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chore(deps): update dependency dart to v3

Renovate requested to merge renovate/dart-3.x into v2

This MR contains the following updates:

Package Update Change
dart (source) major >=2.15.0 <3.0.0 -> <4.0.0

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Release Notes

dart-lang/sdk (dart)

v3.3.3

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v3.3.2

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v3.3.1

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v3.3.0

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Language

Dart 3.3 adds extension types to the language. To use them, set your package's [SDK constraint][language version] lower bound to 3.3 or greater (sdk: '^3.3.0').

Extension types

An extension type wraps an existing type with a different, static-only interface. It works in a way which is in many ways similar to a class that contains a single final instance variable holding the wrapped object, but without the space and time overhead of an actual wrapper object.

Extension types are introduced by extension type declarations. Each such declaration declares a new named type (not just a new name for the same type). It declares a representation variable whose type is the representation type. The effect of using an extension type is that the representation (that is, the value of the representation variable) has the members declared by the extension type rather than the members declared by its "own" type (the representation type). Example:

extension type Meters(int value) {
  String get label => '${value}m';
  Meters operator +(Meters other) => Meters(value + other.value);
}

void main() {
  var m = Meters(42); // Has type `Meters`.
  var m2 = m + m; // OK, type `Meters`.
  // int i = m; // Compile-time error, wrong type.
  // m.isEven; // Compile-time error, no such member.
  assert(identical(m, m.value)); // Succeeds.
}

The declaration Meters is an extension type that has representation type int. It introduces an implicit constructor Meters(int value); and a getter int get value. m and m.value is the very same object, but m has type Meters and m.value has type int. The point is that m has the members of Meters and m.value has the members of int.

Extension types are entirely static, they do not exist at run time. If o is the value of an expression whose static type is an extension type E with representation type R, then o is just a normal object whose run-time type is a subtype of R, exactly like the value of an expression of type R. Also the run-time value of E is R (for example, E == R is true). In short: At run time, an extension type is erased to the corresponding representation type.

A method call on an expression of an extension type is resolved at compile-time, based on the static type of the receiver, similar to how extension method calls work. There is no virtual or dynamic dispatch. This, combined with no memory overhead, means that extension types are zero-cost wrappers around their representation value.

While there is thus no performance cost to using extension types, there is a safety cost. Since extension types are erased at compile time, run-time type tests on values that are statically typed as an extension type will check the type of the representation object instead, and if the type check looks like it tests for an extension type, like is Meters, it actually checks for the representation type, that is, it works exactly like is int at run time. Moreover, as mentioned above, if an extension type is used as a type argument to a generic class or function, the type variable will be bound to the representation type at run time. For example:

void main() {
  var meters = Meters(3);

  // At run time, `Meters` is just `int`.
  print(meters is int); // Prints "true".
  print(<Meters>[] is List<int>); // Prints "true".

  // An explicit cast is allowed and succeeds as well:
  List<Meters> meterList = <int>[1, 2, 3] as List<Meters>;
  print(meterList[1].label); // Prints "2m".
}

Extension types are useful when you are willing to sacrifice some run-time encapsulation in order to avoid the overhead of wrapping values in instances of wrapper classes, but still want to provide a different interface than the wrapped object. An example of that is interop, where you may have data that are not Dart objects to begin with (for example, raw JavaScript objects when using JavaScript interop), and you may have large collections of objects where it's not efficient to allocate an extra object for each element.

Other changes

  • Breaking Change #​54056: The rules for private field promotion have been changed so that an abstract getter is considered promotable if there are no conflicting declarations. There are no conflicting declarations if there are no non-final fields, external fields, concrete getters, or noSuchMethod forwarding getters with the same name in the same library. This makes the implementation more consistent and allows type promotion in a few rare scenarios where it wasn't previously allowed. It is unlikely, but this change could cause a breakage by changing an inferred type in a way that breaks later code. For example:

    class A {
  int? get _field;
}
class B extends A {
  final int? _field;
  B(this._field);
}
test(A a) {
  if (a._field != null) {
    var x = a._field; // Previously had type `int?`; now has type `int`
    ...
    x = null; // Previously allowed; now causes a compile-time error.
  }
}

    Affected code can be fixed by adding an explicit type annotation. For example, in the above snippet, var x can be changed to int? x.

    It's also possible that some continuous integration configurations might fail if they have been configured to treat warnings as errors, because the expanded type promotion could lead to one of the following warnings:

    • unnecessary_non_null_assertion
    • unnecessary_cast
    • invalid_null_aware_operator

    These warnings can be addressed in the usual way, by removing the unnecessary operation in the first two cases, or changing ?. to . in the third case.

    To learn more about other rules surrounding type promotion, check out the guide on Fixing type promotion failures.

