Updated stdlib to use @discardableResult and _ = .

stdlib/private/SwiftPrivate/ShardedAtomicCounter.swift

@@ -48,7 +48,7 @@ public struct _stdlib_ShardedAtomicCounter {
 
   public func add(_ operand: Int, randomInt: Int) {
     let shardIndex = Int(UInt(bitPattern: randomInt) % UInt(self._shardsCount))
-    _swift_stdlib_atomicFetchAddInt(
+    _ = _swift_stdlib_atomicFetchAddInt(
       object: self._shardsPtr + shardIndex, operand: operand)
   }
 

stdlib/private/SwiftPrivatePthreadExtras/SwiftPrivatePthreadExtras.swift

@@ -125,7 +125,10 @@ public class _stdlib_Barrier {
   }
 
   deinit {
-    _stdlib_pthread_barrier_destroy(_pthreadBarrierPtr)
+    let ret = _stdlib_pthread_barrier_destroy(_pthreadBarrierPtr)
+    if ret != 0 {
+      fatalError("_stdlib_pthread_barrier_destroy() failed")
+    }
   }
 
   public func wait() {

stdlib/public/SDK/CoreGraphics/CGFloat.swift.gyb

@@ -465,24 +465,28 @@ public func /=(lhs: inout CGFloat, rhs: CGFloat) {
 
 @_transparent
 @available(*, unavailable, message: "use += 1")
+@discardableResult
 public prefix func ++(rhs: inout CGFloat) -> CGFloat {
   fatalError("++ is not available")
 }
 
 @_transparent
 @available(*, unavailable, message: "use -= 1")
+@discardableResult
 public prefix func --(rhs: inout CGFloat) -> CGFloat {
   fatalError("-- is not available")
 }
 
 @_transparent
 @available(*, unavailable, message: "use += 1")
+@discardableResult
 public postfix func ++(lhs: inout CGFloat) -> CGFloat {
   fatalError("++ is not available")
 }
 
 @_transparent
 @available(*, unavailable, message: "use -= 1")
+@discardableResult
 public postfix func --(lhs: inout CGFloat) -> CGFloat {
   fatalError("-- is not available")
 }

stdlib/public/SwiftOnoneSupport/SwiftOnoneSupport.swift

@@ -145,6 +145,7 @@ struct _Prespecialize {
   }
 
   // Force pre-specialization of Range<Int>
+  @discardableResult
   static internal func _specializeRanges() -> Int {
     let a = [Int](repeating: 1, count: 10)
     var count = 0

stdlib/public/core/ArrayBuffer.swift

@@ -202,6 +202,7 @@ extension _ArrayBuffer {
   /// Copy the elements in `bounds` from this buffer into uninitialized
   /// memory starting at `target`.  Return a pointer past-the-end of the
   /// just-initialized memory.
+  @discardableResult
   public func _copyContents(
     subRange bounds: Range<Int>,
     initializing target: UnsafeMutablePointer<Element>

stdlib/public/core/ArrayBufferProtocol.swift

@@ -29,6 +29,7 @@ public protocol _ArrayBufferProtocol
   /// Copy the elements in `bounds` from this buffer into uninitialized
   /// memory starting at `target`.  Return a pointer past-the-end of the
   /// just-initialized memory.
+  @discardableResult
   func _copyContents(
     subRange bounds: Range<Int>,
     initializing target: UnsafeMutablePointer<Element>

stdlib/public/core/Arrays.swift.gyb

@@ -793,7 +793,7 @@ ${SubscriptDocComment}
 % if Self != 'Array':
     _buffer._checkValidSubscript(index)
 % else:
-    _checkSubscript(index, wasNativeTypeChecked: true)
+    _ = _checkSubscript(index, wasNativeTypeChecked: true)
 % end
   }
 

stdlib/public/core/BridgeObjectiveC.swift

@@ -61,6 +61,7 @@ public protocol _ObjectiveCBridgeable {
   ///   information is provided for the convenience of the runtime's `dynamic_cast`
   ///   implementation, so that it need not look into the optional representation
   ///   to determine success.
+  @discardableResult
   static func _conditionallyBridgeFromObjectiveC(
     _ source: _ObjectiveCType,
     result: inout Self?
@@ -255,7 +256,7 @@ public func _conditionallyBridgeFromObjectiveC<T>(
   }
 
   var result: T?
-  _bridgeNonVerbatimFromObjectiveCConditional(x, T.self, &result)
+  _ = _bridgeNonVerbatimFromObjectiveCConditional(x, T.self, &result)
   return result
 }
 

stdlib/public/core/Character.swift

@@ -219,7 +219,7 @@ public struct Character :
         u16 = u16 << 16
         u16 = u16 | UInt64($0)
       }
-      transcode(
+      _ = transcode(
         _SmallUTF8(u8).makeIterator(),
         from: UTF8.self, to: UTF16.self,
         stoppingOnError: false,

stdlib/public/core/Collection.swift

@@ -1301,7 +1301,7 @@ extension Collection {
     }
 
     if maxSplits == 0 || isEmpty {
-      appendSubsequence(end: endIndex)
+      _ = appendSubsequence(end: endIndex)
       return result
     }
 
