fix(swift): preserve fractional date seconds

packages/quicktype-core/src/language/Swift/SwiftRenderer.ts

@@ -808,9 +808,15 @@ export class SwiftRenderer extends ConvenienceRenderer {
                 this.emitBlock(
                     "if #available(iOS 10.0, OSX 10.12, tvOS 10.0, watchOS 3.0, *)",
                     () => {
-                        this.emitLine(
-                            "encoder.dateEncodingStrategy = .iso8601",
-                        );
+                        this.emitMultiline(`encoder.dateEncodingStrategy = .custom { date, encoder in
+    let formatter = ISO8601DateFormatter()
+    if #available(iOS 11.0, OSX 10.13, tvOS 11.0, watchOS 4.0, *),
+        date.timeIntervalSince1970.truncatingRemainder(dividingBy: 1) != 0 {
+        formatter.formatOptions.insert(.withFractionalSeconds)
+    }
+    var container = encoder.singleValueContainer()
+    try container.encode(formatter.string(from: date))
+}`);
                     },
                 );
             } else {

test/inputs/schema/date-time.10.json

@@ -0,0 +1,7 @@
+{
+  "date": "2024-02-29",
+  "time": "23:59:59.999Z",
+  "date-time": "2000-02-29T00:30:00.123+02:00",
+  "union-array": ["2024-02-29", "00:00:00Z"],
+  "complex-union-array": ["2024-02-29T23:59:59.999Z", "bar", -1]
+}

test/languages.ts

@@ -879,6 +879,7 @@ export const SwiftLanguage: Language = {
         { "coding-keys-protocol": "CaseIterable" },
         ["simple-object.json", { "coding-keys-protocol": "CaseIterable" }],
         { "support-linux": "false" },
+        ["date-time.schema", { "support-linux": "false" }],
         { "coding-keys": "false" },
         { "struct-or-class": "class" },
         { sendable: "true" },