Libraries
dart:core
  • String.fromCharCodes now allow start and end to be after the end of the Iterable argument, just like skip and take does on an Iterable.
dart:ffi
  • In addition to functions, @Native can now be used on fields.
  • Allow taking the address of native functions and fields via Native.addressOf.
  • The elementAt pointer arithmetic extension methods on core Pointer types are now deprecated. Migrate to the new - and + operators instead.
  • The experimental and deprecated @FfiNative annotation has been removed. Usages should be updated to use the @Native annotation.
dart:js_interop
  • Breaking Change in the representation of JS types #​52687: JS types like JSAny were previously represented using a custom erasure of @staticInterop types that were compiler-specific. They are now represented as extension types where their representation types are compiler-specific. This means that user-defined @staticInterop types that implemented JSAny or JSObject can no longer do so and need to use JSObject.fromInteropObject. Going forward, it's recommended to use extension types to define interop APIs. Those extension types can still implement JS types.
  • JSArray and JSPromise generics: JSArray and JSPromise are now generic types whose type parameter is a subtype of JSAny?. Conversions to and from these types are changed to account for the type parameters of the Dart or JS type, respectively.
  • Breaking Change in names of extensions: Some dart:js_interop extension members are moved to different extensions on the same type or a supertype to better organize the API surface. See JSAnyUtilityExtension and JSAnyOperatorExtension for the new extensions. This shouldn't make a difference unless the extension names were explicitly used.
  • Add importModule to allow users to dynamically import modules using the JS import() expression.
dart:js_interop_unsafe
  • Add has helper to make hasProperty calls more concise.
dart:typed_data

  • BREAKING CHANGE (https://github.com/dart-lang/sdk/issues/53218) The unmodifiable view classes for typed data are deprecated. Instead of using the constructors for these classes to create an unmodifiable view, e.g.

    Uint8List data = ...
final readOnlyView = UnmodifiableUint8ListView(data);

    use the new asUnmodifiableView() methods:

    Uint8List data = ...
final readOnlyView = data.asUnmodifiableView();

    The reason for this change is to allow more flexibility in the implementation of typed data so the native and web platforms can use different strategies for ensuring typed data has good performance.

    The deprecated types will be removed in a future Dart version.

dart:nativewrappers
  • Breaking Change #​51896: The NativeWrapperClasses are marked base so that none of their subtypes can be implemented. Implementing subtypes can lead to crashes when passing such native wrapper to a native call, as it will try to unwrap a native field that doesn't exist.
Tools
Dart command line
  • The dart create command now uses v3 of package:lints, including multiple new recommended lints by default. To learn more about the updated collection of lints, check out the package:lints 3.0.0 changelog entry.
DevTools
  • Updated DevTools to version 2.31.1 from 2.28.1. To learn more, check out the release notes for versions 2.29.0, 2.30.0, and 2.31.0.
Wasm compiler (dart2wasm)
  • Breaking Change #​54004: dart:js_util, package:js, and dart:js are now disallowed from being imported when compiling with dart2wasm. Prefer using dart:js_interop and dart:js_interop_unsafe.
Development JavaScript compiler (DDC)

  • Type arguments of package:js interop types are now printed as any instead of being omitted. This is simply a change to the textual representation of package js types that have type arguments. These type arguments are still completely ignored by the type system at runtime.

  • Removed "implements <...>" text from the Chrome custom formatter display for Dart classes. This information provides little value and keeping it imposes an unnecessary maintenance cost.

Production JavaScript compiler (dart2js)
  • Breaking Change #​54201: The Invocation that is passed to noSuchMethod will no longer have a minified memberName, even when dart2js is invoked with --minify. See #​54201 for more details.
Analyzer
  • You can now suppress diagnostics in pubspec.yaml files by adding an # ignore: <diagnostic_id> comment.
  • Invalid dart doc comment directives are now reported.
  • The [flutter_style_todos][flutter_style_todos] lint now has a quick fix.
Linter
  • Removed the iterable_contains_unrelated_type and list_remove_unrelated_type lints. Consider migrating to the expanded [collection_methods_unrelated_type][collection_methods_unrelated_type] lint.
  • Removed various lints that are no longer necessary with sound null safety:
    • always_require_non_null_named_parameters
    • avoid_returning_null,
    • avoid_returning_null_for_future

v3.2.6

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v3.2.5

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v3.2.4

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v3.2.3

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This is a patch release that:

  • Disallows final fields to be used in a constant context during analysis (issue #​54232).
  • Upgrades Dart DevTools to version 2.28.4 (issue #​54213).
  • Fixes new AOT snapshots in the SDK failing with SIGILL in ARM environments that don't support the integer division instructions or x86-64 environments that don't support SSE4.1 (issue #​54215).

v3.2.2

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This is a patch release that:

  • Adjusts the nullablity computations in the implementation of the upper bound algorithm in the compiler frontend (issue #​53999).

  • Fixes missing closure code completion entries for function parameters for LSP-based editors like VS Code (issue #​54112).

v3.2.1

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This is a patch release that:

  • Fixes the left/mobile sidebar being empty on non-class pages in documentation generated with dart doc (issue #​54073).

  • Fixes a JSON array parsing bug that causes a segmentation fault when flutter test is invoked with the --coverage flag (SDK issue #​54059, Flutter issue #​124145).

