Revert "Hide features support behind a ENABLE_PUB_FEATURES environment variable (#1694)"

This reverts commit 43336bd.

We're ready to release this feature.

Author: nex3

lib/src/pubspec.dart

@@ -1,7 +1,6 @@
 // Copyright (c) 2012, 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.
-import 'dart:io';
 
 import 'package:collection/collection.dart';
 import 'package:path/path.dart' as path;
@@ -63,13 +62,6 @@ Using a default value of `true`.
 /// Whether or not to warn about pre-release SDK overrides.
 bool get warnAboutPreReleaseSdkOverrides => allowPreReleaseSdkValue != 'quiet';
 
-/// Whether or not `features` are enabled.
-///
-/// This can be overridden manually or by setting the ENABLE_PUB_FEATURES
-/// environment variable to "true".
-bool featuresEnabled =
-    Platform.environment["ENABLE_PUB_FEATURES"]?.toLowerCase() != "true";
-
 /// The parsed contents of a pubspec file.
 ///
 /// The fields of a pubspec are, for the most part, validated when they're first
@@ -203,21 +195,12 @@ class Pubspec {
 
   Map<String, Feature> get features {
     if (_features != null) return _features;
-
     var features = fields['features'];
     if (features == null) {
       _features = const {};
       return _features;
     }
 
-    // Disable features support unless we have this environment variable set.
-    if (!featuresEnabled) {
-      _error(
-          'Pub `features` support is not enabled but found a pubspec that '
-          'uses it:\n$fields',
-          fields.nodes['features'].span);
-    }
-
     if (features is! Map) {
       _error('"features" field must be a map.', fields.nodes['features'].span);
     }

test/global/activate/feature_test.dart

@@ -4,13 +4,9 @@
 
 import 'package:test/test.dart';
 
-import 'package:pub/src/pubspec.dart';
 import '../../test_pub.dart';
 
 main() {
-  // Explicitly enable `features` support.
-  featuresEnabled = true;
-
   test('enables default-on features by default', () async {
     await servePackages((builder) {
       builder.serve("foo", "1.0.0", pubspec: {

test/pubspec_test.dart

@@ -35,9 +35,6 @@ class MockSource extends Source {
 }
 
 main() {
-  // Explicitly enable `features` support.
-  featuresEnabled = true;
-
   group('parse()', () {
     var sources = new SourceRegistry();
     sources.register(new MockSource());

test/validator/dependency_test.dart

@@ -11,7 +11,6 @@ import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
 
 import 'package:pub/src/entrypoint.dart';
-import 'package:pub/src/pubspec.dart';
 import 'package:pub/src/validator.dart';
 import 'package:pub/src/validator/dependency.dart';
 
@@ -61,9 +60,6 @@ Future setUpDependency(Map dep, {List<String> hostedVersions}) {
 }
 
 main() {
-  // Explicitly enable `features` support.
-  featuresEnabled = true;
-
   group('should consider a package valid if it', () {
     test('looks normal', () async {
       await d.validPackage.create();

test/version_solver_test.dart

@@ -16,9 +16,6 @@ import 'descriptor.dart' as d;
 import 'test_pub.dart';
 
 main() {
-  // Explicitly enable `features` support.
-  featuresEnabled = true;
-
   group('basic graph', basicGraph);
   group('with lockfile', withLockFile);
   group('root dependency', rootDependency);