Github Copilot Custom Instructions for Flutter / Dart based on Effective Dart

effective-dart-copilot-instructions.md

Github Copilot Custom Instructions for Effective Dart

The following can be included as part of the [.github/copilot-instructions.md])https://docs.github.com/en/copilot/how-tos/custom-instructions) file.

Coding Standards

Follow Effective Dart guidelines for consistent Documentation & Coding.

Glossary

• A library member is a top-level field, getter, setter, or function. Basically, anything at the top level that isn't a type.
• A class member is a constructor, field, getter, setter, function, or operator declared inside a class. Class members can be instance or static, abstract or concrete.
• A member is either a library member or a class member.
• A variable, when used generally, refers to top-level variables, parameters, and local variables. It doesn't include static or instance fields.
• A type is any named type declaration: a class, typedef, or enum.
• A property is a top-level variable, getter (inside a class or at the top level, instance or static), setter (same), or field (instance or static). Roughly any "field-like" named construct.

Summary of all rules

Style

Identifiers

• DO name types using UpperCamelCase.
• DO name extensions using UpperCamelCase.
• DO name packages, directories, and source files using lowercase_with_underscores.
• DO name import prefixes using lowercase_with_underscores.
• DO name other identifiers using lowerCamelCase.
• PREFER using lowerCamelCase for constant names.
• DO capitalize acronyms and abbreviations longer than two letters like words.
• PREFER using wildcards for unused callback parameters.
• DON'T use a leading underscore for identifiers that aren't private.
• DON'T use prefix letters.
• DON'T explicitly name libraries.

Ordering

• DO place dart: imports before other imports.
• DO place package: imports before relative imports.
• DO specify exports in a separate section after all imports.
• DO sort sections alphabetically.

Formatting

• DO format your code using dart format.
• CONSIDER changing your code to make it more formatter-friendly.
• PREFER lines 80 characters or fewer.
• DO use curly braces for all flow control statements.

Documentation

Comments

• DO format comments like sentences.
• DON'T use block comments for documentation.

Doc Comments

• DO use /// doc comments to document members and types.
• PREFER writing doc comments for public APIs.
• CONSIDER writing a library-level doc comment.
• CONSIDER writing doc comments for private APIs.
• DO start doc comments with a single-sentence summary.
• DO separate the first sentence of a doc comment into its own paragraph.
• AVOID redundancy with the surrounding context.
• PREFER starting comments of a function or method with third-person verbs if its main purpose is a side effect.
• PREFER starting a non-boolean variable or property comment with a noun phrase.
• PREFER starting a boolean variable or property comment with "Whether" followed by a noun or gerund phrase.
• PREFER a noun phrase or non-imperative verb phrase for a function or method if returning a value is its primary purpose.
• DON'T write documentation for both the getter and setter of a property.
• PREFER starting library or type comments with noun phrases.
• CONSIDER including code samples in doc comments.
• DO use square brackets in doc comments to refer to in-scope identifiers.
• DO use prose to explain parameters, return values, and exceptions.
• DO put doc comments before metadata annotations.

Markdown

• AVOID using markdown excessively.
• AVOID using HTML for formatting.
• PREFER backtick fences for code blocks.

Writing

• PREFER brevity.
• AVOID abbreviations and acronyms unless they are obvious.
• PREFER using "this" instead of "the" to refer to a member's instance.

Usage

Libraries

• DO use strings in part of directives.
• DON'T import libraries that are inside the src directory of another package.
• DON'T allow an import path to reach into or out of lib.
• PREFER relative import paths.

Null

• DON'T explicitly initialize variables to null.
• DON'T use an explicit default value of null.
• DON'T use true or false in equality operations.
• AVOID late variables if you need to check whether they are initialized.
• CONSIDER type promotion or null-check patterns for using nullable types.

Strings

• DO use adjacent strings to concatenate string literals.
• PREFER using interpolation to compose strings and values.
• AVOID using curly braces in interpolation when not needed.