@@ -1426,6 +1426,7 @@ extension Collection where SubSequence == Self {
 extension Sequence
   where Self : _ArrayProtocol, Self.Element == Self.Iterator.Element {
   // A fast implementation for when you are backed by a contiguous array.
+  @discardableResult
   public func _copyContents(
     initializing ptr: UnsafeMutablePointer<Iterator.Element>
   ) -> UnsafeMutablePointer<Iterator.Element> {

stdlib/public/core/ContiguousArrayBuffer.swift

@@ -384,6 +384,7 @@ public struct _ContiguousArrayBuffer<Element> : _ArrayBufferProtocol {
   /// Copy the elements in `bounds` from this buffer into uninitialized
   /// memory starting at `target`.  Return a pointer past-the-end of the
   /// just-initialized memory.
+  @discardableResult
   public func _copyContents(
     subRange bounds: Range<Int>,
     initializing target: UnsafeMutablePointer<Element>

stdlib/public/core/FixedPoint.swift.gyb

@@ -609,6 +609,7 @@ extension ${Self} {
 
 @_transparent
 @available(*, unavailable, message: "it has been removed in Swift 3")
+@discardableResult
 public prefix func ++ (x: inout ${Self}) -> ${Self} {
   x = x + 1
   return x
@@ -616,6 +617,7 @@ public prefix func ++ (x: inout ${Self}) -> ${Self} {
 
 @_transparent
 @available(*, unavailable, message: "it has been removed in Swift 3")
+@discardableResult
 public postfix func ++ (x: inout ${Self}) -> ${Self} {
   let ret = x
   x = x + 1
@@ -624,6 +626,7 @@ public postfix func ++ (x: inout ${Self}) -> ${Self} {
 
 @_transparent
 @available(*, unavailable, message: "it has been removed in Swift 3")
+@discardableResult
 public prefix func -- (x: inout ${Self}) -> ${Self} {
   x = x - 1
   return x
@@ -631,6 +634,7 @@ public prefix func -- (x: inout ${Self}) -> ${Self} {
 
 @_transparent
 @available(*, unavailable, message: "it has been removed in Swift 3")
+@discardableResult
 public postfix func -- (x: inout ${Self}) -> ${Self} {
   let ret = x
   x = x - 1

stdlib/public/core/FloatingPointTypes.swift.gyb

@@ -872,21 +872,25 @@ public func %=(lhs: inout ${Self}, rhs: ${Self}) {
 
 @_transparent
 @available(*, unavailable, message: "use += 1")
+@discardableResult
 public prefix func ++(rhs: inout ${Self}) -> ${Self} {
   fatalError("++ is not available")
 }
 @_transparent
 @available(*, unavailable, message: "use -= 1")
+@discardableResult
 public prefix func --(rhs: inout ${Self}) -> ${Self} {
   fatalError("-- is not available")
 }
 @_transparent
 @available(*, unavailable, message: "use += 1")
+@discardableResult
 public postfix func ++(lhs: inout ${Self}) -> ${Self} {
   fatalError("++ is not available")
 }
 @_transparent
 @available(*, unavailable, message: "use -= 1")
+@discardableResult
 public postfix func --(lhs: inout ${Self}) -> ${Self} {
   fatalError("-- is not available")
 }

stdlib/public/core/HashedCollections.swift.gyb

@@ -579,6 +579,7 @@ public struct Set<Element : Hashable> :
   ///   distinguishable from `newMember`, e.g. via `===`).
   ///
   /// - Postcondition: `self.contains(newMember)`.
+  @discardableResult
   public mutating func insert(
     _ newMember: Element
   ) -> (inserted: Bool, memberAfterInsert: Element) {
@@ -592,6 +593,7 @@ public struct Set<Element : Hashable> :
   ///   `===`), or `nil` if no such element existed.
   ///
   /// - Postcondition: `self.contains(newMember)`
+  @discardableResult
   public mutating func update(with newMember: Element) -> Element? {
     return _variantStorage.updateValue(newMember, forKey: newMember)
   }
@@ -610,6 +612,7 @@ public struct Set<Element : Hashable> :
   /// - Parameter member: The element to remove from the set.
   /// - Returns: The value of the `member` parameter if it was a member of the
   ///   set; otherwise, `nil`.
+  @discardableResult
   public mutating func remove(_ member: Element) -> Element? {
     return _variantStorage.removeValue(forKey: member)
   }

stdlib/public/core/Index.swift

@@ -14,21 +14,25 @@
 public protocol _Incrementable : Equatable {}
 
 @available(*, unavailable, message: "Use \'-= 1\' or call collection.prior(Index)")
+@discardableResult
 public prefix func -- <T : _Incrementable> (i: inout T) -> T {
   Builtin.unreachable()
 }
 
