dart-sdk/tools/experimental_features.yaml

# Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
# for details. All rights reserved. Use of this source code is governed by a
# BSD-style license that can be found in the LICENSE file.

# Experimental features are described in docs/process/experimental-flags.md
#
# Despite the name, they are not limited to experiments, and are often
# used to enable new features or enhancements that are being
# developed and are not yet shipped. Experimental feature flags are expected
# to be relatively short-lived. Some features behind experiment flags
# may get cancelled and never ship.
#
# ### Code Generation
#
# When you change this file, run the following to update analyzer, kernel, and
# vm:
#
# analyzer:
#   dart pkg/analyzer/tool/experiments/generate.dart
#
# Also, pkg/analyzer/lib/src/dart/analysis/driver.dart will need a bump in
# DATA_VERSION if making changes that change the "index" of any previous flags,
# e.g. if adding a new flag that doesn't happen to be lexicographically last.
#
# kernel:
#   dart pkg/front_end/tool/fasta.dart generate-experimental-flags
#
# vm:
#   dart tools/generate_experimental_flags.dart
#
# ### Overview
#
# This document consists mostly of a map called "features".
# Each entry in this map corresponds to an experiment,
# and contains the following parts:
#
# 1. help: (required text)
#    A human readable description of the experiment.
#
# 2. enabledIn: (optional #.#)
#    The Dart SDK version (<major>.<minor>) in which the experiment is shipping.
#
#    If this field is specified, then the experiment is enabled regardless of
#    the actual version of the SDK. If this field is omitted, then the
#    experiment is disabled by default, but may be enabled by specifying the
#    flag on the command line. (e.g. --enable-experiment=non-nullable)
#
#    A version less than this version may be specified in a .packages file
#    or in a library language version override (e.g. // @dart = 2.1)
#    to disable this feature. For more on library language version override, see
#    https://github.com/dart-lang/language/blob/master/accepted/future-releases/language-versioning/language-versioning.md
#
# 3. expired: (optional boolean)
#    If true, then the experiment can no longer be enabled by specifying the
#    flag on the command line, and the corresponding entry is slated for
#    eventual removal from this file. If this field is omitted, then 'expired'
#    is considered to be false.
#
# 4. validation: (optional string)
#    If provided this should be a program that prints "feature enabled" on
#    stdout if the feature is enabled, and throws or fails to compile otherwise.
#    The intended use for this is to be able to run generic tests for each
#    experiment.
#
# Using the above fields, experiments pass through several states:
#
# Disabled:
#    When an experiment is first added to this file, the 'enabledIn' and
# 'expired' fields are omitted and the experiment is disabled by default,
# but may be enabled by specifying the flag on the command line.
# The implementation teams begin building support for the feature,
# guarded by the flag.  Users can enable the flag and begin to try out
# the feature as it is being developed.
#
# Experimental release:
#    When an experiment is released, then the 'experimentalReleaseVersion' field
# is added indicating which version of the SDK contains this new language
# feature for libraries and packages in mentioned in
# `sdk/lib/_internal/allowed_experiments.json`. For other libraries and
# packages, passing the experiment flag is still required to turn on the
# experiment.
#
# Shipped:
#    When an experiment is shipped, then the 'enabledIn' field is added
# indicating which version of the SDK contains this new language feature.
# At this point, specifying the flag on the command line has no effect because
# the experiment is enabled by default and cannot be disabled.
#
# Retired or Rejected:
#    At some point, the 'expired' field is added to the experiment indicating
# that the flag is to be retired if the experiment has shipped or that the
# entire experiment was rejected if the experiment has not shipped. It also
# indicates that the corresponding entry is slated for eventual removal
# from this file. Users specifying this flag on the command line should receive
# a warning that the experiment has been retired or rejected, but the tool
# should continue to run.
#
# In addition, there is also a value called "current-version"
# specifying the version of Dart that is currently being developed.
# Dart source files that don't specify their own version will be
# presumed to be in this version.  Experiment flags will not affect
# files that specify an earlier version.
#
# Furthermore, most of the above was designed with language features
# (spanning both CFE and Analyzer) in mind, but didn't take into account
# features in individual products (e.g. in CFE that has no influence on
# Analyzer). As a stepping-stone to allow for this usage as well, a "category"
# is also available. If no "category" is specified it's assumed to be the
# default 'language' "category" with code generated for both CFE and Analyzer,
# while other categories can be tailored more specifically.

current-version: '3.0.0'

features:
  variance:
    help: "Sound variance"

  value-class:
    help: "Value class"

  extension-types:
    help: "Extension Types"

  const-functions:
    help: "Allow more of the Dart language to be executed in const expressions."