  • Upgrades Dart DevTools to version 2.28.3 (issue #​54085).

v3.2.0

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Language

Dart 3.2 adds the following features. To use them, set your package's SDK constraint lower bound to 3.2 or greater (sdk: '^3.2.0').

  • Private field promotion: In most circumstances, the types of private final fields can now be promoted by null checks and is tests. For example:

    class Example {
  final int? _privateField;
  Example(this._privateField);

  f() {
    if (_privateField != null) {
      // _privateField has now been promoted; you can use it without
      // null checking it.
      int i = _privateField; // OK
    }
  }
}

// Private field promotions also work from outside of the class:
f(Example x) {
  if (x._privateField != null) {
    int i = x._privateField; // OK
  }
}

    To ensure soundness, a field is not eligible for field promotion in the following circumstances:

    • If it's not final (because a non-final field could be changed in between the test and the usage, invalidating the promotion).
    • If it's overridden elsewhere in the library by a concrete getter or a non-final field (because an access to an overridden field might resolve at runtime to the overriding getter or field).
    • If it's not private (because a non-private field might be overridden elsewhere in the program).
    • If it has the same name as a concrete getter or a non-final field in some other unrelated class in the library (because a class elsewhere in the program might extend one of the classes and implement the other, creating an override relationship between them).
    • If there is a concrete class C in the library whose interface contains a getter with the same name, but C does not have an implementation of that getter (such unimplemented getters aren't safe for field promotion, because they are implicitly forwarded to noSuchMethod, which might not return the same value each time it's called).

  • Breaking Change #​53167: Use a more precise split point for refutable patterns. Previously, in an if-case statement, if flow analysis could prove that the scrutinee expression was guaranteed to throw an exception, it would sometimes fail to propagate type promotions implied by the pattern to the (dead) code that follows. This change makes the type promotion behavior of if-case statements consistent regardless of whether the scrutinee expression throws an exception.

    No live code is affected by this change, but there is a small chance that the change in types will cause a compile-time error to appear in some dead code in the user's project, where no compile-time error appeared previously.

Libraries
dart:async
  • Added broadcast parameter to Stream.empty constructor.
dart:cli
  • Breaking change #​52121:
    • waitFor is disabled by default and slated for removal in 3.4. Attempting to call this function will now throw an exception. Users that still depend on waitFor can enable it by passing --enable_deprecated_wait_for flag to the VM.
dart:convert
  • Breaking change #​52801:
    • Changed return types of utf8.encode() and Utf8Codec.encode() from List<int> to Uint8List.
dart:developer
  • Deprecated the Service.getIsolateID method.
  • Added getIsolateId method to Service.
  • Added getObjectId method to Service.
dart:ffi
  • Added the NativeCallable.isolateLocal constructor. This creates NativeCallables with the same functionality as Pointer.fromFunction, except that NativeCallable accepts closures.
  • Added the NativeCallable.keepIsolateAlive method, which determines whether the NativeCallable keeps the isolate that created it alive.
  • All NativeCallable constructors can now accept closures. Previously NativeCallables had the same restrictions as Pointer.fromFunction, and could only create callbacks for static functions.
  • Breaking change #​53311: NativeCallable.nativeFunction now throws an error if is called after the NativeCallable has already been closed. Calls to close after the first are now ignored.
dart:io

  • Breaking change #​53005: The headers returned by HttpClientResponse.headers and HttpRequest.headers no longer include trailing whitespace in their values.

  • Breaking change #​53227: Folded headers values returned by HttpClientResponse.headers and HttpRequest.headers now have a space inserted at the fold point.

