Fix field ordering for subcommands deriving from a non-Command base type.

Base type fields now come first, and the fields from the command come last.

Author: rstarkov

Src/CommandLine.cs

@@ -338,18 +338,13 @@ private static FieldInfo[] getEligibleFields(Type type)
     {
         var bindingFlags = BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;
 
-        // Get all fields from the type
-        var fields = type.GetFields(bindingFlags).ToList();
+        // Include this type, plus all base types in the chain until we find one with CommandNameAttribute or CommandLineAttribute
+        var types = type.SelectChain(t => t.BaseType)
+            .TakeWhile(t => t == type || (t != typeof(object) && !t.IsDefined<CommandNameAttribute>() && !t.IsDefined<CommandLineAttribute>()));
+        // Starting with the deepest base type, get all fields from all the above types
+        var fields = types.Reverse().SelectMany(t => t.GetFields(bindingFlags)).ToArray();
 
-        // Keep adding fields from the base type until we find one with CommandNameAttribute or CommandLineAttribute
-        var testType = type.BaseType;
-        while (testType != typeof(object) && !testType.IsDefined<CommandNameAttribute>() && !testType.IsDefined<CommandLineAttribute>())
-        {
-            fields.AddRange(testType.GetFields(bindingFlags));
-            testType = testType.BaseType;
-        }
-
-        return fields.ToArray();
+        return fields;
     }
 
     private static Type[] getDirectSubcommands(Type type)

Tests/CommandLineTests.cs

@@ -64,6 +64,26 @@ public ConsoleColoredString Validate()
             return null;
         }
     }
+
+    [CommandLine]
+    abstract class CmdBase3
+    {
+        [IsPositional, IsMandatory]
+        public string Base;
+    }
+
+    abstract class CmdSubBase3 : CmdBase3
+    {
+        [IsPositional, IsMandatory]
+        public string SubBase;
+    }
+
+    [CommandName("sub")]
+    sealed class CmdSubcmd3 : CmdSubBase3
+    {
+        [IsPositional, IsMandatory]
+        public string ItemName;
+    }
 #pragma warning restore 0649 // Field is never assigned to, and will always have its default value null
 
     [Fact]
@@ -158,4 +178,15 @@ public static void TestSubcommandValidation()
         Assert.Equal("item", cs2.ItemName);
         Assert.Equal(1, CmdSubcmd2.ValidateCalled);
     }
+
+    [Fact]
+    public static void TestSubcommandIntermediate()
+    {
+        var c3 = CommandLineParser.Parse<CmdBase3>(["base", "sub", "subbase", "item"]);
+        Assert.IsType<CmdSubcmd3>(c3);
+        var cs3 = (CmdSubcmd3) c3;
+        Assert.Equal("base", cs3.Base);
+        Assert.Equal("subbase", cs3.SubBase);
+        Assert.Equal("item", cs3.ItemName);
+    }
 }