Official Dart lint rules

The Dart linter is a static analyzer for identifying possible problems in your Dart source code. More than a hundred linter rules are available, checking anything from potential typing issues, coding style, and formatting. This package - package:lints - contains the lint settings recommended by the Dart team.

Lint sets

This package includes two sets of lints:

• Core lints: Lints that help identify critical issues that are likely to lead to problems when running or consuming Dart code. All code should pass these lints.

• Recommended lints: Lints that help identify additional issues that may lead to problems when running or consuming Dart code, and lints that enforce writing Dart using a single, idiomatic style and format. All code is encouraged to pass these lints. The recommended lints include all the core lints.

Additionally, a third lint set - package:flutter_lints - extends the recommended set with additional recommended Flutter-specific lints.

The Dart team will likely not provide recommendations past the core and recommended sets (e.g., a strict rule set). However, there are many such rule sets in the ecosystem (available at pub-web.flutter-io.cn).

Rule set authors: consider adding the lints topic to your pubspec to allow easier discovery (e.g., pub-web.flutter-io.cn/packages?q=topic:lints). For more information about topics, see dart.dev/tools/pub/pubspec#topics.

Where these lints are used

When creating new Dart project using the dart create command, the lints from package:lints are enabled by default.

When uploading a package to the pub-web.flutter-io.cn package repository, packages are awarded pub points based on how many of the 'core' lints pass.

Enabling the lints

For new apps created with dart create the recommended set of lints are enabled by default.

For existing apps or packages, you can enable these lints via:

1. In a terminal, located at the root of your package, run this command:

   dart pub add --dev lints
   

2. Create a new analysis_options.yaml file, next to the pubspec, that includes the lints package:

   include: package:lints/recommended.yaml
   

   or:

   include: package:lints/core.yaml
   

Customizing the predefined lint sets

For details on customizing static analysis above and beyond the predefined lint sets, see customizing static analysis.

Evolving the lint sets

The Dart language changes and the ecosystem continues to develop new best practices, so the lint sets must be periodically updated to reflect the best way we know to write Dart code. The process we use is:

1. Anyone can file an issue to discuss a potential change to a lint set (i.e., adding or removing a lint from one or both sets; if you're proposing an entirely new lint, the place to suggest that is at the linter repo). Feedback is welcome from any Dart user.

2. Periodically, a group of Dart and Flutter team members meet to review the suggestions and decide what to adopt.

3. The lists are updated and a new version of the package is published.

Lint set contents

Core lints

To use these lints create an analysis_options.yaml file with: include: package:lints/core.yaml.

Lint Rules	Description
avoid_empty_else	Avoid empty else statements.
avoid_relative_lib_imports	Avoid relative imports for files in lib/.
avoid_shadowing_type_parameters	Avoid shadowing type parameters.
avoid_types_as_parameter_names	Avoid types as parameter names.
await_only_futures	Await only futures.
camel_case_extensions	Name extensions using UpperCamelCase.
camel_case_types	Name types using UpperCamelCase.
curly_braces_in_flow_control_structures	DO use curly braces for all flow control structures.
depend_on_referenced_packages	Depend on referenced packages.
empty_catches	Avoid empty catch blocks.
file_names	Name source files using lowercase_with_underscores.
hash_and_equals	Always override hashCode if overriding ==.
iterable_contains_unrelated_type	Invocation of Iterable
list_remove_unrelated_type	Invocation of remove with references of unrelated types.
no_duplicate_case_values	Don't use more than one case with same value.
non_constant_identifier_names	Name non-constant identifiers using lowerCamelCase.
null_check_on_nullable_type_parameter	Don't use null check on a potentially nullable type parameter.
package_prefixed_library_names	Prefix library names with the package name and a dot-separated path.
prefer_generic_function_type_aliases	Prefer generic function type aliases.
prefer_is_empty	Use isEmpty for Iterables and Maps.
prefer_is_not_empty	Use isNotEmpty for Iterables and Maps.
prefer_iterable_whereType	Prefer to use whereType on iterable.
prefer_typing_uninitialized_variables	Prefer typing uninitialized variables and fields.
provide_deprecation_message	Provide a deprecation message, via @Deprecated("message").
unnecessary_overrides	Don't override a method to do a super method invocation with the same parameters.
unrelated_type_equality_checks	Equality operator == invocation with references of unrelated types.
valid_regexps	Use valid regular expression syntax.
void_checks	Don't assign to void.

