Message: RazorLight.TemplateCompilationException : Failed to compile generated Razor template:

I updated to latest Microsoft.AspNetCore.App 2.1.4 and now FluentEmail.Razor won’t work.

Any time I try to send email using a razor template now I get this exception:

RazorLight.TemplateCompilationException : Failed to compile generated Razor template:
- (3:29) The type or namespace name 'Razor' does not exist in the namespace 'RazorLight' (are you missing an assembly reference?)
- (3:63) Predefined type 'System.String' is not defined or imported
- (3:104) Predefined type 'System.Type' is not defined or imported
- (7:10) The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
- (8:10) The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
- (9:10) The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
- (10:10) The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
- (11:56) The type or namespace name 'TemplatePage<>' does not exist in the namespace 'RazorLight' (are you missing an assembly reference?)
- (11:69) Cannot define a class or member that utilizes 'dynamic' because the compiler required type 'System.Runtime.CompilerServices.DynamicAttribute' cannot be found. Are you missing a reference?
- (11:69) Predefined type 'System.Boolean' is not defined or imported
- (14:66) The return type of an async method must be void, Task or Task<T>
- (14:38) The type or namespace name 'System' could not be found in the global namespace (are you missing an assembly reference?)
- (14:66) 'GeneratedTemplate.ExecuteAsync()': no suitable method found to override
- (16:12) Predefined type 'System.Object' is not defined or imported
- (16:12) The name 'BeginContext' does not exist in the current context
- (16:25) Predefined type 'System.Int32' is not defined or imported
- (16:28) Predefined type 'System.Int32' is not defined or imported
- (16:31) Predefined type 'System.Boolean' is not defined or imported
- (17:12) Predefined type 'System.Object' is not defined or imported
- (17:12) The name 'WriteLiteral' does not exist in the current context
- (17:25) Predefined type 'System.String' is not defined or imported
- (18:12) Predefined type 'System.Object' is not defined or imported
- (18:12) The name 'EndContext' does not exist in the current context
- (19:12) Predefined type 'System.Object' is not defined or imported
- (19:12) The name 'BeginContext' does not exist in the current context
- (19:25) Predefined type 'System.Int32' is not defined or imported
- (19:28) Predefined type 'System.Int32' is not defined or imported
- (19:32) Predefined type 'System.Boolean' is not defined or imported
- (0:3) Predefined type 'System.Object' is not defined or imported
- (0:3) The name 'Write' does not exist in the current context
- (0:9) Predefined type 'System.Object' is not defined or imported
- (0:9) The name 'Model' does not exist in the current context
- (25:12) Predefined type 'System.Object' is not defined or imported
- (25:12) The name 'EndContext' does not exist in the current context
- (26:12) Predefined type 'System.Object' is not defined or imported
- (26:12) The name 'BeginContext' does not exist in the current context
- (26:25) Predefined type 'System.Int32' is not defined or imported
- (26:29) Predefined type 'System.Int32' is not defined or imported
- (26:34) Predefined type 'System.Boolean' is not defined or imported
- (27:12) Predefined type 'System.Object' is not defined or imported
- (27:12) The name 'WriteLiteral' does not exist in the current context
- (27:25) Predefined type 'System.String' is not defined or imported
- (28:12) Predefined type 'System.Object' is not defined or imported
- (28:12) The name 'EndContext' does not exist in the current context
- (29:12) Predefined type 'System.Object' is not defined or imported
- (29:12) The name 'BeginWriteAttribute' does not exist in the current context
- (29:32) Predefined type 'System.String' is not defined or imported
- (29:40) Predefined type 'System.String' is not defined or imported
- (29:52) Predefined type 'System.Int32' is not defined or imported
- (29:57) Predefined type 'System.String' is not defined or imported
- (29:63) Predefined type 'System.Int32' is not defined or imported
- (29:68) Predefined type 'System.Int32' is not defined or imported
- (4:0) Predefined type 'System.Object' is not defined or imported
- (4:0) The name 'WriteAttributeValue' does not exist in the current context
- (4:20) Predefined type 'System.String' is not defined or imported
- (4:24) Predefined type 'System.Int32' is not defined or imported
- (4:29) Predefined type 'System.Object' is not defined or imported
- (4:29) The name 'Model' does not exist in the current context
- (4:48) Predefined type 'System.Int32' is not defined or imported
- (4:53) Predefined type 'System.Int32' is not defined or imported
- (4:57) Predefined type 'System.Boolean' is not defined or imported
- (35:12) Predefined type 'System.Object' is not defined or imported
- (35:12) The name 'EndWriteAttribute' does not exist in the current context
- (36:12) Predefined type 'System.Object' is not defined or imported
- (36:12) The name 'BeginContext' does not exist in the current context
- (36:25) Predefined type 'System.Int32' is not defined or imported
- (36:30) Predefined type 'System.Int32' is not defined or imported
- (36:33) Predefined type 'System.Boolean' is not defined or imported
- (37:12) Predefined type 'System.Object' is not defined or imported
- (37:12) The name 'WriteLiteral' does not exist in the current context
- (37:25) Predefined type 'System.String' is not defined or imported
- (38:12) Predefined type 'System.Object' is not defined or imported
- (38:12) The name 'EndContext' does not exist in the current context
- (39:12) Predefined type 'System.Object' is not defined or imported
- (39:12) The name 'BeginContext' does not exist in the current context
- (39:25) Predefined type 'System.Int32' is not defined or imported
- (39:30) Predefined type 'System.Int32' is not defined or imported
- (39:34) Predefined type 'System.Boolean' is not defined or imported
- (4:27) Predefined type 'System.Object' is not defined or imported
- (4:27) The name 'Write' does not exist in the current context
- (4:33) Predefined type 'System.Object' is not defined or imported
- (4:33) The name 'Model' does not exist in the current context
- (45:12) Predefined type 'System.Object' is not defined or imported
- (45:12) The name 'EndContext' does not exist in the current context
- (46:12) Predefined type 'System.Object' is not defined or imported
- (46:12) The name 'BeginContext' does not exist in the current context
- (46:25) Predefined type 'System.Int32' is not defined or imported
- (46:30) Predefined type 'System.Int32' is not defined or imported
- (46:35) Predefined type 'System.Boolean' is not defined or imported
- (47:12) Predefined type 'System.Object' is not defined or imported
- (47:12) The name 'WriteLiteral' does not exist in the current context
- (47:25) Predefined type 'System.String' is not defined or imported
- (48:12) Predefined type 'System.Object' is not defined or imported
- (48:12) The name 'EndContext' does not exist in the current context
- (14:66) 'GeneratedTemplate.ExecuteAsync()': not all code paths return a value

