
1714 /// refer to external crates. The path prefix `crate::` should be used
1715 /// instead to reference items from the crate root.
1717 /// If you switch the compiler from the 2015 to 2018 edition without
1718 /// updating the code, then it will fail to compile if the old style paths
1719 /// are used. You can manually change the paths to use the `crate::`
1720 /// prefix to transition to the 2018 edition.
1722 /// This lint solves the problem automatically. It is "allow" by default
1723 /// because the code is perfectly valid in the 2015 edition. The [`cargo
1724 /// fix`] tool with the `--edition` flag will switch this lint to "warn"
1725 /// and automatically apply the suggested fix from the compiler. This
1726 /// provides a completely automated way to update old code to the 2018
1729 /// [editions]: https://doc.rust-lang.org/edition-guide/
1730 /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
1731 pub ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
1733 "fully qualified paths that start with a module name \
1734 instead of `crate`, `self`, or an extern crate name",
1735 @future_incompatible = FutureIncompatibleInfo {
1736 reference: "issue #53130 <https://github.com/rust-lang/rust/issues/53130>",
1737 reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
1742 /// The `illegal_floating_point_literal_pattern` lint detects
1743 /// floating-point literals used in patterns.
1760 /// Previous versions of the compiler accepted floating-point literals in
1761 /// patterns, but it was later determined this was a mistake. The
1762 /// semantics of comparing floating-point values may not be clear in a
1763 /// pattern when contrasted with "structural equality". Typically you can
1764 /// work around this by using a [match guard], such as:
1770 /// y if y == 5.0 => {}
1775 /// This is a [future-incompatible] lint to transition this to a hard
1776 /// error in the future. See [issue #41620] for more details.
1778 /// [issue #41620]: https://github.com/rust-lang/rust/issues/41620
1779 /// [match guard]: https://doc.rust-lang.org/reference/expressions/match-expr.html#match-guards
1780 /// [future-incompatible]: ../index.md#future-incompatible-lints
1781 pub ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
1783 "floating-point literals cannot be used in patterns",
1784 @future_incompatible = FutureIncompatibleInfo {
1785 reference: "issue #41620 <https://github.com/rust-lang/rust/issues/41620>",
1790 /// The `unstable_name_collisions` lint detects that you have used a name
1791 /// that the standard library plans to add in the future.
1796 /// trait MyIterator : Iterator {
1797 /// // is_sorted is an unstable method that already exists on the Iterator trait
1798 /// fn is_sorted(self) -> bool where Self: Sized {true}
1801 /// impl<T: ?Sized> MyIterator for T where T: Iterator { }
1803 /// let x = vec![1, 2, 3];
1804 /// let _ = x.iter().is_sorted();
1811 /// When new methods are added to traits in the standard library, they are
1812 /// usually added in an "unstable" form which is only available on the
1813 /// [nightly channel] with a [`feature` attribute]. If there is any
1814 /// pre-existing code which extends a trait to have a method with the same
1815 /// name, then the names will collide. In the future, when the method is
1816 /// stabilized, this will cause an error due to the ambiguity. This lint
1817 /// is an early-warning to let you know that there may be a collision in
1818 /// the future. This can be avoided by adding type annotations to
1819 /// disambiguate which trait method you intend to call, such as
1820 /// `MyIterator::is_sorted(my_iter)` or renaming or removing the method.
1822 /// [nightly channel]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
1823 /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
1824 pub UNSTABLE_NAME_COLLISIONS,
1826 "detects name collision with an existing but unstable method",
1827 @future_incompatible = FutureIncompatibleInfo {
1828 reason: FutureIncompatibilityReason::Custom(
1829 "once this associated item is added to the standard library, \
1830 the ambiguity may cause an error or change in behavior!"
1832 reference: "issue #48919 <https://github.com/rust-lang/rust/issues/48919>",
1833 // Note: this item represents future incompatibility of all unstable functions in the
1834 // standard library, and thus should never be removed or changed to an error.
1839 /// The `irrefutable_let_patterns` lint detects [irrefutable patterns]
1840 /// in [`if let`]s, [`while let`]s, and `if let` guards.
1845 /// if let _ = 123 {
1846 /// println!("always runs!");
1854 /// There usually isn't a reason to have an irrefutable pattern in an
1855 /// `if let` or `while let` statement, because the pattern will always match
1856 /// successfully. A [`let`] or [`loop`] statement will suffice. However,
1857 /// when generating code with a macro, forbidding irrefutable patterns
1858 /// would require awkward workarounds in situations where the macro
1859 /// doesn't know if the pattern is refutable or not. This lint allows
1860 /// macros to accept this form, while alerting for a possibly incorrect
1861 /// use in normal code.
1863 /// See [RFC 2086] for more details.
1865 /// [irrefutable patterns]: https://doc.rust-lang.org/reference/patterns.html#refutability
1866 /// [`if let`]: https://doc.rust-lang.org/reference/expressions/if-expr.html#if-let-expressions
1867 /// [`while let`]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#predicate-pattern-loops
1868 /// [`let`]: https://doc.rust-lang.org/reference/statements.html#let-statements
1869 /// [`loop`]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#infinite-loops
1870 /// [RFC 2086]: https://github.com/rust-lang/rfcs/blob/master/text/2086-allow-if-let-irrefutables.md
1871 pub IRREFUTABLE_LET_PATTERNS,
1873 "detects irrefutable patterns in `if let` and `while let` statements"
1877 /// The `unused_labels` lint detects [labels] that are never used.
1879 /// [labels]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#loop-labels
1884 /// 'unused_label: loop {}
1891 /// Unused labels may signal a mistake or unfinished code. To silence the
1892 /// warning for the individual label, prefix it with an underscore such as
1896 "detects labels that are never used"
1900 /// The `where_clauses_object_safety` lint detects for [object safety] of
1901 /// [where clauses].
1903 /// [object safety]: https://doc.rust-lang.org/reference/items/traits.html#object-safety
1904 /// [where clauses]: https://doc.rust-lang.org/reference/items/generics.html#where-clauses
1911 /// trait X { fn foo(&self) where Self: Trait; }
1913 /// impl X for () { fn foo(&self) {} }
1915 /// impl Trait for dyn X {}
1917 /// // Segfault at opt-level 0, SIGILL otherwise.
1918 /// pub fn main() { <dyn X as X>::foo(&()); }
1925 /// The compiler previously allowed these object-unsafe bounds, which was
1926 /// incorrect. This is a [future-incompatible] lint to transition this to
1927 /// a hard error in the future. See [issue #51443] for more details.
1929 /// [issue #51443]: https://github.com/rust-lang/rust/issues/51443
1930 /// [future-incompatible]: ../index.md#future-incompatible-lints
1931 pub WHERE_CLAUSES_OBJECT_SAFETY,
1933 "checks the object safety of where clauses",
1934 @future_incompatible = FutureIncompatibleInfo {
1935 reference: "issue #51443 <https://github.com/rust-lang/rust/issues/51443>",
1940 /// The `proc_macro_derive_resolution_fallback` lint detects proc macro
1941 /// derives using inaccessible names from parent modules.
1945 /// ```rust,ignore (proc-macro)
1947 /// #![crate_type = "proc-macro"]
1949 /// extern crate proc_macro;
1951 /// use proc_macro::*;
1953 /// #[proc_macro_derive(Foo)]
1954 /// pub fn foo1(a: TokenStream) -> TokenStream {
1956 /// "mod __bar { static mut BAR: Option<Something> = None; }".parse().unwrap()
1960 /// ```rust,ignore (needs-dependency)
1963 /// extern crate foo;
1965 /// struct Something;
1973 /// This will produce:
1976 /// warning: cannot find type `Something` in this scope
1977 /// --> src/main.rs:8:10
1979 /// 8 | #[derive(Foo)]
1980 /// | ^^^ names from parent modules are not accessible without an explicit import
1982 /// = note: `#[warn(proc_macro_derive_resolution_fallback)]` on by default
1983 /// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
1984 /// = note: for more information, see issue #50504 <https://github.com/rust-lang/rust/issues/50504>
1989 /// If a proc-macro generates a module, the compiler unintentionally
1990 /// allowed items in that module to refer to items in the crate root
1991 /// without importing them. This is a [future-incompatible] lint to
1992 /// transition this to a hard error in the future. See [issue #50504] for
1995 /// [issue #50504]: https://github.com/rust-lang/rust/issues/50504
1996 /// [future-incompatible]: ../index.md#future-incompatible-lints
1997 pub PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
1999 "detects proc macro derives using inaccessible names from parent modules",
2000 @future_incompatible = FutureIncompatibleInfo {
2001 reference: "issue #83583 <https://github.com/rust-lang/rust/issues/83583>",
2002 reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
2007 /// The `macro_use_extern_crate` lint detects the use of the
2008 /// [`macro_use` attribute].