dart:isolate
  • Added Isolate.packageConfigSync and Isolate.resolvePackageUriSync APIs.
dart:js_interop
  • Breaking Change on JSNumber.toDart and Object.toJS: JSNumber.toDart is removed in favor of toDartDouble and toDartInt to make the type explicit. Object.toJS is also removed in favor of Object.toJSBox. Previously, this function would allow Dart objects to flow into JS unwrapped on the JS backends. Now, there's an explicit wrapper that is added and unwrapped via JSBoxedDartObject.toDart. Similarly, JSExportedDartObject is renamed to JSBoxedDartObject and the extensions ObjectToJSExportedDartObject and JSExportedDartObjectToObject are renamed to ObjectToJSBoxedDartObject and JSBoxedDartObjectToObject in order to avoid confusion with @JSExport.
  • Type parameters in external APIs: Type parameters must now be bound to a static interop type or one of the dart:js_interop types like JSNumber when used in an external API. This only affects dart:js_interop classes and not package:js or other forms of JS interop.
  • Subtyping dart:js_interop types: @staticInterop types can subtype only JSObject and JSAny from the set of JS types in dart:js_interop. Subtyping other types from dart:js_interop would result in confusing type errors before, so this makes it a static error.
  • Global context of dart:js_interop and @staticInterop APIs: Static interop APIs will now use the same global context as non-static interop instead of globalThis to avoid a greater migration. Static interop APIs, either through dart:js_interop or the @staticInterop annotation, have used JavaScript's globalThis as the global context. This is relevant to things like external top-level members or external constructors, as this is the root context we expect those members to reside in. Historically, this was not the case in dart2js and DDC. We used either self or DDC's global in non-static interop APIs with package:js. So, static interop APIs will now use one of those global contexts. Functionally, this should matter in only a very small number of cases, like when using older browser versions. dart:js_interop's globalJSObject is also renamed to globalContext and returns the global context used in the lowerings.
  • Breaking Change on Types of dart:js_interop External APIs: External JS interop APIs when using dart:js_interop are restricted to a set of allowed types. Namely, this includes the primitive types like String, JS types from dart:js_interop, and other static interop types (either through @staticInterop or extension types).
  • Breaking Change on dart:js_interop isNull and isUndefined: null and undefined can only be discerned in the JS backends. dart2wasm conflates the two values and treats them both as Dart null. Therefore, these two helper methods should not be used on dart2wasm and will throw to avoid potentially erroneous code.
  • Breaking Change on dart:js_interop typeofEquals and instanceof: Both APIs now return a bool instead of a JSBoolean. typeofEquals also now takes in a String instead of a JSString.
  • Breaking Change on dart:js_interop JSAny and JSObject: These types can only be implemented, and no longer extended, by user @staticInterop types.
  • Breaking Change on dart:js_interop JSArray.withLength: This API now takes in an int instead of JSNumber.
Tools
Development JavaScript compiler (DDC)
  • Applications compiled by DDC will no longer add members to the native JavaScript Object prototype.
  • Breaking change for JS interop with Symbols and BigInts: JavaScript Symbols and BigInts are now associated with their own interceptor and should not be used with package:js classes. These types were being intercepted with the assumption that they are a subtype of JavaScript's Object, but this is incorrect. This lead to erroneous behavior when using these types as Dart Objects. See #​53106 for more details. Use dart:js_interop's JSSymbol and JSBigInt with extension types to interop with these types.
Production JavaScript compiler (dart2js)
  • Breaking change for JS interop with Symbols and BigInts: JavaScript Symbols and BigInts are now associated with their own interceptor and should not be used with package:js classes. These types were being intercepted with the assumption that they are a subtype of JavaScript's Object, but this is incorrect. This lead to erroneous behavior when using these types as Dart Objects. See #​53106 for more details. Use dart:js_interop's JSSymbol and JSBigInt with extension types to interop with these types.
Dart command line
  • The dart create command has a new cli template to quickly create Dart command-line applications with basic argument parsing capabilities. To learn more about using the template, run dart help create.
Dart format
  • Always split enum declarations containing a line comment.
  • Fix regression in splitting type annotations with library prefixes.
  • Support --enable-experiment command-line option to enable language experiments.
DevTools
Linter
  • Added the experimental [annotate_redeclares][annotate_redeclares] lint.
  • Marked the [use_build_context_synchronously][use_build_context_synchronously] lint as stable.
Pub
  • New option dart pub upgrade --tighten which will update dependencies' lower bounds in pubspec.yaml to match the current version.
  • The commands dart pub get/add/upgrade will now show if a dependency changed between direct, dev and transitive dependency.
  • The command dart pub upgrade no longer shows unchanged dependencies.

v3.1.5

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This is a patch release that:

  • Fixes an issue affecting Dart compiled to JavaScript running in Node.js 21. A change in Node.js 21 affected the Dart Web compiler runtime. This patch release accommodates for those changes (issue #​53810).

v3.1.4

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This is a patch release that:

  • Fixes an issue in the Dart VM, users are not being able to see value of variables while debugging code (issue [#​53747]).

v3.1.3

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This is a patch release that:

  • Fixes a bug in dart2js which would cause the compiler to crash when using @staticInterop @anonymous factory constructors with type parameters (see issue #​53579 for more details).

  • The standalone Dart VM now exports symbols only for the Dart_* embedding API functions, avoiding conflicts with other DSOs loaded into the same process, such as shared libraries loaded through dart:ffi, that may have different versions of the same symbols (issue [#​53503]).

  • Fixes an issue with super slow access to variables while debugging. The fix avoids searching static functions in the imported libraries as references to members are fully resolved by the front-end. (issue #​53541)

v3.1.2

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This is a patch release that:

  • Fixes a bug in dart2js which crashed the compiler when a typed record pattern was used outside the scope of a function body, such as in a field initializer. For example final x = { for (var (int a,) in someList) a: a }; (issue #​53449)

  • Fixes an expedient issue of users seeing an unhandled exception pause in the debugger, please see https://github.com/dart-lang/sdk/issues/53450 for more details. The fix uses try/catch in lookupAddresses instead of Future error so that we don't see an unhandled exception pause in the debugger (issue #​53450)

v3.1.1

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This is a patch release that:

  • Fixes a bug in the parser which prevented a record pattern from containing a nested record pattern, where the nested record pattern uses record destructuring shorthand syntax, for example final ((:a, :b), c) = record; (issue #​53352).

