XML documentation for Argument<T> class (#1100)

* Add XML documentation to the Argument{T} class

Author: pieter-venter

src/System.CommandLine/Argument{T}.cs

@@ -5,13 +5,22 @@
 
 namespace System.CommandLine
 {
+    ///<inheritdoc/>
     public class Argument<T> : Argument
     {
+        /// <summary>
+        /// Initializes a new instance of the Argument class.
+        /// </summary>
         public Argument()
         {
             ArgumentType = typeof(T);
         }
 
+        /// <summary>
+        /// Initializes a new instance of the Argument class.
+        /// </summary>
+        /// <param name="name">The name of the argument.</param>
+        /// <param name="description">The description of the argument, shown in help.</param>
         public Argument(
             string name, 
             string? description = null) : base(name)
@@ -20,6 +29,13 @@ public Argument(
             Description = description;
         }
 
+        /// <summary>
+        /// Initializes a new instance of the Argument class.
+        /// </summary>
+        /// <param name="name">The name of the argument.</param>
+        /// <param name="getDefaultValue">The delegate to invoke to return the default value.</param>
+        /// <param name="description">The description of the argument, shown in help.</param>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="getDefaultValue"/> is null.</exception>
         public Argument(
             string name, 
             Func<T> getDefaultValue, 
@@ -35,6 +51,11 @@ public Argument(
             Description = description;
         }
 
+        /// <summary>
+        /// Initializes a new instance of the Argument class.
+        /// </summary>
+        /// <param name="getDefaultValue">The delegate to invoke to return the default value.</param>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="getDefaultValue"/> is null.</exception>
         public Argument(Func<T> getDefaultValue) : this()
         {
             if (getDefaultValue is null)
@@ -45,6 +66,13 @@ public Argument(Func<T> getDefaultValue) : this()
             SetDefaultValueFactory(() => getDefaultValue());
         }
 
+        /// <summary>
+        /// Initializes a new instance of the Argument class.
+        /// </summary>
+        /// <param name="name">The name of the argument.</param>
+        /// <param name="parse">A custom argument parser.</param>
+        /// <param name="isDefault"><c>true</c> to use the <paramref name="parse"/> result as default value.</param>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="parse"/> is null.</exception>
         public Argument(
             string? name,
             ParseArgument<T> parse, 
@@ -82,6 +110,11 @@ public Argument(
             };
         }
 
+        /// <summary>
+        /// Initializes a new instance of the Argument class.
+        /// </summary>
+        /// <param name="parse">A custom argument parser.</param>
+        /// <param name="isDefault"><c>true</c> to use the <paramref name="parse"/> result as default value.</param>
         public Argument(ParseArgument<T> parse, bool isDefault = false) : this(null, parse, isDefault)
         {
         }