2012 /// ```rust,ignore (needs extern crate)
2013 /// #![deny(macro_use_extern_crate)]
2016 /// extern crate serde_json;
2019 /// let _ = json!{{}};
2023 /// This will produce:
2026 /// error: deprecated `#[macro_use]` attribute used to import macros should be replaced at use sites with a `use` item to import the macro instead
2027 /// --> src/main.rs:3:1
2029 /// 3 | #[macro_use]
2032 /// note: the lint level is defined here
2033 /// --> src/main.rs:1:9
2035 /// 1 | #![deny(macro_use_extern_crate)]
2036 /// | ^^^^^^^^^^^^^^^^^^^^^^
2041 /// The [`macro_use` attribute] on an [`extern crate`] item causes
2042 /// macros in that external crate to be brought into the prelude of the
2043 /// crate, making the macros in scope everywhere. As part of the efforts
2044 /// to simplify handling of dependencies in the [2018 edition], the use of
2045 /// `extern crate` is being phased out. To bring macros from extern crates
2046 /// into scope, it is recommended to use a [`use` import].
2048 /// This lint is "allow" by default because this is a stylistic choice
2049 /// that has not been settled, see [issue #52043] for more information.
2051 /// [`macro_use` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#the-macro_use-attribute
2052 /// [`use` import]: https://doc.rust-lang.org/reference/items/use-declarations.html
2053 /// [issue #52043]: https://github.com/rust-lang/rust/issues/52043
2054 pub MACRO_USE_EXTERN_CRATE,
2056 "the `#[macro_use]` attribute is now deprecated in favor of using macros \
2057 via the module system"
2061 /// The `macro_expanded_macro_exports_accessed_by_absolute_paths` lint
2062 /// detects macro-expanded [`macro_export`] macros from the current crate
2063 /// that cannot be referred to by absolute paths.
2065 /// [`macro_export`]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
2069 /// ```rust,compile_fail
2070 /// macro_rules! define_exported {
2073 /// macro_rules! exported {
2079 /// define_exported!();
2082 /// crate::exported!();
2090 /// The intent is that all macros marked with the `#[macro_export]`
2091 /// attribute are made available in the root of the crate. However, when a
2092 /// `macro_rules!` definition is generated by another macro, the macro
2093 /// expansion is unable to uphold this rule. This is a
2094 /// [future-incompatible] lint to transition this to a hard error in the
2095 /// future. See [issue #53495] for more details.
2097 /// [issue #53495]: https://github.com/rust-lang/rust/issues/53495
2098 /// [future-incompatible]: ../index.md#future-incompatible-lints
2099 pub MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
2101 "macro-expanded `macro_export` macros from the current crate \
2102 cannot be referred to by absolute paths",
2103 @future_incompatible = FutureIncompatibleInfo {
2104 reference: "issue #52234 <https://github.com/rust-lang/rust/issues/52234>",
2110 /// The `explicit_outlives_requirements` lint detects unnecessary
2111 /// lifetime bounds that can be inferred.
2115 /// ```rust,compile_fail
2116 /// # #![allow(unused)]
2117 /// #![deny(explicit_outlives_requirements)]
2119 /// struct SharedRef<'a, T>
2131 /// If a `struct` contains a reference, such as `&'a T`, the compiler
2132 /// requires that `T` outlives the lifetime `'a`. This historically
2133 /// required writing an explicit lifetime bound to indicate this
2134 /// requirement. However, this can be overly explicit, causing clutter and
2135 /// unnecessary complexity. The language was changed to automatically
2136 /// infer the bound if it is not specified. Specifically, if the struct
2137 /// contains a reference, directly or indirectly, to `T` with lifetime
2138 /// `'x`, then it will infer that `T: 'x` is a requirement.
2140 /// This lint is "allow" by default because it can be noisy for existing
2141 /// code that already had these requirements. This is a stylistic choice,
2142 /// as it is still valid to explicitly state the bound. It also has some
2143 /// false positives that can cause confusion.
2145 /// See [RFC 2093] for more details.
2147 /// [RFC 2093]: https://github.com/rust-lang/rfcs/blob/master/text/2093-infer-outlives.md
2148 pub EXPLICIT_OUTLIVES_REQUIREMENTS,
2150 "outlives requirements can be inferred"
2154 /// The `indirect_structural_match` lint detects a `const` in a pattern
2155 /// that manually implements [`PartialEq`] and [`Eq`].
2157 /// [`PartialEq`]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html
2158 /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
2162 /// ```rust,compile_fail
2163 /// #![deny(indirect_structural_match)]
2165 /// struct NoDerive(i32);
2166 /// impl PartialEq for NoDerive { fn eq(&self, _: &Self) -> bool { false } }
2167 /// impl Eq for NoDerive { }
2168 /// #[derive(PartialEq, Eq)]
2169 /// struct WrapParam<T>(T);
2170 /// const WRAP_INDIRECT_PARAM: & &WrapParam<NoDerive> = & &WrapParam(NoDerive(0));
2172 /// match WRAP_INDIRECT_PARAM {
2173 /// WRAP_INDIRECT_PARAM => { }
2183 /// The compiler unintentionally accepted this form in the past. This is a
2184 /// [future-incompatible] lint to transition this to a hard error in the
2185 /// future. See [issue #62411] for a complete description of the problem,
2186 /// and some possible solutions.
2188 /// [issue #62411]: https://github.com/rust-lang/rust/issues/62411
2189 /// [future-incompatible]: ../index.md#future-incompatible-lints
2190 pub INDIRECT_STRUCTURAL_MATCH,
2192 "constant used in pattern contains value of non-structural-match type in a field or a variant",
2193 @future_incompatible = FutureIncompatibleInfo {
2194 reference: "issue #62411 <https://github.com/rust-lang/rust/issues/62411>",
2199 /// The `deprecated_in_future` lint is internal to rustc and should not be
2200 /// used by user code.
2202 /// This lint is only enabled in the standard library. It works with the
2203 /// use of `#[rustc_deprecated]` with a `since` field of a version in the
2204 /// future. This allows something to be marked as deprecated in a future
2205 /// version, and then this lint will ensure that the item is no longer
2206 /// used in the standard library. See the [stability documentation] for
2209 /// [stability documentation]: https://rustc-dev-guide.rust-lang.org/stability.html#rustc_deprecated
2210 pub DEPRECATED_IN_FUTURE,
2212 "detects use of items that will be deprecated in a future version",
2213 report_in_external_macro
2217 /// The `pointer_structural_match` lint detects pointers used in patterns whose behaviour
2218 /// cannot be relied upon across compiler versions and optimization levels.
2222 /// ```rust,compile_fail
2223 /// #![deny(pointer_structural_match)]
2224 /// fn foo(a: usize, b: usize) -> usize { a + b }
2225 /// const FOO: fn(usize, usize) -> usize = foo;
2238 /// Previous versions of Rust allowed function pointers and wide raw pointers in patterns.
