[plugin] Use Amazon Linux 2023 as default base image for Swift 6.3+

Plugins/AWSLambdaPackager/Plugin.swift

@@ -339,7 +339,8 @@ struct AWSLambdaPackager: CommandPlugin {
                                           (default is latest)
                                           This parameter cannot be used when --base-docker-image  is specified.
             --base-docker-image <name>    The name of the base docker image to use for the build.
-                                          (default : swift-<version>:amazonlinux2)
+                                          (default: swift:<version>-amazonlinux2023 for Swift >= 6.3,
+                                           swift:<version>-amazonlinux2 for earlier versions)
                                           This parameter cannot be used when --swift-version is specified.
             --disable-docker-image-update Do not attempt to update the docker image
             --container-cli <name>        The container CLI to use (docker or container)
@@ -484,8 +485,38 @@ private struct Configuration: CustomStringConvertible {
         }
 
         let swiftVersion = swiftVersionArgument.first ?? .none  // undefined version will yield the latest docker image
+
+        // Swift 6.3+ uses amazonlinux2023, earlier versions use amazonlinux2
+        let amazonLinuxVersion: String
+        if let version = swiftVersion {
+            let components = version.split(separator: ".").compactMap { Int($0) }
+            if components.count >= 2 {
+                let major = components[0]
+                let minor = components[1]
+                amazonLinuxVersion = (major > 6 || (major == 6 && minor >= 3)) ? "amazonlinux2023" : "amazonlinux2"
+            } else if let major = components.first {
+                // treat "6" (no minor) as possibly 6.0, hence amazonlinux2
+                amazonLinuxVersion = major > 6 ? "amazonlinux2023" : "amazonlinux2"
+            } else {
+                amazonLinuxVersion = "amazonlinux2023"
+            }
+        } else {
+            // no version specified means "latest", which is >= 6.3
+            amazonLinuxVersion = "amazonlinux2023"
+        }
+
         self.baseDockerImage =
-            baseDockerImageArgument.first ?? "swift:\(swiftVersion.map { $0 + "-" } ?? "")amazonlinux2"
+            baseDockerImageArgument.first ?? "swift:\(swiftVersion.map { $0 + "-" } ?? "")\(amazonLinuxVersion)"
+
+        if verboseArgument {
+            if baseDockerImageArgument.isEmpty {
+                print(
+                    "swift version: \(swiftVersion ?? "latest"), amazon linux version: \(amazonLinuxVersion), base docker image: \(self.baseDockerImage)"
+                )
+            } else {
+                print("base docker image (user provided): \(self.baseDockerImage)")
+            }
+        }
 
         self.disableDockerImageUpdate = disableDockerImageUpdateArgument
         self.containerCLI = try ContainerCLI.parse(