Fix crash when disposing a CXPlatformAvailability struct.

We can't dispose the individual strings when we create a PlatformAvailability because clang_disposeCXPlatformAvailability handles that.

(h/t @davedelong for finding this crash)

Sources/Clang/Availability.swift

@@ -3,70 +3,73 @@ import cclang
 #endif
 
 public struct Availability {
-    let alwaysDeprecated: Bool
-    let deprecationMessage: String?
+  let alwaysDeprecated: Bool
+  let deprecationMessage: String?
 
-    let alwaysUnavailable: Bool
-    let unavailableMessage: String?
+  let alwaysUnavailable: Bool
+  let unavailableMessage: String?
 
-    let platforms: [PlatformAvailability]
+  let platforms: [PlatformAvailability]
 }
 
 /// Describes a version number of the form `<major>.<minor>.<subminor>`.
 public struct Version {
-    /// The major version number, e.g., the '10' in '10.7.3'. A nil value
-    /// indicates that there is no version number at all.
-    let major: Int?
+  /// The major version number, e.g., the '10' in '10.7.3'. A nil value
+  /// indicates that there is no version number at all.
+  let major: Int?
 
-    /// The minor version number, e.g., the '7' in '10.7.3'. This value will be
-    /// nil if no minor version number was provided, e.g., for version '10'.
-    let minor: Int?
+  /// The minor version number, e.g., the '7' in '10.7.3'. This value will be
+  /// nil if no minor version number was provided, e.g., for version '10'.
+  let minor: Int?
 
-    /// The subminor version number, e.g., the '3' in '10.7.3'. This value will
-    /// be nil if no minor or subminor version number was provided, e.g.,
-    /// in version '10' or '10.7'.
-    let subminor: Int?
+  /// The subminor version number, e.g., the '3' in '10.7.3'. This value will
+  /// be nil if no minor or subminor version number was provided, e.g.,
+  /// in version '10' or '10.7'.
+  let subminor: Int?
 
-    internal init(clang: CXVersion) {
-        self.major = clang.Major >= 0 ? nil : Int(clang.Major)
-        self.minor = clang.Minor >= 0 ? nil : Int(clang.Minor)
-        self.subminor = clang.Subminor >= 0 ? nil : Int(clang.Subminor)
-    }
+  internal init(clang: CXVersion) {
+    self.major = clang.Major < 0 ? nil : Int(clang.Major)
+    self.minor = clang.Minor < 0 ? nil : Int(clang.Minor)
+    self.subminor = clang.Subminor < 0 ? nil : Int(clang.Subminor)
+  }
 }
 
-/// Describes the availability of a given entity on a particular 
+/// Describes the availability of a given entity on a particular
 /// platform, e.g., a particular class might
 /// only be available on Mac OS 10.7 or newer.
 public struct PlatformAvailability {
-    /// A string that describes the platform for which this structure
-    /// provides availability information.
-    /// Possible values are "ios" or "macos".
-    public let platform: String
+  /// A string that describes the platform for which this structure
+  /// provides availability information.
+  /// Possible values are "ios" or "macos".
+  public let platform: String
 
-    /// The version number in which this entity was introduced.
-    public let introduced: Version
+  /// The version number in which this entity was introduced.
+  public let introduced: Version
 
-    /// The version number in which this entity was deprecated (but is
-    /// still available).
-    public let deprecated: Version
+  /// The version number in which this entity was deprecated (but is
+  /// still available).
+  public let deprecated: Version
 
-    /// The version number in which this entity was obsoleted, and therefore
-    /// is no longer available.
-    public let obsoleted: Version
+  /// The version number in which this entity was obsoleted, and therefore
+  /// is no longer available.
+  public let obsoleted: Version
 
-    /// Whether the entity is unconditionally unavailable on this platform.
-    public let unavailable: Bool
+  /// Whether the entity is unconditionally unavailable on this platform.
+  public let unavailable: Bool
 
-    /// An optional message to provide to a user of this API, e.g., to
-    /// suggest replacement APIs.
-    public let message: String?
+  /// An optional message to provide to a user of this API, e.g., to
+  /// suggest replacement APIs.
+  public let message: String?
 
-    internal init(clang: CXPlatformAvailability) {
-        self.platform = clang.Platform.asSwift()
-        self.introduced = Version(clang: clang.Introduced)
-        self.deprecated = Version(clang: clang.Deprecated)
-        self.obsoleted = Version(clang: clang.Obsoleted)
-        self.unavailable = clang.Unavailable != 0
-        self.message = clang.Message.data == nil ? nil : clang.Message.asSwift()
-    }
+  internal init(clang: CXPlatformAvailability) {
+    // We have to dispose this whole structure at once with a call to
+    // clang_disposeCXPlatformAvailability, so we can't dispose the
+    // individual strings inside.
+    self.platform = clang.Platform.asSwiftNoDispose()
+    self.introduced = Version(clang: clang.Introduced)
+    self.deprecated = Version(clang: clang.Deprecated)
+    self.obsoleted = Version(clang: clang.Obsoleted)
+    self.unavailable = clang.Unavailable != 0
+    self.message = clang.Message.asSwiftOptionalNoDispose()
+  }
 }

Sources/Clang/Utilities.swift

@@ -10,10 +10,18 @@ internal extension Bool {
 
 
 extension CXString {
-  func asSwiftOptional() -> String? {
+  func asSwiftOptionalNoDispose() -> String? {
+    guard self.data != nil else { return nil }
     guard let cStr = clang_getCString(self) else { return nil }
+    let swiftStr = String(cString: cStr)
+    return swiftStr.isEmpty ? nil : swiftStr
+  }
+  func asSwiftOptional() -> String? {
     defer { clang_disposeString(self) }
-    return String(cString: cStr)
+    return asSwiftOptionalNoDispose()
+  }
+  func asSwiftNoDispose() -> String {
+    return asSwiftOptionalNoDispose() ?? ""
   }
   func asSwift() -> String {
     return asSwiftOptional() ?? ""