  macros:
    help: "Static meta-programming"

  inference-update-2:
    help: "Type promotion for fields"

  inline-class:
    help: "Inline class"

  sealed-class:
    help: "Sealed class"
    enabledIn: '3.0.0'
    validation: |
      sealed class A {}
      void main() {
        print('feature enabled');
      }      

  class-modifiers:
    help: "Class modifiers"
    enabledIn: '3.0.0'
    validation: |
      interface class A {}
      void main() {
        print('feature enabled');
      }      

# Experiment flag only used for testing.
  test-experiment:
    help: >-
      Has no effect. Can be used for testing the --enable-experiment
      command line functionality.      

#
# Flags below this line are shipped, retired, or rejected, cannot be specified
# on the command line, and will eventually be removed.
#

  alternative-invalidation-strategy:
    help: "Alternative invalidation strategy for incremental compilation."
    category: "CFE"
    enabledIn: '2.18.0'
    expired: true

  nonfunction-type-aliases:
    help: "Type aliases define a <type>, not just a <functionType>"
    enabledIn: '2.13.0'
    validation: |
      typedef S = String;
      void main() {
        S s = 'feature enabled';
        print(s);
      }      
    expired: true

  non-nullable:
    help: "Non Nullable by default"
    experimentalReleaseVersion: '2.10.0'
    enabledIn: '2.12.0'
    validation: |
      void main() {
        int? a = null;
        print('feature enabled');
      }      
    expired: true

  extension-methods:
    help: "Extension Methods"
    enabledIn: '2.6.0'
    expired: true

  constant-update-2018:
    help: "Enhanced constant expressions"
    enabledIn: '2.0.0'
    expired: true

  control-flow-collections:
    help: "Control Flow Collections"
    enabledIn: '2.0.0'
    expired: true

  generic-metadata:
    help: >-
      Allow annotations to accept type arguments;
      also allow generic function types as type arguments.      
    enabledIn: '2.14.0'
    expired: true

  set-literals:
    help: "Set Literals"
    enabledIn: '2.0.0'
    expired: true

  spread-collections:
    help: "Spread Collections"
    enabledIn: '2.0.0'
    expired: true

  triple-shift:
    help: "Triple-shift operator"
    enabledIn: '2.14.0'
    validation: |
      class A {
        operator>>>(int k) => 42;
      }
      void main() {
        if ((A() >>> 1) == 42) print('feature enabled');
      }      
    expired: true

  constructor-tearoffs:
    help: "Allow constructor tear-offs and explicit generic instantiations."
    enabledIn: '2.15.0'
    validation: |
      class A {
        A() {
          print('feature enabled');
        }
      }
      void main() {
        var c = A.new;
        c();
      }      
    expired: true

  enhanced-enums:
    help: "Enhanced Enums"
    enabledIn: '2.17.0'
    validation: |
      enum T {
        t();
        void test() {
          print('feature enabled');
        }
      }
      void main() {
        T.t.test();
      }      
    expired: true

  named-arguments-anywhere:
    help: "Named Arguments Anywhere"
    enabledIn: '2.17.0'
    validation: |
      void test(String msg, {bool enabled = false}) {
        if (enabled) {
          print(msg);
        }
      }
      void main() {
        test(enabled : true, 'feature enabled');
      }      
    expired: true

  super-parameters:
    help: "Super-Initializer Parameters"
    enabledIn: '2.17.0'
    validation: |
      class B {
        final String foo;
         B(this.foo);
      }
      class C extends B {
        C(super.foo);
      }
      void main(){
        print(C('feature enabled').foo);
      }      
    expired: true

  inference-update-1:
    help: "Horizontal type inference for function expressions passed to generic invocations."
    enabledIn: '2.18.0'
    expired: true
    validation: |
      void test(List<int> list) {
        var a = list.fold(0, (x, y) => x + y);
        f(a);
      }
      void f<T>(T t) {
        if (T == int) {
          print('feature enabled');
        }
      }
      void main() {
        test([1, 2, 3]);
      }      

  unnamed-libraries:
    help: "Unnamed libraries"
    enabledIn: '2.19.0'
    validation: |
      library;
      void main() => print('feature enabled');      

  records:
    help: "Records"
    enabledIn: '3.0.0'
    validation: |
      final x = ('feature', a: 'enabled');
      void main() {
        print('${x.$1} ${x.a}');
      }      

  patterns:
    help: "Patterns"
    enabledIn: '3.0.0'
    validation: |
      void main() {
        final [a, b] = ['feature', 'enabled'];
        print('$a $b');
      }