[stdlib] [SR-4005] Allow heterogenous comparisons in elementsEqual (#8045)

* [SR-4005] Allow heterogenous comparisons in elementsEqual

When a user is supplying a predicate to compare the type equivalence
isn’t required

* elementsEqualWithPredicate tests

Compares a string of a number with an integer value by using the
elementsEqualPredicate closure

* Update test expectations to use new sequence element types

* Update hardcoded test to reference sequence

stdlib/private/StdlibCollectionUnittest/CheckSequenceType.swift

@@ -78,6 +78,33 @@ public struct ElementsEqualTest {
   }
 }
 
+public struct ElementsEqualWithPredicateTest {
+    public let expected: Bool
+    public let sequence: [Int]
+    public let other: [String]
+    public let predicate: (Int, String) -> Bool
+    public let expectedLeftoverSequence: [Int]
+    public let expectedLeftoverOther: [String]
+    public let loc: SourceLoc
+    
+    public init(
+        _ expected: Bool, _ sequence: [Int], _ other: [String],
+        _ predicate: @escaping (Int, String) -> Bool,
+        _ expectedLeftoverSequence: [Int],
+        _ expectedLeftoverOther: [String],
+        file: String = #file, line: UInt = #line,
+        comment: String = ""
+        ) {
+        self.expected = expected
+        self.sequence = sequence
+        self.other = other
+        self.predicate = predicate
+        self.expectedLeftoverSequence = expectedLeftoverSequence
+        self.expectedLeftoverOther = expectedLeftoverOther
+        self.loc = SourceLoc(file, line, comment: "test data" + comment)
+    }
+}
+
 public struct EnumerateTest {
   public let expected: [(Int, Int)]
   public let sequence: [Int]
@@ -450,6 +477,30 @@ public let elementsEqualTests: [ElementsEqualTest] = [
   ElementsEqualTest(false, [ 1, 2 ], [ 1, 2, 3, 4 ], [], [ 4 ]),
 ].flatMap { [ $0, $0.flip() ] }
 
+func elementsEqualPredicate(_ x: Int, y: String) -> Bool {
+    if let intVal = Int(y) {
+        return x == intVal
+    } else {
+        return false
+    }
+}
+
+public let elementsEqualWithPredicateTests: [ElementsEqualWithPredicateTest] = [
+    ElementsEqualWithPredicateTest(true, [], [], elementsEqualPredicate, [], []),
+    
+    ElementsEqualWithPredicateTest(false, [ 1 ], [], elementsEqualPredicate, [ 1 ], []),
+    ElementsEqualWithPredicateTest(false, [], [ "1" ], elementsEqualPredicate, [], [ "1" ]),
+    
+    ElementsEqualWithPredicateTest(false, [ 1, 2 ], [], elementsEqualPredicate, [ 1, 2 ], []),
+    ElementsEqualWithPredicateTest(false, [], [ "1", "2" ], elementsEqualPredicate, [], [ "1", "2" ]),
+    
+    ElementsEqualWithPredicateTest(false, [ 1, 2, 3, 4 ], [ "1", "2" ], elementsEqualPredicate, [ 3, 4 ], []),
+    ElementsEqualWithPredicateTest(false, [ 1, 2 ], [ "1", "2", "3", "4" ], elementsEqualPredicate, [], [ "3", "4" ]),
+    
+    ElementsEqualWithPredicateTest(true, [ 1, 2, 3, 4 ], [ "1", "2", "3", "4" ], elementsEqualPredicate, [], []),
+    ElementsEqualWithPredicateTest(true, [ 1, 2 ], [ "1", "2" ], elementsEqualPredicate, [], []),
+]
+
 public let enumerateTests = [
   EnumerateTest([], []),
   EnumerateTest([ (0, 10) ], [ 10 ]),

stdlib/public/core/SequenceAlgorithms.swift.gyb

@@ -338,12 +338,14 @@ ${equivalenceExplanation}
   public func elementsEqual<OtherSequence>(
     _ other: OtherSequence${"," if preds else ""}
 %   if preds:
-    by areEquivalent: (Element, Element) throws -> Bool
+    by areEquivalent: (Element, OtherSequence.Element) throws -> Bool
 %   end
   ) ${rethrows_}-> Bool
     where
-    OtherSequence: Sequence,
+    OtherSequence: Sequence${" {" if preds else ","}
+%   if not preds:
     OtherSequence.Element == Element {
+%   end
 
     var iter1 = self.makeIterator()
     var iter2 = other.makeIterator()

test/IDE/complete_from_stdlib.swift

@@ -170,7 +170,8 @@ func testArchetypeReplacement3 (_ a : [Int]) {
 // PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceVar]/Super:            first[#Int?#]
 // PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super:         map({#(transform): (Int) throws -> T##(Int) throws -> T#})[' rethrows'][#[T]#]
 // PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super:         dropLast({#(n): Int#})[#ArraySlice<Int>#]
-// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super:         elementsEqual({#(other): Sequence#}, {#by: (Int, Int) throws -> Bool##(Int, Int) throws -> Bool#})[' rethrows'][#Bool#]
+// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super:         elementsEqual({#(other): Sequence#}, {#by: (Int, Sequence.Element) throws -> Bool##(Int, Sequence.Element) throws -> Bool#})[' rethrows'][#Bool#]; name=elementsEqual(other: Sequence, by: (Int, Sequence.Element) throws -> Bool) rethrows
+// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super:         elementsEqual({#(other): Sequence#})[#Bool#]; name=elementsEqual(other: Sequence)
 
 
 protocol P2 {

test/api-digester/source-stability.swift.expected

@@ -328,6 +328,7 @@ Func ReversedRandomAccessCollection.index(_:offsetBy:) has return type change fr
 Func ReversedRandomAccessCollection.index(_:offsetBy:limitedBy:) has return type change from ReversedRandomAccessIndex<Base>? to ReversedRandomAccessCollection.Index?
 Func ReversedRandomAccessCollection.index(after:) has return type change from ReversedRandomAccessIndex<Base> to ReversedRandomAccessCollection.Index
 Func ReversedRandomAccessCollection.index(before:) has return type change from ReversedRandomAccessIndex<Base> to ReversedRandomAccessCollection.Index
+Func Sequence.elementsEqual(_:by:) has parameter 1 type change from (Self.Iterator.Element, Self.Iterator.Element) throws -> Bool to (Self.Element, OtherSequence.Element) throws -> Bool
 Func Set.formSymmetricDifference(_:) has parameter 0 type change from Set<Element> to Set<Set.Element>
 Func Set.index(after:) has return type change from SetIndex<Element> to Set<Element>.Index
 Func Set.index(of:) has return type change from SetIndex<Element>? to Set<Element>.Index?