feat: Implement support for creating simple policy fragments

example/source/AuthenticationFragment.cs

@@ -0,0 +1,14 @@
+using Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring;
+using Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring.Expressions;
+
+namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Example;
+
+[Document("auth-fragment", Type = DocumentType.Fragment)]
+public class AuthenticationFragment : IFragment
+{
+    public void Fragment(IFragmentContext context)
+    {
+        context.SetHeader("X-Auth-Fragment", "true");
+        context.AuthenticationBasic("{{username}}", "{{password}}");
+    }
+}

src/Authoring/Attributes/DocumentAttribute.cs

@@ -4,7 +4,9 @@
 namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring;
 
 [AttributeUsage(AttributeTargets.Class)]
-public class DocumentAttribute(string? name = null, DocumentScope scope = DocumentScope.Any) : Attribute
+public class DocumentAttribute(string? name = null) : Attribute
 {
     public string? Name { get; } = name;
+    public DocumentScope Scope { get; init; } = DocumentScope.Any;
+    public DocumentType Type { get; init; } = DocumentType.Policy;
 }

src/Authoring/DocumentScope.cs

@@ -6,4 +6,9 @@ namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring;
 public enum DocumentScope
 {
     Any = 0, Global, Workspace, Product, Api, Operation
+}
+
+public enum DocumentType
+{
+    Policy = 0, Fragment
 }

src/Authoring/IFragment.cs

@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Authoring;
+
+/// <summary>
+/// Interface for policy fragments. Policy fragments are reusable policy elements 
+/// that can be included in policy definitions using the include-fragment policy.
+/// </summary>
+public interface IFragment
+{
+    /// <summary>
+    /// Defines the policy elements that make up this fragment.
+    /// The policies defined in this method will be compiled directly into the fragment.
+    /// </summary>
+    /// <param name="context">The fragment context providing access to all policy operations.</param>
+    void Fragment(IFragmentContext context);
+}

src/Core/Compiling/DocumentCompiler.cs

@@ -22,11 +22,22 @@ public DocumentCompiler(Lazy<BlockCompiler> blockCompiler)
 
     public IDocumentCompilationResult Compile(Compilation compilation, ClassDeclarationSyntax document)
     {
-        var methods = document.DescendantNodes()
-            .OfType<MethodDeclarationSyntax>();
-        var policyDocument = new XElement("policies");
-        DocumentCompilationContext context = new(compilation, document, policyDocument);
+        var semanticModel = compilation.GetSemanticModel(document.SyntaxTree);
+        var documentType = document.ExtractDocumentType(semanticModel);
+        var methods = document.DescendantNodes().OfType<MethodDeclarationSyntax>();
+        var rootElement = new XElement(documentType == DocumentType.Fragment ? "fragment" : "policies");
+        var context = new DocumentCompilationContext(compilation, document, rootElement);
 
+        if (documentType == DocumentType.Fragment)
+            CompileFragment(context, methods);
+        else
+            CompilePolicy(context, methods);
+
+        return context;
+    }
+
+    private void CompilePolicy(DocumentCompilationContext context, IEnumerable<MethodDeclarationSyntax> methods)
+    {
         foreach (var method in methods)
         {
             var sectionName = method.Identifier.ValueText switch
@@ -45,12 +56,30 @@ public IDocumentCompilationResult Compile(Compilation compilation, ClassDeclarat
 
             CompileSection(context, sectionName, method);
         }
-
-        return context;
     }
 
+    private void CompileFragment(DocumentCompilationContext context, IEnumerable<MethodDeclarationSyntax> methods)
+    {
+        var fragmentMethod = methods.FirstOrDefault(m => m.Identifier.ValueText == "Fragment");
+
+        if (fragmentMethod != null && ValidateMethodBody(fragmentMethod, context))
+        {
+            _blockCompiler.Value.Compile(context, fragmentMethod.Body!);
+        }
+    }
 
     private void CompileSection(DocumentCompilationContext context, string section, MethodDeclarationSyntax method)
+    {
+        if (!ValidateMethodBody(method, context))
+            return;
+
+        var sectionElement = new XElement(section);
+        var sectionContext = new DocumentCompilationContext(context, sectionElement);
+        _blockCompiler.Value.Compile(sectionContext, method.Body!);
+        context.AddPolicy(sectionElement);
+    }
+
+    private bool ValidateMethodBody(MethodDeclarationSyntax method, DocumentCompilationContext context)
     {
         if (method.Body is null)
         {
@@ -59,12 +88,8 @@ private void CompileSection(DocumentCompilationContext context, string section,
                 method.GetLocation(),
                 method.Identifier.ValueText
             ));
-            return;
+            return false;
         }
-
-        var sectionElement = new XElement(section);
-        var sectionContext = new DocumentCompilationContext(context, sectionElement);
-        _blockCompiler.Value.Compile(sectionContext, method.Body);
-        context.AddPolicy(sectionElement);
+        return true;
     }
 }

src/Core/Compiling/SyntaxExtensions.cs

@@ -33,6 +33,14 @@ public static string ExtractDocumentFileName(this ClassDeclarationSyntax documen
         return attributeArgumentExpression?.Token.ValueText ?? document.Identifier.ValueText;
     }
 