Recommended lints

To use these lints create an analysis_options.yaml file with: include: package:lints/recommended.yaml.

Lint Rules	Description
annotate_overrides	Annotate overridden members.
avoid_function_literals_in_foreach_calls	Avoid using forEach with a function literal.
avoid_init_to_null	Don't explicitly initialize variables to null.
avoid_null_checks_in_equality_operators	Don't check for null in custom == operators.
avoid_renaming_method_parameters	Don't rename parameters of overridden methods.
avoid_return_types_on_setters	Avoid return types on setters.
avoid_returning_null_for_void	Avoid returning null for void.
avoid_single_cascade_in_expression_statements	Avoid single cascade in expression statements.
constant_identifier_names	Prefer using lowerCamelCase for constant names.
control_flow_in_finally	Avoid control flow in finally blocks.
empty_constructor_bodies	Use ; instead of {} for empty constructor bodies.
empty_statements	Avoid empty statements.
exhaustive_cases	Define case clauses for all constants in enum-like classes.
implementation_imports	Don't import implementation files from another package.
library_names	Name libraries using lowercase_with_underscores.
library_prefixes	Use lowercase_with_underscores when specifying a library prefix.
library_private_types_in_public_api	Avoid using private types in public APIs.
no_leading_underscores_for_library_prefixes	Avoid leading underscores for library prefixes.
no_leading_underscores_for_local_identifiers	Avoid leading underscores for local identifiers.
null_closures	Do not pass null as an argument where a closure is expected.
overridden_fields	Don't override fields.
package_names	Use lowercase_with_underscores for package names.
prefer_adjacent_string_concatenation	Use adjacent strings to concatenate string literals.
prefer_collection_literals	Use collection literals when possible.
prefer_conditional_assignment	Prefer using ??= over testing for null.
prefer_contains	Use contains for List and String instances.
prefer_equal_for_default_values	Use = to separate a named parameter from its default value.
prefer_final_fields	Private field could be final.
prefer_for_elements_to_map_fromIterable	Prefer 'for' elements when building maps from iterables.
prefer_function_declarations_over_variables	Use a function declaration to bind a function to a name.
prefer_if_null_operators	Prefer using if null operators.
prefer_initializing_formals	Use initializing formals when possible.
prefer_inlined_adds	Inline list item declarations where possible.
prefer_interpolation_to_compose_strings	Use interpolation to compose strings and values.
prefer_is_not_operator	Prefer is! operator.
prefer_null_aware_operators	Prefer using null aware operators.
prefer_spread_collections	Use spread collections when possible.
prefer_void_to_null	Don't use the Null type, unless you are positive that you don't want void.
recursive_getters	Property getter recursively returns itself.
slash_for_doc_comments	Prefer using /// for doc comments.
type_init_formals	Don't type annotate initializing formals.
unnecessary_brace_in_string_interps	Avoid using braces in interpolation when not needed.
unnecessary_const	Avoid const keyword.
unnecessary_constructor_name	Unnecessary .new constructor name.
unnecessary_getters_setters	Avoid wrapping fields in getters and setters just to be "safe".
unnecessary_late	Don't specify the late modifier when it is not needed.
unnecessary_new	Unnecessary new keyword.
unnecessary_null_aware_assignments	Avoid null in null-aware assignment.
unnecessary_null_in_if_null_operators	Avoid using null in if null operators.
unnecessary_nullable_for_final_variable_declarations	Use a non-nullable type for a final variable initialized with a non-nullable value.
unnecessary_string_escapes	Remove unnecessary backslashes in strings.
unnecessary_string_interpolations	Unnecessary string interpolation.
unnecessary_this	Don't access members with this unless avoiding shadowing.
use_function_type_syntax_for_parameters	Use generic function type syntax for parameters.
use_rethrow_when_possible	Use rethrow to rethrow a caught exception.