Improve error message when using xcodes select without Xcode installed

Sources/XcodesKit/XcodeSelect.swift

@@ -24,6 +24,13 @@ public func selectXcode(shouldPrint: Bool, pathOrVersion: String, directory: Pat
 
         let versionToSelect = pathOrVersion.isEmpty ? Version.fromXcodeVersionFile() : Version(xcodeVersion: pathOrVersion)
         let installedXcodes = Current.files.installedXcodes(directory)
+
+        if installedXcodes.isEmpty {
+            Current.logging.log("No Xcode version installed. Please run 'xcodes install' and try again.".red)
+            Current.shell.exit(1)
+            return Promise(error: XcodeSelectError.noInstalledXcodes)
+        }
+
         if let version = versionToSelect,
            let installedXcode = installedXcodes.first(withVersion: version) {
             let selectedInstalledXcodeVersion = installedXcodes.first { output.out.hasPrefix($0.path.string) }.map { $0.version }
@@ -153,13 +160,16 @@ public func selectXcodeAtPath(_ pathString: String) -> Promise<ProcessOutput> {
 public enum XcodeSelectError: LocalizedError {
     case invalidPath(String)
     case invalidIndex(min: Int, max: Int, given: String?)
+    case noInstalledXcodes
 
     public var errorDescription: String? {
         switch self {
         case .invalidPath(let pathString):
             return "Not a valid Xcode path: \(pathString)"
         case .invalidIndex(let min, let max, let given):
             return "Not a valid number. Expecting a whole number between \(min)-\(max), but given \(given ?? "nothing")."
+        case .noInstalledXcodes:
+            return "No Xcode version installed. Please run 'xcodes install' and try again."
         }
     }
 }

Tests/XcodesKitTests/XcodesKitTests.swift

@@ -954,6 +954,22 @@ final class XcodesKitTests: XCTestCase {
         """)
     }
 
+    func test_SelectXcode_WithNoInstalledVersions_LogsError() {
+        var log = ""
+        Current.files.installedXcodes = { _ in [] } // Simulate no installed Xcodes
+        XcodesKit.Current.logging.log = { log = $0 }
+
+        let expectation = XCTestExpectation(description: "Select Xcode")
+        selectXcode(shouldPrint: false, pathOrVersion: "", directory: Path.root.join("Applications"))
+            .ensure {
+                XCTAssertEqual(log, "No Xcode version installed. Please run 'xcodes install' and try again.")
+                expectation.fulfill()
+            }
+            .cauterize()
+
+        wait(for: [expectation], timeout: 0.5)
+    }
+
     func test_SelectPath() {
         var log = ""
         XcodesKit.Current.logging.log = { log.append($0 + "\n") }