Follow the 'required' argument for nested validations

Sources/Vapor/Validation/Validation.swift

@@ -29,9 +29,17 @@ public struct Validation {
         self.init { container in
             let result: ValidatorResult
             do {
-                let nested = try container.nestedContainer(keyedBy: ValidationKey.self, forKey: key)
-                let results = validations.validate(nested)
-                result = ValidatorResults.Nested(results: results.results)
+                if container.contains(key), !required, try container.decodeNil(forKey: key) {
+                    result = ValidatorResults.Skipped()
+                } else if container.contains(key) {
+                    let nested = try container.nestedContainer(keyedBy: ValidationKey.self, forKey: key)
+                    let results = validations.validate(nested)
+                    result = ValidatorResults.Nested(results: results.results)
+                } else if required {
+                    result = ValidatorResults.Missing()
+                } else {
+                    result = ValidatorResults.Skipped()
+                }
             } catch {
                 result = ValidatorResults.Codable(error: error)
             }

Tests/VaporTests/ValidationTests.swift

@@ -16,6 +16,7 @@ class ValidationTests: XCTestCase {
                 "name": "Zizek",
                 "age": 3
             },
+            "favoritePet": null,
             "isAdmin": true
         }
         """
@@ -80,6 +81,53 @@ class ValidationTests: XCTestCase {
             XCTAssertEqual("\(error)",
                            "isAdmin is not a(n) Bool")
         }
+
+        let validOptionalFavoritePet = """
+        {
+            "name": "Tanner",
+            "age": 24,
+            "gender": "male",
+            "email": "me@tanner.xyz",
+            "luckyNumber": 5,
+            "profilePictureURL": "https://foo.jpg",
+            "preferredColors": ["blue"],
+            "pet": {
+                "name": "Zizek",
+                "age": 3
+            },
+            "favoritePet": {
+                "name": "Zizek",
+                "age": 3
+            },
+            "isAdmin": true
+        }
+        """
+        XCTAssertNoThrow(try User.validate(json: validOptionalFavoritePet))
+
+        let invalidOptionalFavoritePet = """
+        {
+            "name": "Tanner",
+            "age": 24,
+            "gender": "male",
+            "email": "me@tanner.xyz",
+            "luckyNumber": 5,
+            "profilePictureURL": "https://foo.jpg",
+            "preferredColors": ["blue"],
+            "pet": {
+                "name": "Zizek",
+                "age": 3
+            },
+            "favoritePet": {
+                "name": "Zi!zek",
+                "age": 3
+            },
+            "isAdmin": true
+        }
+        """
+        XCTAssertThrowsError(try User.validate(json: invalidOptionalFavoritePet)) { error in
+            XCTAssertEqual("\(error)",
+                           "favoritePet name contains '!' (allowed: whitespace, A-Z, a-z, 0-9)")
+        }
     }
 
     func testCatchError() throws {
@@ -310,6 +358,7 @@ private final class User: Validatable, Codable {
     var gender: Gender
     var email: String?
     var pet: Pet
+    var favoritePet: Pet?
     var luckyNumber: Int?
     var profilePictureURL: String?
     var preferredColors: [String]
@@ -358,6 +407,12 @@ private final class User: Validatable, Codable {
                     is: .count(5...) && .characterSet(.alphanumerics + .whitespaces))
             pet.add("age", as: Int.self, is: .range(3...))
         }
+        // optional favorite pet validations
+        v.add("favoritePet", required: false) { pet in
+            pet.add("name", as: String.self,
+                    is: .count(5...) && .characterSet(.alphanumerics + .whitespaces))
+            pet.add("age", as: Int.self, is: .range(3...))
+        }
         v.add("isAdmin", as: Bool.self)
     }
 }