#778: Suppress builtin -h,--help from usage text when command already contains an option using -h

Sources/ArgumentParser/Usage/HelpGenerator.swift

@@ -519,7 +519,19 @@ extension BidirectionalCollection where Element == ParsableCommand.Type {
       })
     else { return ArgumentSet() }
     self.versionArgumentDefinition().map { arguments.append($0) }
-    self.helpArgumentDefinition().map { arguments.append($0) }
+
+    let shouldAppendBuiltinHelp = !arguments
+      .flatMap(\.names)
+      .contains { name in
+        if case .short(let char, _) = name {
+          return char == "h"
+        }
+        return false
+      }
+
+    if shouldAppendBuiltinHelp {
+      self.helpArgumentDefinition().map { arguments.append($0) }
+    }
 
     // To add when 'dump-help' is public API:
     // arguments.append(self.dumpHelpArgumentDefinition())

Tests/ArgumentParserUnitTests/HelpGenerationTests.swift

@@ -1493,3 +1493,28 @@ extension HelpGenerationTests {
     #endif
   }
 }
+
+extension HelpGenerationTests {
+  struct Issue778: ParsableCommand {
+    @Argument(help: "The phrase to repeat.")
+    var phrase: String
+
+    @Option(name: .shortAndLong, help: "The name of the talking horse.")
+    var horse: String
+  }
+
+  func testCommandWithShortOptionNameHDoesNotIncludeBuiltInHelp() {
+    AssertHelp(
+      .default, for: Issue778.self, columns: nil,
+      equals: """
+        USAGE: issue778 <phrase> --horse <horse>
+
+        ARGUMENTS:
+          <phrase>                The phrase to repeat.
+
+        OPTIONS:
+          -h, --horse <horse>     The name of the talking horse.
+
+        """)
+  }
+}