Merge pull request #4577 from LuckyPennySoftware/4563-provide-better-diagnostic-exceptions-for-expression-tree-errors

Provide better exceptions for errors when building the mapping plan

Author: jbogard

src/AutoMapper/Execution/TypeMapPlanBuilder.cs

@@ -254,7 +254,14 @@ private void AddPathMaps(List<Expression> actions)
                 continue;
             }
 
-            actions.Add(TryPathMap(pathMap));
+            try
+            {
+                actions.Add(TryPathMap(pathMap));
+            }
+            catch (Exception e) when (e is not AutoMapperConfigurationException)
+            {
+                throw new AutoMapperMappingException("Error building path mapping strategy.", e, pathMap);
+            }
         }
     }
 
@@ -287,14 +294,21 @@ private void AddPropertyMaps(List<Expression> actions)
                 continue;
             }
 
-            var property = TryMemberMap(propertyMap,
-                CreatePropertyMapFunc(propertyMap, _destination, propertyMap.DestinationMember));
-            if (_typeMap.ConstructorParameterMatches(propertyMap.DestinationName))
+            try
             {
-                property = _initialDestination.IfNullElse(_configuration.Default(property.Type), property);
+                var property = TryMemberMap(propertyMap,
+                    CreatePropertyMapFunc(propertyMap, _destination, propertyMap.DestinationMember));
+                if (_typeMap.ConstructorParameterMatches(propertyMap.DestinationName))
+                {
+                    property = _initialDestination.IfNullElse(_configuration.Default(property.Type), property);
+                }
+            
+                actions.Add(property);
+            }
+            catch (Exception e) when (e is not AutoMapperConfigurationException)
+            {
+                throw new AutoMapperMappingException("Error building member mapping strategy.", e, propertyMap);
             }
-
-            actions.Add(property);
         }
     }
 
@@ -366,9 +380,16 @@ private Expression ConstructorMapping(ConstructorMap constructorMap)
         List<Expression> body = [];
         foreach (var parameter in constructorMap.CtorParams)
         {
-            var variable = Variable(parameter.DestinationType, parameter.DestinationName);
-            variables.Add(variable);
-            body.Add(Assign(variable, CreateConstructorParameterExpression(parameter)));
+            try
+            {
+                var variable = Variable(parameter.DestinationType, parameter.DestinationName);
+                variables.Add(variable);
+                body.Add(Assign(variable, CreateConstructorParameterExpression(parameter)));
+            }
+            catch (Exception e) when (e is not AutoMapperConfigurationException)
+            {
+                throw new AutoMapperMappingException("Error building constructor parameter mapping strategy.", e, parameter);
+            }
         }
 
         body.Add(CheckReferencesCache(New(constructorMap.Ctor, variables)));

src/AutoMapper/QueryableExtensions/ProjectionBuilder.cs

@@ -110,10 +110,18 @@ void ProjectProperties()
                     {
                         continue;
                     }
-                    var propertyProjection = TryProjectMember(propertyMap);
-                    if(propertyProjection != null)
+
+                    try
                     {
-                        propertiesProjections.Add(Bind(propertyMap.DestinationMember, propertyProjection));
+                        var propertyProjection = TryProjectMember(propertyMap);
+                        if(propertyProjection != null)
+                        {
+                            propertiesProjections.Add(Bind(propertyMap.DestinationMember, propertyProjection));
+                        }
+                    }
+                    catch (Exception e) when (e is not AutoMapperConfigurationException)
+                    {
+                        throw new AutoMapperMappingException("Error building queryable mapping strategy.", e, propertyMap);
                     }
                 }
             }
@@ -209,7 +217,17 @@ IProjectionMapper GetProjectionMapper()
             {
                 { CustomCtorExpression: LambdaExpression ctorExpression } => (NewExpression)ctorExpression.ReplaceParameters(instanceParameter),
                 { ConstructorMap: { CanResolve: true } constructorMap } =>
-                    New(constructorMap.Ctor, constructorMap.CtorParams.Select(map => TryProjectMember(map, map.DefaultValue(null)) ?? Default(map.DestinationType))),
+                    New(constructorMap.Ctor, constructorMap.CtorParams.Select(map =>
+                    {
+                        try
+                        {
+                            return TryProjectMember(map, map.DefaultValue(null)) ?? Default(map.DestinationType);
+                        }
+                        catch (Exception e) when (e is not AutoMapperConfigurationException)
+                        {
+                            throw new AutoMapperMappingException("Error building constructor projection strategy.", e, map);
+                        }
+                    })),
                 _ => New(typeMap.DestinationType)
             };
         }

src/AutoMapper/TypeMap.cs

@@ -204,8 +204,15 @@ public void Seal(IGlobalConfiguration configuration)
             return;
         }
         _sealed = true;
-        _details?.Seal(configuration, this);
-        MapExpression = Projection ? EmptyLambda : CreateMapperLambda(configuration);
+        try
+        {
+            _details?.Seal(configuration, this);
+            MapExpression = Projection ? EmptyLambda : CreateMapperLambda(configuration);
+        }
+        catch (Exception e) when (e is not AutoMapperConfigurationException)
+        {
+            throw new AutoMapperMappingException("Error creating mapping strategy.", e, this);
+        }
         SourceTypeDetails = null;
         DestinationTypeDetails = null;
     }

src/UnitTests/ForPath.cs

@@ -250,11 +250,11 @@ public class SourceModel
     [Fact]
     public void Should_throw_exception()
     {
-        Assert.Throws<NullReferenceException>(() =>
+        Assert.Throws<AutoMapperMappingException>(() =>
         {
             var cfg = new MapperConfiguration(config =>
             {
-                Assert.Throws<System.ArgumentNullException>(() =>
+                Assert.Throws<ArgumentNullException>(() =>
                 {
                     config.CreateMap<SourceModel, DestinationModel>()
                         .ForPath(sourceModel => sourceModel.Name, opts => opts.MapFrom<string>(null));