Merge pull request #2 from ahoppen/throwing-decoding

Allow ByteTree deserialisation functions to throw

Author: nkcsgexi

Sources/SwiftSyntax/ByteTreeDeserialization.swift

@@ -22,6 +22,17 @@ struct ByteTreeUserInfoKey: Hashable {
   }
 }
 
+public enum ByteTreeDecodingError: Error, CustomStringConvertible {
+  case invalidEnumRawValue(type: String, value: Int)
+
+  public var description: String {
+    switch self {
+      case .invalidEnumRawValue(let type, let value):
+        return "Invalid raw value \"\(value)\" for \(type)"
+    }
+  }
+}
+
 /// A type that can be deserialized from ByteTree into a scalar value that
 /// doesn't have any child nodes
 protocol ByteTreeScalarDecodable {
@@ -32,7 +43,8 @@ protocol ByteTreeScalarDecodable {
   ///   - size: The length of the serialized data in bytes
   /// - Returns: The deserialized value
   static func read(from pointer: UnsafeRawPointer, size: Int,
-                   userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>) -> Self
+                   userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>
+  ) throws -> Self
 }
 
 /// A type that can be deserialized from ByteTree into an object with child
@@ -50,7 +62,8 @@ protocol ByteTreeObjectDecodable {
   /// - Returns: The deserialized object
   static func read(from reader: UnsafeMutablePointer<ByteTreeObjectReader>, 
                    numFields: Int, 
-                   userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>) -> Self
+                   userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>
+  ) throws -> Self
 }
 
 // MARK: - Reader objects
@@ -92,9 +105,9 @@ struct ByteTreeObjectReader {
   /// - Returns: The decoded field
   mutating func readField<FieldType: ByteTreeScalarDecodable>(
     _ objectType: FieldType.Type, index: Int
-  ) -> FieldType {
+  ) throws -> FieldType {
     advanceAndValidateIndex(index)
-    return reader.pointee.read(objectType)
+    return try reader.pointee.read(objectType)
   }
 
   /// Read the field at the given index as the specified type. All indicies must
@@ -107,9 +120,9 @@ struct ByteTreeObjectReader {
   /// - Returns: The decoded field
   mutating func readField<FieldType: ByteTreeObjectDecodable>(
     _ objectType: FieldType.Type, index: Int
-  ) -> FieldType {
+  ) throws -> FieldType {
     advanceAndValidateIndex(index)
-    return reader.pointee.read(objectType)
+    return try reader.pointee.read(objectType)
   }
 
   /// Read and immediately discard the field at the specified index. This
@@ -180,7 +193,7 @@ struct ByteTreeReader {
   ) throws -> T {
     var reader = ByteTreeReader(pointer: pointer, userInfo: userInfo)
     try reader.readAndValidateProtocolVersion(protocolVersionValidation)
-    return reader.read(rootObjectType)
+    return try reader.read(rootObjectType)
   }
 
   /// Deserialize an object tree from the ByteTree data at the given memory
@@ -275,15 +288,15 @@ struct ByteTreeReader {
   /// - Returns: The deserialized object
   fileprivate mutating func read<T: ByteTreeObjectDecodable>(
     _ objectType: T.Type
-  ) -> T {
+  ) throws -> T {
     let numFields = readObjectLength()
     var objectReader = ByteTreeObjectReader(reader: &self,
                                             numFields: numFields)
     defer {
       objectReader.finalize()
     }
-    return T.read(from: &objectReader, numFields: numFields, 
-                  userInfo: userInfo)
+    return try T.read(from: &objectReader, numFields: numFields, 
+                      userInfo: userInfo)
   }
 
