Add option to include fields that are equal to the default value in the JSON encoding

Author: mrabiciu

Sources/SwiftProtobuf/JSONEncodingOptions.swift

@@ -40,6 +40,11 @@ public struct JSONEncodingOptions: Sendable {
   /// by keys in lexographical order. This is an implementation detail
   /// and subject to change.
   public var useDeterministicOrdering: Bool = false
+    
+  /// Include fields that are equal to the default value in the JSON encoding.
+  /// This only applies to non-optional fields. Optional fields that are unset will still be 
+  /// omitted from encoded JSON.
+  public var includeDefaultValues: Bool = false
 
   public init() {}
 }

Sources/SwiftProtobuf/JSONEncodingVisitor.swift

@@ -21,6 +21,7 @@ internal struct JSONEncodingVisitor: Visitor {
   private var nameMap: _NameMap
   private var extensions: ExtensionFieldValueSet?
   private let options: JSONEncodingOptions
+  let traversalOptions: TraversalOptions
 
   /// The JSON text produced by the visitor, as raw UTF8 bytes.
   var dataResult: [UInt8] {
@@ -41,6 +42,7 @@ internal struct JSONEncodingVisitor: Visitor {
       throw JSONEncodingError.missingFieldNames
     }
     self.options = options
+    traversalOptions = TraversalOptions(visitDefaultValues: options.includeDefaultValues)
   }
 
   mutating func startArray() {
@@ -143,7 +145,6 @@ internal struct JSONEncodingVisitor: Visitor {
     fieldNumber: Int,
     encode: (inout JSONEncoder, T) throws -> ()
   ) throws {
-    assert(!value.isEmpty)
     try startField(for: fieldNumber)
     var comma = false
     encoder.startArray()
@@ -318,7 +319,6 @@ internal struct JSONEncodingVisitor: Visitor {
   }
 
   mutating func visitRepeatedMessageField<M: Message>(value: [M], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try startField(for: fieldNumber)
     var comma = false
     encoder.startArray()
@@ -351,7 +351,6 @@ internal struct JSONEncodingVisitor: Visitor {
   }
 
   mutating func visitRepeatedGroupField<G: Message>(value: [G], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     // Google does not serialize groups into JSON
   }
 

Sources/SwiftProtobuf/Visitor.swift

@@ -31,6 +31,8 @@ import Foundation
 /// used for serialization.  It is implemented by each serialization protocol:
 /// Protobuf Binary, Protobuf Text, JSON, and the Hash encoder.
 public protocol Visitor {
+    
+    var traversalOptions: TraversalOptions { get }
 
   /// Called for each non-repeated float field
   ///
@@ -445,8 +447,27 @@ public protocol Visitor {
   mutating func visitUnknown(bytes: Data) throws
 }
 
+/// Provides options for how visitor traversal should be carried out
+public struct TraversalOptions {
+  static let `default` = TraversalOptions()
+    
+  /// Determines if non-optional fields that are equal to their default values should be visited.
+  /// Defaults to `false`.
+  public var visitDefaultValues: Bool
+
+  public init(visitDefaultValues: Bool = false) {
+    self.visitDefaultValues = visitDefaultValues
+  }
+}
+
+
 /// Forwarding default implementations of some visitor methods, for convenience.
 extension Visitor {
+    
+  // Use the default traversal options if not set
+  public var traversalOptions: TraversalOptions {
+    .default
+  }
 
   // Default definitions of numeric serializations.
   //
@@ -492,126 +513,108 @@ extension Visitor {
   // repeated values differently from singular, so overrides these.
 
   public mutating func visitRepeatedFloatField(value: [Float], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularFloatField(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedDoubleField(value: [Double], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularDoubleField(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedInt32Field(value: [Int32], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularInt32Field(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedInt64Field(value: [Int64], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularInt64Field(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedUInt32Field(value: [UInt32], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularUInt32Field(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedUInt64Field(value: [UInt64], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularUInt64Field(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedSInt32Field(value: [Int32], fieldNumber: Int) throws {
-      assert(!value.isEmpty)
       for v in value {
           try visitSingularSInt32Field(value: v, fieldNumber: fieldNumber)
       }
   }
 
   public mutating func visitRepeatedSInt64Field(value: [Int64], fieldNumber: Int) throws {
-      assert(!value.isEmpty)
       for v in value {
           try visitSingularSInt64Field(value: v, fieldNumber: fieldNumber)
       }
   }
 
   public mutating func visitRepeatedFixed32Field(value: [UInt32], fieldNumber: Int) throws {
-      assert(!value.isEmpty)
       for v in value {
           try visitSingularFixed32Field(value: v, fieldNumber: fieldNumber)
       }
   }
 
   public mutating func visitRepeatedFixed64Field(value: [UInt64], fieldNumber: Int) throws {
-      assert(!value.isEmpty)
       for v in value {
           try visitSingularFixed64Field(value: v, fieldNumber: fieldNumber)
       }
   }
 
   public mutating func visitRepeatedSFixed32Field(value: [Int32], fieldNumber: Int) throws {
-      assert(!value.isEmpty)
       for v in value {
           try visitSingularSFixed32Field(value: v, fieldNumber: fieldNumber)
       }
   }
 