2239 /// While these work in many cases as expected by users, it is possible that due to
2240 /// optimizations pointers are "not equal to themselves" or pointers to different functions
2241 /// compare as equal during runtime. This is because LLVM optimizations can deduplicate
2242 /// functions if their bodies are the same, thus also making pointers to these functions point
2243 /// to the same location. Additionally functions may get duplicated if they are instantiated
2244 /// in different crates and not deduplicated again via LTO.
2245 pub POINTER_STRUCTURAL_MATCH,
2247 "pointers are not structural-match",
2248 @future_incompatible = FutureIncompatibleInfo {
2249 reference: "issue #62411 <https://github.com/rust-lang/rust/issues/70861>",
2254 /// The `nontrivial_structural_match` lint detects constants that are used in patterns,
2255 /// whose type is not structural-match and whose initializer body actually uses values
2256 /// that are not structural-match. So `Option<NotStructuralMatch>` is ok if the constant
2261 /// ```rust,compile_fail
2262 /// #![deny(nontrivial_structural_match)]
2264 /// #[derive(Copy, Clone, Debug)]
2265 /// struct NoDerive(u32);
2266 /// impl PartialEq for NoDerive { fn eq(&self, _: &Self) -> bool { false } }
2267 /// impl Eq for NoDerive { }
2269 /// const INDEX: Option<NoDerive> = [None, Some(NoDerive(10))][0];
2270 /// match None { Some(_) => panic!("whoops"), INDEX => dbg!(INDEX), };
2278 /// Previous versions of Rust accepted constants in patterns, even if those constants' types
2279 /// did not have `PartialEq` derived. Thus the compiler falls back to runtime execution of
2280 /// `PartialEq`, which can report that two constants are not equal even if they are
2282 pub NONTRIVIAL_STRUCTURAL_MATCH,
2284 "constant used in pattern of non-structural-match type and the constant's initializer \
2285 expression contains values of non-structural-match types",
2286 @future_incompatible = FutureIncompatibleInfo {
2287 reference: "issue #73448 <https://github.com/rust-lang/rust/issues/73448>",
2292 /// The `ambiguous_associated_items` lint detects ambiguity between
2293 /// [associated items] and [enum variants].
2295 /// [associated items]: https://doc.rust-lang.org/reference/items/associated-items.html
2296 /// [enum variants]: https://doc.rust-lang.org/reference/items/enumerations.html
2300 /// ```rust,compile_fail
2307 /// fn foo() -> Self::V;
2312 /// // `Self::V` is ambiguous because it may refer to the associated type or
2313 /// // the enum variant.
2314 /// fn foo() -> Self::V { 0 }
2322 /// Previous versions of Rust did not allow accessing enum variants
2323 /// through [type aliases]. When this ability was added (see [RFC 2338]), this
2324 /// introduced some situations where it can be ambiguous what a type
2325 /// was referring to.
2327 /// To fix this ambiguity, you should use a [qualified path] to explicitly
2328 /// state which type to use. For example, in the above example the
2329 /// function can be written as `fn f() -> <Self as Tr>::V { 0 }` to
2330 /// specifically refer to the associated type.
2332 /// This is a [future-incompatible] lint to transition this to a hard
2333 /// error in the future. See [issue #57644] for more details.
2335 /// [issue #57644]: https://github.com/rust-lang/rust/issues/57644
2336 /// [type aliases]: https://doc.rust-lang.org/reference/items/type-aliases.html#type-aliases
2337 /// [RFC 2338]: https://github.com/rust-lang/rfcs/blob/master/text/2338-type-alias-enum-variants.md
2338 /// [qualified path]: https://doc.rust-lang.org/reference/paths.html#qualified-paths
2339 /// [future-incompatible]: ../index.md#future-incompatible-lints
2340 pub AMBIGUOUS_ASSOCIATED_ITEMS,
2342 "ambiguous associated items",
2343 @future_incompatible = FutureIncompatibleInfo {
2344 reference: "issue #57644 <https://github.com/rust-lang/rust/issues/57644>",
2349 /// The `mutable_borrow_reservation_conflict` lint detects the reservation
2350 /// of a two-phased borrow that conflicts with other shared borrows.
2355 /// let mut v = vec![0, 1, 2];
2356 /// let shared = &v;
2357 /// v.push(shared.len());
2364 /// This is a [future-incompatible] lint to transition this to a hard error
2365 /// in the future. See [issue #59159] for a complete description of the
2366 /// problem, and some possible solutions.
2368 /// [issue #59159]: https://github.com/rust-lang/rust/issues/59159
2369 /// [future-incompatible]: ../index.md#future-incompatible-lints
2370 pub MUTABLE_BORROW_RESERVATION_CONFLICT,
2372 "reservation of a two-phased borrow conflicts with other shared borrows",
2373 @future_incompatible = FutureIncompatibleInfo {
2374 reason: FutureIncompatibilityReason::Custom(
2375 "this borrowing pattern was not meant to be accepted, \
2376 and may become a hard error in the future"
2378 reference: "issue #59159 <https://github.com/rust-lang/rust/issues/59159>",
2383 /// The `soft_unstable` lint detects unstable features that were
2384 /// unintentionally allowed on stable.
2388 /// ```rust,compile_fail
2390 /// extern crate test;
2393 /// fn name(b: &mut test::Bencher) {
2402 /// The [`bench` attribute] was accidentally allowed to be specified on
2403 /// the [stable release channel]. Turning this to a hard error would have
2404 /// broken some projects. This lint allows those projects to continue to
2405 /// build correctly when [`--cap-lints`] is used, but otherwise signal an
2406 /// error that `#[bench]` should not be used on the stable channel. This
2407 /// is a [future-incompatible] lint to transition this to a hard error in
2408 /// the future. See [issue #64266] for more details.
2410 /// [issue #64266]: https://github.com/rust-lang/rust/issues/64266
2411 /// [`bench` attribute]: https://doc.rust-lang.org/nightly/unstable-book/library-features/test.html
2412 /// [stable release channel]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
2413 /// [`--cap-lints`]: https://doc.rust-lang.org/rustc/lints/levels.html#capping-lints
2414 /// [future-incompatible]: ../index.md#future-incompatible-lints
2417 "a feature gate that doesn't break dependent crates",
2418 @future_incompatible = FutureIncompatibleInfo {
2419 reference: "issue #64266 <https://github.com/rust-lang/rust/issues/64266>",
2424 /// The `inline_no_sanitize` lint detects incompatible use of
2425 /// [`#[inline(always)]`][inline] and [`#[no_sanitize(...)]`][no_sanitize].
2427 /// [inline]: https://doc.rust-lang.org/reference/attributes/codegen.html#the-inline-attribute
2428 /// [no_sanitize]: https://doc.rust-lang.org/nightly/unstable-book/language-features/no-sanitize.html
2433 /// #![feature(no_sanitize)]
2435 /// #[inline(always)]
2436 /// #[no_sanitize(address)]
2448 /// The use of the [`#[inline(always)]`][inline] attribute prevents the
2449 /// the [`#[no_sanitize(...)]`][no_sanitize] attribute from working.
2450 /// Consider temporarily removing `inline` attribute.
2451 pub INLINE_NO_SANITIZE,
2453 "detects incompatible use of `#[inline(always)]` and `#[no_sanitize(...)]`",
2457 /// The `asm_sub_register` lint detects using only a subset of a register
2458 /// for inline asm inputs.
2462 /// ```rust,ignore (fails on non-x86_64)
2463 /// #[cfg(target_arch="x86_64")]
2464 /// use std::arch::asm;
2467 /// #[cfg(target_arch="x86_64")]
2469 /// asm!("mov {0}, {0}", in(reg) 0i16);
2474 /// This will produce:
2477 /// warning: formatting may not be suitable for sub-register argument
2478 /// --> src/main.rs:7:19
2480 /// 7 | asm!("mov {0}, {0}", in(reg) 0i16);
2481 /// | ^^^ ^^^ ---- for this argument
2483 /// = note: `#[warn(asm_sub_register)]` on by default
2484 /// = help: use the `x` modifier to have the register formatted as `ax`
2485 /// = help: or use the `r` modifier to keep the default formatting of `rax`
2490 /// Registers on some architectures can use different names to refer to a
2491 /// subset of the register. By default, the compiler will use the name for
2492 /// the full register size. To explicitly use a subset of the register,
2493 /// you can override the default by using a modifier on the template
2494 /// string operand to specify when subregister to use. This lint is issued
2495 /// if you pass in a value with a smaller data type than the default
2496 /// register size, to alert you of possibly using the incorrect width. To
2497 /// fix this, add the suggested modifier to the template, or cast the
2498 /// value to the correct size.