   /// Read the next field in the tree as a scalar of the specified type.
@@ -292,12 +305,12 @@ struct ByteTreeReader {
   /// - Returns: The deserialized scalar
   fileprivate mutating func read<T: ByteTreeScalarDecodable>(
     _ scalarType: T.Type
-  ) -> T {
+  ) throws -> T {
     let fieldSize = readScalarLength()
     defer {
       pointer = pointer.advanced(by: fieldSize)
     }
-    return T.read(from: pointer, size: fieldSize, userInfo: userInfo)
+    return try T.read(from: pointer, size: fieldSize, userInfo: userInfo)
   }
 
   /// Discard the next scalar field, advancing the pointer to the next field
@@ -347,12 +360,12 @@ extension Optional: ByteTreeObjectDecodable
   static func read(from reader: UnsafeMutablePointer<ByteTreeObjectReader>, 
                    numFields: Int, 
                    userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>
-  ) -> Optional<Wrapped> {
+  ) throws -> Optional<Wrapped> {
     if numFields == 0 {
       return nil
     } else {
-      return Wrapped.read(from: reader, numFields: numFields,
-                          userInfo: userInfo)
+      return try Wrapped.read(from: reader, numFields: numFields,
+                              userInfo: userInfo)
     }
   }
 }
@@ -363,9 +376,9 @@ extension Array: ByteTreeObjectDecodable
   static func read(from reader: UnsafeMutablePointer<ByteTreeObjectReader>, 
                    numFields: Int, 
                    userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>
-  ) -> Array<Element> {
-    return (0..<numFields).map {
-      return reader.pointee.readField(Element.self, index: $0)
+  ) throws -> Array<Element> {
+    return try (0..<numFields).map {
+      return try reader.pointee.readField(Element.self, index: $0)
     }
   }
 }

Sources/SwiftSyntax/RawSyntax.swift

@@ -409,33 +409,32 @@ extension RawSyntax: ByteTreeObjectDecodable {
   static func read(from reader: UnsafeMutablePointer<ByteTreeObjectReader>, 
                    numFields: Int, 
                    userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>
-  ) -> RawSyntax {
+  ) throws -> RawSyntax {
     let syntaxNode: RawSyntax
-    let type = reader.pointee.readField(SyntaxType.self, index: 0)
-    let id = reader.pointee.readField(SyntaxNodeId.self, index: 1)
+    let type = try reader.pointee.readField(SyntaxType.self, index: 0)
+    let id = try reader.pointee.readField(SyntaxNodeId.self, index: 1)
     switch type {
     case .token:
-      let presence = reader.pointee.readField(SourcePresence.self, index: 2)
-      let kind = reader.pointee.readField(TokenKind.self, index: 3)
-      let leadingTrivia = reader.pointee.readField(Trivia.self, index: 4)
-      let trailingTrivia = reader.pointee.readField(Trivia.self, index: 5)
+      let presence = try reader.pointee.readField(SourcePresence.self, index: 2)
+      let kind = try reader.pointee.readField(TokenKind.self, index: 3)
+      let leadingTrivia = try reader.pointee.readField(Trivia.self, index: 4)
+      let trailingTrivia = try reader.pointee.readField(Trivia.self, index: 5)
       syntaxNode = RawSyntax(kind: kind, leadingTrivia: leadingTrivia,
                              trailingTrivia: trailingTrivia,
                              presence: presence, id: id)
     case .layout:
-      let presence = reader.pointee.readField(SourcePresence.self, index: 2)
-      let kind = reader.pointee.readField(SyntaxKind.self, index: 3)
-      let layout = reader.pointee.readField([RawSyntax?].self, index: 4)
+      let presence = try reader.pointee.readField(SourcePresence.self, index: 2)
+      let kind = try reader.pointee.readField(SyntaxKind.self, index: 3)
+      let layout = try reader.pointee.readField([RawSyntax?].self, index: 4)
       syntaxNode = RawSyntax(kind: kind, layout: layout, presence: presence,
                              id: id)
     case .omitted:
       guard let lookupFunc = userInfo.pointee[.omittedNodeLookupFunction] as?
         (SyntaxNodeId) -> RawSyntax? else {
-          fatalError("omittedNodeLookupFunction is required when decoding an " +
-                     "incrementally transferred syntax tree")
+          throw IncrementalDecodingError.noLookupFunctionPassed
       }
       guard let lookupNode = lookupFunc(id) else {
-        fatalError("Node lookup for id \(id) failed")
+        throw IncrementalDecodingError.nodeLookupFailed(id)
       }
       syntaxNode = lookupNode
     }

