Factor out the common decodeJSON from all the wrappers

While here, simplify the encodedJSONString implementations as well.
In particular, since these all return Swift String instances, we
should just use that directly instead of relying on lower-level JSON
encoding tools and then converting to String.

Author: tbkka

Sources/SwiftProtobuf/Google_Protobuf_Wrappers+Extensions.swift

@@ -32,6 +32,14 @@ protocol ProtobufWrapper {
   init(_ value: WrappedType.BaseType)
 }
 
+extension ProtobufWrapper {
+  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
+    var v: WrappedType.BaseType?
+    try WrappedType.decodeSingular(value: &v, from: &decoder)
+    value = v ?? WrappedType.proto3DefaultValue
+  }
+}
+
 extension Google_Protobuf_DoubleValue:
   ProtobufWrapper, ExpressibleByFloatLiteral, _CustomJSONCodable {
 
@@ -48,15 +56,16 @@ extension Google_Protobuf_DoubleValue:
   }
 
   func encodedJSONString(options: JSONEncodingOptions) throws -> String {
-    var encoder = JSONEncoder()
-    encoder.putDoubleValue(value: value)
-    return encoder.stringResult
-  }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
+    if value.isFinite {
+      // Swift 4.2 and later guarantees that this is accurate
+      // enough to parse back to the exact value on the other end.
+      return value.description
+    } else {
+      // Protobuf-specific handling of NaN and infinities
+      var encoder = JSONEncoder()
+      encoder.putDoubleValue(value: value)
+      return encoder.stringResult
+    }
   }
 }
 
@@ -76,15 +85,16 @@ extension Google_Protobuf_FloatValue:
   }
 
   func encodedJSONString(options: JSONEncodingOptions) throws -> String {
-    var encoder = JSONEncoder()
-    encoder.putFloatValue(value: value)
-    return encoder.stringResult
-  }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
+    if value.isFinite {
+      // Swift 4.2 and later guarantees that this is accurate
+      // enough to parse back to the exact value on the other end.
+      return value.description
+    } else {
+      // Protobuf-specific handling of NaN and infinities
+      var encoder = JSONEncoder()
+      encoder.putFloatValue(value: value)
+      return encoder.stringResult
+    }
   }
 }
 
@@ -104,15 +114,7 @@ extension Google_Protobuf_Int64Value:
   }
 
   func encodedJSONString(options: JSONEncodingOptions) throws -> String {
-    var encoder = JSONEncoder()
-    encoder.putInt64(value: value)
-    return encoder.stringResult
-  }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
+    return "\"" + String(value) + "\""
   }
 }
 
@@ -132,15 +134,7 @@ extension Google_Protobuf_UInt64Value:
   }
 
   func encodedJSONString(options: JSONEncodingOptions) throws -> String {
-    var encoder = JSONEncoder()
-    encoder.putUInt64(value: value)
-    return encoder.stringResult
-  }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
+    return "\"" + String(value) + "\""
   }
 }
 
@@ -162,12 +156,6 @@ extension Google_Protobuf_Int32Value:
   func encodedJSONString(options: JSONEncodingOptions) throws -> String {
     return String(value)
   }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
-  }
 }
 
 extension Google_Protobuf_UInt32Value:
@@ -188,12 +176,6 @@ extension Google_Protobuf_UInt32Value:
   func encodedJSONString(options: JSONEncodingOptions) throws -> String {
     return String(value)
   }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
-  }
 }
 
 extension Google_Protobuf_BoolValue:
@@ -214,12 +196,6 @@ extension Google_Protobuf_BoolValue:
   func encodedJSONString(options: JSONEncodingOptions) throws -> String {
     return value ? "true" : "false"
   }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
-  }
 }
 
 extension Google_Protobuf_StringValue:
@@ -252,12 +228,6 @@ extension Google_Protobuf_StringValue:
     encoder.putStringValue(value: value)
     return encoder.stringResult
   }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
-  }
 }
 
 extension Google_Protobuf_BytesValue: ProtobufWrapper, _CustomJSONCodable {
@@ -274,10 +244,4 @@ extension Google_Protobuf_BytesValue: ProtobufWrapper, _CustomJSONCodable {
     encoder.putBytesValue(value: value)
     return encoder.stringResult
   }
-
-  mutating func decodeJSON(from decoder: inout JSONDecoder) throws {
-    var v: WrappedType.BaseType?
-    try WrappedType.decodeSingular(value: &v, from: &decoder)
-    value = v ?? WrappedType.proto3DefaultValue
-  }
 }