conditionally use swift 5.3 features

Author: literalpie

Sources/swift-doc/Subcommands/Generate.swift

@@ -133,11 +133,24 @@ extension SwiftDoc {
 }
 
 func fetchRemoteCSS() throws -> Data {
+  #if swift(>=5.3)
   let cssURL = Bundle.module.url(forResource: "all.min", withExtension: "css")!
   return try Data(contentsOf: cssURL)
+  #else
+  let url = URL(string: "https://raw.githubusercontent.com/SwiftDocOrg/swift-doc/master/Resources/all.min.css")!
+  return try Data(contentsOf: url)
+  #endif
 }
 
 func fetchRemoteJS() throws -> Data {
-    let jsURL = Bundle.module.url(forResource: "all", withExtension: "js")!
+  #if swift(>=5.3)
+  let jsURL = Bundle.module.url(forResource: "all", withExtension: "js")!
   return try Data(contentsOf: jsURL)
+  #else
+  return Data("""
+  window.addEventListener("load", ()=>{
+    document.querySelector(".theme-select-container").hidden = true;
+  })
+  """.utf8)
+  #endif
 }