v3.1.0

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Libraries
dart:async
  • Breaking change #​52334:
    • Added the interface modifier to purely abstract classes: MultiStreamController, StreamConsumer, StreamIterator and StreamTransformer. As a result, these types can only be implemented, not extended or mixed in.
dart:core
  • Uri.base on native platforms now respects IOOverrides overriding current directory (#​39796).
dart:ffi
  • Added the NativeCallable class, which can be used to create callbacks that allow native code to call into Dart code from any thread. See NativeCallable.listener. In future releases, NativeCallable will be updated with more functionality, and will become the recommended way of creating native callbacks for all use cases, replacing Pointer.fromFunction.
dart:io
  • Breaking change #​51486:
    • Added sameSite to the Cookie class.
    • Added class SameSite.
  • Breaking change #​52027: FileSystemEvent is sealed. This means that FileSystemEvent cannot be extended or implemented.
  • Added a deprecation warning when Platform is instantiated.
  • Added Platform.lineTerminator which exposes the character or characters that the operating system uses to separate lines of text, e.g., "\r\n" on Windows.
dart:js_interop
  • Object literal constructors: ObjectLiteral is removed from dart:js_interop. It's no longer needed in order to declare an object literal constructor with inline classes. As long as an external constructor has at least one named parameter, it'll be treated as an object literal constructor. If you want to create an object literal with no named members, use {}.jsify().
Other libraries
package:js
  • Breaking change to @staticInterop and external extension members: external @staticInterop members and external extension members can no longer be used as tear-offs. Declare a closure or a non-external method that calls these members, and use that instead.
  • Breaking change to @staticInterop and external extension members: external @staticInterop members and external extension members will generate slightly different JS code for methods that have optional parameters. Whereas before, the JS code passed in the default value for missing optionals, it will now pass in only the provided members. This aligns with how JS parameters work, where omitted parameters are actually omitted. For example, calling external void foo([int a, int b]) as foo(0) will now result in foo(0), and not foo(0, null).
Tools
DevTools
Linter

v3.0.7

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This is a patch release that:

  • Fixes a bug in dart2js which would cause certain uses of records to lead to bad codegen causing a TypeError or NoSuchMethodError to be thrown at runtime (issue #​53001).

v3.0.6

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This is a patch release that:

  • Fixes a flow in flow analysis that causes it to sometimes ignore destructuring assignments (issue #​52767).
  • Fixes an infinite loop in some web development compiles that include is or as expressions involving record types with named fields (issue #​52869).
  • Fixes a memory leak in Dart analyzer's file-watching (issue #​52791).
  • Fixes a memory leak of file system watcher related data structures (issue #​52793).

v3.0.5

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This is a patch release that:

  • Fixes a bad cast in the frontend which can manifest as a crash in the dart2js ListFactorySpecializer during Flutter web builds (issue #​52403).

v3.0.4

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This is a patch release that:

  • dart format now handles formatting nullable record types with no fields (dart_style issue #​1224).
  • Fixes error when using records when targeting the web in development mode (issue #​52480).

v3.0.3

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This is a patch release that:

  • Fixes an AOT compiler crash when generating an implicit getter returning an unboxed record (issue #​52449).
  • Fixes a situation in which variables appearing in multiple branches of an or-pattern might be erroneously reported as being mismatched (issue #​52373).
  • Adds missing interface modifiers on the purely abstract classes MultiStreamController, StreamConsumer, StreamIterator and StreamTransformer (issue #​52334).
  • Fixes an error during debugging when InternetAddress.tryParse is used (issue #​52423).
  • Fixes a VM issue causing crashes on hot reload (issue #​126884).
  • Improves linter support (issue #​4195).
  • Fixes an issue in variable patterns preventing users from expressing a pattern match using a variable or wildcard pattern with a nullable record type (issue #​52439).
  • Updates warnings and provide instructions for updating the Dart pub cache on Windows (issue #​52386).

v3.0.2

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This is a patch release that:

  • Fixes a dart2js crash when using a switch case expression on a record where the fields don't match the cases (issue #​52438).
  • Add class modifier chips on class and mixin pages generated with dart doc (issue #​3392).
  • Fixes a situation causing the parser to fail resulting in an infinite loop leading to higher memory usage (issue #​52352).
  • Add clear errors when mixing inheritance in pre and post Dart 3 libraries (issue: #​52078).

v3.0.1

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This is a patch release that:

  • Fixes a compiler crash involving redirecting factories and FFI (issue #​124369).
  • Fixes a dart2js crash when using a combination of local functions, generics, and records (issue #​51899).
  • Fixes incorrect error using a void in a switch case expression (issue #​52191).
  • Fixes a false error when using in switch case expressions when the switch refers to a private getter (issue #​52041).
  • Prevent the use of when and as as variable names in patterns (issue #​52260).
  • Fixes an inconsistency in type promotion between the analyzer and VM (issue #​52241).
  • Improve performance on functions with many parameters (issue #​1212).

v3.0.0

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Language

Dart 3.0 adds the following features. To use them, set your package's SDK constraint lower bound to 3.0 or greater (sdk: '^3.0.0').

