[Foundation] Correct case of over-released data contents when specifying .none as a deallocator

stdlib/public/SDK/Foundation/Data.swift

@@ -91,7 +91,7 @@ public final class _DataStorage {
             num -= pages
         }
         if num > 0 {
-            memmove(dest, source, num)
+            memmove(dest, source!, num)
         }
     }
 
@@ -500,7 +500,7 @@ public final class _DataStorage {
             }
             if replacementLength != 0 {
                 if replacementBytes != nil {
-                    memmove(mutableBytes! + start, replacementBytes, replacementLength)
+                    memmove(mutableBytes! + start, replacementBytes!, replacementLength)
                 } else {
                     memset(mutableBytes! + start, 0, replacementLength)
                 }
@@ -822,7 +822,10 @@ public final class _DataStorage {
             if lhs.bytes == rhs.bytes {
                 return true
             }
-            return memcmp(lhs._bytes, rhs._bytes, length1) == 0
+            if length1 > 0 {
+                return memcmp(lhs._bytes!, rhs._bytes!, length1) == 0
+            }
+            return true
         }
     }
 
@@ -932,15 +935,15 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
         /// A custom deallocator.
         case custom((UnsafeMutableRawPointer, Int) -> Void)
 
-        fileprivate var _deallocator : ((UnsafeMutableRawPointer, Int) -> Void)? {
+        fileprivate var _deallocator : ((UnsafeMutableRawPointer, Int) -> Void) {
 #if DEPLOYMENT_RUNTIME_SWIFT
             switch self {
             case .unmap:
                 return { __NSDataInvokeDeallocatorUnmap($0, $1) }
             case .free:
                 return { __NSDataInvokeDeallocatorFree($0, $1) }
             case .none:
-                return nil
+                return { _, _ in }
             case .custom(let b):
                 return { (ptr, len) in
                     b(ptr, len)
@@ -955,7 +958,7 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
             case .free:
                 return { __NSDataInvokeDeallocatorFree($0, $1) }
             case .none:
-                return nil
+                return { _, _ in }
             case .custom(let b):
                 return { (ptr, len) in
                     b(ptr, len)
@@ -1639,7 +1642,10 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
         if backing1.bytes == backing2.bytes {
             return true
         }
-        return memcmp(backing1.bytes, backing2.bytes, length1) == 0
+        if length1 > 0 {
+            return memcmp(backing1.bytes!, backing2.bytes!, length1) == 0
+        }
+        return true
     }
 }
 

test/stdlib/TestData.swift

@@ -898,6 +898,15 @@ class TestData : TestDataSuper {
 
         expectTrue(deallocated)
     }
+
+    func test_doubleDeallocation() {
+        let data = "12345679".data(using: .utf8)!
+        let len = data.withUnsafeBytes { (bytes: UnsafePointer<UInt8>) -> Int in
+            let slice = Data(bytesNoCopy: UnsafeMutablePointer(mutating: bytes), count: 1, deallocator: .none)
+            return slice.count
+        }
+        expectEqual(len, 1)
+    }
 }
 
 #if !FOUNDATION_XCTEST
@@ -941,6 +950,7 @@ DataTests.test("test_classForCoder") { TestData().test_classForCoder() }
 DataTests.test("test_AnyHashableContainingData") { TestData().test_AnyHashableContainingData() }
 DataTests.test("test_AnyHashableCreatedFromNSData") { TestData().test_AnyHashableCreatedFromNSData() }
 DataTests.test("test_noCopyBehavior") { TestData().test_noCopyBehavior() }
+DataTests.test("test_doubleDeallocation") { TestData().test_doubleDeallocation() }
 
 // XCTest does not have a crash detection, whereas lit does
 DataTests.test("bounding failure subdata") {