Add option to include fields that are equal to the default value in t…

…he JSON encoding

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 || (!isGroupOrMessage && fieldDescriptor.file.syntax == .proto2)
+    }
 
     init(descriptor: FieldDescriptor,
          generatorOptions: GeneratorOptions,
@@ -194,31 +198,59 @@ class MessageFieldGenerator: FieldGeneratorBase, FieldGenerator {
             traitsArg = ""
         }
 
-        let varName = hasFieldPresence ? "v" : storedProperty
-
         var usesLocals = false
-        let conditional: String
+        let conditionals: [(condition: String, varName: String)]
         if isRepeated {  // Also covers maps
-            conditional = "!\(varName).isEmpty"
+            conditionals = [
+                (condition: "visitDefaultValues || !\(storedProperty).isEmpty", varName: storedProperty)
+            ]
         } else if hasFieldPresence {
-            conditional = "let v = \(storedProperty)"
             usesLocals = true
+            if !isGroupOrMessage, fieldDescriptor.file.syntax == .proto2 {
+                conditionals = [
+                    (condition: "let v = \(storedProperty)", varName: "v"),
+                    (condition: "visitDefaultValues", varName: swiftName),
+                ]
+            } else {
+                conditionals = [
+                    (condition: "let v = \(storedProperty)", varName: "v"),
+                ]
+            }
         } else {
             // At this point, the fields would be a primative type, and should only
             // be visted if it is the non default value.
             switch fieldDescriptor.type {
             case .string, .bytes:
-                conditional = ("!\(varName).isEmpty")
+                conditionals = [
+                    (condition: "visitDefaultValues || !\(storedProperty).isEmpty", varName: storedProperty)
+                ]
             default:
-                conditional = ("\(varName) != \(swiftDefaultValue)")
+                conditionals = [
+                    (condition: "visitDefaultValues || \(storedProperty) != \(swiftDefaultValue)", varName: storedProperty)
+                ]
             }
         }
         assert(usesLocals == generateTraverseUsesLocals)
         let prefix = usesLocals ? "try { " : ""
         let suffix = usesLocals ? " }()" : ""
+        for (i, conditional) in conditionals.enumerated() {
+            if i == 0 {
+                p.print("\(prefix)if \(conditional.condition) {")
+            } else {
+                p.print("} else if \(conditional.condition) {")
+            }
+            p.printIndented("try visitor.\(visitMethod)(\(traitsArg)value: \(conditional.varName), fieldNumber: \(number))")
+            if i == conditionals.count - 1 {
+                p.print("}\(suffix)")
+            }
 
-        p.print("\(prefix)if \(conditional) {")
-        p.printIndented("try visitor.\(visitMethod)(\(traitsArg)value: \(varName), fieldNumber: \(number))")
-        p.print("}\(suffix)")
+        }
+//        p.print("\(prefix)if \(conditional) {")
+//        p.printIndented("try visitor.\(visitMethod)(\(traitsArg)value: \(varName), fieldNumber: \(number))")
+//        if shouldIncludeElseWithDefaultValueVisit {
+//            p.print("} else {")
+//            p.printIndented("try visitor.\(visitMethod)(\(traitsArg)value: \(swiftDefaultValue), fieldNumber: \(number))")
+//        }
+//        p.print("}\(suffix)")
     }
 }

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)