Allow for customizing function handlers

Author: Florian Kroenert

.devcontainer/Dockerfile

@@ -0,0 +1,9 @@
+# Base image: Node 18 + .NET SDK 6
+FROM mcr.microsoft.com/devcontainers/dotnet:0-6.0
+
+# Install Node.js 18 (overwrite if not already present)
+RUN curl -fsSL https://deb.nodesource.com/setup_18.x | bash - \
+  && apt-get update && apt-get install -y nodejs
+
+# Set user to vscode (standard user in devcontainers)
+USER vscode

.devcontainer/devcontainer.json

@@ -0,0 +1,22 @@
+{
+    "name": "Xrm-Templating-Language",
+    "build": {
+      "dockerfile": "Dockerfile"
+    },
+    "settings": {
+      "terminal.integrated.defaultProfile.linux": "bash"
+    },
+    "customizations": {
+      "vscode": {
+        "extensions": [
+          "ms-dotnettools.csharp",
+          "dbaeumer.vscode-eslint",
+          "esbenp.prettier-vscode",
+          "ms-dotnettools.csdevkit",
+          "microsoft-isvexptools.powerplatform-vscode"
+        ]
+      }
+    },
+    "forwardPorts": [5000, 5001, 4280],
+    "remoteUser": "vscode"
+}

src/lib/Xrm.Oss.XTL.Interpreter/InterpreterConfig.cs

@@ -6,6 +6,7 @@
 using System.Runtime.Serialization.Json;
 using System.Text;
 using System.Threading.Tasks;
+using static Xrm.Oss.XTL.Interpreter.XTLInterpreter;
 
 namespace Xrm.Oss.XTL.Interpreter
 {
@@ -39,6 +40,8 @@ public class InterpreterConfig : IConfig
         [DataMember(Name = "snippetConfig")]
         public SnippetConfig SnippetConfig { get; set; }
 
+        public Dictionary<string, FunctionHandler> CustomHandlers { get; set; }
+
         public static InterpreterConfig Parse(string json)
         {
             if (string.IsNullOrEmpty(json))

src/lib/Xrm.Oss.XTL.Interpreter/XTLInterpreter.cs

@@ -7,6 +7,8 @@
 
 namespace Xrm.Oss.XTL.Interpreter
 {
+    public delegate ValueExpression FunctionHandler(Entity primary, IOrganizationService service, ITracingService tracing, InterpreterConfig interpreterConfig, List<ValueExpression> parameters);
+
     public class XTLInterpreter
     {
         private int _position;
@@ -19,8 +21,6 @@ public class XTLInterpreter
         private ITracingService _tracing;
         private InterpreterConfig _interpreterConfig;
 
-        public delegate ValueExpression FunctionHandler(Entity primary, IOrganizationService service, ITracingService tracing, InterpreterConfig interpreterConfig, List<ValueExpression> parameters);
-
         private Dictionary<string, FunctionHandler> _handlers = new Dictionary<string, FunctionHandler>
         {
             { "And", FunctionHandlers.And },
@@ -255,7 +255,7 @@ private List<ValueExpression> Expression(char[] terminators, Dictionary<string,
 
         private ValueExpression ApplyExpression (string name, List<ValueExpression> parameters, Dictionary<string, ValueExpression> formulaArgs = null) 
         {
-            if (!_handlers.ContainsKey(name)) {
+            if (!_handlers.ContainsKey(name) && !(_interpreterConfig?.CustomHandlers?.ContainsKey(name) ?? false)) {
                 throw new InvalidPluginExecutionException($"Function {name} is not known!");
             }
 
@@ -267,11 +267,22 @@ private ValueExpression ApplyExpression (string name, List<ValueExpression> para
 
             var lazyExecution = new Lazy<ValueExpression>(() =>
             {
-                _tracing.Trace($"Processing handler {name}");
-                var result = _handlers[name](_primary, _service, _tracing, _interpreterConfig, parameters);
-                _tracing.Trace($"Successfully processed handler {name}");
+                if (_interpreterConfig?.CustomHandlers?.ContainsKey(name) ?? false)
+                {
+                    _tracing.Trace($"Processing custom handler {name}");
+                    var result = _handlers[name](_primary, _service, _tracing, _interpreterConfig, parameters);
+                    _tracing.Trace($"Successfully processed custom handler {name}");
+
+                    return result;
+                }
+                else
+                {
+                    _tracing.Trace($"Processing default handler {name}");
+                    var result = _handlers[name](_primary, _service, _tracing, _interpreterConfig, parameters);
+                    _tracing.Trace($"Successfully processed default handler {name}");
 
-                return result;
+                    return result;
+                }
             });
 
             return new ValueExpression(lazyExecution);
@@ -312,7 +323,7 @@ private ValueExpression Formula(Dictionary<string, ValueExpression> args)
                 Match(')');
 
                 var usedReservedWords = variableNames
-                    .Where(n => new List<string> { "true", "false", "null" }.Concat(_handlers.Keys).Contains(n))
+                    .Where(n => new List<string> { "true", "false", "null" }.Concat(_handlers.Keys).Concat(_interpreterConfig?.CustomHandlers?.Keys ?? new List<string>()).Contains(n))
                     .ToList();
 
                 if (usedReservedWords.Count > 0)