Fix showing help message when “-h” is given as an input for an array type argument (#149) (#166)

When argument is an array and no input is given but “-h”, if you throw an Error in Validate function, it prints error and short usage instead of help message.
This patch checks built-in flags before throwing a validation error.

Solves #149

Co-authored-by: ibrahim oktay <[email protected]>

Author: ibrahimoktay

Sources/ArgumentParser/Parsing/CommandParser.swift

@@ -159,6 +159,7 @@ extension CommandParser {
       do {
         try parsedCommand.validate()
       } catch {
+        try checkForBuiltInFlags(split)
         throw CommandError(commandStack: commandStack, parserError: ParserError.userValidationError(error))
       }
 

Tests/ArgumentParserUnitTests/HelpGenerationTests.swift

@@ -318,4 +318,27 @@ extension HelpGenerationTests {
     """)
   }
 
+  struct K: ParsableCommand {
+    @Argument(help: "A list of paths.")
+    var paths: [String]
+    
+    func validate() throws {
+      if paths.isEmpty {
+        throw ValidationError("At least one path must be specified.")
+      }
+    }
+  }
+  
+  func testHelpWithNoValueForArray() {
+    AssertHelp(for: K.self, equals: """
+    USAGE: k [<paths> ...]
+
+    ARGUMENTS:
+      <paths>                 A list of paths.
+
+    OPTIONS:
+      -h, --help              Show help information.
+
+    """)
+  }
 }