rustc_lint

Module builtin

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Lints in the Rust compiler.

This contains lints which can feasibly be implemented as their own AST visitor. Also see rustc_session::lint::builtin, which contains the definitions of lints that are emitted directly inside the main compiler.

To add a new lint to rustc, declare it here using declare_lint!(). Then add code to emit the new lint in the appropriate circumstances. You can do that in an existing LintPass if it makes sense, or in a new LintPass, or using Session::add_lint elsewhere in the compiler. Only do the latter if the check can’t be written cleanly as a LintPass (also, note that such lints will need to be defined in rustc_session::lint::builtin, not here).

If you define a new EarlyLintPass, you will also need to add it to the add_early_builtin! or add_early_builtin_with_new! invocation in lib.rs. Use the former for unit-like structs and the latter for structs with a pub fn new().

If you define a new LateLintPass, you will also need to add it to the late_lint_methods! invocation in lib.rs.

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Statics§

  • ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE
    The absolute_paths_not_starting_with_crate lint detects fully qualified paths that start with a module name instead of crate, self, or an extern crate name
  • AMBIGUOUS_ASSOCIATED_ITEMS
    The ambiguous_associated_items lint detects ambiguity between associated items and enum variants.
  • AMBIGUOUS_GLOB_IMPORTS
    The ambiguous_glob_imports lint detects glob imports that should report ambiguity errors, but previously didn’t do that due to rustc bugs.
  • AMBIGUOUS_GLOB_REEXPORTS
    The ambiguous_glob_reexports lint detects cases where names re-exported via globs collide. Downstream users trying to use the same name re-exported from multiple globs will receive a warning pointing out redefinition of the same name.
  • ANONYMOUS_PARAMETERS
    The anonymous_parameters lint detects anonymous parameters in trait definitions.
  • ARITHMETIC_OVERFLOW
    The arithmetic_overflow lint detects that an arithmetic operation will overflow.
  • ASM_SUB_REGISTER
    The asm_sub_register lint detects using only a subset of a register for inline asm inputs.
  • BAD_ASM_STYLE
    The bad_asm_style lint detects the use of the .intel_syntax and .att_syntax directives.
  • BARE_TRAIT_OBJECTS
    The bare_trait_objects lint suggests using dyn Trait for trait objects.
  • BINARY_ASM_LABELS
    The binary_asm_labels lint detects the use of numeric labels containing only binary digits in the inline asm! macro.
  • BINDINGS_WITH_VARIANT_NAME
    The bindings_with_variant_name lint detects pattern bindings with the same name as one of the matched variants.
  • BREAK_WITH_LABEL_AND_LOOP
    The break_with_label_and_loop lint detects labeled break expressions with an unlabeled loop as their value expression.
  • CENUM_IMPL_DROP_CAST
    The cenum_impl_drop_cast lint detects an as cast of a field-less enum that implements Drop.
  • COHERENCE_LEAK_CHECK
    The coherence_leak_check lint detects conflicting implementations of a trait that are only distinguished by the old leak-check code.
  • CONFLICTING_REPR_HINTS
    The conflicting_repr_hints lint detects repr attributes with conflicting hints.
  • CONST_EVALUATABLE_UNCHECKED
    The const_evaluatable_unchecked lint detects a generic constant used in a type.
  • CONST_ITEM_MUTATION
    The const_item_mutation lint detects attempts to mutate a const item.
  • DEAD_CODE
    The dead_code lint detects unused, unexported items.
  • DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK
    The dependency_on_unit_never_type_fallback lint detects cases where code compiles with never type fallback being (), but will stop compiling with fallback being !.
  • DEPRECATED
    The deprecated lint detects use of deprecated items.
  • DEPRECATED_IN_FUTURE
    The deprecated_in_future lint is internal to rustc and should not be used by user code.
  • DEPRECATED_SAFE_2024
    The deprecated_safe_2024 lint detects unsafe functions being used as safe functions.
  • DEPRECATED_WHERE_CLAUSE_LOCATION
    The deprecated_where_clause_location lint detects when a where clause in front of the equals in an associated type.
