remove requirment on macOS 10.13 (#156)

motivation: simplify downstream libraries

changes: precondition out debugging uses cases on macOS < 10.13

Package.swift

@@ -4,9 +4,6 @@ import PackageDescription
 
 let package = Package(
     name: "swift-aws-lambda-runtime",
-    platforms: [
-        .macOS(.v10_13),
-    ],
     products: [
         // this library exports `AWSLambdaRuntimeCore` and adds Foundation convenience methods
         .library(name: "AWSLambdaRuntime", targets: ["AWSLambdaRuntime"]),

Sources/AWSLambdaEvents/Utils/DateWrappers.swift

@@ -28,13 +28,27 @@ public struct ISO8601Coding: Decodable {
     public init(from decoder: Decoder) throws {
         let container = try decoder.singleValueContainer()
         let dateString = try container.decode(String.self)
-        guard let date = Self.dateFormatter.date(from: dateString) else {
+        guard let date = Self.decodeDate(from: dateString) else {
             throw DecodingError.dataCorruptedError(in: container, debugDescription:
-                "Expected date to be in iso8601 date format, but `\(dateString)` does not forfill format")
+                "Expected date to be in ISO8601 date format, but `\(dateString)` is not in the correct format")
         }
         self.wrappedValue = date
     }
 
+    private static func decodeDate(from string: String) -> Date? {
+        #if os(Linux)
+        return Self.dateFormatter.date(from: string)
+        #elseif os(macOS)
+        if #available(macOS 10.12, *) {
+            return Self.dateFormatter.date(from: string)
+        } else {
+            // unlikely *debugging* use case of swift 5.2+ on older macOS
+            preconditionFailure("Unsporrted macOS version")
+        }
+        #endif
+    }
+
+    @available(macOS 10.12, *)
     private static let dateFormatter = ISO8601DateFormatter()
 }
 
@@ -49,14 +63,30 @@ public struct ISO8601WithFractionalSecondsCoding: Decodable {
     public init(from decoder: Decoder) throws {
         let container = try decoder.singleValueContainer()
         let dateString = try container.decode(String.self)
-        guard let date = Self.dateFormatter.date(from: dateString) else {
+        guard let date = Self.decodeDate(from: dateString) else {
             throw DecodingError.dataCorruptedError(in: container, debugDescription:
-                "Expected date to be in iso8601 date format with fractional seconds, but `\(dateString)` does not forfill format")
+                "Expected date to be in ISO8601 date format with fractional seconds, but `\(dateString)` is not in the correct format")
         }
         self.wrappedValue = date
     }
 
+    private static func decodeDate(from string: String) -> Date? {
+        #if os(Linux)
+        return Self.dateFormatter.date(from: string)
+        #elseif os(macOS)
+        if #available(macOS 10.13, *) {
+            return self.dateFormatter.date(from: string)
+        } else {
+            // unlikely *debugging* use case of swift 5.2+ on older macOS
+            preconditionFailure("Unsporrted macOS version")
+        }
+        #endif
+    }
+
+    @available(macOS 10.13, *)
     private static let dateFormatter: ISO8601DateFormatter = Self.createDateFormatter()
+
+    @available(macOS 10.13, *)
     private static func createDateFormatter() -> ISO8601DateFormatter {
         let formatter = ISO8601DateFormatter()
         formatter.formatOptions = [
@@ -88,7 +118,7 @@ public struct RFC5322DateTimeCoding: Decodable {
         }
         guard let date = Self.dateFormatter.date(from: string) else {
             throw DecodingError.dataCorruptedError(in: container, debugDescription:
-                "Expected date to be in RFC5322 date-time format with fractional seconds, but `\(string)` does not forfill format")
+                "Expected date to be in RFC5322 date-time format with fractional seconds, but `\(string)` is not in the correct format")
         }
         self.wrappedValue = date
     }

Tests/AWSLambdaEventsTests/Utils/DateWrapperTests.swift

@@ -43,7 +43,7 @@ class DateWrapperTests: XCTestCase {
             }
 
             XCTAssertEqual(context.codingPath.compactMap { $0.stringValue }, ["date"])
-            XCTAssertEqual(context.debugDescription, "Expected date to be in iso8601 date format, but `\(date)` does not forfill format")
+            XCTAssertEqual(context.debugDescription, "Expected date to be in ISO8601 date format, but `\(date)` is not in the correct format")
             XCTAssertNil(context.underlyingError)
         }
     }
@@ -75,7 +75,7 @@ class DateWrapperTests: XCTestCase {
             }
 
             XCTAssertEqual(context.codingPath.compactMap { $0.stringValue }, ["date"])
-            XCTAssertEqual(context.debugDescription, "Expected date to be in iso8601 date format with fractional seconds, but `\(date)` does not forfill format")
+            XCTAssertEqual(context.debugDescription, "Expected date to be in ISO8601 date format with fractional seconds, but `\(date)` is not in the correct format")
             XCTAssertNil(context.underlyingError)
         }
     }
@@ -133,7 +133,7 @@ class DateWrapperTests: XCTestCase {
             }
 
             XCTAssertEqual(context.codingPath.compactMap { $0.stringValue }, ["date"])
-            XCTAssertEqual(context.debugDescription, "Expected date to be in RFC5322 date-time format with fractional seconds, but `\(date)` does not forfill format")
+            XCTAssertEqual(context.debugDescription, "Expected date to be in RFC5322 date-time format with fractional seconds, but `\(date)` is not in the correct format")
             XCTAssertNil(context.underlyingError)
         }
     }