Improve the error message when ExtensionParameters are executed in in…

…valid contexts

When the data context stack is shallower than expected,
it might receive null control.

src/Framework/Framework/Compilation/ControlTree/BindingExtensionParameter.cs

@@ -77,7 +77,8 @@ public class CurrentCollectionIndexExtensionParameter : BindingExtensionParamete
         }
 
         internal static int GetIndex(DotvvmBindableObject c) =>
-            (c.GetAllAncestors(true, false)
+            (c.NotNull("control is null, is the binding executed in the right data context?")
+            .GetAllAncestors(true, false)
             .OfType<DataItemContainer>()
             .FirstOrDefault() ?? throw new DotvvmControlException(c, "Could not find ancestor DataItemContainer that stores the current collection index."))
             .DataItemIndex ?? throw new DotvvmControlException(c, "Nearest DataItemContainer does have the collection index specified.");
@@ -141,18 +142,25 @@ public class InjectedServiceExtensionParameter : BindingExtensionParameter
         public InjectedServiceExtensionParameter(string identifier, ITypeDescriptor type)
             : base(identifier, type, inherit: true) { }
 
+        private static MethodInfo ResolveStaticCommandServiceMethod = typeof(InjectedServiceExtensionParameter).GetMethod(nameof(ResolveStaticCommandService), BindingFlags.NonPublic | BindingFlags.Static)!;
+
         public override Expression GetServerEquivalent(Expression controlParameter)
         {
             var type = ResolvedTypeDescriptor.ToSystemType(this.ParameterType);
-            var expr = ExpressionUtils.Replace((DotvvmBindableObject c) => ResolveStaticCommandService(c, type), controlParameter);
-            return Expression.Convert(expr, type);
+            return Expression.Call(
+                ResolveStaticCommandServiceMethod.MakeGenericMethod(type),
+                controlParameter
+            );
         }
 
-        private object ResolveStaticCommandService(DotvvmBindableObject c, Type type)
+        private static T ResolveStaticCommandService<T>(DotvvmBindableObject control)
         {
-            var context = (IDotvvmRequestContext)c.GetValue(Internal.RequestContextProperty, true).NotNull();
+            if (control is null)
+                throw new ArgumentNullException(nameof(control), "control is null, is the binding executed in the right data context?");
+            var context = (IDotvvmRequestContext)control.GetValue(Internal.RequestContextProperty, true)
+                .NotNull("Current control does not not have the Internal.RequestContextProperty property");
 #pragma warning disable CS0618
-            return context.Services.GetRequiredService<IStaticCommandServiceLoader>().GetStaticCommandService(type, context);
+            return (T)context.Services.GetRequiredService<IStaticCommandServiceLoader>().GetStaticCommandService(typeof(T), context);
 #pragma warning restore CS0618
         }
 
@@ -229,7 +237,7 @@ public override Expression GetServerEquivalent(Expression controlParameter)
 
         internal static ClaimsPrincipal? GetUser(DotvvmBindableObject control)
         {
-            var context = control.GetValue(Internal.RequestContextProperty) as IDotvvmRequestContext;
+            var context = control.NotNull("control is null, is the binding executed in the right data context?").GetValue(Internal.RequestContextProperty) as IDotvvmRequestContext;
             return context?.HttpContext?.User ?? new ClaimsPrincipal();
         }
 

src/Framework/Framework/Utils/FunctionalExtensions.cs

@@ -3,6 +3,7 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
+using System.Runtime.CompilerServices;
 using System.Text;
 using System.Threading.Tasks;
 
@@ -100,9 +101,19 @@ public static int FindIndex<T>(this IEnumerable<T> enumerable, Func<T, bool> pre
             return -1;
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static T NotNull<T>([NotNull] this T? target, string message = "Unexpected null value.")
-            where T : class =>
-            target ?? throw new Exception(message);
+            where T : class
+        {
+            if (target is null)
+                NotNullThrowHelper(message);
+            return target;
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        [DoesNotReturn]
+        private static void NotNullThrowHelper(string message) =>
+            throw new Exception(message);
 
         public static SortedDictionary<K, V> ToSorted<K, V>(this IDictionary<K, V> d, IComparer<K>? c = null)
             where K: notnull =>

src/Tests/Binding/BindingCompilationTests.cs

@@ -1207,6 +1207,28 @@ public void Error_DifferentDataContext()
             );
         }
 
+        [TestMethod]
+        public void Error_MissingDataContext_ExtensionParameter()
+        {
+            var type = DataContextStack.Create(typeof(string), parent: DataContextStack.Create(typeof(TestViewModel), extensionParameters: [ new InjectedServiceExtensionParameter("config", ResolvedTypeDescriptor.Create(typeof(DotvvmConfiguration)))]));
+            var control = new PlaceHolder();
+            var context = DotvvmTestHelper.CreateContext();
+            control.SetDataContextType(type.Parent);
+            control.DataContext = new TestViewModel();
+            control.SetValue(Internal.RequestContextProperty, context);
+
+            var nested = new PlaceHolder();
+            control.Children.Add(nested);
+
+            var exception = XAssert.ThrowsAny<Exception>(() => ExecuteBinding("config.ApplicationPhysicalPath", type, nested));
+            XAssert.Contains("data context", exception.Message);
+
+            // check that the error goes away when the data context is set properly
+            nested.SetDataContextType(type);
+            nested.DataContext = "test";
+            Assert.AreEqual(".", ExecuteBinding("config.ApplicationPhysicalPath", type, nested));
+        }
+
         [TestMethod]
         public void NullableIntAssignment()
         {