  • DEREF_NULLPTR
    The deref_nullptr lint detects when an null pointer is dereferenced, which causes undefined behavior.
  • DUPLICATE_MACRO_ATTRIBUTES
    The duplicate_macro_attributes lint detects when a #[test]-like built-in macro attribute is duplicated on an item. This lint may trigger on bench, cfg_eval, test and test_case.
  • ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT
    The elided_lifetimes_in_associated_constant lint detects elided lifetimes in associated constants when there are other lifetimes in scope. This was accidentally supported, and this lint was later relaxed to allow eliding lifetimes to 'static when there are no lifetimes in scope.
  • ELIDED_LIFETIMES_IN_PATHS
    The elided_lifetimes_in_paths lint detects the use of hidden lifetime parameters.
  • ELIDED_NAMED_LIFETIMES
    The elided_named_lifetimes lint detects when an elided lifetime ends up being a named lifetime, such as 'static or some lifetime parameter 'a.
  • ELLIPSIS_INCLUSIVE_RANGE_PATTERNS
    The ellipsis_inclusive_range_patterns lint detects the ... range pattern, which is deprecated.
  • EXPLICIT_BUILTIN_CFGS_IN_FLAGS
    The explicit_builtin_cfgs_in_flags lint detects builtin cfgs set via the --cfg flag.
  • EXPLICIT_OUTLIVES_REQUIREMENTS
    The explicit_outlives_requirements lint detects unnecessary lifetime bounds that can be inferred.
  • EXPORTED_PRIVATE_DEPENDENCIES
    The exported_private_dependencies lint detects private dependencies that are exposed in a public interface.
  • FFI_UNWIND_CALLS
    The ffi_unwind_calls lint detects calls to foreign functions or function pointers with C-unwind or other FFI-unwind ABIs.
  • FORBIDDEN_LINT_GROUPS
    The forbidden_lint_groups lint detects violations of forbid applied to a lint group. Due to a bug in the compiler, these used to be overlooked entirely. They now generate a warning.
  • FUNCTION_ITEM_REFERENCES
    The function_item_references lint detects function references that are formatted with fmt::Pointer or transmuted.
  • FUZZY_PROVENANCE_CASTS
    The fuzzy_provenance_casts lint detects an as cast between an integer and a pointer.
  • HIDDEN_GLOB_REEXPORTS
    The hidden_glob_reexports lint detects cases where glob re-export items are shadowed by private items.
  • ILL_FORMED_ATTRIBUTE_INPUT
    The ill_formed_attribute_input lint detects ill-formed attribute inputs that were previously accepted and used in practice.
  • INCOMPLETE_FEATURES
    The incomplete_features lint detects unstable features enabled with the feature attribute that may function improperly in some or all cases.
  • INCOMPLETE_INCLUDE
    The incomplete_include lint detects the use of the include! macro with a file that contains more than one expression.
  • INEFFECTIVE_UNSTABLE_TRAIT_IMPL
    The ineffective_unstable_trait_impl lint detects #[unstable] attributes which are not used.
  • INLINE_NO_SANITIZE
    The inline_no_sanitize lint detects incompatible use of #[inline(always)] and #[no_sanitize(...)].
  • INTERNAL_FEATURES
    The internal_features lint detects unstable features enabled with the feature attribute that are internal to the compiler or standard library.
  • INVALID_DOC_ATTRIBUTES
    The invalid_doc_attributes lint detects when the #[doc(...)] is misused.
  • INVALID_MACRO_EXPORT_ARGUMENTS
    The invalid_macro_export_arguments lint detects cases where #[macro_export] is being used with invalid arguments.
  • INVALID_TYPE_PARAM_DEFAULT
    The invalid_type_param_default lint detects type parameter defaults erroneously allowed in an invalid location.
  • INVALID_VALUE
    The invalid_value lint detects creating a value that is not valid, such as a null reference.
  • IRREFUTABLE_LET_PATTERNS
    The irrefutable_let_patterns lint detects irrefutable patterns in if lets, while lets, and if let guards.