2500 /// See [register template modifiers] in the reference for more details.
2502 /// [register template modifiers]: https://doc.rust-lang.org/nightly/reference/inline-assembly.html#template-modifiers
2503 pub ASM_SUB_REGISTER,
2505 "using only a subset of a register for inline asm inputs",
2509 /// The `bad_asm_style` lint detects the use of the `.intel_syntax` and
2510 /// `.att_syntax` directives.
2514 /// ```rust,ignore (fails on non-x86_64)
2515 /// #[cfg(target_arch="x86_64")]
2516 /// use std::arch::asm;
2519 /// #[cfg(target_arch="x86_64")]
2523 /// "movq %{0}, %{0}", in(reg) 0usize
2529 /// This will produce:
2532 /// warning: avoid using `.att_syntax`, prefer using `options(att_syntax)` instead
2533 /// --> src/main.rs:8:14
2535 /// 8 | ".att_syntax",
2538 /// = note: `#[warn(bad_asm_style)]` on by default
2543 /// On x86, `asm!` uses the intel assembly syntax by default. While this
2544 /// can be switched using assembler directives like `.att_syntax`, using the
2545 /// `att_syntax` option is recommended instead because it will also properly
2546 /// prefix register placeholders with `%` as required by AT&T syntax.
2549 "incorrect use of inline assembly",
2553 /// The `unsafe_op_in_unsafe_fn` lint detects unsafe operations in unsafe
2554 /// functions without an explicit unsafe block.
2558 /// ```rust,compile_fail
2559 /// #![deny(unsafe_op_in_unsafe_fn)]
2561 /// unsafe fn foo() {}
2563 /// unsafe fn bar() {
2574 /// Currently, an [`unsafe fn`] allows any [unsafe] operation within its
2575 /// body. However, this can increase the surface area of code that needs
2576 /// to be scrutinized for proper behavior. The [`unsafe` block] provides a
2577 /// convenient way to make it clear exactly which parts of the code are
2578 /// performing unsafe operations. In the future, it is desired to change
2579 /// it so that unsafe operations cannot be performed in an `unsafe fn`
2580 /// without an `unsafe` block.
2582 /// The fix to this is to wrap the unsafe code in an `unsafe` block.
2584 /// This lint is "allow" by default since this will affect a large amount
2585 /// of existing code, and the exact plan for increasing the severity is
2586 /// still being considered. See [RFC #2585] and [issue #71668] for more
2589 /// [`unsafe fn`]: https://doc.rust-lang.org/reference/unsafe-functions.html
2590 /// [`unsafe` block]: https://doc.rust-lang.org/reference/expressions/block-expr.html#unsafe-blocks
2591 /// [unsafe]: https://doc.rust-lang.org/reference/unsafety.html
2592 /// [RFC #2585]: https://github.com/rust-lang/rfcs/blob/master/text/2585-unsafe-block-in-unsafe-fn.md
2593 /// [issue #71668]: https://github.com/rust-lang/rust/issues/71668
2594 pub UNSAFE_OP_IN_UNSAFE_FN,
2596 "unsafe operations in unsafe functions without an explicit unsafe block are deprecated",
2600 /// The `cenum_impl_drop_cast` lint detects an `as` cast of a field-less
2601 /// `enum` that implements [`Drop`].
2603 /// [`Drop`]: https://doc.rust-lang.org/std/ops/trait.Drop.html
2608 /// # #![allow(unused)]
2613 /// impl Drop for E {
2614 /// fn drop(&mut self) {
2615 /// println!("Drop");
2621 /// let i = e as u32;
2629 /// Casting a field-less `enum` that does not implement [`Copy`] to an
2630 /// integer moves the value without calling `drop`. This can result in
2631 /// surprising behavior if it was expected that `drop` should be called.
2632 /// Calling `drop` automatically would be inconsistent with other move
2633 /// operations. Since neither behavior is clear or consistent, it was
2634 /// decided that a cast of this nature will no longer be allowed.
2636 /// This is a [future-incompatible] lint to transition this to a hard error
2637 /// in the future. See [issue #73333] for more details.
2639 /// [future-incompatible]: ../index.md#future-incompatible-lints
2640 /// [issue #73333]: https://github.com/rust-lang/rust/issues/73333
2641 /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
2642 pub CENUM_IMPL_DROP_CAST,
2644 "a C-like enum implementing Drop is cast",
2645 @future_incompatible = FutureIncompatibleInfo {
2646 reference: "issue #73333 <https://github.com/rust-lang/rust/issues/73333>",
2651 /// The `fuzzy_provenance_casts` lint detects an `as` cast between an integer
2657 /// #![feature(strict_provenance)]
2658 /// #![warn(fuzzy_provenance_casts)]
2661 /// let _dangling = 16_usize as *const u8;
2669 /// This lint is part of the strict provenance effort, see [issue #95228].
2670 /// Casting an integer to a pointer is considered bad style, as a pointer
2671 /// contains, besides the *address* also a *provenance*, indicating what
2672 /// memory the pointer is allowed to read/write. Casting an integer, which
2673 /// doesn't have provenance, to a pointer requires the compiler to assign
2674 /// (guess) provenance. The compiler assigns "all exposed valid" (see the
2675 /// docs of [`ptr::from_exposed_addr`] for more information about this
2676 /// "exposing"). This penalizes the optimiser and is not well suited for
2677 /// dynamic analysis/dynamic program verification (e.g. Miri or CHERI
2680 /// It is much better to use [`ptr::with_addr`] instead to specify the
2681 /// provenance you want. If using this function is not possible because the
2682 /// code relies on exposed provenance then there is as an escape hatch
2683 /// [`ptr::from_exposed_addr`].
2685 /// [issue #95228]: https://github.com/rust-lang/rust/issues/95228
2686 /// [`ptr::with_addr`]: https://doc.rust-lang.org/core/ptr/fn.with_addr
2687 /// [`ptr::from_exposed_addr`]: https://doc.rust-lang.org/core/ptr/fn.from_exposed_addr
2688 pub FUZZY_PROVENANCE_CASTS,
2690 "a fuzzy integer to pointer cast is used",
2691 @feature_gate = sym::strict_provenance;
2695 /// The `lossy_provenance_casts` lint detects an `as` cast between a pointer
2701 /// #![feature(strict_provenance)]
2702 /// #![warn(lossy_provenance_casts)]
2706 /// let _addr: usize = &x as *const u8 as usize;
2714 /// This lint is part of the strict provenance effort, see [issue #95228].
2715 /// Casting a pointer to an integer is a lossy operation, because beyond
2716 /// just an *address* a pointer may be associated with a particular
2717 /// *provenance*. This information is used by the optimiser and for dynamic
2718 /// analysis/dynamic program verification (e.g. Miri or CHERI platforms).
2720 /// Since this cast is lossy, it is considered good style to use the
2721 /// [`ptr::addr`] method instead, which has a similar effect, but doesn't
2722 /// "expose" the pointer provenance. This improves optimisation potential.
2723 /// See the docs of [`ptr::addr`] and [`ptr::expose_addr`] for more information
2724 /// about exposing pointer provenance.
2726 /// If your code can't comply with strict provenance and needs to expose
2727 /// the provenance, then there is [`ptr::expose_addr`] as an escape hatch,
2728 /// which preserves the behaviour of `as usize` casts while being explicit
2729 /// about the semantics.
