Add extension methods to package:collection. (flutter#135)

Add a number of useful extension methods to `List` and `Iterable`, and to a few other types.

A good part of these extensions are backed by the algorithms of `algorithms.dart`, which is expanded to support them:

* Added `quickSort`.
* Add extra optional `Random` argument to `shuffle`.
* Generalize some of the functions in algorithms.dart to work on specific properties of the objects (`binarySearchBy`,
`lowerBoundBy`, `insertionSortBy`, `quickSortBy`, `mergeSortBy`).

The new methods are not exported from the library yet, they are intended to be used through the extension.

Author: lrhn

.travis.yml

@@ -20,7 +20,7 @@ jobs:
     - stage: test
       name: "Vm Tests"
       os: linux
-      script: pub run --enable-experiment=non-nullable test -p vm 
+      script: pub run --enable-experiment=non-nullable test -p vm
     - stage: test
       name: "Web Tests"
       os: linux

CHANGELOG.md

@@ -3,6 +3,14 @@
 * Remove the unusable setter `UnionSetController.set=`. This was mistakenly
   added to the public API but could never be called.
 
+* Add extra optional `Random` argument to `shuffle`.
+
+* Add a large number of extension methods on `Iterable` and `List` types,
+  and on a few other types.
+  These either provide easy access to the operations from `algorithms.dart`,
+  or provide convenience variants of existing `Iterable` and `List` methods
+  like `singleWhereOrNull` or `forEachIndexed`.
+
 ## 1.15.0-nullsafety.3
 
 * Allow 2.10 stable and 2.11.0 dev SDK versions.

analysis_options.yaml

@@ -1,4 +1,4 @@
-include: package:pedantic/analysis_options.yaml
+include: package:pedantic/analysis_options.1.9.0.yaml
 analyzer:
   errors:
     unused_element: error
@@ -7,39 +7,21 @@ analyzer:
     dead_code: error
   enable-experiment:
     - non-nullable
-
 linter:
   rules:
     # Errors
-    - avoid_empty_else
     - control_flow_in_finally
     - empty_statements
     - hash_and_equals
     - implementation_imports
     - test_types_in_equals
     - throw_in_finally
-    - unrelated_type_equality_checks
-    - valid_regexps
 
     # Style
-    - avoid_init_to_null
     - avoid_private_typedef_functions
     - avoid_renaming_method_parameters
-    - avoid_return_types_on_setters
     - await_only_futures
     - camel_case_types
     - directives_ordering
-    - empty_catches
-    - empty_constructor_bodies
-    - library_names
-    - library_prefixes
     - non_constant_identifier_names
     - only_throw_errors
-    - prefer_equal_for_default_values
-    - prefer_final_fields
-    - prefer_generic_function_type_aliases
-    - prefer_is_not_empty
-    - slash_for_doc_comments
-    - type_init_formals
-    - unnecessary_const
-    - unnecessary_new

lib/algorithms.dart

@@ -6,4 +6,5 @@
 @Deprecated('Will be removed in collection 2.0.0.')
 library dart.pkg.collection.algorithms;
 
-export 'src/algorithms.dart';
+export 'src/algorithms.dart'
+    show binarySearch, insertionSort, lowerBound, mergeSort, shuffle, reverse;

lib/collection.dart

@@ -2,7 +2,8 @@
 // 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.
 
-export 'src/algorithms.dart';
+export 'src/algorithms.dart'
+    show binarySearch, insertionSort, lowerBound, mergeSort, shuffle, reverse;
 export 'src/canonicalized_map.dart';
 export 'src/combined_wrappers/combined_iterable.dart';
 export 'src/combined_wrappers/combined_list.dart';
@@ -12,7 +13,9 @@ export 'src/equality.dart';
 export 'src/equality_map.dart';
 export 'src/equality_set.dart';
 export 'src/functions.dart';
+export 'src/iterable_extensions.dart';
 export 'src/iterable_zip.dart';
+export 'src/list_extensions.dart';
 export 'src/priority_queue.dart';
 export 'src/queue_list.dart';
 export 'src/union_set.dart';