   public mutating func visitRepeatedSFixed64Field(value: [Int64], fieldNumber: Int) throws {
-      assert(!value.isEmpty)
       for v in value {
           try visitSingularSFixed64Field(value: v, fieldNumber: fieldNumber)
       }
   }
 
   public mutating func visitRepeatedBoolField(value: [Bool], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularBoolField(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedStringField(value: [String], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularStringField(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedBytesField(value: [Data], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularBytesField(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedEnumField<E: Enum>(value: [E], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
         try visitSingularEnumField(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedMessageField<M: Message>(value: [M], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularMessageField(value: v, fieldNumber: fieldNumber)
     }
   }
 
   public mutating func visitRepeatedGroupField<G: Message>(value: [G], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     for v in value {
       try visitSingularGroupField(value: v, fieldNumber: fieldNumber)
     }
@@ -623,73 +626,59 @@ extension Visitor {
   // overridden by Protobuf Binary and Text.
 
   public mutating func visitPackedFloatField(value: [Float], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitRepeatedFloatField(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedDoubleField(value: [Double], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitRepeatedDoubleField(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedInt32Field(value: [Int32], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitRepeatedInt32Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedInt64Field(value: [Int64], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitRepeatedInt64Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedUInt32Field(value: [UInt32], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitRepeatedUInt32Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedUInt64Field(value: [UInt64], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitRepeatedUInt64Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedSInt32Field(value: [Int32], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitPackedInt32Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedSInt64Field(value: [Int64], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitPackedInt64Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedFixed32Field(value: [UInt32], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitPackedUInt32Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedFixed64Field(value: [UInt64], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitPackedUInt64Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedSFixed32Field(value: [Int32], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitPackedInt32Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedSFixed64Field(value: [Int64], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitPackedInt64Field(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedBoolField(value: [Bool], fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitRepeatedBoolField(value: value, fieldNumber: fieldNumber)
   }
 
   public mutating func visitPackedEnumField<E: Enum>(value: [E],
                                             fieldNumber: Int) throws {
-    assert(!value.isEmpty)
     try visitRepeatedEnumField(value: value, fieldNumber: fieldNumber)
   }
 

Sources/protoc-gen-swift/FieldGenerator.swift

@@ -21,6 +21,9 @@ import SwiftProtobuf
 /// Interface for field generators.
 protocol FieldGenerator {
   var number: Int { get }
+    
+  /// If the field uses the `visitDefaultValues` flag in its `generateTraverse` implementation.
+  var usesDefaultValueFlagForTraversal: Bool { get }
 
   /// Name mapping entry for the field.
   var fieldMapNames: String { get }

Sources/protoc-gen-swift/MessageFieldGenerator.swift

@@ -47,6 +47,10 @@ class MessageFieldGenerator: FieldGeneratorBase, FieldGenerator {
         return false
       }
     }
+  
+    var usesDefaultValueFlagForTraversal: Bool {
+        !hasFieldPresence
+    }
 
     init(descriptor: FieldDescriptor,
          generatorOptions: GeneratorOptions,
@@ -199,7 +203,7 @@ class MessageFieldGenerator: FieldGeneratorBase, FieldGenerator {
         var usesLocals = false
         let conditional: String
         if isRepeated {  // Also covers maps
-            conditional = "!\(varName).isEmpty"
+            conditional = "visitDefaultValues || !\(varName).isEmpty"
         } else if hasFieldPresence {
             conditional = "let v = \(storedProperty)"
             usesLocals = true
@@ -208,9 +212,9 @@ class MessageFieldGenerator: FieldGeneratorBase, FieldGenerator {
             // be visted if it is the non default value.
             switch fieldDescriptor.type {
             case .string, .bytes:
-                conditional = ("!\(varName).isEmpty")
+                conditional = ("visitDefaultValues || !\(varName).isEmpty")
             default:
-                conditional = ("\(varName) != \(swiftDefaultValue)")
+                conditional = ("visitDefaultValues || \(varName) != \(swiftDefaultValue)")
             }
         }
         assert(usesLocals == generateTraverseUsesLocals)

Sources/protoc-gen-swift/MessageGenerator.swift

@@ -322,7 +322,12 @@ class MessageGenerator {
   /// - Parameter p: The code printer.
   private func generateTraverse(printer p: inout CodePrinter) {
     p.print("\(visibility)func traverse<V: \(namer.swiftProtobufModulePrefix)Visitor>(visitor: inout V) throws {")
+      
     p.withIndentation { p in
+      if fields.contains(where: { $0.usesDefaultValueFlagForTraversal }) {
+        p.print("let visitDefaultValues = visitor.traversalOptions.visitDefaultValues")
+      }
+
       generateWithLifetimeExtension(printer: &p, throws: true) { p in
         if let storage = storage {
           storage.generatePreTraverse(printer: &p)

Sources/protoc-gen-swift/OneofGenerator.swift

@@ -29,6 +29,7 @@ class OneofGenerator {
         let swiftDefaultValue: String
         let protoGenericType: String
         let comments: String
+        let usesDefaultValueFlagForTraversal: Bool = false
 
         var isGroupOrMessage: Bool {
             switch fieldDescriptor.type {