2731 /// [issue #95228]: https://github.com/rust-lang/rust/issues/95228
2732 /// [`ptr::addr`]: https://doc.rust-lang.org/core/ptr/fn.addr
2733 /// [`ptr::expose_addr`]: https://doc.rust-lang.org/core/ptr/fn.expose_addr
2734 pub LOSSY_PROVENANCE_CASTS,
2736 "a lossy pointer to integer cast is used",
2737 @feature_gate = sym::strict_provenance;
2741 /// The `const_evaluatable_unchecked` lint detects a generic constant used
2747 /// const fn foo<T>() -> usize {
2748 /// if std::mem::size_of::<*mut T>() < 8 { // size of *mut T does not depend on T
2756 /// let _ = [0; foo::<T>()];
2764 /// In the 1.43 release, some uses of generic parameters in array repeat
2765 /// expressions were accidentally allowed. This is a [future-incompatible]
2766 /// lint to transition this to a hard error in the future. See [issue
2767 /// #76200] for a more detailed description and possible fixes.
2769 /// [future-incompatible]: ../index.md#future-incompatible-lints
2770 /// [issue #76200]: https://github.com/rust-lang/rust/issues/76200
2771 pub CONST_EVALUATABLE_UNCHECKED,
2773 "detects a generic constant is used in a type without a emitting a warning",
2774 @future_incompatible = FutureIncompatibleInfo {
2775 reference: "issue #76200 <https://github.com/rust-lang/rust/issues/76200>",
2780 /// The `function_item_references` lint detects function references that are
2781 /// formatted with [`fmt::Pointer`] or transmuted.
2783 /// [`fmt::Pointer`]: https://doc.rust-lang.org/std/fmt/trait.Pointer.html
2791 /// println!("{:p}", &foo);
2799 /// Taking a reference to a function may be mistaken as a way to obtain a
2800 /// pointer to that function. This can give unexpected results when
2801 /// formatting the reference as a pointer or transmuting it. This lint is
2802 /// issued when function references are formatted as pointers, passed as
2803 /// arguments bound by [`fmt::Pointer`] or transmuted.
2804 pub FUNCTION_ITEM_REFERENCES,
2806 "suggest casting to a function pointer when attempting to take references to function items",
2810 /// The `uninhabited_static` lint detects uninhabited statics.
2817 /// static EXTERN: Void;
2825 /// Statics with an uninhabited type can never be initialized, so they are impossible to define.
2826 /// However, this can be side-stepped with an `extern static`, leading to problems later in the
2827 /// compiler which assumes that there are no initialized uninhabited places (such as locals or
2828 /// statics). This was accidentally allowed, but is being phased out.
2829 pub UNINHABITED_STATIC,
2831 "uninhabited static",
2832 @future_incompatible = FutureIncompatibleInfo {
2833 reference: "issue #74840 <https://github.com/rust-lang/rust/issues/74840>",
2838 /// The `useless_deprecated` lint detects deprecation attributes with no effect.
2842 /// ```rust,compile_fail
2845 /// #[deprecated = "message"]
2846 /// impl Default for X {
2847 /// fn default() -> Self {
2857 /// Deprecation attributes have no effect on trait implementations.
2858 pub USELESS_DEPRECATED,
2860 "detects deprecation attributes with no effect",
2864 /// The `undefined_naked_function_abi` lint detects naked function definitions that
2865 /// either do not specify an ABI or specify the Rust ABI.
2870 /// #![feature(naked_functions)]
2872 /// use std::arch::asm;
2875 /// pub fn default_abi() -> u32 {
2876 /// unsafe { asm!("", options(noreturn)); }
2880 /// pub extern "Rust" fn rust_abi() -> u32 {
2881 /// unsafe { asm!("", options(noreturn)); }
2889 /// The Rust ABI is currently undefined. Therefore, naked functions should
2890 /// specify a non-Rust ABI.
2891 pub UNDEFINED_NAKED_FUNCTION_ABI,
2893 "undefined naked function ABI"
2897 /// The `ineffective_unstable_trait_impl` lint detects `#[unstable]` attributes which are not used.
2901 /// ```rust,compile_fail
2902 /// #![feature(staged_api)]
2904 /// #[derive(Clone)]
2905 /// #[stable(feature = "x", since = "1")]
2908 /// #[unstable(feature = "y", issue = "none")]
2909 /// impl Copy for S {}
2916 /// `staged_api` does not currently support using a stability attribute on `impl` blocks.
2917 /// `impl`s are always stable if both the type and trait are stable, and always unstable otherwise.
2918 pub INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
2920 "detects `#[unstable]` on stable trait implementations for stable types"
2924 /// The `semicolon_in_expressions_from_macros` lint detects trailing semicolons
2925 /// in macro bodies when the macro is invoked in expression position.
2926 /// This was previous accepted, but is being phased out.
2930 /// ```rust,compile_fail
2931 /// #![deny(semicolon_in_expressions_from_macros)]
2932 /// macro_rules! foo {
2937 /// let val = match true {
2948 /// Previous, Rust ignored trailing semicolon in a macro
2949 /// body when a macro was invoked in expression position.
2950 /// However, this makes the treatment of semicolons in the language
2951 /// inconsistent, and could lead to unexpected runtime behavior
2952 /// in some circumstances (e.g. if the macro author expects
2953 /// a value to be dropped).
2955 /// This is a [future-incompatible] lint to transition this
2956 /// to a hard error in the future. See [issue #79813] for more details.
2958 /// [issue #79813]: https://github.com/rust-lang/rust/issues/79813
2959 /// [future-incompatible]: ../index.md#future-incompatible-lints
2960 pub SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
2962 "trailing semicolon in macro body used as expression",
2963 @future_incompatible = FutureIncompatibleInfo {
2964 reference: "issue #79813 <https://github.com/rust-lang/rust/issues/79813>",
2969 /// The `legacy_derive_helpers` lint detects derive helper attributes
2970 /// that are used before they are introduced.
2974 /// ```rust,ignore (needs extern crate)
2975 /// #[serde(rename_all = "camelCase")]
2976 /// #[derive(Deserialize)]
2977 /// struct S { /* fields */ }
2983 /// warning: derive helper attribute is used before it is introduced
2984 /// --> $DIR/legacy-derive-helpers.rs:1:3
2986 /// 1 | #[serde(rename_all = "camelCase")]
2989 /// 2 | #[derive(Deserialize)]
2990 /// | ----------- the attribute is introduced here
2995 /// Attributes like this work for historical reasons, but attribute expansion works in
2996 /// left-to-right order in general, so, to resolve `#[serde]`, compiler has to try to "look
2997 /// into the future" at not yet expanded part of the item , but such attempts are not always
3000 /// To fix the warning place the helper attribute after its corresponding derive.
3001 /// ```rust,ignore (needs extern crate)
3002 /// #[derive(Deserialize)]
3003 /// #[serde(rename_all = "camelCase")]
3004 /// struct S { /* fields */ }
3006 pub LEGACY_DERIVE_HELPERS,
3008 "detects derive helper attributes that are used before they are introduced",
3009 @future_incompatible = FutureIncompatibleInfo {
3010 reference: "issue #79202 <https://github.com/rust-lang/rust/issues/79202>",
3015 /// The `large_assignments` lint detects when objects of large
3016 /// types are being moved around.
3020 /// ```rust,ignore (can crash on some platforms)
3021 /// let x = [0; 50000];
3028 /// warning: moving a large value
3029 /// --> $DIR/move-large.rs:1:3
3031 /// - Copied large value here
3036 /// When using a large type in a plain assignment or in a function
3037 /// argument, idiomatic code can be inefficient.
3038 /// Ideally appropriate optimizations would resolve this, but such
3039 /// optimizations are only done in a best-effort manner.
3040 /// This lint will trigger on all sites of large moves and thus allow the
3041 /// user to resolve them in code.
3042 pub LARGE_ASSIGNMENTS,
3044 "detects large moves or copies",
3048 /// The `deprecated_cfg_attr_crate_type_name` lint detects uses of the
3049 /// `#![cfg_attr(..., crate_type = "...")]` and
3050 /// `#![cfg_attr(..., crate_name = "...")]` attributes to conditionally
3051 /// specify the crate type and name in the source code.
