Fix #2973: SortByColumns runtime error when called through UDF with missing columns

src/libraries/Microsoft.PowerFx.Interpreter/Functions/LibraryTable.cs

@@ -894,7 +894,12 @@ public static async ValueTask<FormulaValue> SortByColumns(EvalVisitor runner, Ev
             {
                 var columnName = ((StringValue)args[i]).Value;
 
-                if (!arg0.Type.FieldNames.Contains(columnName))
+                // Use the compile-time result type (irContext.ResultType) rather than the
+                // actual runtime arg0.Type, which may be narrower when this function is
+                // called through a UDF with a table that omits optional columns.
+                // Missing columns are returned as Blank by RecordValue.GetFieldAsync.
+                // See https://github.com/microsoft/Power-Fx/issues/2973
+                if (!((TableType)irContext.ResultType).FieldNames.Contains(columnName))
                 {
                     return CreateInvalidSortColumnError(irContext, runner.CultureInfo, columnName);
                 }
@@ -961,7 +966,13 @@ public static async ValueTask<FormulaValue> SortByColumnsOrderTable(EvalVisitor
         {
             var arg0 = (TableValue)args[0];
             var columnName = ((StringValue)args[1]).Value;
-            if (!arg0.Type.FieldNames.Contains(columnName))
+
+            // Use the compile-time result type (irContext.ResultType) rather than the
+            // actual runtime arg0.Type, which may be narrower when this function is
+            // called through a UDF with a table that omits optional columns.
+            // Missing columns are returned as Blank by RecordValue.GetFieldAsync.
+            // See https://github.com/microsoft/Power-Fx/issues/2973
+            if (!((TableType)irContext.ResultType).FieldNames.Contains(columnName))
             {
                 return CreateInvalidSortColumnError(irContext, runner.CultureInfo, columnName);
             }

src/tests/Microsoft.PowerFx.Interpreter.Tests.Shared/RecalcEngineTests.cs

@@ -2379,6 +2379,39 @@ public void UDFAggregateInputErrorMessage(string userDefinitions, string evalExp
             Assert.Contains(expectedError, ex.InnerExceptions.First().Message);
         }
 
+        // Regression test for https://github.com/microsoft/Power-Fx/issues/2973
+        // SortByColumns should not throw when called via a UDF and the actual argument table
+        // omits one of the sort columns. Missing columns should be treated as Blank.
+        [Fact]
+        public void SortByColumns_UDF_MissingField()
+        {
+            var engine = new RecalcEngine();
+
+            // Define types and UDF matching the issue repro exactly.
+            engine.AddUserDefinitions(
+                "Person := Type( { Name: Text, Age: Number } );" +
+                "People := Type( [ Person ] );" +
+                "SortedPeople(list:People):People = SortByColumns(list, \"Name\", SortOrder.Ascending, \"Age\", SortOrder.Ascending);");
+
+            // AC-1: Missing Age column - should succeed and return sorted table, not an error.
+            var result = engine.Eval("SortedPeople([{Name:\"John\"},{Name:\"Jane\"}])");
+            Assert.IsNotType<ErrorValue>(result);
+            Assert.IsAssignableFrom<TableValue>(result);
+            var rows = ((TableValue)result).Rows.ToList();
+            Assert.Equal(2, rows.Count);
+            Assert.Equal("Jane", ((StringValue)rows[0].Value.GetField("Name")).Value);
+            Assert.Equal("John", ((StringValue)rows[1].Value.GetField("Name")).Value);
+
+            // AC-2: Full columns present - should continue to work.
+            result = engine.Eval("SortedPeople([{Name:\"John\", Age:30},{Name:\"Jane\", Age:40}])");
+            Assert.IsNotType<ErrorValue>(result);
+            Assert.IsAssignableFrom<TableValue>(result);
+            rows = ((TableValue)result).Rows.ToList();
+            Assert.Equal(2, rows.Count);
+            Assert.Equal("Jane", ((StringValue)rows[0].Value.GetField("Name")).Value);
+            Assert.Equal("John", ((StringValue)rows[1].Value.GetField("Name")).Value);
+        }
+
         #region Test
 
         private readonly StringBuilder _updates = new StringBuilder();