  • Records: Records are anonymous immutable data structures that let you aggregate multiple values together, similar to tuples in other languages. With records, you can return multiple values from a function, create composite map keys, or use them any other place where you want to bundle a couple of objects together.

    For example, using a record to return two values:

    (double x, double y) geoLocation(String name) {
  if (name == 'Nairobi') {
    return (-1.2921, 36.8219);
  } else {
    ...
  }
}

  • Pattern matching: Expressions build values out of smaller pieces. Conversely, patterns are an expressive tool for decomposing values back into their constituent parts. Patterns can call getters on an object, access elements from a list, pull fields out of a record, etc. For example, we can destructure the record from the previous example like so:

    var (lat, long) = geoLocation('Nairobi');
print('Nairobi is at $lat, $long.');

    Patterns can also be used in switch cases. There, you can destructure values and also test them to see if they have a certain type or value:

    switch (object) {
  case [int a]:
    print('A list with a single integer element $a');
  case ('name', _):
    print('A two-element record whose first field is "name".');
  default: print('Some other object.');
}

    Also, as you can see, non-empty switch cases no longer need break; statements.

    Breaking change: Dart 3.0 interprets switch cases as patterns instead of constant expressions. Most constant expressions found in switch cases are valid patterns with the same meaning (named constants, literals, etc.). You may need to tweak a few constant expressions to make them valid. This only affects libraries that have upgraded to language version 3.0.

  • Switch expressions: Switch expressions allow you to use patterns and multi-way branching in contexts where a statement isn't allowed:

    return TextButton(
  onPressed: _goPrevious,
  child: Text(switch (page) {
    0 => 'Exit story',
    1 => 'First page',
    _ when page == _lastPage => 'Start over',
    _ => 'Previous page',
  }),
);

  • If-case statements and elements: A new if construct that matches a value against a pattern and executes the then or else branch depending on whether the pattern matches:

    if (json case ['user', var name]) {
  print('Got user message for user $name.');
}

    There is also a corresponding if-case element that can be used in collection literals.

  • Sealed classes: When you mark a type sealed, the compiler ensures that switches on values of that type exhaustively cover every subtype. This enables you to program in an algebraic datatype style with the compile-time safety you expect:

    sealed class Amigo {}
class Lucky extends Amigo {}
class Dusty extends Amigo {}
class Ned extends Amigo {}

String lastName(Amigo amigo) =>
    switch (amigo) {
      Lucky _ => 'Day',
      Ned _   => 'Nederlander',
    };

    In this last example, the compiler reports an error that the switch doesn't cover the subclass Dusty.

  • Class modifiers: New modifiers final, interface, base, and mixin on class and mixin declarations let you control how the type can be used. By default, Dart is flexible in that a single class declaration can be used as an interface, a superclass, or even a mixin. This flexibility can make it harder to evolve an API over time without breaking users. We mostly keep the current flexible defaults, but these new modifiers give you finer-grained control over how the type can be used.

    Breaking change: Class declarations from libraries that have been upgraded to Dart 3.0 can no longer be used as mixins by default. If you want the class to be usable as both a class and a mixin, mark it mixin class. If you want it to be used only as a mixin, make it a mixin declaration. If you haven't upgraded a class to Dart 3.0, you can still use it as a mixin.

  • Breaking change #​50902: Dart reports a compile-time error if a continue statement targets a label that is not a loop (for, do and while statements) or a switch member. Fix this by changing the continue to target a valid labeled statement.

  • Breaking change language/#​2357: Starting in language version 3.0, Dart reports a compile-time error if a colon (:) is used as the separator before the default value of an optional named parameter. Fix this by changing the colon (:) to an equal sign (=).

Libraries
General changes
  • Breaking Change: Non-mixin classes in the platform libraries can no longer be mixed in, unless they are explicitly marked as mixin class. The following existing classes have been made mixin classes:
    • Iterable
    • IterableMixin (now alias for Iterable)
    • IterableBase (now alias for Iterable)
    • ListMixin
    • SetMixin
    • MapMixin
    • LinkedListEntry
    • StringConversionSink
dart:core

  • Added bool.parse and bool.tryParse static methods.

  • Added DateTime.timestamp() constructor to get current time as UTC.

  • The type of RegExpMatch.pattern is now RegExp, not just Pattern.

  • Breaking change #​49529:

