Work around runtime issue introduced in 0.4.3 (#342)

* Add dummy property as workaround for #338

The addition of _hiddenFromHelp to OptionGroup in 0.4.3 triggered
a Swift IRGen issue. Adding this dummy variable works around the
issue in at least some cases.

* Don't include _hiddenFromHelp props in other property wrappers

This resolves another crashing issue described in rdar://80796582,
where defining an OptionGroup that isn't used results in a runtime
segfault when compiled in release mode.

Author: natecook1000

Sources/ArgumentParser/Parsable Properties/Argument.swift

@@ -27,8 +27,7 @@ public struct Argument<Value>:
   Decodable, ParsedWrapper
 {
   internal var _parsedValue: Parsed<Value>
-  internal var _hiddenFromHelp: Bool = false
-    
+
   internal init(_parsedValue: Parsed<Value>) {
     self._parsedValue = _parsedValue
   }

Sources/ArgumentParser/Parsable Properties/Flag.swift

@@ -39,8 +39,7 @@
 @propertyWrapper
 public struct Flag<Value>: Decodable, ParsedWrapper {
   internal var _parsedValue: Parsed<Value>
-  internal var _hiddenFromHelp: Bool = false
-    
+
   internal init(_parsedValue: Parsed<Value>) {
     self._parsedValue = _parsedValue
   }

Sources/ArgumentParser/Parsable Properties/Option.swift

@@ -29,8 +29,7 @@
 @propertyWrapper
 public struct Option<Value>: Decodable, ParsedWrapper {
   internal var _parsedValue: Parsed<Value>
-  internal var _hiddenFromHelp: Bool = false
-    
+  
   internal init(_parsedValue: Parsed<Value>) {
     self._parsedValue = _parsedValue
   }

Sources/ArgumentParser/Parsable Properties/OptionGroup.swift

@@ -33,6 +33,10 @@ public struct OptionGroup<Value: ParsableArguments>: Decodable, ParsedWrapper {
   internal var _parsedValue: Parsed<Value>
   internal var _hiddenFromHelp: Bool = false
 
+  // FIXME: Adding this property works around the crasher described in
+  // https://github.com/apple/swift-argument-parser/issues/338
+  internal var _dummy: Bool = false
+
   internal init(_parsedValue: Parsed<Value>) {
     self._parsedValue = _parsedValue
   }

Sources/ArgumentParser/Parsable Types/ParsableArguments.swift

@@ -233,6 +233,10 @@ protocol ArgumentSetProvider {
   var _hiddenFromHelp: Bool { get }
 }
 
+extension ArgumentSetProvider {
+  var _hiddenFromHelp: Bool { false }
+}
+
 extension ArgumentSet {
   init(_ type: ParsableArguments.Type, creatingHelp: Bool = false) {