Asp.Net 5.0 Blazor Assembly.Load does not create types that link to types in loaded assemblies

[allderidge]

Describe the bug

When using Blazor running in the browser with dotnet 5.0.0-preview.8.20407.11 an assembly loaded using Assembly.Load(byte[] rawAssembly, byte[]? rawSymbolStore) will create types that reference assemblies that appear to be duplicates of assemblies that have already been loaded preventing any use of shared types. This behavior is different to other non WASM runtimes and to the dotnet 3.2.0 WASM runtime.

The bug is not present in the release of WASM Blazor in dotnet core 3.2.0 and was found during an upgrade of existing code.

E.g.

• A Type A implements interface IA
• Interface IA is defined in an assembly that the a Blazor component is build against
• Type A is defined in an project that references the project interface IA is present in
• Interface IA will be resolved when the Blazor component loads.
• Type A is defined in an assembly loaded by Assembly.Load
• In the dotnet 5.0 WASM runtime the interface IA implemented by Type A is defined in an assembly that is different to the interface IA referenced by the Blazor component meaning that the component cannot cast Type A to Interface IA.
• The same code run in a stardard dotnet 5.0 runtime is correctly able to perform the cast.

To Reproduce

A reproduction based on the Blazor starter project is available from: https://github.com/allderidge/BlazorBugReport_AssemblyLoad

There are two solutions:

• AssemblyLoadTest_5_0/AssemblyLoadTest.sln Reproduces the bug and illustrates that a test in a standard runtime passes.
• AssemblyLoadTest_3_2_0/AssemblyLoadTest.sln Illustrates the bug is not present in the dotnet core 3.2

The web page shown running in dotnet 5.0:

The web page shown running in dotnet core 3.2

Illustrative code

var assemblyData = await Client.GetFromJsonAsync<DynamicAssembly>("Assembly");
var assembly = Assembly.Load(assemblyData.AssemblyDllBytes, assemblyData.AssemblyPdbBytes);

var dynamicType = assembly.GetType("AssemblyLoadTest.Dynamic.SharedInterfaceImplementation", true) ?? throw new ApplicationException("Unable to load dynamic type");
var sharedInterface = dynamicType.GetInterfaces().First(e => e.Name == nameof(ISharedInterface));
SharedAssemblyMatches = sharedInterface.Assembly == typeof(ISharedInterface).Assembly;  // should be true, false in bug repo
SharedInterfaceMatches = sharedInterface == typeof(ISharedInterface); // should be true, false in bug repo

var instance = Activator.CreateInstance(dynamicType);
CanCast = instance is ISharedInterface;  // should be true, false in bug repo

Name = ((ISharedInterface)instance).HelloWorldName; // causes a invalid cast exception

Further technical details

• ASP.NET Core version: 5.0.0-preview.8.20414.8
• Include the output of dotnet --info

 Version:   5.0.100-preview.8.20417.9
 Commit:    fc62663a35

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18363
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\5.0.100-preview.8.20417.9\

Host (useful for support):
  Version: 5.0.0-preview.8.20407.11
  Commit:  bf456654f9

.NET SDKs installed:
  2.1.504 [C:\Program Files\dotnet\sdk]
  2.1.602 [C:\Program Files\dotnet\sdk]
  2.1.700-preview-009601 [C:\Program Files\dotnet\sdk]
  3.0.100-preview4-011223 [C:\Program Files\dotnet\sdk]
  3.1.103 [C:\Program Files\dotnet\sdk]
  3.1.200 [C:\Program Files\dotnet\sdk]
  3.1.300-preview-015048 [C:\Program Files\dotnet\sdk]
  3.1.302 [C:\Program Files\dotnet\sdk]
  3.1.402 [C:\Program Files\dotnet\sdk]
  5.0.100-preview.8.20417.9 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.All 2.1.8 [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 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.8 [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 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview4-19216-03 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.0-preview.8.20414.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.8 [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 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview4-27615-11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.0-preview.8.20407.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview4-27613-28 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.0-preview.8.20411.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

• The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version
  Microsoft Visual Studio Enterprise 2019 Preview Version 16.8.0 Preview 2.1

[pranavkm]

I suspect you'll need to load things in to the default load context AssemblyLoadContext.Default.LoadFromStream. Assembly.Load in .NET Core loads assemblies in an assembly specific load context.

[allderidge]

Using AssemblyLoadContext.Default.LoadFromStream as an alternative does successfully load the assembly so that a cast to a common interface can be performed.

I think the implementation of the custom AssemblyLoadContext created during Assembly.Load has an issue in that it should not be loading any other assemblies other than the one its given, finding other assemblies should delegate to AssemblyLoadContext.Default.

Tagging subscribers to this area: @vitek-karas, @agocke
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[lewing]

cc @CoffeeFlux

Tagging subscribers to this area: @CoffeeFlux
See info in area-owners.md if you want to be subscribed.

[CoffeeFlux]

I assume this is the result of our bundle check being very early in the loading algorithm, so if the assembly isn't loaded in the custom ALC it tries the load it in via the bundle before checking the default context. The solution is probably to just move the bundle check later in the process, after we've checked the default ALC.

This is maybe worth backporting, so I'll have a fix up ASAP. I'll add a test as well. Thanks for such a detailed bug report, it makes a fix much easier!