[cxx-interop] Conform std::set to ExpressibleByArrayLiteral

Swift's own `Set` conforms to `ExpressibleByArrayLiteral`. This change conforms instantiations of C++ `std::set` to `ExpressibleByArrayLiteral` as well.

This makes it possible to pass an array literal as an argument to a function that takes a `std::set` as parameter.

rdar://137126325

Author: egorzhdan

lib/ClangImporter/ClangDerivedConformances.cpp

@@ -883,6 +883,8 @@ void swift::conformToCxxSetIfNeeded(ClangImporter::Implementation &impl,
 
   impl.addSynthesizedTypealias(decl, ctx.Id_Element,
                                valueType->getUnderlyingType());
+  impl.addSynthesizedTypealias(decl, ctx.Id_ArrayLiteralElement,
+                               valueType->getUnderlyingType());
   impl.addSynthesizedTypealias(decl, ctx.getIdentifier("Size"),
                                sizeType->getUnderlyingType());
   impl.addSynthesizedTypealias(decl, ctx.getIdentifier("InsertionResult"),

stdlib/public/Cxx/CxxSet.swift

@@ -16,7 +16,7 @@
 /// `std::multiset` conform to this protocol.
 ///
 /// - SeeAlso: `CxxUniqueSet`
-public protocol CxxSet<Element> {
+public protocol CxxSet<Element>: ExpressibleByArrayLiteral {
   associatedtype Element
   associatedtype Size: BinaryInteger
 
@@ -47,6 +47,11 @@ extension CxxSet {
     }
   }
 
+  @inlinable
+  public init(arrayLiteral elements: Element...) {
+    self.init(elements)
+  }
+
   /// Returns a Boolean value that indicates whether the given element exists
   /// in the set.
   @inlinable

test/Interop/Cxx/stdlib/use-std-set.swift

@@ -75,6 +75,51 @@ StdSetTestSuite.test("UnorderedSetOfCInt.init()") {
     expectTrue(s.contains(3))
 }
 
+StdSetTestSuite.test("SetOfCInt as ExpressibleByArrayLiteral") {
+    let s: SetOfCInt = [1, 3, 5]
+    expectTrue(s.contains(1))
+    expectFalse(s.contains(2))
+    expectTrue(s.contains(3))
+
+    func takesSetOfCInt(_ s: SetOfCInt) {
+        expectTrue(s.contains(1))
+        expectTrue(s.contains(2))
+        expectFalse(s.contains(3))
+    }
+
+    takesSetOfCInt([1, 2])
+}
+
+StdSetTestSuite.test("UnorderedSetOfCInt as ExpressibleByArrayLiteral") {
+    let s: UnorderedSetOfCInt = [1, 3, 5]
+    expectTrue(s.contains(1))
+    expectFalse(s.contains(2))
+    expectTrue(s.contains(3))
+
+    func takesUnorderedSetOfCInt(_ s: UnorderedSetOfCInt) {
+        expectTrue(s.contains(1))
+        expectTrue(s.contains(2))
+        expectFalse(s.contains(3))
+    }
+
+    takesUnorderedSetOfCInt([1, 2])
+}
+
+StdSetTestSuite.test("MultisetOfCInt as ExpressibleByArrayLiteral") {
+    let s: MultisetOfCInt = [1, 1, 3]
+    expectTrue(s.contains(1))
+    expectFalse(s.contains(2))
+    expectTrue(s.contains(3))
+
+    func takesMultisetOfCInt(_ s: MultisetOfCInt) {
+        expectTrue(s.contains(1))
+        expectTrue(s.contains(2))
+        expectFalse(s.contains(3))
+    }
+
+    takesMultisetOfCInt([1, 1, 2])
+}
+
 StdSetTestSuite.test("SetOfCInt.insert") {
     var s = SetOfCInt()
     expectFalse(s.contains(123))