Result StackTrace:	
at RazorLight.Compilation.RoslynCompilationService.CompileAndEmit(GeneratedRazorTemplate razorTemplate)
   at RazorLight.TemplateFactoryProvider.CreateFactory(GeneratedRazorTemplate razorTemplate)
   at RazorLight.TemplateFactoryProvider.CreateFactoryAsync(String templateKey)
   at RazorLight.RazorLightEngine.CompileTemplateAsync(String key)
   at RazorLight.RazorLightEngine.CompileRenderAsync(String key, Object model, Type modelType, ExpandoObject viewBag)
   at FluentEmail.Razor.RazorRenderer.ParseAsync[T](String template, T model, Boolean isHtml)
   at FluentEmail.Razor.RazorRenderer.FluentEmail.Core.Interfaces.ITemplateRenderer.Parse[T](String template, T model, Boolean isHtml)
   at FluentEmail.Core.Email.UsingTemplateFromFile[T](String filename, T model, Boolean isHtml)

I downloaded source code and ran. The exception is generated in RazorRenderer.cs the string ITemplateRenderer.Parse<T>(string template, T model, bool isHtml).

Error is missing reference in RazorLight library and happens on a fresh project setup.

EDIT: The issue is resolve by updating the RazorLight version to beta1 and adding to csproj:

  <PropertyGroup>
    <PreserveCompilationContext>true</PreserveCompilationContext>
  </PropertyGroup>

I will create PR

[rdhainaut]

@aatmmr just to be sure, Can you check if you have the correct using in your file.

@using RazorLight
@using System

[rdhainaut]

I think in .Net Core 3, you should use <PreserveCompilationContext>true</PreserveCompilationContext> <PreserveCompilationReferences>true</PreserveCompilationReferences>