TopLevelParameterNameAnalyzer threw an exception of type System.NullReferenceException.

[twitchax]

Describe the bug

The warning below is emitted when building my project.

CSC : warning AD0001: Analyzer 'Microsoft.AspNetCore.Mvc.Analyzers.TopLevelParameterNameAnalyzer' threw an exception of type 'System.NullReferenceException' with message 'Object reference not set to an instance of an object.'.

To Reproduce

1. Install .NET Core SDK 3.0.100.
2. git clone git@github.com:twitchax/AspNetCore.Proxy.git
3. dotnet test

Expected behavior

No warnings.

Screenshots

N/A.

Additional context

.NET Core SDK (reflecting any global.json):
 Version:   3.0.100
 Commit:    04339c3a26

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18362
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.0.100\

Host (useful for support):
  Version: 3.0.0
  Commit:  7d57652f33

.NET Core SDKs installed:
  1.0.4 [C:\Program Files\dotnet\sdk]
  1.1.0-preview1-005051 [C:\Program Files\dotnet\sdk]
  1.1.0-preview1-005077 [C:\Program Files\dotnet\sdk]
  1.1.0-preview1-005098 [C:\Program Files\dotnet\sdk]
  1.1.0 [C:\Program Files\dotnet\sdk]
  2.0.0-preview1-005977 [C:\Program Files\dotnet\sdk]
  2.0.0-preview2-006497 [C:\Program Files\dotnet\sdk]
  2.0.0 [C:\Program Files\dotnet\sdk]
  2.0.2-vspre-006949 [C:\Program Files\dotnet\sdk]
  2.0.2 [C:\Program Files\dotnet\sdk]
  2.1.1-preview-007094 [C:\Program Files\dotnet\sdk]
  2.1.1-preview-007165 [C:\Program Files\dotnet\sdk]
  2.1.1 [C:\Program Files\dotnet\sdk]
  2.1.2 [C:\Program Files\dotnet\sdk]
  2.1.4 [C:\Program Files\dotnet\sdk]
  2.1.100-preview-007326 [C:\Program Files\dotnet\sdk]
  2.1.100-preview-007363 [C:\Program Files\dotnet\sdk]
  2.1.100 [C:\Program Files\dotnet\sdk]
  2.1.200-preview-007474 [C:\Program Files\dotnet\sdk]
  2.1.200-preview-007597 [C:\Program Files\dotnet\sdk]
  2.1.200 [C:\Program Files\dotnet\sdk]
  2.1.201 [C:\Program Files\dotnet\sdk]
  2.1.202 [C:\Program Files\dotnet\sdk]
  2.1.301 [C:\Program Files\dotnet\sdk]
  2.1.400-preview-009171 [C:\Program Files\dotnet\sdk]
  2.1.402 [C:\Program Files\dotnet\sdk]
  2.1.600-preview-009426 [C:\Program Files\dotnet\sdk]
  2.1.600-preview-009472 [C:\Program Files\dotnet\sdk]
  2.1.602 [C:\Program Files\dotnet\sdk]
  2.2.102 [C:\Program Files\dotnet\sdk]
  2.2.401 [C:\Program Files\dotnet\sdk]
  3.0.100 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 1.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.0-preview1-002111-00 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.0-preview2-25407-01 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[twitchax]

Well, frustratingly, I opened up the latest VS 2019 Preview, and now the warnings have disappeared.

However, the warnings continue to appear:

• In WSL with 3.0.100.
• In an ubuntu docker container with 3.0.100.
• In my GitHub Action build, which is an ubuntu docker container with 3.0.100.

Is there a delta in the toolchains between the .NET Core 3.0 SDK and the VS 2019 16.3.0 toolchain that would cause this to only appear on a bare machine with .NET Core 3.0, while not appearing on a machine with VS 2019 16.3.0?

[pranavkm]

@twitchax the test app is using a 3.0.0 of Microsoft.AspNetCore.TestHost which is effectively lifting the tests to compile the app against 3.0.0 versions of ASP.NET Core. Your app is still targeting .NET Core 2.2. Given there were many breaking changes in 3.0, I don't think you want to mix the two versions when testing.

Consider changing the test app to target 2.2.x version of TestHost or migrating your application to .NET Core 3.0. Alternatively, you should be able to suppress the analyzer in the test project.

---

More details:
The null refs is a result of one of the breaking changes in 3.0 - some types that were formerly pub-internal were moved to a public interface while also changing their namespace. The app's package reference to Microsoft.AspNetCore.Mvc to 2.2.0 gets lifted to the 3.0.0 framework reference in the test app, but the analyzer package remains 2.2.0. You effectively get this:

This might fall in to the category of the SDK lifting the 2.2 analyzer package reference to a 3.0 version if it sees a FrameworkReference to Microsoft.AspNetCore.App, but I'm not sure how trivial that is.

[mkArtakMSFT]

While this seems to be a non-supported scenario, let's try to polish up the analyzer to account for this scenarios too.

[Shiko1st]

I have the same problem after migration to core 3, visual studio is 16.3.7

[yuchen-w]

Without disabling the Code Analysis (Project Settings > Code Analysis > Run On Build) this error prevents my project from building in Visual Studio.

VS version: 16.3.9
.NET Core SDK: 3.0.100

As you can see my project after upgrading from .net core 2.2 to 3.0 has references to two different versions of Microsoft.AspNetCore.Mvc.Analyzers

[sm-g]

@yuchen-w You probably have nuget package which have 2.2.0 as dependency, like: