Made required behaviour for CliArgument and CliOption more sensible

        If the decorated property has a default value (set via a property initializer), the argument/option is detected as "not required".
        If the decorated property does not have a default value, the argument/option is detected as "required".

        If you want to force an argument/option to be required, set this property to `true`. In that case,
        the default value for the decorated property will be ignored (if exists).
        If you want to force an argument/option to be not required, set this property to `false`.

Author: calacayir

docs/README.md

@@ -141,15 +141,21 @@ You see this result:
 ```console
 Required argument missing for command: 'TestApp'.
 ```
-This is because a `CliArgument` decorated property is required by default (`CliArgument.Required` property's default value is `true`).
-A `CliArgument` is a parameter for the command itself (for the root command - the exe in this case), that's why it's required by default.
+This is because a `CliArgument` or `CliOption` decorated property is required if the decorated property does not have a 
+default value (set via a property initializer) or if it's not forced via attribute property `Required`.
 
-If you want to make a `CliArgument` optional, set `CliArgument.Required` property to `false` and set a default value for the decorated property.
-In that case, the default value for the decorated property will be used when the user does not specify the argument on the command line.
+If you want to make a `CliArgument` or `CliOption` optional (not required), set a default value for the decorated property:
 ```c#
-[CliArgument(Required = false)]
+[CliArgument]
 public string Argument1 { get; set; } = "DefaultForArgument1";
 ```
+or set `Required` property to `false`, to force it:
+```c#
+[CliArgument(Required = false)]
+public string Argument1 { get; set; }
+```
+In that case, the default value for the decorated property will be used when the user does not specify the argument on the command line.
+
 ---
 When you run,
 ```console
@@ -165,15 +171,21 @@ Handler for 'TestApp.Commands.RootCliCommand' is run:
 Value for Option1 property is 'DefaultForOption1'
 Value for Argument1 property is 'NewValueForArgument1'
 ```
-This is because a `CliOption` decorated property is not required by default (`CliOption.Required` property's default value is `false`).
-A `CliOption` is optional, as the name implies, for the command itself (for the root command - the exe in this case), that's why it's not required by default.
+This is because a `CliArgument` or `CliOption` decorated property is not required if the decorated property has a 
+default value (set via a property initializer) or if it's not forced via attribute property `Required`.
 
-If you want to make a `CliOption` required, set `CliArgument.Required` property to `true`.
-In that case, the default value for the decorated property will be ignored (if exists) and the user has to specify the option on the command line.
+If you want to make a `CliArgument` or `CliOption` required, remove the default value for the decorated property:
 ```c#
-[CliOption(Required = true)]
+[CliOption]
 public string Option1 { get; set; }
 ```
+or set `Required` property to `true`, to force it:
+```c#
+[CliOption(Required = true)]
+public string Option1 { get; set; } = "DefaultForOption1";
+```
+In that case, the default value for the decorated property will be ignored (if exists) and the user has to specify the option on the command line.
+
 ---
 When you run,
 ```console

src/Directory.Build.props

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <!-- https://learn.microsoft.com/en-us/dotnet/core/project-sdk/msbuild-props#generateassemblyinfo -->
     <LangVersion>10.0</LangVersion>
-    <VersionPrefix>1.5.6</VersionPrefix>
+    <VersionPrefix>1.5.7</VersionPrefix>
     <Product>DotMake Command-Line</Product>
     <Company>DotMake</Company>
     <!-- Copyright is also used for NuGet metadata -->

src/DotMake.CommandLine.Shared/Attributes/CliArgumentAttribute.cs

@@ -4,7 +4,10 @@ namespace DotMake.CommandLine
 {
     /// <summary>
     /// Specifies a class property that represents an argument which is a value that can be passed on the command line to a command or an option.
-    /// <para>Note that arguments are required by default, see <see cref="Required"/> property for details.</para>
+    /// <para>
+    /// Note that an argument is required if the decorated property does not have a default value (set via a property initializer),
+    /// see <see cref="Required"/> property for details.
+    /// </para>
     /// <para>
     /// <b>Arguments:</b> An argument is a value passed to an option or a command. The following examples show an argument for the <c>verbosity</c> option and an argument for the <c>build</c> command.
     /// <code>
@@ -57,18 +60,23 @@ public class CliArgumentAttribute : Attribute
 
         /// <summary>
         /// Gets or sets a value indicating whether the argument is required when its parent command is invoked.
-        /// Default is <see langword="true" /> for arguments.
+        /// Default is auto-detected.
+        /// <para>
+        /// If the decorated property has a default value (set via a property initializer), the argument is detected as "not required".
+        /// If the decorated property does not have a default value, the argument is detected as "required".
+        /// </para>
         /// <para>
-        /// When an argument is required and its parent command is invoked without it,
-        /// an error message is displayed and the command handler isn't called.
+        /// If you want to force an argument to be required, set this property to <see langword="true"/>. In that case,
+        /// the default value for the decorated property will be ignored (if exists).
+        /// If you want to force an argument to be not required, set this property to <see langword="false"/>.
         /// </para>
         /// <para>
-        /// If you want to make a CliArgument optional, set this property to <see langword="false"/> and set a default value
-        /// for the decorated property.In that case, the default value for the decorated property will be used when the user
-        /// does not specify the argument on the command line.
+        /// When an argument is required, the argument has to be specified on the command line and if its parent command is invoked
+        /// without it, an error message is displayed and the command handler isn't called.
+        /// When an argument is not required, the argument doesn't have to be specified on the command line, the default value provides the argument value.
         /// </para>
         /// </summary>
-        public bool Required { get; set; } = true;
+        public bool Required { get; set; }
 
         /// <summary>
         /// Gets or sets the arity of the argument. The arity refers to the number of values that can be passed on the command line.

src/DotMake.CommandLine.Shared/Attributes/CliOptionAttribute.cs

@@ -4,7 +4,10 @@ namespace DotMake.CommandLine
 {
     /// <summary>
     /// Specifies a class property that represents an option which is a named parameter and a value for that parameter, that is used on the command line.
-    /// <para>Note that options are not required by default (optional as the name implies), see <see cref="Required"/> property for details.</para>
+    /// <para>
+    /// Note that an option is required if the decorated property does not have a default value (set via a property initializer),
+    /// see <see cref="Required"/> property for details.
+    /// </para>
     /// <para>
     /// <b>Options:</b> An option is a named parameter that can be passed to a command. The POSIX convention is to prefix the option name with two hyphens (<c>--</c>).
     /// The following example shows two options:
@@ -75,15 +78,20 @@ public class CliOptionAttribute : Attribute
 
         /// <summary>
         /// Gets or sets a value indicating whether the option is required when its parent command is invoked.
-        /// Default is <see langword="false" /> for options.
+        /// Default is auto-detected.
+        /// <para>
+        /// If the decorated property has a default value (set via a property initializer), the option is detected as "not required".
+        /// If the decorated property does not have a default value, the option is detected as "required".
+        /// </para>
         /// <para>
-        /// When an option is required and its parent command is invoked without it,
-        /// an error message is displayed and the command handler isn't called.
+        /// If you want to force an option to be required, set this property to <see langword="true"/>. In that case,
+        /// the default value for the decorated property will be ignored (if exists).
+        /// If you want to force an option to be not required, set this property to <see langword="false"/>.
         /// </para>
         /// <para>
-        /// If you want to make a CliOption required, set this property to <see langword="true"/>. In that case,
-        /// the default value for the decorated property will be ignored (if exists) and the user has to specify
-        /// the option on the command line.
+        /// When an option is required, the option has to be specified on the command line and if its parent command is invoked
+        /// without it, an error message is displayed and the command handler isn't called.
+        /// When an option is not required, the option doesn't have to be specified on the command line, the default value provides the option value.
         /// </para>
         /// </summary>
         public bool Required { get; set; }

src/DotMake.CommandLine.SourceGeneration/CliArgumentInfo.cs

@@ -4,6 +4,7 @@
 using System.Linq;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
 
 namespace DotMake.CommandLine.SourceGeneration
 {
@@ -43,6 +44,9 @@ public CliArgumentInfo(ISymbol symbol, SyntaxNode syntaxNode, AttributeData attr
             if (AttributeArguments.TryGetValue(AttributeRequiredProperty, out var requiredTypedConstant)
                 && requiredTypedConstant.Value != null)
                 Required = (bool)requiredTypedConstant.Value;
+            else
+                Required = (SyntaxNode is PropertyDeclarationSyntax propertyDeclarationSyntax
+                            && propertyDeclarationSyntax.Initializer == null);
         }
 
         public CliArgumentInfo(GeneratorAttributeSyntaxContext attributeSyntaxContext)
@@ -60,7 +64,7 @@ public CliArgumentInfo(GeneratorAttributeSyntaxContext attributeSyntaxContext)
 
         public CliCommandInfo Parent { get; }
 
-        public bool Required { get; } = CliArgumentAttribute.Default.Required;
+        public bool Required { get; }
 
         public CliArgumentParseInfo ParseInfo { get; set; }
 

src/DotMake.CommandLine.SourceGeneration/CliOptionInfo.cs

@@ -4,6 +4,7 @@
 using System.Linq;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
 
 namespace DotMake.CommandLine.SourceGeneration
 {
@@ -23,8 +24,7 @@ public class CliOptionInfo : CliSymbolInfo, IEquatable<CliOptionInfo>
         public static readonly Dictionary<string, string> PropertyMappings = new Dictionary<string, string>
         {
             { nameof(CliOptionAttribute.HelpName), "ArgumentHelpName"},
-            { nameof(CliOptionAttribute.Hidden), "IsHidden"},
-            { nameof(CliOptionAttribute.Required), "IsRequired"}
+            { nameof(CliOptionAttribute.Hidden), "IsHidden"}
         };
 
         public CliOptionInfo(ISymbol symbol, SyntaxNode syntaxNode, AttributeData attributeData, SemanticModel semanticModel, CliCommandInfo parent)
@@ -49,6 +49,9 @@ public CliOptionInfo(ISymbol symbol, SyntaxNode syntaxNode, AttributeData attrib
             if (AttributeArguments.TryGetValue(AttributeRequiredProperty, out var requiredTypedConstant)
                 && requiredTypedConstant.Value != null)
                 Required = (bool)requiredTypedConstant.Value;
+            else
+                Required = (SyntaxNode is PropertyDeclarationSyntax propertyDeclarationSyntax
+                            && propertyDeclarationSyntax.Initializer == null);
         }
 
         public CliOptionInfo(GeneratorAttributeSyntaxContext attributeSyntaxContext)
@@ -121,6 +124,7 @@ public void AppendCSharpCreateString(CodeStringBuilder sb, string varName, strin
                         case AttributeAliasesProperty:
                         case AttributeGlobalProperty:
                         case AttributeAllowedValuesProperty:
+                        case AttributeRequiredProperty:
                             continue;
                         case AttributeArityProperty:
                             var arity = kvp.Value.ToCSharpString().Split('.').Last();
@@ -134,6 +138,8 @@ public void AppendCSharpCreateString(CodeStringBuilder sb, string varName, strin
                             break;
                     }
                 }
+
+                sb.AppendLine($"IsRequired = {Required.ToString().ToLowerInvariant()},");
             }
 
             if (AttributeArguments.TryGetValue(AttributeAllowedValuesProperty, out var allowedValuesTypedConstant)

src/DotMake.CommandLine/DotMake.CommandLine.csproj

@@ -19,7 +19,13 @@
     <Description>Declarative syntax for System.CommandLine via attributes for easy, fast, strongly-typed (no reflection) usage. Includes a source generator which automagically converts your classes to CLI commands and properties to CLI options or CLI arguments.</Description>
     <PackageTags>command-line CLI console System.CommandLine declarative attributes parsing command argument option generator</PackageTags>
     <PackageReleaseNotes>
-      - Fixed net472 and netstandard2.0 support. ModuleInitializerAttribute will be generated for legacy projects (missing before net5.0).
+      - Made required behaviour for `CliArgument` and `CliOption` more sensible:
+        If the decorated property has a default value (set via a property initializer), the argument/option is detected as "not required".
+        If the decorated property does not have a default value, the argument/option is detected as "required".
+
+        If you want to force an argument/option to be required, set this property to `true`. In that case,
+        the default value for the decorated property will be ignored (if exists).
+        If you want to force an argument/option to be not required, set this property to `false`.
     </PackageReleaseNotes>
   </PropertyGroup>
 

src/TestApp/GeneratedFiles/DotMake.CommandLine.SourceGeneration/DotMake.CommandLine.SourceGeneration.CliCommandGenerator/ArgumentConverterCliCommandBuilder-f61jepm.g.cs

@@ -1,5 +1,5 @@
 // <auto-generated />
-// Generated by DotMake.CommandLine.SourceGeneration v1.5.6.0
+// Generated by DotMake.CommandLine.SourceGeneration v1.5.7.0
 // Roslyn (Microsoft.CodeAnalysis) v4.800.23.57201
 // Generation: 1
 
@@ -36,8 +36,8 @@ public override System.CommandLine.Command Build()
                 )
             )
             {
+                IsRequired = true,
             };
-            option0.SetDefaultValue(defaultClass.Opt);
             option0.AddAlias("-o");
             rootCommand.Add(option0);
 
@@ -53,8 +53,8 @@ public override System.CommandLine.Command Build()
             )
             {
                 AllowMultipleArgumentsPerToken = true,
+                IsRequired = true,
             };
-            option1.SetDefaultValue(defaultClass.OptArray);
             rootCommand.Add(option1);
 
             // Option for 'OptNullable' property
@@ -67,8 +67,8 @@ public override System.CommandLine.Command Build()
                 )
             )
             {
+                IsRequired = true,
             };
-            option2.SetDefaultValue(defaultClass.OptNullable);
             rootCommand.Add(option2);
 
             // Option for 'OptEnumerable' property
@@ -82,8 +82,8 @@ public override System.CommandLine.Command Build()
                 )
             )
             {
+                IsRequired = true,
             };
-            option3.SetDefaultValue(defaultClass.OptEnumerable);
             rootCommand.Add(option3);
 
             // Option for 'OptList' property
@@ -97,8 +97,8 @@ public override System.CommandLine.Command Build()
                 )
             )
             {
+                IsRequired = true,
             };
-            option4.SetDefaultValue(defaultClass.OptList);
             rootCommand.Add(option4);
 
             // Option for 'OptCustomList' property
@@ -112,8 +112,8 @@ public override System.CommandLine.Command Build()
                 )
             )
             {
+                IsRequired = true,
             };
-            option5.SetDefaultValue(defaultClass.OptCustomList);
             rootCommand.Add(option5);
 
             // Argument for 'Arg' property

src/TestApp/GeneratedFiles/DotMake.CommandLine.SourceGeneration/DotMake.CommandLine.SourceGeneration.CliCommandGenerator/AsyncIntReturnCliCommandBuilder-7vdns44.g.cs

@@ -1,5 +1,5 @@
 // <auto-generated />
-// Generated by DotMake.CommandLine.SourceGeneration v1.5.6.0
+// Generated by DotMake.CommandLine.SourceGeneration v1.5.7.0
 // Roslyn (Microsoft.CodeAnalysis) v4.800.23.57201
 // Generation: 1
 
@@ -38,6 +38,7 @@ public override System.CommandLine.Command Build()
             )
             {
                 Description = "Description for Option1",
+                IsRequired = false,
             };
             option0.SetDefaultValue(defaultClass.Option1);
             option0.AddAlias("-o");

src/TestApp/GeneratedFiles/DotMake.CommandLine.SourceGeneration/DotMake.CommandLine.SourceGeneration.CliCommandGenerator/AsyncVoidReturnCliCommandBuilder-7ha5x0r.g.cs

@@ -1,5 +1,5 @@
 // <auto-generated />
-// Generated by DotMake.CommandLine.SourceGeneration v1.5.6.0
+// Generated by DotMake.CommandLine.SourceGeneration v1.5.7.0
 // Roslyn (Microsoft.CodeAnalysis) v4.800.23.57201
 // Generation: 1
 
@@ -38,6 +38,7 @@ public override System.CommandLine.Command Build()
             )
             {
                 Description = "Description for Option1",
+                IsRequired = false,
             };
             option0.SetDefaultValue(defaultClass.Option1);
             option0.AddAlias("-o");