Sources/SwiftSyntax/TokenKind.swift.gyb

@@ -114,31 +114,32 @@ extension TokenKind: ByteTreeObjectDecodable {
   static func read(from reader: UnsafeMutablePointer<ByteTreeObjectReader>, 
                    numFields: Int, 
                    userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>
-  ) -> TokenKind {
+  ) throws -> TokenKind {
     // Explicitly spell out all TokenKinds to keep the serialized value stable
     // even if its members get reordered or members get removed
-    let kind = reader.pointee.readField(UInt8.self, index: 0)
+    let kind = try reader.pointee.readField(UInt8.self, index: 0)
     switch kind {
     case 0: return .eof
 % for token in SYNTAX_TOKENS:
     case ${token.serialization_code}:
 %   if token.text: # The token does not have text associated with it
       return .${token.swift_kind()}
 %   else:
-      let text = reader.pointee.readField(String.self, index: 1)
+      let text = try reader.pointee.readField(String.self, index: 1)
       return .${token.swift_kind()}(text)
 %   end
 % end
     default:
       if numFields > 1 {
         // Default to an unknown token with the passed text if we don't know 
         // its kind.
-        let text = reader.pointee.readField(String.self, index: 1)
+        let text = try reader.pointee.readField(String.self, index: 1)
         return .unknown(text)
       } else {
         // If we were not passed the token's text, we cannot recover since we 
         // would lose roundtripness.
-        fatalError("Unknown TokenKind \(kind)")
+        throw ByteTreeDecodingError.invalidEnumRawValue(type: "\(self)", 
+                                                        value: Int(kind))
       }
     }
   }

Sources/SwiftSyntax/Trivia.swift.gyb

@@ -224,9 +224,9 @@ extension Trivia: ByteTreeObjectDecodable {
   static func read(from reader: UnsafeMutablePointer<ByteTreeObjectReader>, 
                    numFields: Int, 
                    userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>
-  ) -> Trivia {
-    let pieces = [TriviaPiece].read(from: reader, numFields: numFields,
-                                    userInfo: userInfo)
+  ) throws -> Trivia {
+    let pieces = try [TriviaPiece].read(from: reader, numFields: numFields,
+                                        userInfo: userInfo)
     return Trivia(pieces: pieces)
   }
 }
@@ -235,21 +235,22 @@ extension TriviaPiece: ByteTreeObjectDecodable {
   static func read(from reader: UnsafeMutablePointer<ByteTreeObjectReader>, 
                    numFields: Int, 
                    userInfo: UnsafePointer<[ByteTreeUserInfoKey: Any]>
-  ) -> TriviaPiece {
-    let kind = reader.pointee.readField(UInt8.self, index: 0)
+  ) throws -> TriviaPiece {
+    let kind = try reader.pointee.readField(UInt8.self, index: 0)
     switch kind {
 % for trivia in TRIVIAS:
     case ${trivia.serialization_code}:
 %   if trivia.is_collection():
-      let count = Int(reader.pointee.readField(UInt32.self, index: 1))
+      let count = Int(try reader.pointee.readField(UInt32.self, index: 1))
       return .${trivia.lower_name}s(count)      
 %   else:
-      let text = reader.pointee.readField(String.self, index: 1)
+      let text = try reader.pointee.readField(String.self, index: 1)
       return .${trivia.lower_name}(text)      
 %   end
 % end
     default:
-      fatalError("Unknown trivia piece kind \(kind)")
+      throw ByteTreeDecodingError.invalidEnumRawValue(type: "\(self)", 
+                                                      value: Int(kind))
     }
   }
 }