v3.8.0

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Released on: 2025-05-20

Language

Dart 3.8 adds null-aware elements to the language. To use them, set
your package's [SDK constraint][language version] lower bound to 3.8
or greater (sdk: '^3.8.0').

Null-Aware Elements

Null-aware elements make it easier to omit a value from a collection literal if
it's null. The syntax works in list literals, set literals, and map literals.
For map literals, both null-aware keys and values are supported. Here is an
example a list literal written in both styles, without the null-aware elements
language feature and with it:

String? lunch = isTuesday ? 'tacos!' : null;

var withoutNullAwareElements = [
  if (lunch != null) lunch,
  if (lunch.length != null) lunch.length!,
  if (lunch.length case var length?) length,
];

var withNullAwareElements = [
  ?lunch,
  ?lunch.length,
  ?lunch.length,
];

Full details are in the feature specification.

Libraries

dart:core

• Added Iterable.withIterator constructor.

dart:io

• Added HttpClientBearerCredentials.
• Updated Stdout.supportsAnsiEscapes and Stdin.supportsAnsiEscapes to
  return true for TERM containing tmux values.

dart:html

• Breaking change: Native classes in dart:html, like HtmlElement, can no
  longer be extended. Long ago, to support custom elements, element classes
  exposed a .created constructor that adhered to the v0.5 spec of web
  components. On this release, those constructors have been removed and with
  that change, the classes can no longer be extended. In a future change, they
  may be marked as interface classes as well. This is a follow up from an
  earlier breaking change in 3.0.0 that removed the registerElement APIs. See
  #​53264 for details.

dart:ffi

• Added Array.elements which exposes an Iterable over the Array's content.

Tools

Analyzer

• The analyzer now supports "doc imports," a new comment-based syntax which
  enables external elements to be referenced in documentation comments without
  actually importing them. See the
  documentation
  for details.
• Code completion is improved to offer more valid suggestions. In particular,
  the suggestions are improved when completing text in a comment reference on a
  documentation comment for an extension, a typedef, or a directive (an import,
  an export, or a library). Additionally, instance members can now be suggested
  in a documentation comment reference.
• Offer additional assist to wrap a Flutter widget with a FutureBuilder widget.
• Add a quick assist to wrap with ValueListenableBuilder.
• Add a quick fix to convert an (illegal) extension field declaration into a
  getter declaration.
• Add a quick fix to help code comply with a few lint rules that encourage
  omitting types: omit_local_variable_types,
  omit_obvious_local_variable_types, and omit_obvious_property_types.
• Add a quick fix to create an extension method to resolve an "undefined method
  invocation" error.
• Renaming a closure parameter is now possible.
• Renaming a field now adjusts implicit this references in order to avoid
  name collisions.
• Renaming a field formal parameter now properly renames known super-parameters
  in subclasses in other libraries.
• Renaming a method parameter now properly renames across the type hierarchy.
• The "encapsulate field" quick assist now works on final fields.
• The "inline method" refactoring now properly handles inner closures.
• The quick fix that adds names to a show clause or removes names from a
  hide clause can now add or remove multiple names simultaneously, in order to
  resolve as many "undefined" errors as possible.
• The "remove const" quick fix now operates on more types of code.
• The "add missing required argument" quick fix can now add multiple missing
  required arguments.
• Add a new warning that reports an import or export directive with multiple
  show or hide clauses, which are never necessary.
• Add a quick fix for this warning.
• Add LSP document links for lint rules in analysis options files.
• Add LSP document links for dependency packages in pubspec files.
• Fix various issues around patterns, like highlighting, navigation, and
  autocompletion.
• Add the [use_null_aware_elements][use_null_aware_elements] lint rule.
• Add the experimental [unnecessary_ignore][unnecessary_ignore] lint rule.
• (Thanks @​FMorschel for many of the above
  enhancements!)

Dart Development Compiler (dartdevc)

In order to align with dart2js semantics, DDC will now throw a runtime error
when a redirecting factory is torn off and one of its optional non-nullable
parameters is provided no value. The implicit null passed to the factory will
not match the non-nullable type and this will now throw.

In the future this will likely be a compile-time error and will be entirely
disallowed.

Dart to Javascript Compiler (dart2js)

Removed the --experiment-new-rti and --use-old-rti flags.

Dart Native Compiler

Added cross-compilation for the Linux x64 and Linux ARM64 target platforms.

Dart format

In 3.7.0, we released a largely rewritten formatter supporting a new
"tall" style. Since then, we've gotten a lot of feedback and bug
reports and made a number of fixes in response to that.

Features

Some users strongly prefer the old behavior where a trailing comma will be
preserved by the formatter and force the surrounding construct to split. That
behavior is supported again (but off by default) and can enabled by adding this
to a surrounding analysis_options.yaml file:

formatter:
  trailing_commas: preserve

This is similar to how trailing commas work in the old short style formatter
applied to code before language version 3.7.

Bug fixes

• Don't add a trailing comma in lists that don't allow it, even when there is
  a trailing comment (#​1639).

Style changes

The following style changes are language versioned and only affect code whose
language version is 3.8 or later. Dart code at 3.7 or earlier is formatted the
same as it was before.

• Allow more code on the same line as a named argument or =>.

  // Before:
  function(
    name:
        (param) => another(
          argument1,
          argument2,
        ),
  );
  
  // After:
  function(
    name: (param) => another(
      argument1,
      argument3,
    ),
  );

• Allow the target or property chain part of a split method chain on the RHS of
  =, :, and =>.

  // Before:
  variable =
      target.property
          .method()
          .another();
  
  // After:
  variable = target.property
      .method()
      .another();

• Allow the condition part of a split conditional expression on the RHS of =,
  :, and =>.

  // Before:
  variable =
      condition
      ? longThenBranch
      : longElseBranch;
  
  // After:
  variable = condition
      ? longThenBranch
      : longElseBranch;

• Don't indent conditional branches redundantly after =, :, and =>.

  // Before:
  function(
    argument:
        condition
            ? thenBranch
            : elseBranch,
  )
  
  // After:
  function(
    argument:
        condition
        ? thenBranch
        : elseBranch,
  )

• Indent conditional branches past the operators.

  // Before:
  condition
      ? thenBranch +
          anotherOperand
      : elseBranch(
        argument,
      );
  
  // After:
  condition
      ? thenBranch +
            anotherOperand
      : elseBranch(
          argument,
        );

• Block format record types in typedefs:

  // Before:
  typedef ExampleRecordTypedef =
      (
        String firstParameter,
        int secondParameter,
        String thirdParameter,
        String fourthParameter,
      );
  
  // After:
  typedef ExampleRecordTypedef = (
    String firstParameter,
    int secondParameter,
    String thirdParameter,
    String fourthParameter,
  );

• Eagerly split argument lists whose contents are complex enough to be easier
  to read spread across multiple lines even if they would otherwise fit on a
  single line.

  The heuristic is that the argument list must contain at least three named
  arguments, some of which are nested and some of which are not.

  // Before:
  TabBar(tabs: [Tab(text: 'A'), Tab(text: 'B')], labelColor: Colors.white70);
  
  // After:
  TabBar(
    tabs: [
      Tab(text: 'A'),
      Tab(text: 'B'),
    ],
    labelColor: Colors.white70,
  );