3056 /// #![cfg_attr(debug_assertions, crate_type = "lib")]
3064 /// The `#![crate_type]` and `#![crate_name]` attributes require a hack in
3065 /// the compiler to be able to change the used crate type and crate name
3066 /// after macros have been expanded. Neither attribute works in combination
3067 /// with Cargo as it explicitly passes `--crate-type` and `--crate-name` on
3068 /// the commandline. These values must match the value used in the source
3069 /// code to prevent an error.
3071 /// To fix the warning use `--crate-type` on the commandline when running
3072 /// rustc instead of `#![cfg_attr(..., crate_type = "...")]` and
3073 /// `--crate-name` instead of `#![cfg_attr(..., crate_name = "...")]`.
3074 pub DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
3076 "detects usage of `#![cfg_attr(..., crate_type/crate_name = \"...\")]`",
3077 @future_incompatible = FutureIncompatibleInfo {
3078 reference: "issue #91632 <https://github.com/rust-lang/rust/issues/91632>",
3083 /// The `unexpected_cfgs` lint detects unexpected conditional compilation conditions.
3088 /// rustc --check-cfg 'names()'
3091 /// ```rust,ignore (needs command line option)
3096 /// This will produce:
3099 /// warning: unknown condition name used
3100 /// --> lint_example.rs:1:7
3102 /// 1 | #[cfg(widnows)]
3105 /// = note: `#[warn(unexpected_cfgs)]` on by default
3110 /// This lint is only active when a `--check-cfg='names(...)'` option has been passed
3111 /// to the compiler and triggers whenever an unknown condition name or value is used.
3112 /// The known condition include names or values passed in `--check-cfg`, `--cfg`, and some
3113 /// well-knows names and values built into the compiler.
3114 pub UNEXPECTED_CFGS,
3116 "detects unexpected names and values in `#[cfg]` conditions",
3119 declare_lint_pass! {
3120 /// Does nothing as a lint pass, but registers some `Lint`s
3121 /// that are used by other parts of the compiler.
3123 FORBIDDEN_LINT_GROUPS,
3124 ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
3125 ARITHMETIC_OVERFLOW,
3126 UNCONDITIONAL_PANIC,
3128 UNUSED_EXTERN_CRATES,
3129 UNUSED_CRATE_DEPENDENCIES,
3130 UNUSED_QUALIFICATIONS,
3132 UNFULFILLED_LINT_EXPECTATIONS,
3137 UNREACHABLE_PATTERNS,
3138 OVERLAPPING_RANGE_ENDPOINTS,
3139 BINDINGS_WITH_VARIANT_NAME,
3144 UNKNOWN_CRATE_TYPES,
3146 TRIVIAL_NUMERIC_CASTS,
3148 EXPORTED_PRIVATE_DEPENDENCIES,
3149 PUB_USE_OF_PRIVATE_EXTERN_CRATE,
3150 INVALID_TYPE_PARAM_DEFAULT,
3152 RENAMED_AND_REMOVED_LINTS,
3153 UNALIGNED_REFERENCES,
3154 CONST_ITEM_MUTATION,
3155 PATTERNS_IN_FNS_WITHOUT_BODY,
3156 MISSING_FRAGMENT_SPECIFIER,
3157 LATE_BOUND_LIFETIME_ARGUMENTS,
3158 ORDER_DEPENDENT_TRAIT_OBJECTS,
3159 COHERENCE_LEAK_CHECK,
3163 UNCONDITIONAL_RECURSION,
3164 SINGLE_USE_LIFETIMES,
3167 TYVAR_BEHIND_RAW_POINTER,
3168 ELIDED_LIFETIMES_IN_PATHS,
3170 ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
3171 UNSTABLE_NAME_COLLISIONS,
3172 IRREFUTABLE_LET_PATTERNS,
3173 WHERE_CLAUSES_OBJECT_SAFETY,
3174 PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
3175 MACRO_USE_EXTERN_CRATE,
3176 MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
3177 ILL_FORMED_ATTRIBUTE_INPUT,
3178 CONFLICTING_REPR_HINTS,
3179 META_VARIABLE_MISUSE,
3180 DEPRECATED_IN_FUTURE,
3181 AMBIGUOUS_ASSOCIATED_ITEMS,
3182 MUTABLE_BORROW_RESERVATION_CONFLICT,
3183 INDIRECT_STRUCTURAL_MATCH,
3184 POINTER_STRUCTURAL_MATCH,
3185 NONTRIVIAL_STRUCTURAL_MATCH,
3190 UNSAFE_OP_IN_UNSAFE_FN,
3192 CENUM_IMPL_DROP_CAST,
3193 FUZZY_PROVENANCE_CASTS,
3194 LOSSY_PROVENANCE_CASTS,
3195 CONST_EVALUATABLE_UNCHECKED,
3196 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
3199 FUNCTION_ITEM_REFERENCES,
3202 INVALID_DOC_ATTRIBUTES,
3203 SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
3204 RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
3205 LEGACY_DERIVE_HELPERS,
3206 PROC_MACRO_BACK_COMPAT,
3207 RUST_2021_INCOMPATIBLE_OR_PATTERNS,
3209 RUST_2021_PRELUDE_COLLISIONS,
3210 RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
3211 UNSUPPORTED_CALLING_CONVENTIONS,
3212 BREAK_WITH_LABEL_AND_LOOP,
3214 NON_EXHAUSTIVE_OMITTED_PATTERNS,
3215 TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
3216 DEREF_INTO_DYN_SUPERTRAIT,
3217 DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
3218 DUPLICATE_MACRO_ATTRIBUTES,
3219 SUSPICIOUS_AUTO_TRAIT_IMPLS,
3221 DEPRECATED_WHERE_CLAUSE_LOCATION,
3227 /// The `unused_doc_comments` lint detects doc comments that aren't used
3241 /// `rustdoc` does not use doc comments in all positions, and so the doc
3242 /// comment will be ignored. Try changing it to a normal comment with `//`
3243 /// to avoid the warning.
3244 pub UNUSED_DOC_COMMENTS,
3246 "detects doc comments that aren't used by rustdoc"
3250 /// The `rust_2021_incompatible_closure_captures` lint detects variables that aren't completely
3251 /// captured in Rust 2021, such that the `Drop` order of their fields may differ between
3252 /// Rust 2018 and 2021.
3254 /// It can also detect when a variable implements a trait like `Send`, but one of its fields does not,
3255 /// and the field is captured by a closure and used with the assumption that said field implements
3256 /// the same trait as the root variable.
3258 /// ### Example of drop reorder
3260 /// ```rust,compile_fail
3261 /// #![deny(rust_2021_incompatible_closure_captures)]
3262 /// # #![allow(unused)]
3264 /// struct FancyInteger(i32);
3266 /// impl Drop for FancyInteger {
3267 /// fn drop(&mut self) {
3268 /// println!("Just dropped {}", self.0);
3272 /// struct Point { x: FancyInteger, y: FancyInteger }
3275 /// let p = Point { x: FancyInteger(10), y: FancyInteger(20) };
3283 /// // ... More code ...
3291 /// In the above example, `p.y` will be dropped at the end of `f` instead of
3292 /// with `c` in Rust 2021.
3294 /// ### Example of auto-trait
3296 /// ```rust,compile_fail
3297 /// #![deny(rust_2021_incompatible_closure_captures)]
3298 /// use std::thread;
3300 /// struct Pointer(*mut i32);
3301 /// unsafe impl Send for Pointer {}
3305 /// let fptr = Pointer(&mut f as *mut i32);
3306 /// thread::spawn(move || unsafe {
3316 /// In the above example, only `fptr.0` is captured in Rust 2021.
3317 /// The field is of type `*mut i32`, which doesn't implement `Send`,
3318 /// making the code invalid as the field cannot be sent between threads safely.
