[swift-syntax-dev-utils] Throw an error in if an executable could not be found

Author: ahoppen

SwiftSyntaxDevUtils/Sources/swift-syntax-dev-utils/commands/VerifySourceCode.swift

@@ -36,16 +36,12 @@ struct VerifySourceCode: ParsableCommand, SourceCodeGeneratorCommand {
 
     logSection("Verifing code generated files")
 
-    guard let diffExec = Paths.diffExec else {
-      throw ScriptExectutionError(message: "Didn't find a diff execution path")
-    }
-
     for module in modules {
       let selfGeneratedDir = tempDir.appendingPathComponent(module).appendingPathComponent("generated")
       let userGeneratedDir = Paths.sourcesDir.appendingPathComponent(module).appendingPathComponent("generated")
 
       let process = ProcessRunner(
-        executableURL: diffExec,
+        executableURL: try Paths.diffExec,
         arguments: [
           "--recursive",
           "--exclude",

SwiftSyntaxDevUtils/Sources/swift-syntax-dev-utils/common/BuildCommand.swift

@@ -86,16 +86,8 @@ extension BuildCommand {
   @discardableResult
   func invokeXcodeBuild(projectPath: URL, scheme: String) throws -> ProcessResult {
     return try withTemporaryDirectory { tempDir in
-      guard let xcodebuildExec = Paths.xcodebuildExec else {
-        throw ScriptExectutionError(
-          message: """
-            Error: Could not find xcodebuild.
-            Looking at '\(Paths.xcodebuildExec?.path ?? "N/A")'.
-            """
-        )
-      }
       let processRunner = ProcessRunner(
-        executableURL: xcodebuildExec,
+        executableURL: try Paths.xcodebuildExec,
         arguments: [
           "-project", projectPath.path,
           "-scheme", scheme,

SwiftSyntaxDevUtils/Sources/swift-syntax-dev-utils/common/Paths.swift

@@ -61,16 +61,40 @@ enum Paths {
       .appendingPathComponent("lit.py")
   }
 
-  static var python3Exec: URL? {
-    return lookupExecutable(for: "python3")
+  static var python3Exec: URL {
+    get throws {
+      return try lookupExecutable(for: "python3")
+    }
   }
 
-  static var diffExec: URL? {
-    return lookupExecutable(for: "diff")
+  static var diffExec: URL {
+    get throws {
+      return try lookupExecutable(for: "diff")
+    }
   }
 
-  static var xcodebuildExec: URL? {
-    return lookupExecutable(for: "xcodebuild")
+  static var gitExec: URL {
+    get throws {
+      try lookupExecutable(for: "git")
+    }
+  }
+
+  static var swiftExec: URL {
+    get throws {
+      try lookupExecutable(for: "swift")
+    }
+  }
+
+  /// The directory in which swift-format should be built.
+  static var swiftFormatBuildDir: URL {
+    packageDir
+      .appendingPathComponent(".swift-format-build")
+  }
+
+  static var xcodebuildExec: URL {
+    get throws {
+      return try lookupExecutable(for: "xcodebuild")
+    }
   }
 
   private static var envSearchPaths: [URL] {
@@ -98,13 +122,28 @@ enum Paths {
     return ProcessInfo.processInfo.environment[pathArg]
   }
 
-  private static func lookupExecutable(for filename: String) -> URL? {
-    return envSearchPaths.map { $0.appendingPathComponent(filename) }
+  enum ExecutableLookupError: Error, CustomStringConvertible {
+    case notFound(executableName: String)
+
+    var description: String {
+      switch self {
+      case .notFound(executableName: let executableName):
+        return "Executable \(executableName) not found in PATH"
+      }
+    }
+  }
+
+  private static func lookupExecutable(for filename: String) throws -> URL {
+    let executable = envSearchPaths.map { $0.appendingPathComponent(filename) }
       .first(where: { $0.isExecutableFile })
+    guard let executable else {
+      throw ExecutableLookupError.notFound(executableName: filename)
+    }
+    return executable
   }
 }
 
-fileprivate extension URL {
+extension URL {
   var isExecutableFile: Bool {
     return (self.isFile(path) || self.isSymlink(path)) && FileManager.default.isExecutableFile(atPath: path)
   }