  • KEYWORD_IDENTS_2018
    The keyword_idents_2018 lint detects edition keywords being used as an identifier.
  • KEYWORD_IDENTS_2024
    The keyword_idents_2024 lint detects edition keywords being used as an identifier.
  • LARGE_ASSIGNMENTS
    The large_assignments lint detects when objects of large types are being moved around.
  • LATE_BOUND_LIFETIME_ARGUMENTS
    The late_bound_lifetime_arguments lint detects generic lifetime arguments in path segments with late bound lifetime parameters.
  • LEGACY_DERIVE_HELPERS
    The legacy_derive_helpers lint detects derive helper attributes that are used before they are introduced.
  • LONG_RUNNING_CONST_EVAL
    The long_running_const_eval lint is emitted when const eval is running for a long time to ensure rustc terminates even if you accidentally wrote an infinite loop.
  • LOSSY_PROVENANCE_CASTS
    The lossy_provenance_casts lint detects an as cast between a pointer and an integer.
  • MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS
    The macro_expanded_macro_exports_accessed_by_absolute_paths lint detects macro-expanded macro_export macros from the current crate that cannot be referred to by absolute paths.
  • MACRO_USE_EXTERN_CRATE
    The macro_use_extern_crate lint detects the use of the macro_use attribute.
  • META_VARIABLE_MISUSE
    The meta_variable_misuse lint detects possible meta-variable misuse in macro definitions.
  • MISSING_ABI
    The missing_abi lint detects cases where the ABI is omitted from extern declarations.
  • MISSING_COPY_IMPLEMENTATIONS
    The missing_copy_implementations lint detects potentially-forgotten implementations of Copy for public types.
  • MISSING_DEBUG_IMPLEMENTATIONS 🔒
    The missing_debug_implementations lint detects missing implementations of fmt::Debug for public types.
  • MISSING_DOCS
    The missing_docs lint detects missing documentation for public items.
  • MISSING_FRAGMENT_SPECIFIER
    The missing_fragment_specifier lint is issued when an unused pattern in a macro_rules! macro definition has a meta-variable (e.g. $e) that is not followed by a fragment specifier (e.g. :expr).
  • MISSING_UNSAFE_ON_EXTERN
    The missing_unsafe_on_extern lint detects missing unsafe keyword on extern declarations.
  • MUST_NOT_SUSPEND
    The must_not_suspend lint guards against values that shouldn’t be held across suspend points (.await)
  • MUTABLE_TRANSMUTES 🔒
    The mutable_transmutes lint catches transmuting from &T to &mut T because it is undefined behavior.
  • NAMED_ARGUMENTS_USED_POSITIONALLY
    The named_arguments_used_positionally lint detects cases where named arguments are only used positionally in format strings. This usage is valid but potentially very confusing.
  • NAMED_ASM_LABELS
    The named_asm_labels lint detects the use of named labels in the inline asm! macro.
  • NEVER_TYPE_FALLBACK_FLOWING_INTO_UNSAFE
    The never_type_fallback_flowing_into_unsafe lint detects cases where never type fallback affects unsafe function calls.
  • NON_CONTIGUOUS_RANGE_ENDPOINTS
    The non_contiguous_range_endpoints lint detects likely off-by-one errors when using exclusive range patterns.
  • NON_EXHAUSTIVE_OMITTED_PATTERNS
    The non_exhaustive_omitted_patterns lint aims to help consumers of a #[non_exhaustive] struct or enum who want to match all of its fields/variants explicitly.
  • NON_SHORTHAND_FIELD_PATTERNS 🔒
    The non_shorthand_field_patterns lint detects using Struct { x: x } instead of Struct { x } in a pattern.
  • NO_MANGLE_CONST_ITEMS 🔒
    The no_mangle_const_items lint detects any const items with the no_mangle attribute.
  • NO_MANGLE_GENERIC_ITEMS 🔒
    The no_mangle_generic_items lint detects generic items that must be mangled.
  • ORDER_DEPENDENT_TRAIT_OBJECTS
    The order_dependent_trait_objects lint detects a trait coherency violation that would allow creating two trait impls for the same dynamic trait object involving marker traits.