Collections

• DO use collection literals when possible.
• DON'T use .length to see if a collection is empty.
• AVOID using Iterable.forEach() with a function literal.
• DON'T use List.from() unless you intend to change the type of the result.
• DO use whereType() to filter a collection by type.
• DON'T use cast() when a nearby operation will do.
• AVOID using cast().

Functions

• DO use a function declaration to bind a function to a name.
• DON'T create a lambda when a tear-off will do.

Variables

• DO follow a consistent rule for var and final on local variables.
• AVOID storing what you can calculate.

Members

• DON'T wrap a field in a getter and setter unnecessarily.
• PREFER using a final field to make a read-only property.
• CONSIDER using => for simple members.
• DON'T use this. except to redirect to a named constructor or to avoid shadowing.
• DO initialize fields at their declaration when possible.

Constructors

• DO use initializing formals when possible.
• DON'T use late when a constructor initializer list will do.
• DO use ; instead of {} for empty constructor bodies.
• DON'T use new.
• DON'T use const redundantly.

Error Handling

• AVOID catches without on clauses.
• DON'T discard errors from catches without on clauses.
• DO throw objects that implement Error only for programmatic errors.
• DON'T explicitly catch Error or types that implement it.
• DO use rethrow to rethrow a caught exception.

Asynchrony

• PREFER async/await over using raw futures.
• DON'T use async when it has no useful effect.
• CONSIDER using higher-order methods to transform a stream.
• AVOID using Completer directly.
• DO test for Future<T> when disambiguating a FutureOr<T> whose type argument could be Object.

Design

Names

• DO use terms consistently.
• AVOID abbreviations.
• PREFER putting the most descriptive noun last.
• CONSIDER making the code read like a sentence.
• PREFER a noun phrase for a non-boolean property or variable.
• PREFER a non-imperative verb phrase for a boolean property or variable.
• CONSIDER omitting the verb for a named boolean parameter.
• PREFER the "positive" name for a boolean property or variable.
• PREFER an imperative verb phrase for a function or method whose main purpose is a side effect.
• PREFER a noun phrase or non-imperative verb phrase for a function or method if returning a value is its primary purpose.
• CONSIDER an imperative verb phrase for a function or method if you want to draw attention to the work it performs.
• AVOID starting a method name with get.
• PREFER naming a method to___() if it copies the object's state to a new object.
• PREFER naming a method as___() if it returns a different representation backed by the original object.
• AVOID describing the parameters in the function's or method's name.
• DO follow existing mnemonic conventions when naming type parameters.

Libraries

• PREFER making declarations private.
• CONSIDER declaring multiple classes in the same library.

Classes and Mixins

• AVOID defining a one-member abstract class when a simple function will do.
• AVOID defining a class that contains only static members.
• AVOID extending a class that isn't intended to be subclassed.
• DO use class modifiers to control if your class can be extended.
• AVOID implementing a class that isn't intended to be an interface.
• DO use class modifiers to control if your class can be an interface.
• PREFER defining a pure mixin or pure class to a mixin class.

Constructors

• CONSIDER making your constructor const if the class supports it.

Members

• PREFER making fields and top-level variables final.
• DO use getters for operations that conceptually access properties.
• DO use setters for operations that conceptually change properties.
• DON'T define a setter without a corresponding getter.
• AVOID using runtime type tests to fake overloading.
• AVOID public late final fields without initializers.
• AVOID returning nullable Future, Stream, and collection types.
• AVOID returning this from methods just to enable a fluent interface.

Types

• DO type annotate variables without initializers.
• DO type annotate fields and top-level variables if the type isn't obvious.
• DON'T redundantly type annotate initialized local variables.
• DO annotate return types on function declarations.
• DO annotate parameter types on function declarations.
• DON'T annotate inferred parameter types on function expressions.
• DON'T type annotate initializing formals.
• DO write type arguments on generic invocations that aren't inferred.
• DON'T write type arguments on generic invocations that are inferred.
• AVOID writing incomplete generic types.
• DO annotate with dynamic instead of letting inference fail.
• PREFER signatures in function type annotations.
• DON'T specify a return type for a setter.
• DON'T use the legacy typedef syntax.
• PREFER inline function types over typedefs.
• PREFER using function type syntax for parameters.
• AVOID using dynamic unless you want to disable static checking.
• DO use Future<void> as the return type of asynchronous members that do not produce values.
• AVOID using FutureOr<T> as a return type.

