Provide better error messages for underlying shell commands

When shell commands failed a helpful error message wasn't always provided to the user. This change improves the specific XcodeInstaller.Error cases and their error messages. Not all Current.shell command failures are caught and turned into our own error type, so this also improves the fallback behaviour by printing output from Process.PMKError.execution, which is omitted by default.

Sources/XcodesKit/XcodeInstaller.swift

@@ -8,11 +8,42 @@ public final class XcodeInstaller {
     static let XcodeTeamIdentifier = "59GAB85EFG"
     static let XcodeCertificateAuthority = ["Software Signing", "Apple Code Signing Certification Authority", "Apple Root CA"]
 
-    public enum Error: Swift.Error, Equatable {
+    public enum Error: LocalizedError, Equatable {
         case failedToMoveXcodeToApplications
         case failedSecurityAssessment(xcode: InstalledXcode, output: String)
-        case codesignVerifyFailed
+        case codesignVerifyFailed(output: String)
+        case unexpectedCodeSigningIdentity(identifier: String, certificateAuthority: [String])
         case unsupportedFileFormat(extension: String)
+
+        public var errorDescription: String? {
+            switch self {
+            case .failedToMoveXcodeToApplications:
+                return "Failed to move Xcode to the /Applications directory."
+            case .failedSecurityAssessment(let xcode, let output):
+                return """
+                       Xcode \(xcode.version) failed its security assessment with the following output:
+                       \(output)
+                       It remains installed at \(xcode.path) if you wish to use it anyways.
+                       """
+            case .codesignVerifyFailed(let output):
+                return """
+                       The downloaded Xcode failed code signing verification with the following output:
+                       \(output)
+                       """
+            case .unexpectedCodeSigningIdentity(let identity, let certificateAuthority):
+                return """
+                       The downloaded Xcode doesn't have the expected code signing identity.
+                       Got:
+                         \(identity)
+                         \(certificateAuthority)
+                       Expected:
+                         \(XcodeInstaller.XcodeTeamIdentifier)
+                         \(XcodeInstaller.XcodeCertificateAuthority)
+                       """
+            case .unsupportedFileFormat(let fileExtension):
+                return "xcodes doesn't (yet) support installing Xcode from the \(fileExtension) file format."
+            }
+        }
     }
 
     public init() {}
@@ -51,7 +82,7 @@ public final class XcodeInstaller {
             let destinationURL = Path.root.join("Applications").join("Xcode-\(xcode.version.descriptionWithoutBuildMetadata).app").url
             switch archiveURL.pathExtension {
             case "xip":
-                return try unarchiveAndMoveXIP(at: archiveURL, to: destinationURL).map { xcodeURL in
+                return unarchiveAndMoveXIP(at: archiveURL, to: destinationURL).map { xcodeURL in
                     guard 
                         let path = Path(url: xcodeURL),
                         Current.files.fileExists(atPath: path.string),
@@ -90,7 +121,7 @@ public final class XcodeInstaller {
         }
     }
 
-    func unarchiveAndMoveXIP(at source: URL, to destination: URL) throws -> Promise<URL> {
+    func unarchiveAndMoveXIP(at source: URL, to destination: URL) -> Promise<URL> {
         return firstly { () -> Promise<ProcessOutput> in
             return Current.shell.unxip(source)
         }
@@ -122,7 +153,13 @@ public final class XcodeInstaller {
 
     func verifySigningCertificate(of url: URL) -> Promise<Void> {
         return Current.shell.codesignVerify(url)
-            .recover { _ -> Promise<ProcessOutput> in throw Error.codesignVerifyFailed }
+            .recover { error -> Promise<ProcessOutput> in
+                var output = ""
+                if case let Process.PMKError.execution(_, possibleOutput, possibleError) = error {
+                    output = [possibleOutput, possibleError].compactMap { $0 }.joined(separator: "\n")
+                }
+                throw Error.codesignVerifyFailed(output: output)
+            }
             .map { output -> CertificateInfo in
                 // codesign prints to stderr
                 return self.parseCertificateInfo(output.err)
@@ -131,7 +168,7 @@ public final class XcodeInstaller {
                 guard
                     cert.teamIdentifier == XcodeInstaller.XcodeTeamIdentifier,
                     cert.authority == XcodeInstaller.XcodeCertificateAuthority
-                else { throw Error.codesignVerifyFailed }
+                else { throw Error.unexpectedCodeSigningIdentity(identifier: cert.teamIdentifier, certificateAuthority: cert.authority) }
             }
     }
 

Sources/xcodes/main.swift

@@ -19,7 +19,7 @@ try? configuration.load()
 let xcodesUsername = "XCODES_USERNAME"
 let xcodesPassword = "XCODES_PASSWORD"
 
-enum XcodesError: Swift.Error, LocalizedError {
+enum XcodesError: LocalizedError {
     case missingUsernameOrPassword
     case missingSudoerPassword
     case invalidVersion(String)
@@ -271,11 +271,10 @@ let install = Command(usage: "install <version>", flags: [urlFlag]) { flags, arg
     }
     .catch { error in
         switch error {
-        case XcodeInstaller.Error.failedSecurityAssessment(let xcode, let output):
+        case Process.PMKError.execution(let process, let standardOutput, let standardError):
             print("""
-                  Xcode \(xcode.version) failed its security assessment with the following output:
-                  \(output)
-                  It remains installed at \(xcode.path) if you wish to use it anyways.
+                  Failed executing: `\(process)` (\(process.terminationStatus))
+                  \([standardOutput, standardError].compactMap { $0 }.joined(separator: "\n"))
                   """)
         default:
             print(error.legibleLocalizedDescription)

Tests/XcodesKitTests/XcodesKitTests.swift

@@ -89,15 +89,15 @@ final class XcodesKitTests: XCTestCase {
 
         let xcode = Xcode(version: Version("0.0.0")!, url: URL(fileURLWithPath: "/"), filename: "mock")
         installer.installArchivedXcode(xcode, at: URL(fileURLWithPath: "/Xcode-0.0.0.xip"), archiveTrashed: { _ in }, passwordInput: { Promise.value("") })
-            .catch { error in XCTAssertEqual(error as! XcodeInstaller.Error, XcodeInstaller.Error.codesignVerifyFailed) }
+            .catch { error in XCTAssertEqual(error as! XcodeInstaller.Error, XcodeInstaller.Error.codesignVerifyFailed(output: "")) }
     }
 
     func test_InstallArchivedXcode_VerifySigningCertificateDoesntMatch_Throws() {
         Current.shell.codesignVerify = { _ in return Promise.value((0, "", "")) }
 
         let xcode = Xcode(version: Version("0.0.0")!, url: URL(fileURLWithPath: "/"), filename: "mock")
         installer.installArchivedXcode(xcode, at: URL(fileURLWithPath: "/Xcode-0.0.0.xip"), archiveTrashed: { _ in }, passwordInput: { Promise.value("") })
-            .catch { error in XCTAssertEqual(error as! XcodeInstaller.Error, XcodeInstaller.Error.codesignVerifyFailed) }
+            .catch { error in XCTAssertEqual(error as! XcodeInstaller.Error, XcodeInstaller.Error.unexpectedCodeSigningIdentity(identifier: "", certificateAuthority: [])) }
     }
 
     func test_InstallArchivedXcode_TrashesXIPWhenFinished() {