  • OUT_OF_SCOPE_MACRO_CALLS
    The out_of_scope_macro_calls lint detects macro_rules called when they are not in scope, above their definition, which may happen in key-value attributes.
  • OVERLAPPING_RANGE_ENDPOINTS
    The overlapping_range_endpoints lint detects match arms that have range patterns that overlap on their endpoints.
  • PATTERNS_IN_FNS_WITHOUT_BODY
    The patterns_in_fns_without_body lint detects mut identifier patterns as a parameter in functions without a body.
  • PRIVATE_BOUNDS
    The private_bounds lint detects types in a secondary interface of an item, that are more private than the item itself. Secondary interface of an item consists of bounds on generic parameters and where clauses, including supertraits for trait items.
  • PRIVATE_INTERFACES
    The private_interfaces lint detects types in a primary interface of an item, that are more private than the item itself. Primary interface of an item is all its interface except for bounds on generic parameters and where clauses.
  • PRIVATE_MACRO_USE
    The private_macro_use lint detects private macros that are imported with #[macro_use].
  • PROC_MACRO_DERIVE_RESOLUTION_FALLBACK
    The proc_macro_derive_resolution_fallback lint detects proc macro derives using inaccessible names from parent modules.
  • PTR_CAST_ADD_AUTO_TO_OBJECT
    The ptr_cast_add_auto_to_object lint detects casts of raw pointers to trait objects, which add auto traits.
  • PTR_TO_INTEGER_TRANSMUTE_IN_CONSTS
    The ptr_to_integer_transmute_in_consts lint detects pointer to integer transmute in const functions and associated constants.
  • PUB_USE_OF_PRIVATE_EXTERN_CRATE
    The pub_use_of_private_extern_crate lint detects a specific situation of re-exporting a private extern crate.
  • REDUNDANT_IMPORTS
    The redundant_imports lint detects imports that are redundant due to being imported already; either through a previous import, or being present in the prelude.
  • REDUNDANT_LIFETIMES
    The redundant_lifetimes lint detects lifetime parameters that are redundant because they are equal to another named lifetime.
  • REFINING_IMPL_TRAIT_INTERNAL
    The refining_impl_trait_internal lint detects impl Trait return types in method signatures that are refined by a trait implementation, meaning the implementation adds information about the return type that is not present in the trait.
  • REFINING_IMPL_TRAIT_REACHABLE
    The refining_impl_trait_reachable lint detects impl Trait return types in method signatures that are refined by a publically reachable trait implementation, meaning the implementation adds information about the return type that is not present in the trait.
  • RENAMED_AND_REMOVED_LINTS
    The renamed_and_removed_lints lint detects lints that have been renamed or removed.
  • REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS
    The repr_transparent_external_private_fields lint detects types marked #[repr(transparent)] that (transitively) contain an external ZST type marked #[non_exhaustive] or containing private fields
  • RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES
    The rust_2021_incompatible_closure_captures lint detects variables that aren’t completely captured in Rust 2021, such that the Drop order of their fields may differ between Rust 2018 and 2021.
  • RUST_2021_INCOMPATIBLE_OR_PATTERNS
    The rust_2021_incompatible_or_patterns lint detects usage of old versions of or-patterns.
  • RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX
    The rust_2021_prefixes_incompatible_syntax lint detects identifiers that will be parsed as a prefix instead in Rust 2021.
  • RUST_2021_PRELUDE_COLLISIONS
    The rust_2021_prelude_collisions lint detects the usage of trait methods which are ambiguous with traits added to the prelude in future editions.
  • RUST_2024_GUARDED_STRING_INCOMPATIBLE_SYNTAX
    The rust_2024_guarded_string_incompatible_syntax lint detects # tokens that will be parsed as part of a guarded string literal in Rust 2024.
  • RUST_2024_INCOMPATIBLE_PAT
    The rust_2024_incompatible_pat lint detects patterns whose meaning will change in the Rust 2024 edition.