 @available(*, unavailable, message: "Use \'-= 1\' or call collection.prior(Index)")
+@discardableResult
 public postfix func -- <T : _Incrementable> (i: inout T) -> T {
   Builtin.unreachable()
 }
 
 @available(*, unavailable, message: "Use \'+= 1\' or call 'collection.index(after: Index)")
+@discardableResult
 public prefix func ++ <T : _Incrementable> (i: inout T) -> T {
   Builtin.unreachable()
 }
 
 @available(*, unavailable, message: "Use \'+= 1\' or call 'collection.index(after: Index)")
+@discardableResult
 public postfix func ++ <T : _Incrementable> (i: inout T) -> T {
   Builtin.unreachable()
 }

stdlib/public/core/LazyCollection.swift.gyb

@@ -94,6 +94,7 @@ extension ${Self} : Sequence {
     return _base._copyToNativeArrayBuffer()
   }
   
+  @discardableResult
   public func _copyContents(
     initializing ptr: UnsafeMutablePointer<Base.Iterator.Element>
   ) -> UnsafeMutablePointer<Base.Iterator.Element> {

stdlib/public/core/OptionSet.swift

@@ -288,6 +288,7 @@ extension OptionSet where Element == Self {
   ///   non-empty.  Returns `nil` otherwise.
   ///
   /// - Postcondition: `self.contains(e)`
+  @discardableResult
   public mutating func update(with e: Element) -> Element? {
     let r = self.intersection(e)
     self.formUnion(e)

stdlib/public/core/Reflection.swift

@@ -150,6 +150,7 @@ func _getSummary<T>(_ out: UnsafeMutablePointer<String>, x: T) {
 internal func _reflect<T>(_ x: T) -> _Mirror
 
 /// Dump an object's contents using its mirror to the specified output stream.
+@discardableResult
 public func dump<T, TargetStream : OutputStream>(
   _ value: T,
   to target: inout TargetStream,
@@ -174,6 +175,7 @@ public func dump<T, TargetStream : OutputStream>(
 }
 
 /// Dump an object's contents using its mirror to standard output.
+@discardableResult
 public func dump<T>(
   _ value: T,
   name: String? = nil,

stdlib/public/core/Runtime.swift.gyb

@@ -78,6 +78,7 @@ func _stdlib_atomicCompareExchangeStrongPtr<T>(
 }
 
 @_transparent
+@discardableResult
 public // @testable
 func _stdlib_atomicInitializeARCRef(
   object target: UnsafeMutablePointer<AnyObject?>,
@@ -518,7 +519,7 @@ class _SwiftNativeNSEnumerator {}
   @objc dynamic func initializeReturnAutoreleased() {
     // On x86_64 it is sufficient to perform one cycle of return-autoreleased
     // call sequence in order to initialize all required PLT entries.
-    self.returnsAutoreleased(self)
+    _ = self.returnsAutoreleased(self)
   }
 }
 

stdlib/public/core/Sequence.swift

@@ -581,6 +581,7 @@ public protocol Sequence {
 
   /// Copy a Sequence into an array, returning one past the last
   /// element initialized.
+  @discardableResult
   func _copyContents(initializing ptr: UnsafeMutablePointer<Iterator.Element>)
     -> UnsafeMutablePointer<Iterator.Element>
 }
@@ -861,6 +862,7 @@ extension Sequence {
     var result: [AnySequence<Iterator.Element>] = []
     var subSequence: [Iterator.Element] = []
 
