Improve error messages

Bridgecraft/GenerateCommand.swift

@@ -11,13 +11,15 @@ import SourceKittenFramework
 import XcodeEdit
 
 extension GenerateCommand {
-    static func execute(assumeNonnull: Bool,
+    static func execute(verbose: Bool,
+                        assumeNonnull: Bool,
                         sdkOverride: [String],
                         destOverride: [String],
                         outputPath: [String],
                         origProjectPath: String,
                         targetName: String) {
-        let cmd = GenerateCommand(assumeNonnull: assumeNonnull,
+        let cmd = GenerateCommand(verbose: verbose,
+                                  assumeNonnull: assumeNonnull,
                                   sdkOverride: sdkOverride,
                                   destOverride: destOverride,
                                   outputPath: outputPath,
@@ -34,17 +36,20 @@ struct GenerateCommand {
     private let preprocessedURL: URL
     private let outputFileURL: URL?
 
+    private let verbose: Bool
     private let assumeNonnull: Bool
     private let sdkOverride: String?
     private let destOverride: String?
     private let targetName: String
 
-    init(assumeNonnull: Bool,
+    init(verbose: Bool,
+         assumeNonnull: Bool,
          sdkOverride: [String],
          destOverride: [String],
          outputPath: [String],
          origProjectPath: String,
          targetName: String) {
+        self.verbose = verbose
         self.assumeNonnull = assumeNonnull
         self.sdkOverride = sdkOverride.first
         self.destOverride = destOverride.first
@@ -130,7 +135,7 @@ struct GenerateCommand {
                 "-showBuildSettings",
                 "-project", tempProjectURL.path,
                 "-target", targetName
-            ])
+            ], verbose: verbose)
         }
         catch {
             printError("cannot query build settings for \(tempProjectURL.path): \(error)")
@@ -245,7 +250,7 @@ struct GenerateCommand {
 
         let output: String
         do {
-            output = try shell("/usr/bin/xcodebuild", args: args)
+            output = try shell("/usr/bin/xcodebuild", args: args, verbose: verbose)
         }
         catch {
             printError("cannot dry-run build for \(tempProjectURL.path)")
@@ -298,7 +303,7 @@ struct GenerateCommand {
                 "-x", "objective-c", "-C", "-fmodules", "-fimplicit-modules",
                 "-E", bridgingSourceURL.path,
                 "-o", preprocessedURL.path
-                ] + compilerFlags)
+                ] + compilerFlags, verbose: verbose)
         }
         catch {
             printError("failed to preprocess file at \(bridgingSourceURL.path): \(error)")

Bridgecraft/Utils.swift

@@ -13,27 +13,48 @@ enum BridgecraftError: Error {
 }
 
 @discardableResult
-func shell(_ command: String, args: [String]) throws -> String {
+func shell(_ command: String, args: [String], verbose: Bool = false) throws -> String {
+
     let ps = Process()
     ps.launchPath = command
     ps.arguments = args
 
-    let pipe = Pipe()
-    ps.standardOutput = pipe
+    let outputPipe = Pipe()
+    let errorPipe = Pipe()
+    ps.standardOutput = outputPipe
+    ps.standardError = errorPipe
 
     ps.launch()
 
-    var buffer = Data()
+    var outputPipeResult = Data()
+    var errorPipeResult = Data()
+
     while ps.isRunning {
-        buffer.append(pipe.fileHandleForReading.readDataToEndOfFile())
+        outputPipeResult.append(outputPipe.fileHandleForReading.readDataToEndOfFile())
+        errorPipeResult.append(errorPipe.fileHandleForReading.readDataToEndOfFile())
+    }
+
+    guard
+        let output = String(data: outputPipeResult, encoding: String.Encoding.utf8),
+        let error = String(data: errorPipeResult, encoding: String.Encoding.utf8)
+        else {
+            printError("\(command) \(args.joined(separator: " "))")
+            printError("Error parsing the output of the previous command.")
+            throw BridgecraftError.unknown
     }
 
     guard ps.terminationStatus == 0 else {
+        printError("\(command) \(args.joined(separator: " "))")
+        printError("Terminated with the status \(ps.terminationStatus).")
+        printError(output)
+        printError(error)
         throw BridgecraftError.unknown
     }
 
-    guard let output = String(data: buffer, encoding: String.Encoding.utf8) else {
-        throw BridgecraftError.unknown
+    if verbose {
+        print("\(command) \(args.joined(separator: " "))")
+        print(output)
+        printError(error)
     }
 
     return output

Bridgecraft/main.swift

@@ -12,6 +12,7 @@ import Foundation
 let version = "0.3.0"
 
 let generate = command(
+    Flag("verbose", description: "output's all terminal commands and their results"),
     Flag("assume-nonnull", description: "assume that all headers have been audited for nullability"),
     Options<String>("sdk", default: [], count: 1, description: "override the SDK used for the build (see xcodebuild -sdk)"),
     Options<String>("destination", default: [], count: 1, description: "override the destination device used for the build (see xcodebuild -destination)"),