  • RUST_2024_PRELUDE_COLLISIONS
    The rust_2024_prelude_collisions lint detects the usage of trait methods which are ambiguous with traits added to the prelude in future editions.
  • SELF_CONSTRUCTOR_FROM_OUTER_ITEM
    The self_constructor_from_outer_item lint detects cases where the Self constructor was silently allowed due to a bug in the resolver, and which may produce surprising and unintended behavior.
  • SEMICOLON_IN_EXPRESSIONS_FROM_MACROS
    The semicolon_in_expressions_from_macros lint detects trailing semicolons in macro bodies when the macro is invoked in expression position. This was previous accepted, but is being phased out.
  • SINGLE_USE_LIFETIMES
    The single_use_lifetimes lint detects lifetimes that are only used once.
  • SOFT_UNSTABLE
    The soft_unstable lint detects unstable features that were unintentionally allowed on stable.
  • SPECIAL_MODULE_NAME
    The special_module_name lint detects module declarations for files that have a special meaning.
  • STABLE_FEATURES
    The stable_features lint detects a feature attribute that has since been made stable.
  • TEST_UNSTABLE_LINT
    The test_unstable_lint lint tests unstable lints and is perma-unstable.
  • TEXT_DIRECTION_CODEPOINT_IN_COMMENT
    The text_direction_codepoint_in_comment lint detects Unicode codepoints in comments that change the visual representation of text on screen in a way that does not correspond to their on memory representation.
  • TRIVIAL_BOUNDS 🔒
    The trivial_bounds lint detects trait bounds that don’t depend on any type parameters.
  • TRIVIAL_CASTS
    The trivial_casts lint detects trivial casts which could be replaced with coercion, which may require a temporary variable.
  • TRIVIAL_NUMERIC_CASTS
    The trivial_numeric_casts lint detects trivial numeric casts of types which could be removed.
  • TYPE_ALIAS_BOUNDS 🔒
    The type_alias_bounds lint detects bounds in type aliases.
  • TYVAR_BEHIND_RAW_POINTER
    The tyvar_behind_raw_pointer lint detects raw pointer to an inference variable.
  • UNCONDITIONAL_PANIC
    The unconditional_panic lint detects an operation that will cause a panic at runtime.
  • UNCONDITIONAL_RECURSION
    The unconditional_recursion lint detects functions that cannot return without calling themselves.
  • UNCOVERED_PARAM_IN_PROJECTION
    The uncovered_param_in_projection lint detects a violation of one of Rust’s orphan rules for foreign trait implementations that concerns the use of type parameters inside trait associated type paths (“projections”) whose output may not be a local type that is mistakenly considered to “cover” said parameters which is unsound and which may be rejected by a future version of the compiler.
  • UNDEFINED_NAKED_FUNCTION_ABI
    The undefined_naked_function_abi lint detects naked function definitions that either do not specify an ABI or specify the Rust ABI.
  • UNEXPECTED_CFGS
    The unexpected_cfgs lint detects unexpected conditional compilation conditions.
  • UNFULFILLED_LINT_EXPECTATIONS
    The unfulfilled_lint_expectations lint detects when a lint expectation is unfulfilled.
  • UNGATED_ASYNC_FN_TRACK_CALLER 🔒
    The ungated_async_fn_track_caller lint warns when the #[track_caller] attribute is used on an async function without enabling the corresponding unstable feature flag.
  • UNINHABITED_STATIC
    The uninhabited_static lint detects uninhabited statics.
  • UNKNOWN_CRATE_TYPES
    The unknown_crate_types lint detects an unknown crate type found in a crate_type attribute.
  • UNKNOWN_LINTS
    The unknown_lints lint detects unrecognized lint attributes.
  • UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES
    The unknown_or_malformed_diagnostic_attributes lint detects unrecognized or otherwise malformed diagnostic attributes.
  • UNNAMEABLE_TEST_ITEMS
    The unnameable_test_items lint detects #[test] functions that are not able to be run by the test harness because they are in a position where they are not nameable.
  • UNNAMEABLE_TYPES
    The unnameable_types lint detects types for which you can get objects of that type, but cannot name the type itself.