3319 pub RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
3321 "detects closures affected by Rust 2021 changes",
3322 @future_incompatible = FutureIncompatibleInfo {
3323 reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
3324 explain_reason: false,
3328 declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);
3331 /// The `missing_abi` lint detects cases where the ABI is omitted from
3332 /// extern declarations.
3336 /// ```rust,compile_fail
3337 /// #![deny(missing_abi)]
3339 /// extern fn foo() {}
3346 /// Historically, Rust implicitly selected C as the ABI for extern
3347 /// declarations. We expect to add new ABIs, like `C-unwind`, in the future,
3348 /// though this has not yet happened, and especially with their addition
3349 /// seeing the ABI easily will make code review easier.
3352 "No declared ABI for extern declaration"
3356 /// The `invalid_doc_attributes` lint detects when the `#[doc(...)]` is
3361 /// ```rust,compile_fail
3362 /// #![deny(warnings)]
3364 /// pub mod submodule {
3365 /// #![doc(test(no_crate_inject))]
3373 /// Previously, there were very like checks being performed on `#[doc(..)]`
3374 /// unlike the other attributes. It'll now catch all the issues that it
3375 /// silently ignored previously.
3376 pub INVALID_DOC_ATTRIBUTES,
3378 "detects invalid `#[doc(...)]` attributes",
3379 @future_incompatible = FutureIncompatibleInfo {
3380 reference: "issue #82730 <https://github.com/rust-lang/rust/issues/82730>",
3385 /// The `proc_macro_back_compat` lint detects uses of old versions of certain
3386 /// proc-macro crates, which have hardcoded workarounds in the compiler.
3390 /// ```rust,ignore (needs-dependency)
3392 /// use time_macros_impl::impl_macros;
3394 /// impl_macros!(Foo);
3397 /// This will produce:
3400 /// warning: using an old version of `time-macros-impl`
3401 /// ::: $DIR/group-compat-hack.rs:27:5
3403 /// LL | impl_macros!(Foo);
3404 /// | ------------------ in this macro invocation
3406 /// = note: `#[warn(proc_macro_back_compat)]` on by default
3407 /// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
3408 /// = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
3409 /// = note: the `time-macros-impl` crate will stop compiling in futures version of Rust. Please update to the latest version of the `time` crate to avoid breakage
3410 /// = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
3415 /// Eventually, the backwards-compatibility hacks present in the compiler will be removed,
3416 /// causing older versions of certain crates to stop compiling.
3417 /// This is a [future-incompatible] lint to ease the transition to an error.
3418 /// See [issue #83125] for more details.
3420 /// [issue #83125]: https://github.com/rust-lang/rust/issues/83125
3421 /// [future-incompatible]: ../index.md#future-incompatible-lints
3422 pub PROC_MACRO_BACK_COMPAT,
3424 "detects usage of old versions of certain proc-macro crates",
3425 @future_incompatible = FutureIncompatibleInfo {
3426 reference: "issue #83125 <https://github.com/rust-lang/rust/issues/83125>",
3427 reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
3432 /// The `rust_2021_incompatible_or_patterns` lint detects usage of old versions of or-patterns.
3436 /// ```rust,compile_fail
3437 /// #![deny(rust_2021_incompatible_or_patterns)]
3439 /// macro_rules! match_any {
3440 /// ( $expr:expr , $( $( $pat:pat )|+ => $expr_arm:expr ),+ ) => {
3443 /// $( $pat => $expr_arm, )+
3450 /// let result: Result<i64, i32> = Err(42);
3451 /// let int: i64 = match_any!(result, Ok(i) | Err(i) => i.into());
3452 /// assert_eq!(int, 42);
3460 /// In Rust 2021, the `pat` matcher will match additional patterns, which include the `|` character.
3461 pub RUST_2021_INCOMPATIBLE_OR_PATTERNS,
3463 "detects usage of old versions of or-patterns",
3464 @future_incompatible = FutureIncompatibleInfo {
3465 reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/or-patterns-macro-rules.html>",
3466 reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
3471 /// The `rust_2021_prelude_collisions` lint detects the usage of trait methods which are ambiguous
3472 /// with traits added to the prelude in future editions.
3476 /// ```rust,compile_fail
3477 /// #![deny(rust_2021_prelude_collisions)]
3480 /// fn try_into(self) -> Result<String, !>;
3483 /// impl Foo for &str {
3484 /// fn try_into(self) -> Result<String, !> {
3485 /// Ok(String::from(self))
3490 /// let x: String = "3".try_into().unwrap();
3492 /// // This call to try_into matches both Foo:try_into and TryInto::try_into as
3493 /// // `TryInto` has been added to the Rust prelude in 2021 edition.
3494 /// println!("{x}");
3502 /// In Rust 2021, one of the important introductions is the [prelude changes], which add
3503 /// `TryFrom`, `TryInto`, and `FromIterator` into the standard library's prelude. Since this
3504 /// results in an ambiguity as to which method/function to call when an existing `try_into`
3505 /// method is called via dot-call syntax or a `try_from`/`from_iter` associated function
3506 /// is called directly on a type.
3508 /// [prelude changes]: https://blog.rust-lang.org/inside-rust/2021/03/04/planning-rust-2021.html#prelude-changes
3509 pub RUST_2021_PRELUDE_COLLISIONS,
3511 "detects the usage of trait methods which are ambiguous with traits added to the \
3512 prelude in future editions",
3513 @future_incompatible = FutureIncompatibleInfo {
3514 reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/prelude.html>",
3515 reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
3520 /// The `rust_2021_prefixes_incompatible_syntax` lint detects identifiers that will be parsed as a
3521 /// prefix instead in Rust 2021.
3525 /// ```rust,edition2018,compile_fail
3526 /// #![deny(rust_2021_prefixes_incompatible_syntax)]
3528 /// macro_rules! m {
3529 /// (z $x:expr) => ();
3539 /// In Rust 2015 and 2018, `z"hey"` is two tokens: the identifier `z`
3540 /// followed by the string literal `"hey"`. In Rust 2021, the `z` is
3541 /// considered a prefix for `"hey"`.
3543 /// This lint suggests to add whitespace between the `z` and `"hey"` tokens
3544 /// to keep them separated in Rust 2021.
3545 // Allow this lint -- rustdoc doesn't yet support threading edition into this lint's parser.
3546 #[allow(rustdoc::invalid_rust_codeblocks)]
3547 pub RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
3549 "identifiers that will be parsed as a prefix in Rust 2021",
3550 @future_incompatible = FutureIncompatibleInfo {
3551 reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/reserving-syntax.html>",
3552 reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
3558 /// The `unsupported_calling_conventions` lint is output whenever there is a use of the
3559 /// `stdcall`, `fastcall`, `thiscall`, `vectorcall` calling conventions (or their unwind
3560 /// variants) on targets that cannot meaningfully be supported for the requested target.
3562 /// For example `stdcall` does not make much sense for a x86_64 or, more apparently, powerpc
3563 /// code, because this calling convention was never specified for those targets.
3565 /// Historically MSVC toolchains have fallen back to the regular C calling convention for
3566 /// targets other than x86, but Rust doesn't really see a similar need to introduce a similar
3567 /// hack across many more targets.
3571 /// ```rust,ignore (needs specific targets)
3572 /// extern "stdcall" fn stdcall() {}
3575 /// This will produce:
3578 /// warning: use of calling convention not supported on this target
3579 /// --> $DIR/unsupported.rs:39:1
3581 /// LL | extern "stdcall" fn stdcall() {}
3582 /// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3584 /// = note: `#[warn(unsupported_calling_conventions)]` on by default
3585 /// = warning: this was previously accepted by the compiler but is being phased out;
3586 /// it will become a hard error in a future release!
3587 /// = note: for more information, see issue ...
3592 /// On most of the targets the behaviour of `stdcall` and similar calling conventions is not
3593 /// defined at all, but was previously accepted due to a bug in the implementation of the
3595 pub UNSUPPORTED_CALLING_CONVENTIONS,
3597 "use of unsupported calling convention",
3598 @future_incompatible = FutureIncompatibleInfo {
3599 reference: "issue #87678 <https://github.com/rust-lang/rust/issues/87678>",
3604 /// The `break_with_label_and_loop` lint detects labeled `break` expressions with
3605 /// an unlabeled loop as their value expression.
