Stop trapping on validation errors

With backtrace support built into command-line Swift, calling `fatalError`
for configuration/validation errors isn't very effective, since the error
messages get hidden by the backtrace. This switches to simply printing
the validation message to stderr and exiting with a failing error code,
which possibly should have always been the behavior.

Author: natecook1000

Sources/ArgumentParser/Parsable Properties/Argument.swift

@@ -82,7 +82,7 @@ public struct Argument<Value>:
       case .value(let v):
         return v
       case .definition:
-        fatalError(directlyInitializedError)
+        configurationFailure(directlyInitializedError)
       }
     }
     set {

Sources/ArgumentParser/Parsable Properties/Flag.swift

@@ -107,7 +107,7 @@ public struct Flag<Value>: Decodable, ParsedWrapper {
       case .value(let v):
         return v
       case .definition:
-        fatalError(directlyInitializedError)
+        configurationFailure(directlyInitializedError)
       }
     }
     set {

Sources/ArgumentParser/Parsable Properties/Option.swift

@@ -87,7 +87,7 @@ public struct Option<Value>: Decodable, ParsedWrapper {
       case .value(let v):
         return v
       case .definition:
-        fatalError(directlyInitializedError)
+        configurationFailure(directlyInitializedError)
       }
     }
     set {

Sources/ArgumentParser/Parsable Properties/OptionGroup.swift

@@ -101,7 +101,7 @@ public struct OptionGroup<Value: ParsableArguments>: Decodable, ParsedWrapper {
       case .value(let v):
         return v
       case .definition:
-        fatalError(directlyInitializedError)
+        configurationFailure(directlyInitializedError)
       }
     }
     set {

Sources/ArgumentParser/Parsable Types/ParsableArguments.swift

@@ -290,7 +290,7 @@ extension ArgumentSet {
     do {
       try type._validate(parent: parent)
     } catch {
-      assertionFailure("\(error)")
+      configurationFailure("\(error)")
     }
     #endif
 
@@ -321,11 +321,23 @@ extension ArgumentSet {
   }
 }
 
+/// Prints the given message to standard error and exits with a failure code.
+///
+/// - Parameter message: The message to print to standard error. `message`
+///   should be pre-wrapped, if desired.
+func configurationFailure(_ message: String) -> Never {
+  var errorOut = Platform.standardError
+  print("\n")
+  print(String(repeating: "-", count: 70))
+  print(message, to: &errorOut)
+  print(String(repeating: "-", count: 70))
+  print("\n")
+  Platform.exit(Platform.exitCodeFailure)
+}
+
 /// The fatal error message to display when someone accesses a
 /// `ParsableArguments` type after initializing it directly.
 internal let directlyInitializedError = """
-
-  --------------------------------------------------------------------
   Can't read a value from a parsable argument definition.
 
   This error indicates that a property declared with an `@Argument`,
@@ -335,6 +347,4 @@ internal let directlyInitializedError = """
   To get a valid value, either call one of the static parsing methods
   (`parse`, `parseAsRoot`, or `main`) or define an initializer that
   initializes _every_ property of your parsable type.
-  --------------------------------------------------------------------
-
   """

Sources/ArgumentParser/Parsable Types/ParsableCommand.swift

@@ -215,17 +215,13 @@ extension ParsableCommand {
       guard sub.configuration.subcommands.isEmpty else { continue }
       guard sub is AsyncParsableCommand.Type else { continue }
 
-      fatalError(
+      configurationFailure(
         """
-
-        --------------------------------------------------------------------
         Asynchronous subcommand of a synchronous root.
 
         The asynchronous command `\(sub)` is declared as a subcommand of the synchronous root command `\(root)`.
 
         With this configuration, your asynchronous `run()` method will not be called. To fix this issue, change `\(root)`'s `ParsableCommand` conformance to `AsyncParsableCommand`.
-        --------------------------------------------------------------------
-
         """.wrapped(to: 70))
     }
   }
@@ -256,25 +252,19 @@ extension ParsableCommand {
 func failAsyncHierarchy(
   rootCommand: ParsableCommand.Type, subCommand: ParsableCommand.Type
 ) -> Never {
-  fatalError(
+  configurationFailure(
     """
-
-    --------------------------------------------------------------------
     Asynchronous subcommand of a synchronous root.
 
     The asynchronous command `\(subCommand)` is declared as a subcommand of the synchronous root command `\(rootCommand)`.
 
     With this configuration, your asynchronous `run()` method will not be called. To fix this issue, change `\(rootCommand)`'s `ParsableCommand` conformance to `AsyncParsableCommand`.
-    --------------------------------------------------------------------
-
     """.wrapped(to: 70))
 }
 
 func failAsyncPlatform(rootCommand: ParsableCommand.Type) -> Never {
-  fatalError(
+  configurationFailure(
     """
-
-    --------------------------------------------------------------------
     Asynchronous root command needs availability annotation.
 
     The asynchronous root command `\(rootCommand)` needs an availability annotation in order to be executed asynchronously. To fix this issue, add the following availability attribute to your `\(rootCommand)` declaration or set the minimum platform in your "Package.swift" file.
@@ -283,7 +273,5 @@ func failAsyncPlatform(rootCommand: ParsableCommand.Type) -> Never {
       + """
 
       @available(macOS 10.15, macCatalyst 13, iOS 13, tvOS 13, watchOS 6, *)
-      --------------------------------------------------------------------
-
       """)
 }

Sources/ArgumentParser/Parsing/CommandParser.swift

@@ -48,15 +48,18 @@ struct CommandParser {
     } catch Tree<ParsableCommand.Type>.InitializationError.recursiveSubcommand(
       let command)
     {
-      fatalError(
-        "The ParsableCommand \"\(command)\" can't have itself as its own subcommand."
-      )
-    } catch Tree<ParsableCommand.Type>.InitializationError.aliasMatchingCommand(
-      let command)
+      configurationFailure(
+        """
+        The command \"\(command)\" can't have itself as its own subcommand.
+        """.wrapped(to: 70))
+    } catch Tree<ParsableCommand.Type>
+      .InitializationError.aliasMatchingCommand(let command)
     {
-      fatalError(
-        "The ParsableCommand \"\(command)\" can't have an alias with the same name as the command itself."
-      )
+      configurationFailure(
+        """
+        The command \"\(command)\" can't have an alias with the same name \
+        as the command itself.
+        """.wrapped(to: 70))
     } catch {
       fatalError("Unexpected error: \(error).")
     }

Sources/ArgumentParser/Validators/ParsableArgumentsValidation.swift

@@ -54,13 +54,9 @@ struct ParsableArgumentsValidationError: Error, CustomStringConvertible {
           .hangingIndentingEachLine(by: 2)
       }
     return """
-
-      --------------------------------------------------------------------
       Validation failed for `\(parsableArgumentsType)`:
 
       \(errorDescriptions.joined(separator: "\n"))
-      --------------------------------------------------------------------
-
       """
   }
 }