Update the Trace function to return a Void type (#2650)

The Trace function doesn't return anything. For legacy reasons, it currently returns DType.Boolean (when it was created, we didn't have DType.Void). This PR updates it to return Void instead.

src/libraries/Microsoft.PowerFx.Core/Texl/Builtins/Trace.cs

@@ -44,6 +44,13 @@ namespace Microsoft.PowerFx.Core.Texl.Builtins
             yield return new[] { TexlStrings.TraceArg1, TexlStrings.TraceArg2, TexlStrings.TraceArg3, TexlStrings.TraceArg4 };
         }
 
+        public override bool CheckTypes(CheckTypesContext context, TexlNode[] args, DType[] argTypes, IErrorContainer errors, out DType returnType, out Dictionary<TexlNode, DType> nodeToCoercedTypeMap)
+        {
+            var result = base.CheckTypes(context, args, argTypes, errors, out returnType, out nodeToCoercedTypeMap);
+            returnType = context.Features.PowerFxV1CompatibilityRules ? DType.Void : DType.Boolean;
+            return result;
+        }
+
         public override void CheckSemantics(TexlBinding binding, TexlNode[] args, DType[] argTypes, IErrorContainer errors)
         {
             Contracts.AssertValue(args);

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

@@ -2797,7 +2797,7 @@ namespace Microsoft.PowerFx.Functions
                 throw new CustomFunctionErrorException(ex.Message);
             }
 
-            return FormulaValue.New(true);
+            return irContext.ResultType._type.Kind == DKind.Boolean ? FormulaValue.New(true) : FormulaValue.NewVoid();
         }
     }
 }

src/tests/Microsoft.PowerFx.Core.Tests.Shared/TexlTests.cs

@@ -2693,6 +2693,25 @@ namespace Microsoft.PowerFx.Core.Tests
                 features: Features.PowerFxV1);
         }
 
+        [Theory]
+        [InlineData("Trace(\"hello\")")]
+        [InlineData("Trace(\"hello\", TraceSeverity.Warning)")]
+        [InlineData("Trace(\"hello\", TraceSeverity.Warning, { a: 1 })")]
+        public void TexlFunctionTypeSemanticsTrace(string expression)
+        {
+            foreach (var powerFxV1 in new[] { false, true })
+            {
+                var features = powerFxV1 ? Features.PowerFxV1 : Features.None;
+                var engine = new Engine(new PowerFxConfig(features));
+                var options = new ParserOptions() { AllowsSideEffects = true };
+                var result = engine.Check(expression, options);
+
+                var expectedType = powerFxV1 ? DType.Void : DType.Boolean;
+                Assert.Equal(expectedType, result.Binding.ResultType);
+                Assert.True(result.IsSuccess);
+            }
+        }
+
         [Theory]
         [InlineData("Concat([], \"\")")]
         [InlineData("Concat([1, 2, 3], Text(Value))")]