  • UNREACHABLE_CODE
    The unreachable_code lint detects unreachable code paths.
  • UNREACHABLE_PATTERNS
    The unreachable_patterns lint detects unreachable patterns.
  • UNREACHABLE_PUB
    The unreachable_pub lint triggers for pub items not reachable from other crates - that means neither directly accessible, nor reexported, nor leaked through things like return types.
  • UNSAFE_ATTR_OUTSIDE_UNSAFE
    The unsafe_attr_outside_unsafe lint detects a missing unsafe keyword on attributes considered unsafe.
  • UNSAFE_CODE 🔒
    The unsafe_code lint catches usage of unsafe code and other potentially unsound constructs like no_mangle, export_name, and link_section.
  • UNSAFE_OP_IN_UNSAFE_FN
    The unsafe_op_in_unsafe_fn lint detects unsafe operations in unsafe functions without an explicit unsafe block.
  • UNSTABLE_FEATURES 🔒
    The unstable_features lint detects uses of #![feature].
  • UNSTABLE_NAME_COLLISIONS
    The unstable_name_collisions lint detects that you have used a name that the standard library plans to add in the future.
  • UNSTABLE_SYNTAX_PRE_EXPANSION
    The unstable_syntax_pre_expansion lint detects the use of unstable syntax that is discarded during attribute expansion.
  • UNSUPPORTED_CALLING_CONVENTIONS
    The unsupported_calling_conventions lint is output whenever there is a use of the stdcall, fastcall, thiscall, vectorcall calling conventions (or their unwind variants) on targets that cannot meaningfully be supported for the requested target.
  • UNSUPPORTED_FN_PTR_CALLING_CONVENTIONS
    The unsupported_fn_ptr_calling_conventions lint is output whenever there is a use of a target dependent calling convention on a target that does not support this calling convention on a function pointer.
  • UNUSED_ASSIGNMENTS
    The unused_assignments lint detects assignments that will never be read.
  • UNUSED_ASSOCIATED_TYPE_BOUNDS
    The unused_associated_type_bounds lint is emitted when an associated type bound is added to a trait object, but the associated type has a where Self: Sized bound, and is thus unavailable on the trait object anyway.
  • UNUSED_ATTRIBUTES
    The unused_attributes lint detects attributes that were not used by the compiler.
  • UNUSED_CRATE_DEPENDENCIES
    The unused_crate_dependencies lint detects crate dependencies that are never used.
  • UNUSED_DOC_COMMENTS
    The unused_doc_comments lint detects doc comments that aren’t used by rustdoc.
  • UNUSED_EXTERN_CRATES
    The unused_extern_crates lint guards against extern crate items that are never used.
  • UNUSED_FEATURES
    The unused_features lint detects unused or unknown features found in crate-level feature attributes.
  • UNUSED_IMPORTS
    The unused_imports lint detects imports that are never used.
  • UNUSED_LABELS
    The unused_labels lint detects labels that are never used.
  • UNUSED_LIFETIMES
    The unused_lifetimes lint detects lifetime parameters that are never used.
  • UNUSED_MACROS
    The unused_macros lint detects macros that were not used.
  • UNUSED_MACRO_RULES
    The unused_macro_rules lint detects macro rules that were not used.
  • UNUSED_MUT
    The unused_mut lint detects mut variables which don’t need to be mutable.
  • UNUSED_QUALIFICATIONS
    The unused_qualifications lint detects unnecessarily qualified names.
  • UNUSED_UNSAFE
    The unused_unsafe lint detects unnecessary use of an unsafe block.
  • UNUSED_VARIABLES
    The unused_variables lint detects variables which are not used in any way.
  • USELESS_DEPRECATED
    The useless_deprecated lint detects deprecation attributes with no effect.
  • WARNINGS
    The warnings lint allows you to change the level of other lints which produce warnings.
  • WASM_C_ABI
    The wasm_c_abi lint detects crate dependencies that are incompatible with future versions of Rust that will emit spec-compliant C ABI.
  • WHILE_TRUE 🔒
    The while_true lint detects while true { }.

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