[SE-0270] Add Collection Operations on Noncontiguous Elements (#69766)

* Adds RangeSet/DiscontiguousSlice to the stdlib

* Remove redundant DiscontiguousSlice.Index: Comparable conformance

* Attempt to fix embedded build

* Attempt to fix macOS test failures

* Fix Constaints/members.swift failure on linux

* Add exceptions to ABI/source checker to fix macOS tests

* Fix incremental dependency test failure

* Remove inlining/unfreeze implementation for future improvements

* Simplify indices(where:) implementation

* Address review feedback

* Add test for underscored, public slice members

* Address feedback on inlining, hashing, and initializing with unordered arrays

* Fix ABI checker issues

* Remove MutableCollection extension for DiscontiguousSlice

* Make insertion return a discardable Bool

* Fix ABI checker tests

* Fix other ABI checker tests due to dropping MutableCollection subscript

Author: jmschonfeld

stdlib/public/core/CMakeLists.txt

@@ -71,6 +71,7 @@ split_embedded_sources(
     NORMAL DictionaryCasting.swift
     NORMAL DictionaryStorage.swift
     NORMAL DictionaryVariant.swift
+    NORMAL DiscontiguousSlice.swift
     NORMAL DropWhile.swift
     NORMAL Dump.swift
   EMBEDDED EmptyCollection.swift
@@ -129,6 +130,8 @@ split_embedded_sources(
   EMBEDDED RandomAccessCollection.swift
   EMBEDDED Range.swift
   EMBEDDED RangeReplaceableCollection.swift
+    NORMAL RangeSet.swift
+    NORMAL RangeSetRanges.swift
     NORMAL ReflectionMirror.swift
   EMBEDDED Repeat.swift
     NORMAL REPL.swift

stdlib/public/core/CollectionAlgorithms.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -209,6 +209,74 @@ extension BidirectionalCollection where Element: Equatable {
   }
 }
 
+//===----------------------------------------------------------------------===//
+// indices(where:) / indices(of:)
+//===----------------------------------------------------------------------===//
+
+#if !$Embedded
+extension Collection {
+  /// Returns the indices of all the elements that match the given predicate.
+  ///
+  /// For example, you can use this method to find all the places that a
+  /// vowel occurs in a string.
+  ///
+  ///     let str = "Fresh cheese in a breeze"
+  ///     let vowels: Set<Character> = ["a", "e", "i", "o", "u"]
+  ///     let allTheVowels = str.indices(where: { vowels.contains($0) })
+  ///     // str[allTheVowels].count == 9
+  ///
+  /// - Parameter predicate: A closure that takes an element as its argument
+  ///   and returns a Boolean value that indicates whether the passed element
+  ///   represents a match.
+  /// - Returns: A set of the indices of the elements for which `predicate`
+  ///   returns `true`.
+  ///
+  /// - Complexity: O(*n*), where *n* is the length of the collection.
+  @available(SwiftStdlib 5.11, *)
+  @inlinable
+  public func indices(
+    where predicate: (Element) throws -> Bool
+  ) rethrows -> RangeSet<Index> {
+    var result: [Range<Index>] = []
+    var end = startIndex
+    while let begin = try self[end...].firstIndex(where: predicate) {
+      end = try self[begin...].prefix(while: predicate).endIndex
+      result.append(begin ..< end)
+
+      guard end < self.endIndex else {
+        break
+      }
+      self.formIndex(after: &end)
+    }
+
+    return RangeSet(_orderedRanges: result)
+  }
+}
+
+extension Collection where Element: Equatable {
+  /// Returns the indices of all the elements that are equal to the given
+  /// element.
+  ///
+  /// For example, you can use this method to find all the places that a
+  /// particular letter occurs in a string.
+  ///
+  ///     let str = "Fresh cheese in a breeze"
+  ///     let allTheEs = str.indices(of: "e")
+  ///     // str[allTheEs].count == 7
+  ///
+  /// - Parameter element: An element to look for in the collection.
+  /// - Returns: A set of the indices of the elements that are equal to
+  ///   `element`.
+  ///
+  /// - Complexity: O(*n*), where *n* is the length of the collection.
+  @available(SwiftStdlib 5.11, *)
+  @inlinable
+  public func indices(of element: Element) -> RangeSet<Index> {
+    indices(where: { $0 == element })
+  }
+}
+#endif
+
 //===----------------------------------------------------------------------===//
 // partition(by:)
 //===----------------------------------------------------------------------===//