+    public static DocumentType ExtractDocumentType(this ClassDeclarationSyntax document, SemanticModel model)
+    {
+        var attributeSyntax = document.AttributeLists.GetFirstAttributeOfType<DocumentAttribute>(model);
+        var fragmentArgument = attributeSyntax?.ArgumentList?.Arguments
+            .FirstOrDefault(arg => arg.Expression.ToString().Contains(nameof(DocumentType.Fragment)));
+        return fragmentArgument != null ? DocumentType.Fragment : DocumentType.Policy;
+    }
+
     public static IEnumerable<ClassDeclarationSyntax> GetDocumentAttributedClasses(this SyntaxNode syntax,
         SemanticModel semanticModel)
     {

src/Templates/content/create-policy-fragment/.template.config/template.json

@@ -0,0 +1,40 @@
+{
+  "$schema": "http://json.schemastore.org/template",
+  "author": "Microsoft",
+  "classifications": [
+    "Policy Toolkit",
+    "Policy Fragment",
+    "Class"
+  ],
+  "name": "Policy Toolkit Policy Fragment Class",
+  "generatorVersions": "[1.0.0.0-*)",
+  "description": "Creates a new Policy Toolkit policy fragment class",
+  "groupIdentity": "Azure.ApiManagement.PolicyToolkit.Templates.PolicyFragment",
+  "identity": "Azure.ApiManagement.PolicyToolkit.Templates.PolicyFragment.1.0",
+  "shortName": "policytoolkitfragment",
+  "tags": {
+    "language": "C#",
+    "type": "item"
+  },
+  "sourceName": "PolicyFragment1",
+  "preferDefaultName": true,
+  "defaultName": "PolicyFragment1",
+  "primaryOutputs": [
+    {
+      "path": ".cs"
+    }
+  ],
+  "symbols": {
+    "DefaultNamespace": {
+      "type": "bind",
+      "binding": "msbuild:RootNamespace",
+      "replaces": "Company.PolicyProject1"
+    }
+  },
+  "constraints": {
+    "csharp-only": {
+      "type": "project-capability",
+      "args": "CSharp"
+    }
+  }
+}

src/Templates/content/create-policy-fragment/PolicyFragment1.cs

@@ -0,0 +1,17 @@
+namespace Company.PolicyProject1;
+
+[Document(Type = DocumentType.Fragment)]
+public class PolicyFragment1 : IFragment
+{
+    public void Fragment(IFragmentContext context)
+    {
+        // Add reusable policy logic here
+        // This fragment can be included in any policy section (inbound, outbound, backend, on-error)
+
+        // Example: Set a common header
+        // context.SetHeader("X-Custom-Header", "fragment-value");
+
+        // Example: Set a variable
+        // context.SetVariable("fragment-processed", "true");
+    }
+}

test/Test.Core/Compiling/DocumentTypeTests.cs

@@ -0,0 +1,100 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.Azure.ApiManagement.PolicyToolkit.Compiling;
+
+[TestClass]
+public class DocumentTypeTests
+{
+    [TestMethod]
+    [DataRow(
+        """
+        [Document]
+        public class PolicyDocument : IDocument
+        {
+            public void Inbound(IInboundContext context)
+            {
+                context.SetHeader("X-Test", "value");
+            }
+        }
+        """,
+        """
+        <policies>
+            <inbound>
+                <set-header name="X-Test" exists-action="override">
+                    <value>value</value>
+                </set-header>
+            </inbound>
+        </policies>
+        """,
+        DisplayName = "Should compile regular policy document with policies root"
+    )]
+    [DataRow(
+        """
+        [Document( Type = DocumentType.Policy )]
+        public class PolicyDocument : IDocument
+        {
+            public void Inbound(IInboundContext context)
+            {
+                context.SetHeader("X-Test", "value");
+            }
+        }
+        """,
+        """
+        <policies>
+            <inbound>
+                <set-header name="X-Test" exists-action="override">
+                    <value>value</value>
+                </set-header>
+            </inbound>
+        </policies>
+        """,
+        DisplayName = "Should compile explicit policy document with policies root"
+    )]
+    [DataRow(
+        """
+        [Document( Type = DocumentType.Fragment )] 
+        public class PolicyFragment : IFragment
+        {
+            public void Fragment(IFragmentContext context)
+            {
+                context.SetHeader("X-Fragment", "fragment-value");
+            }
+        }
+        """,
+        """
+        <fragment>
+            <set-header name="X-Fragment" exists-action="override">
+                <value>fragment-value</value>
+            </set-header>
+        </fragment>
+        """,
+        DisplayName = "Should compile policy fragment with fragment root using Fragment method"
+    )]
+    [DataRow(
+        """
+        [Document("my-fragment", Type = DocumentType.Fragment)]
+        public class NamedPolicyFragment : IFragment
+        {
+            public void Fragment(IFragmentContext context)
+            {
+                context.SetHeader("X-Named-Fragment", "named-value");
+                context.Base();
+            }
+        }
+        """,
+        """
+        <fragment>
+            <set-header name="X-Named-Fragment" exists-action="override">
+                <value>named-value</value>
+            </set-header>
+            <base />
+        </fragment>
+        """,
+        DisplayName = "Should compile named policy fragment with multiple policies using Fragment method"
+    )]
+    public void ShouldCompileDocumentWithCorrectType(string code, string expectedXml)
+    {
+        code.CompileDocument().Should().BeSuccessful().And.DocumentEquivalentTo(expectedXml);
+    }
+}