Improve error messages

Closes #1425

src/activities/Elsa.Activities.Http/Middleware/HttpEndpointMiddleware.cs

@@ -128,7 +128,7 @@ namespace Elsa.Activities.Http.Middleware
                 pendingWorkflowInstance = await workflowInstanceStore.FindByIdAsync(pendingWorkflow.WorkflowInstanceId, cancellationToken);
 
                 if (pendingWorkflowInstance is not null
-                    && pendingWorkflowInstance.WorkflowStatus == Elsa.Models.WorkflowStatus.Faulted
+                    && pendingWorkflowInstance.WorkflowStatus == WorkflowStatus.Faulted
                     && !httpContext.Response.HasStarted)
                 {
                     httpContext.Response.ContentType = "application/json";
@@ -137,6 +137,7 @@ namespace Elsa.Activities.Http.Middleware
                     var faultedResponse = JsonConvert.SerializeObject(new
                     {
                         errorMessage = $"Workflow faulted at {pendingWorkflowInstance.FaultedAt!} with error: {pendingWorkflowInstance.Fault!.Message}",
+                        exception = pendingWorkflowInstance.Fault?.Exception,
                         workflow = new
                         {
                             name = pendingWorkflowInstance.Name,

src/core/Elsa.Abstractions/Models/SimpleException.cs

@@ -1,28 +1,33 @@
 using System;
+using System.Collections;
+using System.Collections.Generic;
 
 namespace Elsa.Models
 {
     public class SimpleException
     {
-        public SimpleException(Type type, string message, string stackTrace, SimpleException? innerException = default)
+        public SimpleException(Type type, string message, string stackTrace, IDictionary data, SimpleException? innerException = default)
         {
             Type = type;
             Message = message;
             StackTrace = stackTrace;
             InnerException = innerException;
+            Data = data;
         }
         
         public Type Type { get; set; }
         public string Message { get; set; }
         public string StackTrace { get; set; }
         public SimpleException? InnerException { get; set; }
+        public IDictionary Data { get; set; }
         
         public static SimpleException? FromException(Exception? ex)
         {
             if (ex == null)
                 return null;
-            
-            var simpleException = new SimpleException(ex.GetType(), ex.Message, ex.StackTrace);
+
+            var exceptionType = ex.GetType();
+            var simpleException = new SimpleException(exceptionType, ex.Message, ex.StackTrace, ex.Data);
 
             if (ex.InnerException != null)
                 simpleException.InnerException = FromException(ex.InnerException);

src/core/Elsa.Abstractions/Models/SimpleExceptionProperty.cs

@@ -0,0 +1,14 @@
+namespace Elsa.Models
+{
+    public class SimpleExceptionProperty
+    {
+        public SimpleExceptionProperty(string name, object value)
+        {
+            Name = name;
+            Value = value;
+        }
+
+        public string Name { get; set; }
+        public object Value { get; set; }
+    }
+}

src/core/Elsa.Core/Exceptions/ExpressionEvaluationException.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace Elsa.Exceptions
+{
+    public class ExpressionEvaluationException : Exception
+    {
+        public string Expression
+        {
+            get => (string)Data[nameof(Expression)];
+            set => Data[nameof(Expression)] = value;
+        }
+
+        public string Syntax
+        {
+            get => (string)Data[nameof(Syntax)];
+            set => Data[nameof(Syntax)] = value;
+        }
+
+        public ExpressionEvaluationException(string message, string expression, string syntax, Exception innerException) : base(message, innerException)
+        {
+            Expression = expression;
+            Syntax = syntax;
+        }
+    }
+}

src/core/Elsa.Core/Expressions/ExpressionEvaluator.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using Elsa.Exceptions;
 using Elsa.Models;
 using Elsa.Services.Models;
 using Microsoft.Extensions.Logging;
@@ -63,7 +64,7 @@ namespace Elsa.Expressions
             catch (Exception e)
             {
                 _logger.LogDebug(e, "Failed to evaluate expression {Expression} using syntax {Syntax}", expression, syntax);
-                throw;
+                throw new ExpressionEvaluationException("Failed to evaluate expression", expression, syntax, e);
             }
         }
     }