.Net: Add support for partial XML and global functions in plan parser (#2824)

- Added support for parsing partial XML by appending a closing tag if
not present.
- Enabled plan creation with global functions by handling cases where
skill name is not provided.
- Updated unit tests to cover these new scenarios.

Fixes #2502

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

Author: lemillermicrosoft

dotnet/src/Extensions/Extensions.UnitTests/Planning/SequentialPlanner/SequentialPlanParserTests.cs

@@ -66,7 +66,7 @@ private void CreateKernelAndFunctionCreateMocks(List<(string name, string skillN
         var functionsView = new FunctionsView();
         foreach (var (name, skillName, description, isSemantic, resultString) in functions)
         {
-            var functionView = new FunctionView(name, skillName, description, new List<ParameterView>(), isSemantic, true);
+            var functionView = new FunctionView(name, skillName, description, new List<ParameterView>() { new(name: "param", description: "description") }, isSemantic, true);
             var mockFunction = CreateMockFunction(functionView);
             functionsView.AddFunction(functionView);
 
@@ -88,6 +88,7 @@ private void CreateKernelAndFunctionCreateMocks(List<(string name, string skillN
                 skills.Setup(x => x.GetFunction(It.Is<string>(s => s == skillName), It.Is<string>(s => s == name)))
                     .Returns(mockFunction.Object);
                 ISKFunction? outFunc = mockFunction.Object;
+                skills.Setup(x => x.TryGetFunction(It.Is<string>(s => s == name), out outFunc)).Returns(true);
                 skills.Setup(x => x.TryGetFunction(It.Is<string>(s => s == skillName), It.Is<string>(s => s == name), out outFunc)).Returns(true);
             }
         }
@@ -196,6 +197,55 @@ public void CanCreatePlanWithTextNodes(string goalText, string planText)
         Assert.Equal("Echo", plan.Steps[0].Name);
     }
 
+    [Theory]
+    [InlineData("Test the functionFlowRunner", @"<goal>Test the functionFlowRunner</goal>
+    <plan>
+    <function.MockSkill.Echo input=""Hello World"" />")]
+    public void CanCreatePlanWithPartialXml(string goalText, string planText)
+    {
+        // Arrange
+        var functions = new List<(string name, string skillName, string description, bool isSemantic, string result)>()
+        {
+            ("Echo", "MockSkill", "Echo an input", true, "Mock Echo Result"),
+        };
+        this.CreateKernelAndFunctionCreateMocks(functions, out var kernel);
+
+        // Act
+        var plan = planText.ToPlanFromXml(goalText, SequentialPlanParser.GetSkillFunction(kernel.CreateNewContext()));
+
+        // Assert
+        Assert.NotNull(plan);
+        Assert.Equal(goalText, plan.Description);
+        Assert.Equal(1, plan.Steps.Count);
+        Assert.Equal("MockSkill", plan.Steps[0].SkillName);
+        Assert.Equal("Echo", plan.Steps[0].Name);
+    }
+
+    [Theory]
+    [InlineData("Test the functionFlowRunner", @"<goal>Test the functionFlowRunner</goal>
+    <plan>
+    <function.Echo input=""Hello World"" />
+    </plan>")]
+    public void CanCreatePlanWithFunctionName(string goalText, string planText)
+    {
+        // Arrange
+        var functions = new List<(string name, string skillName, string description, bool isSemantic, string result)>()
+        {
+            ("Echo", "_GLOBAL_FUNCTIONS_", "Echo an input", true, "Mock Echo Result"),
+        };
+        this.CreateKernelAndFunctionCreateMocks(functions, out var kernel);
+
+        // Act
+        var plan = planText.ToPlanFromXml(goalText, SequentialPlanParser.GetSkillFunction(kernel.CreateNewContext()));
+
+        // Assert
+        Assert.NotNull(plan);
+        Assert.Equal(goalText, plan.Description);
+        Assert.Equal(1, plan.Steps.Count);
+        Assert.Equal("_GLOBAL_FUNCTIONS_", plan.Steps[0].SkillName);
+        Assert.Equal("Echo", plan.Steps[0].Name);
+    }
+
     // Test that contains a #text node in the plan
     [Theory]
     [InlineData(@"

dotnet/src/Extensions/Planning.SequentialPlanner/SequentialPlanParser.cs

@@ -89,6 +89,12 @@ internal static Plan ToPlanFromXml(this string xmlString, string goal, Func<stri
             // '</plan>': Matches the literal string "</plan>", indicating the closing tag of the <plan> element.
             Regex planRegex = new(@"<plan\b[^>]*>(.*?)</plan>", RegexOptions.Singleline);
             Match match = planRegex.Match(xmlString);
+
+            if (!match.Success)
+            {
+                match = planRegex.Match($"{xmlString}</plan>"); // try again with a closing tag
+            }
+
             if (match.Success)
             {
                 string planXml = match.Value;
@@ -205,7 +211,7 @@ internal static Plan ToPlanFromXml(this string xmlString, string goal, Func<stri
     private static void GetSkillFunctionNames(string skillFunctionName, out string skillName, out string functionName)
     {
         var skillFunctionNameParts = skillFunctionName.Split('.');
-        skillName = skillFunctionNameParts?.Length > 0 ? skillFunctionNameParts[0] : string.Empty;
+        skillName = skillFunctionNameParts?.Length > 1 ? skillFunctionNameParts[0] : string.Empty;
         functionName = skillFunctionNameParts?.Length > 1 ? skillFunctionNameParts[1] : skillFunctionName;
     }