Parameters

• AVOID positional boolean parameters.
• AVOID optional positional parameters if the user may want to omit earlier parameters.
• AVOID mandatory parameters that accept a special "no argument" value.
• DO use inclusive start and exclusive end parameters to accept a range.

Equality

• DO override hashCode if you override ==.
• DO make your == operator obey the mathematical rules of equality.
• AVOID defining custom equality for mutable classes.
• DON'T make the parameter to == nullable.

riverpod-copilot-instructions.md

Github Copilot Custom Instructions for Riverpod

The following can be included as part of the [.github/copilot-instructions.md])https://docs.github.com/en/copilot/how-tos/custom-instructions) file.

Riverpod & State Management

Always use Riverpod providers wherever possible, and for state management, as well as user friendly tests. Follow the DO and DON'T guidelines for using Riverpod.

Riverpod DO/DON'T

AVOID initializing providers in a widget

Providers should initialize themselves.
They should not be initialized by an external element such as a widget.

Failing to do so could cause possible race conditions and unexpected behaviors.

DON'T

class WidgetState extends State<MyWidget> {
  @override
  void initState() {
    super.initState();
    // Bad: the provider should initialize itself
    ref.read(provider).init();
  }
}

Consider There is no "one-size fits all" solution to this problem. If your initialization logic depends on factors external to the provider, often the correct place to put such logic is in the onPressed method of a button triggering navigation:

ElevatedButton(
  onPressed: () {
    ref.read(provider).init();
    Navigator.of(context).push(...);
  },
  child: Text('Navigate'),
)

AVOID using providers for Ephemeral state

Providers are designed to be for shared business state. They are not meant to be used for Ephemeral state, such as for:

• The currently selected item.
• Form state/ Because leaving and re-entering the form should typically reset the form state. This includes pressing the back button during a multi-page forms.
• Animations.
• Generally everything that Flutter deals with a "controller" (e.g. TextEditingController).

If you are looking for a way to handle local widget state, consider using flutter_hooks instead.

One reason why this is discouraged is that such state is often scoped to a route.
Failing to do so could break your app's back button, due to a new page overriding the state of a previous page.

For instance say we were to store the currently selected book in a provider:

final selectedBookProvider = StateProvider<String?>((ref) => null);

One challenge we could face is, the navigation history could look like:

/books
/books/42
/books/21

In this scenario, when pressing the back button, we should expect to go back to /books/42. But if we were to use selectedBookProvider to store the selected book, the selected ID would not reset to its previous value, and we would keep seeing /books/21.

DON'T perform side effects during the initialization of a provider

Providers should generally be used to represent a "read" operation. You should not use them for "write" operations, such as submitting a form.
Using providers for such operations could have unexpected behaviors, such as skipping a side-effect if a previous one was performed.

DON'T

final submitProvider = FutureProvider((ref) async {
  final formState = ref.watch(formState);

  // Bad: Providers should not be used for "write" operations.
  return http.post('https://my-api.com', body: formState.toJson());
});

PREFER ref.watch/read/listen (and similar APIs) with statically known providers

Riverpod strongly recommends enabling lint rules (via riverpod_lint).
But for lints to be effective, your code should be written in a way that is statically analysable.

Failing to do so could make it harder to spot bugs or cause false positives with lints.

Do

final provider = Provider((ref) => 42);

...

// OK because the provider is known statically
ref.watch(provider);

Don't

class Example extends ConsumerWidget {
  Example({required this.provider});
  final Provider<int> provider;

  @override
  Widget build(context, ref) {
    // Bad because static analysis cannot know what `provider` is
    ref.watch(provider);
  }
}

AVOID dynamically creating providers

Providers should exclusively be top-level final variables.

Do

final provider = Provider<String>((ref) => 'Hello world');

Don't

class Example {
  // Unsupported operation. Could cause memory leaks and unexpected behaviors.
  final provider = Provider<String>((ref) => 'Hello world');
}