Modify ViewComponent_CannotFindComponent error message (#6263)

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Properties/Resources.Designer.cs

@@ -67,7 +67,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             => string.Format(CultureInfo.CurrentCulture, GetString("ViewComponent_SyncMethod_ShouldReturnValue"), p0, p1);
 
         /// <summary>
-        /// A view component named '{0}' could not be found.
+        /// A view component named '{0}' could not be found. A view component must be a public non-abstract class, not contain any generic parameters, and either be decorated with '{1}' or have a class name ending with the '{2}' suffix. A view component must not be decorated with '{3}'.
         /// </summary>
         internal static string ViewComponent_CannotFindComponent
         {
@@ -75,10 +75,10 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         }
 
         /// <summary>
-        /// A view component named '{0}' could not be found.
+        /// A view component named '{0}' could not be found. A view component must be a public non-abstract class, not contain any generic parameters, and either be decorated with '{1}' or have a class name ending with the '{2}' suffix. A view component must not be decorated with '{3}'.
         /// </summary>
-        internal static string FormatViewComponent_CannotFindComponent(object p0)
+        internal static string FormatViewComponent_CannotFindComponent(object p0, object p1, object p2, object p3)
-            => string.Format(CultureInfo.CurrentCulture, GetString("ViewComponent_CannotFindComponent"), p0);
+            => string.Format(CultureInfo.CurrentCulture, GetString("ViewComponent_CannotFindComponent"), p0, p1, p2, p3);
 
         /// <summary>
         /// An invoker could not be created for the view component '{0}'.

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Resources.resx

@@ -131,7 +131,7 @@
     <value>Method '{0}' of view component '{1}' should be declared to return a value.</value>
   </data>
   <data name="ViewComponent_CannotFindComponent" xml:space="preserve">
-    <value>A view component named '{0}' could not be found.</value>
+    <value>A view component named '{0}' could not be found. A view component must be a public non-abstract class, not contain any generic parameters, and either be decorated with '{1}' or have a class name ending with the '{2}' suffix. A view component must not be decorated with '{3}'.</value>
   </data>
   <data name="ViewComponent_IViewComponentFactory_ReturnedNull" xml:space="preserve">
     <value>An invoker could not be created for the view component '{0}'.</value>

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewComponents/DefaultViewComponentHelper.cs

@@ -98,7 +98,11 @@ namespace Microsoft.AspNetCore.Mvc.ViewComponents
             var descriptor = _selector.SelectComponent(name);
             if (descriptor == null)
             {
-                throw new InvalidOperationException(Resources.FormatViewComponent_CannotFindComponent(name));
+                throw new InvalidOperationException(Resources.FormatViewComponent_CannotFindComponent(
+                    name,
+                    nameof(ViewComponentAttribute),
+                    ViewComponentConventions.ViewComponentSuffix,
+                    nameof(NonViewComponentAttribute)));
             }
 
             return InvokeCoreAsync(descriptor, arguments);
@@ -129,7 +133,10 @@ namespace Microsoft.AspNetCore.Mvc.ViewComponents
             }
 
             throw new InvalidOperationException(Resources.FormatViewComponent_CannotFindComponent(
-                componentType.FullName));
+                componentType.FullName,
+                nameof(ViewComponentAttribute),
+                ViewComponentConventions.ViewComponentSuffix,
+                nameof(NonViewComponentAttribute)));
         }
 
         // Internal for testing

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewComponents/ViewComponentConventions.cs

@@ -9,7 +9,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewComponents
 {
     public static class ViewComponentConventions
     {
-        private const string ViewComponentSuffix = "ViewComponent";
+        public static readonly string ViewComponentSuffix = "ViewComponent";
 
         public static string GetComponentName(TypeInfo componentType)
         {

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/ViewComponentResultTest.cs

@@ -105,7 +105,10 @@ namespace Microsoft.AspNetCore.Mvc
         public async Task ExecuteResultAsync_Throws_IfViewComponentCouldNotBeFound_ByName()
         {
             // Arrange
-            var expected = "A view component named 'Text' could not be found.";
+            var expected = "A view component named 'Text' could not be found. A view component must be " +
+                "a public non-abstract class, not contain any generic parameters, and either be decorated " +
+                "with 'ViewComponentAttribute' or have a class name ending with the 'ViewComponent' suffix. " +
+                "A view component must not be decorated with 'NonViewComponentAttribute'.";
 
             var actionContext = CreateActionContext();
 
@@ -125,7 +128,10 @@ namespace Microsoft.AspNetCore.Mvc
         public async Task ExecuteResultAsync_Throws_IfViewComponentCouldNotBeFound_ByType()
         {
             // Arrange
-            var expected = $"A view component named '{typeof(TextViewComponent).FullName}' could not be found.";
+            var expected = $"A view component named '{typeof(TextViewComponent).FullName}' could not be found. " +
+                "A view component must be a public non-abstract class, not contain any generic parameters, and either be decorated " +
+                "with 'ViewComponentAttribute' or have a class name ending with the 'ViewComponent' suffix. " +
+                "A view component must not be decorated with 'NonViewComponentAttribute'.";
 
             var actionContext = CreateActionContext();
             var services = CreateServices(diagnosticListener: null, context: actionContext.HttpContext);