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 really intended for experiments.)
# They are intended 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.
#
# ### Code Generation
#
# When you change this file, run the following to update analyzer, kernel, and
# vm:
#
# analyzer:
#   dart pkg/analyzer/tool/experiments/generate.dart
#
# kernel:
#   pkg/front_end/tool/fasta 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: '2.16.0'

features:
  variance:
    help: "Sound variance"

  alternative-invalidation-strategy:
    help: "Alternative invalidation strategy for incremental compilation."
    category: "CFE"

  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."

  enhanced-enums:
    help: "Enhanced Enums"

  named-arguments-anywhere:
    help: "Named Arguments Anywhere"

  super-parameters:
    help: "Super-Initializer Parameters"

  macros:
    help: "Static meta-programming"

# 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.
#

  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();
      }