+    @discardableResult
     func appendSubsequence() -> Bool {
       if subSequence.isEmpty && omittingEmptySubsequences {
         return false
@@ -1144,6 +1146,7 @@ extension Sequence {
 }
 
 extension Sequence {
+  @discardableResult
   public func _copyContents(
     initializing ptr: UnsafeMutablePointer<Iterator.Element>
   ) -> UnsafeMutablePointer<Iterator.Element> {

stdlib/public/core/SequenceWrapper.swift

@@ -119,6 +119,7 @@ extension Sequence
 
   /// Copy a Sequence into an array, returning one past the last
   /// element initialized.
+  @discardableResult
   public func _copyContents(
     initializing ptr: UnsafeMutablePointer<Base.Iterator.Element>
   ) -> UnsafeMutablePointer<Base.Iterator.Element> {

stdlib/public/core/SetAlgebra.swift

@@ -184,6 +184,7 @@ public protocol SetAlgebra : Equatable, ArrayLiteralConvertible {
   ///   distinguishable from `newMember`, e.g. via `===`).
   ///
   /// - Postcondition: `self.contains(newMember)`.
+  @discardableResult
   mutating func insert(
     _ newMember: Element
   ) -> (inserted: Bool, memberAfterInsert: Element)
@@ -198,6 +199,7 @@ public protocol SetAlgebra : Equatable, ArrayLiteralConvertible {
   ///   `===`), or returns `nil` if no such element existed.
   ///
   /// - Postcondition: `self.intersection([e]).isEmpty`
+  @discardableResult
   mutating func remove(_ e: Element) -> Element?
 
   /// Inserts `e` unconditionally.
@@ -212,6 +214,7 @@ public protocol SetAlgebra : Equatable, ArrayLiteralConvertible {
   ///   `===`), or returns `nil` if no such element existed.
   ///
   /// - Postcondition: `self.contains(e)`
+  @discardableResult
   mutating func update(with e: Element) -> Element?
   
   /// Adds the elements of the given set to the set.

stdlib/public/core/SliceBuffer.swift

@@ -185,6 +185,7 @@ struct _SliceBuffer<Element> : _ArrayBufferProtocol, RandomAccessCollection {
     return nil
   }
 
+  @discardableResult
   public func _copyContents(
     subRange bounds: Range<Int>,
     initializing target: UnsafeMutablePointer<Element>

test/SourceKit/DocSupport/doc_clang_module.swift.response

@@ -4846,7 +4846,7 @@ var FooSubUnnamedEnumeratorA1: Int { get }
         key.doc.full_as_xml: "<Function><Name>update(with:)</Name><USR>s:FesRxs9OptionSetxzwx7ElementrS_6updateFT4withwxS0__GSqwxS0__</USR><Declaration>mutating func update(with e: Self) -&gt; Self?</Declaration><Abstract><Para>Inserts <codeVoice>e</codeVoice> unconditionally.</Para></Abstract><ResultDiscussion><Para>a former member <codeVoice>r</codeVoice> of <codeVoice>self</codeVoice> such that <codeVoice>self.intersection([e]) == [r]</codeVoice> if <codeVoice>self.intersection([e])</codeVoice> was non-empty.  Returns <codeVoice>nil</codeVoice> otherwise.</Para></ResultDiscussion><Discussion><Postcondition><Para><codeVoice>self.contains(e)</codeVoice></Para></Postcondition></Discussion></Function>",
         key.offset: 1314,
         key.length: 43,
-        key.fully_annotated_decl: "<decl.function.method.instance><syntaxtype.keyword>mutating</syntaxtype.keyword> <syntaxtype.keyword>func</syntaxtype.keyword> <decl.name>update</decl.name>(<decl.var.parameter><decl.var.parameter.argument_label>with</decl.var.parameter.argument_label> <decl.var.parameter.name>e</decl.var.parameter.name>: <decl.var.parameter.type><ref.generic_type_param usr=\"s:tPs9OptionSet4SelfMx\">Self</ref.generic_type_param></decl.var.parameter.type></decl.var.parameter>) -&gt; <decl.function.returntype><ref.generic_type_param usr=\"s:tPs9OptionSet4SelfMx\">Self</ref.generic_type_param>?</decl.function.returntype></decl.function.method.instance>",
+        key.fully_annotated_decl: "<decl.function.method.instance><syntaxtype.attribute.builtin><syntaxtype.attribute.name>@discardableResult</syntaxtype.attribute.name></syntaxtype.attribute.builtin> <syntaxtype.keyword>mutating</syntaxtype.keyword> <syntaxtype.keyword>func</syntaxtype.keyword> <decl.name>update</decl.name>(<decl.var.parameter><decl.var.parameter.argument_label>with</decl.var.parameter.argument_label> <decl.var.parameter.name>e</decl.var.parameter.name>: <decl.var.parameter.type><ref.generic_type_param usr=\"s:tPs9OptionSet4SelfMx\">Self</ref.generic_type_param></decl.var.parameter.type></decl.var.parameter>) -&gt; <decl.function.returntype><ref.generic_type_param usr=\"s:tPs9OptionSet4SelfMx\">Self</ref.generic_type_param>?</decl.function.returntype></decl.function.method.instance>",
         key.entities: [
           {
             key.kind: source.lang.swift.decl.var.local,