3611 /// break 'label loop { break 42; };
3619 /// In Rust, loops can have a label, and `break` expressions can refer to that label to
3620 /// break out of specific loops (and not necessarily the innermost one). `break` expressions
3621 /// can also carry a value expression, which can be another loop. A labeled `break` with an
3622 /// unlabeled loop as its value expression is easy to confuse with an unlabeled break with
3623 /// a labeled loop and is thus discouraged (but allowed for compatibility); use parentheses
3624 /// around the loop expression to silence this warning. Unlabeled `break` expressions with
3625 /// labeled loops yield a hard error, which can also be silenced by wrapping the expression
3627 pub BREAK_WITH_LABEL_AND_LOOP,
3629 "`break` expression with label and unlabeled loop as value expression"
3633 /// The `non_exhaustive_omitted_patterns` lint detects when a wildcard (`_` or `..`) in a
3634 /// pattern for a `#[non_exhaustive]` struct or enum is reachable.
3638 /// ```rust,ignore (needs separate crate)
3640 /// #[non_exhaustive]
3643 /// B, // added variant in non breaking change
3647 /// #![feature(non_exhaustive_omitted_patterns_lint)]
3651 /// #[warn(non_exhaustive_omitted_patterns)]
3656 /// This will produce:
3659 /// warning: reachable patterns not covered of non exhaustive enum
3660 /// --> $DIR/reachable-patterns.rs:70:9
3663 /// | ^ pattern `B` not covered
3665 /// note: the lint level is defined here
3666 /// --> $DIR/reachable-patterns.rs:69:16
3668 /// LL | #[warn(non_exhaustive_omitted_patterns)]
3669 /// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3670 /// = help: ensure that all possible cases are being handled by adding the suggested match arms
3671 /// = note: the matched value is of type `Bar` and the `non_exhaustive_omitted_patterns` attribute was found
3676 /// Structs and enums tagged with `#[non_exhaustive]` force the user to add a
3677 /// (potentially redundant) wildcard when pattern-matching, to allow for future
3678 /// addition of fields or variants. The `non_exhaustive_omitted_patterns` lint
3679 /// detects when such a wildcard happens to actually catch some fields/variants.
3680 /// In other words, when the match without the wildcard would not be exhaustive.
3681 /// This lets the user be informed if new fields/variants were added.
3682 pub NON_EXHAUSTIVE_OMITTED_PATTERNS,
3684 "detect when patterns of types marked `non_exhaustive` are missed",
3685 @feature_gate = sym::non_exhaustive_omitted_patterns_lint;
3689 /// The `text_direction_codepoint_in_comment` lint detects Unicode codepoints in comments that
3690 /// change the visual representation of text on screen in a way that does not correspond to
3691 /// their on memory representation.
3695 /// ```rust,compile_fail
3696 /// #![deny(text_direction_codepoint_in_comment)]
3698 /// println!("{:?}"); // '');
3706 /// Unicode allows changing the visual flow of text on screen in order to support scripts that
3707 /// are written right-to-left, but a specially crafted comment can make code that will be
3708 /// compiled appear to be part of a comment, depending on the software used to read the code.
3709 /// To avoid potential problems or confusion, such as in CVE-2021-42574, by default we deny
3711 pub TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
3713 "invisible directionality-changing codepoints in comment"
3717 /// The `deref_into_dyn_supertrait` lint is output whenever there is a use of the
3718 /// `Deref` implementation with a `dyn SuperTrait` type as `Output`.
3720 /// These implementations will become shadowed when the `trait_upcasting` feature is stabilized.
3721 /// The `deref` functions will no longer be called implicitly, so there might be behavior change.
3725 /// ```rust,compile_fail
3726 /// #![deny(deref_into_dyn_supertrait)]
3727 /// #![allow(dead_code)]
3729 /// use core::ops::Deref;
3733 /// impl<'a> Deref for dyn 'a + B {
3734 /// type Target = dyn A;
3735 /// fn deref(&self) -> &Self::Target {
3740 /// fn take_a(_: &dyn A) { }
3742 /// fn take_b(b: &dyn B) {
3751 /// The dyn upcasting coercion feature adds new coercion rules, taking priority
3752 /// over certain other coercion rules, which will cause some behavior change.
3753 pub DEREF_INTO_DYN_SUPERTRAIT,
3755 "`Deref` implementation usage with a supertrait trait object for output might be shadowed in the future",
3756 @future_incompatible = FutureIncompatibleInfo {
3757 reference: "issue #89460 <https://github.com/rust-lang/rust/issues/89460>",
3762 /// The `duplicate_macro_attributes` lint detects when a `#[test]`-like built-in macro
3763 /// attribute is duplicated on an item. This lint may trigger on `bench`, `cfg_eval`, `test`
3764 /// and `test_case`.
3768 /// ```rust,ignore (needs --test)
3774 /// This will produce:
3777 /// warning: duplicated attribute
3778 /// --> src/lib.rs:2:1
3783 /// = note: `#[warn(duplicate_macro_attributes)]` on by default
3788 /// A duplicated attribute may erroneously originate from a copy-paste and the effect of it
3789 /// being duplicated may not be obvious or desirable.
3791 /// For instance, doubling the `#[test]` attributes registers the test to be run twice with no
3792 /// change to its environment.
3794 /// [issue #90979]: https://github.com/rust-lang/rust/issues/90979
3795 pub DUPLICATE_MACRO_ATTRIBUTES,
3797 "duplicated attribute"
3801 /// The `suspicious_auto_trait_impls` lint checks for potentially incorrect
3802 /// implementations of auto traits.
3807 /// struct Foo<T>(T);
3809 /// unsafe impl<T> Send for Foo<*const T> {}
3816 /// A type can implement auto traits, e.g. `Send`, `Sync` and `Unpin`,
3817 /// in two different ways: either by writing an explicit impl or if
3818 /// all fields of the type implement that auto trait.
3820 /// The compiler disables the automatic implementation if an explicit one
3821 /// exists for given type constructor. The exact rules governing this
3822 /// are currently unsound and quite subtle and and will be modified in the future.
3823 /// This change will cause the automatic implementation to be disabled in more
3824 /// cases, potentially breaking some code.
3825 pub SUSPICIOUS_AUTO_TRAIT_IMPLS,
3827 "the rules governing auto traits will change in the future",
3828 @future_incompatible = FutureIncompatibleInfo {
3829 reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
3830 reference: "issue #93367 <https://github.com/rust-lang/rust/issues/93367>",
3835 /// The `deprecated_where_clause_location` lint detects when a where clause in front of the equals
3836 /// in an associated type.
3841 /// #![feature(generic_associated_types)]
3844 /// type Assoc<'a> where Self: 'a;
3847 /// impl Trait for () {
3848 /// type Assoc<'a> where Self: 'a = ();
3856 /// The preferred location for where clauses on associated types in impls
3857 /// is after the type. However, for most of generic associated types development,
3858 /// it was only accepted before the equals. To provide a transition period and
3859 /// further evaluate this change, both are currently accepted. At some point in
3860 /// the future, this may be disallowed at an edition boundary; but, that is
3861 /// undecided currently.
3862 pub DEPRECATED_WHERE_CLAUSE_LOCATION,
3864 "deprecated where clause location"
3868 /// The `test_unstable_lint` lint tests unstable lints and is perma-unstable.
3873 /// #![allow(test_unstable_lint)]
3880 /// In order to test the behavior of unstable lints, a permanently-unstable
3881 /// lint is required. This lint can be used to trigger warnings and errors
3882 /// from the compiler related to unstable lints.
3883 pub TEST_UNSTABLE_LINT,
3885 "this unstable lint is only for testing",
3886 @feature_gate = sym::test_unstable_lint;