    • Removed the deprecated List constructor, as it wasn't null safe. Use list literals (e.g. [] for an empty list or <int>[] for an empty typed list) or [List.filled][List.filled].
    • Removed the deprecated onError argument on [int.parse][int.parse], [double.parse][double.parse], and [num.parse][num.parse]. Use the [tryParse][tryParse] method instead.
    • Removed the deprecated [proxy][proxy] and [Provisional][Provisional] annotations. The original proxy annotation has no effect in Dart 2, and the Provisional type and [provisional][provisional] constant were only used internally during the Dart 2.0 development process.
    • Removed the deprecated [Deprecated.expires][Deprecated.expires] getter. Use [Deprecated.message][Deprecated.message] instead.
    • Removed the deprecated [CastError][CastError] error. Use [TypeError][TypeError] instead.
    • Removed the deprecated [FallThroughError][FallThroughError] error. The kind of fall-through previously throwing this error was made a compile-time error in Dart 2.0.
    • Removed the deprecated [NullThrownError][NullThrownError] error. This error is never thrown from null safe code.
    • Removed the deprecated [AbstractClassInstantiationError][AbstractClassInstantiationError] error. It was made a compile-time error to call the constructor of an abstract class in Dart 2.0.
    • Removed the deprecated [CyclicInitializationError][CyclicInitializationError]. Cyclic dependencies are no longer detected at runtime in null safe code. Such code will fail in other ways instead, possibly with a StackOverflowError.
    • Removed the deprecated [NoSuchMethodError][NoSuchMethodError] default constructor. Use the [NoSuchMethodError.withInvocation][NoSuchMethodError.withInvocation] named constructor instead.
    • Removed the deprecated [BidirectionalIterator][BidirectionalIterator] class. Existing bidirectional iterators can still work, they just don't have a shared supertype locking them to a specific name for moving backwards.

  • Breaking change when migrating code to Dart 3.0: Some changes to platform libraries only affect code when that code is migrated to language version 3.0.

    • The Function type can no longer be implemented, extended or mixed in. Since Dart 2.0 writing implements Function has been allowed for backwards compatibility, but it has not had any effect. In Dart 3.0, the Function type is final and cannot be subtyped, preventing code from mistakenly assuming it works.

    • The following declarations can only be implemented, not extended:

      • Comparable
      • Exception
      • Iterator
      • Pattern
      • Match
      • RegExp
      • RegExpMatch
      • StackTrace
      • StringSink

      None of these declarations contained any implementation to inherit, and are marked as interface to signify that they are only intended as interfaces.

    • The following declarations can no longer be implemented or extended:

      • MapEntry
      • OutOfMemoryError
      • StackOverflowError
      • Expando
      • WeakReference
      • Finalizer

      The MapEntry value class is restricted to enable later optimizations. The remaining classes are tightly coupled to the platform and not intended to be subclassed or implemented.

dart:async

  • Added extension member wait on iterables and 2-9 tuples of futures.

  • Breaking change #​49529:

    • Removed the deprecated [DeferredLibrary][DeferredLibrary] class. Use the [deferred as][deferred as] import syntax instead.
dart:collection

  • Added extension members nonNulls, firstOrNull, lastOrNull, singleOrNull, elementAtOrNull and indexed on Iterables. Also exported from dart:core.

  • Deprecated the HasNextIterator class (#​50883).

  • Breaking change when migrating code to Dart 3.0: Some changes to platform libraries only affect code when it is migrated to language version 3.0.

    • The following interface can no longer be extended, only implemented:
      • Queue
    • The following implementation classes can no longer be implemented:
      • LinkedList
      • LinkedListEntry
    • The following implementation classes can no longer be implemented or extended:
      • HasNextIterator (Also deprecated.)
      • HashMap
      • LinkedHashMap
      • HashSet
      • LinkedHashSet
      • DoubleLinkedQueue
      • ListQueue
      • SplayTreeMap
      • SplayTreeSet
dart:developer

  • Breaking change #​49529:

    • Removed the deprecated [MAX_USER_TAGS][MAX_USER_TAGS] constant. Use [maxUserTags][maxUserTags] instead.

  • Callbacks passed to registerExtension will be run in the zone from which they are registered.

  • Breaking change #​50231:

    • Removed the deprecated [Metrics][Metrics], [Metric][Metric], [Counter][Counter], and [Gauge][Gauge] classes as they have been broken since Dart 2.0.
dart:ffi
  • The experimental @FfiNative annotation is now deprecated. Usages should be replaced with the new @Native annotation.
dart:html
  • Breaking change: As previously announced, the deprecated registerElement and registerElement2 methods in Document and HtmlDocument have been removed. See #​49536 for details.
dart:math
  • Breaking change when migrating code to Dart 3.0: Some changes to platform libraries only affect code when it is migrated to language version 3.0.
    • The Random interface can only be implemented, not extended.
dart:io
  • Added name and signalNumber to the ProcessSignal class.
  • Deprecate NetworkInterface.listSupported. Has always returned true since Dart 2.3.
  • Finalize httpEnableTimelineLogging parameter name transition from enable to enabled. See #​43638.
  • Favor IPv4 connections over IPv6 when connecting sockets. See #​50868.
  • Breaking change #​51035:
    • Update NetworkProfiling to accommodate new String ids that are introduced in vm_service:11.0.0
dart:js_util
  • Added several helper functions to access more JavaScript operators, like delete and the typeof functionality.
  • jsify is now permissive and has inverse semantics to dartify.
  • jsify and dartify both handle types they understand natively more efficiently.
  • Signature of callMethod has been aligned with the other methods and now takes Object instead of String.
Tools
Observatory
  • Observatory is no longer served by default and users should instead use Dart DevTools. Users requiring specific functionality in Observatory should set the --serve-observatory flag.
Web Dev Compiler (DDC)
  • Removed deprecated command line flags -k, --kernel, and --dart-sdk.
  • The compile time flag --nativeNonNullAsserts, which ensures web library APIs are sound in their nullability, is by default set to true in sound mode. For more information on the flag, see NATIVE_NULL_ASSERTIONS.md.
dart2js
  • The compile time flag --native-null-assertions, which ensures web library APIs are sound in their nullability, is by default set to true in sound mode, unless -O3 or higher is passed, in which case they are not checked. For more information on the flag, see NATIVE_NULL_ASSERTIONS.md.
Dart2js
  • Cleanup related to #​46100: the internal dart2js snapshot fails unless it is called from a supported interface, such as dart compile js, flutter build, or build_web_compilers. This is not expected to be a visible change.
Formatter
  • Format sync* and async* functions with => bodies.
  • Don't split after < in collection literals.
  • Better indentation of multiline function types inside type argument lists.
  • Fix bug where parameter metadata wouldn't always split when it should.
Analyzer
  • Most static analysis "hints" are converted to be "warnings," and any remaining hints are intended to be converted soon after the Dart 3.0 release. This means that any (previously) hints reported by dart analyze are now considered "fatal" (will result in a non-zero exit code). The previous behavior, where such hints (now warnings) are not fatal, can be achieved by using the --no-fatal-warnings flag. This behavior can also be altered, on a code-by-code basis, by changing the severity of rules in an analysis options file.
  • Add static enforcement of the SDK-only @Since annotation. When code in a package uses a Dart SDK element annotated with @Since, analyzer will report a warning if the package's Dart SDK constraint allows versions of Dart which don't include that element.
  • Protects the Dart Analysis Server against extreme memory usage by limiting the number of plugins per analysis context to 1. (issue [#​50981][]).
Linter

Updates the Linter to 1.35.0, which includes changes that

  • add new lints:
    • implicit_reopen
    • unnecessary_breaks
    • type_literal_in_constant_pattern
    • invalid_case_patterns
  • update existing lints to support patterns and class modifiers
  • remove support for:
    • enable_null_safety
    • invariant_booleans
    • prefer_bool_in_asserts
    • prefer_equal_for_default_values
    • super_goes_last
  • fix unnecessary_parenthesis false-positives with null-aware expressions.
  • fix void_checks to allow assignments of Future<dynamic>? to parameters typed FutureOr<void>?.
  • fix use_build_context_synchronously in if conditions.
  • fix a false positive for avoid_private_typedef_functions with generalized type aliases.
  • update unnecessary_parenthesis to detect some doubled parens.
  • update void_checks to allow returning Never as void.
  • update no_adjacent_strings_in_list to support set literals and for- and if-elements.
  • update avoid_types_as_parameter_names to handle type variables.
  • update avoid_positional_boolean_parameters to handle typedefs.
  • update avoid_redundant_argument_values to check parameters of redirecting constructors.
  • improve performance for prefer_const_literals_to_create_immutables.
  • update use_build_context_synchronously to check context properties.
  • improve unnecessary_parenthesis support for property accesses and method invocations.
  • update unnecessary_parenthesis to allow parentheses in more null-aware cascade contexts.
  • update unreachable_from_main to track static elements.
  • update unnecessary_null_checks to not report on arguments passed to Future.value or Completer.complete.
  • mark always_use_package_imports and prefer_relative_imports as incompatible rules.
  • update only_throw_errors to not report on Never-typed expressions.
  • update unnecessary_lambdas to not report with late final variables.
  • update avoid_function_literals_in_foreach_calls to not report with nullable- typed targets.
  • add new lint: deprecated_member_use_from_same_package which replaces the soft-deprecated analyzer hint of the same name.
  • update public_member_api_docs to not require docs on enum constructors.
  • update prefer_void_to_null to not report on as-expressions.
Migration tool removal

The null safety migration tool (dart migrate) has been removed. If you still have code which needs to be migrated to null safety, please run dart migrate using Dart version 2.19, before upgrading to Dart version 3.0.

Pub

  • To preserve compatibility with null-safe code pre Dart 3, Pub will interpret a language constraint indicating a language version of 2.12 or higher and an upper bound of <3.0.0 as <4.0.0.

    For example >=2.19.2 <3.0.0 will be interpreted as >=2.19.2 <4.0.0.

  • dart pub publish will no longer warn about dependency_overrides. Dependency overrides only take effect in the root package of a resolution.

  • dart pub token add now verifies that the given token is valid for including in a header according to RFC 6750 section 2.1. This means they must contain only the characters: ^[a-zA-Z0-9._~+/=-]+$. Before a failure would happen when attempting to send the authorization header.

  • dart pub get and related commands will now by default also update the dependencies in the example folder (if it exists). Use --no-example to avoid this.

  • On Windows the PUB_CACHE has moved to %LOCALAPPDATA%, since Dart 2.8 the PUB_CACHE has been created in %LOCALAPPDATA% when one wasn't present. Hence, this only affects users with a PUB_CACHE created by Dart 2.7 or earlier. If you have path/to/.pub-cache/bin in PATH you may need to update your PATH.

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