MSB4018 on Blazor WASM with .NET 9.0.300

[MRT-77]

Describe the bug

After upgrading Visual Studio to version 17.14.0, I started encountering this issue.
To resolve it, I first performed a Repair using the Visual Studio Installer, but the problem persisted.

For further troubleshooting, I completely uninstalled Visual Studio and installed only the .NET SDK manually.
Then, I installed the required workloads using the CLI. However, even after creating a clean Blazor WebAssembly project and building it, the same error still occurred.

However, I was able to temporarily work around the problem by manually installing .NET SDK 9.0.204 after reinstalling Visual Studio, and then deleting the folder C:\Program Files\dotnet\sdk\9.0.300.
This resolved the build error both in Visual Studio and when using the CLI.

To Reproduce

1. Install .Net SDK 9.0.300
2. Install Workload dotnet workload install wasm-tools
3. Create New Project dotnet new blazorwasm -o _MyCleanApp --framework net9.0
4. Just Build

Exceptions

Restore complete (0.5s)
  _MyCleanApp failed with 1 error(s) (0.3s)
    C:\Program Files\dotnet\sdk\9.0.300\Sdks\Microsoft.NET.Sdk.BlazorWebAssembly\targets\Microsoft.NET.Sdk.BlazorWebAssembly.6_0.targets(125,5): error MSB4018:
      The "DefineStaticWebAssetEndpoints" task failed unexpectedly.
      System.AggregateException: One or more errors occurred. (Last write time for 'D:\_MyCleanApp\bin\Debug\net9.0\wwwroot\_framework\blazor.webassembly.js' is not defined.)
       ---> System.InvalidOperationException: Last write time for 'D:\_MyCleanApp\bin\Debug\net9.0\wwwroot\_framework\blazor.webassembly.js' is not defined.
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.StaticWebAsset.Validate()
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.StaticWebAsset.FromTaskItem(ITaskItem item)
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.DefineStaticWebAssetEndpoints.ParallelWorker.Process(Int32 i, ParallelLoopState _)
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.DefineStaticWebAssetEndpoints.<>c.<Execute>b__16_2(Int32 i, ParallelLoopState loop, ParallelWorker state)
         at System.Threading.Tasks.Parallel.<>c__DisplayClass19_0`2.<ForWorker>b__1(RangeWorker& currentWorker, Int64 timeout, Boolean& replicationDelegateYieldedBeforeCompletion)
      --- End of stack trace from previous location ---
         at System.Threading.Tasks.Parallel.<>c__DisplayClass19_0`2.<ForWorker>b__1(RangeWorker& currentWorker, Int64 timeout, Boolean& replicationDelegateYieldedBeforeCompletion)
         at System.Threading.Tasks.TaskReplicator.Replica.Execute()
         --- End of inner exception stack trace ---
         at System.Threading.Tasks.TaskReplicator.Run[TState](ReplicatableUserAction`1 action, ParallelOptions options, Boolean stopOnFirstFailure)
         at System.Threading.Tasks.Parallel.ForWorker[TLocal,TInt](TInt fromInclusive, TInt toExclusive, ParallelOptions parallelOptions, Action`1 body, Action`2 bodyWithState, Func`4 bodyWithLocal, Func`1 localInit, Action`1 localFinally)
      --- End of stack trace from previous location ---
         at System.Threading.Tasks.Parallel.ForWorker[TLocal,TInt](TInt fromInclusive, TInt toExclusive, ParallelOptions parallelOptions, Action`1 body, Action`2 bodyWithState, Func`4 bodyWithLocal, Func`1 localInit, Action`1 localFinally)
         at System.Threading.Tasks.Parallel.For[TLocal](Int32 fromInclusive, Int32 toExclusive, Func`1 localInit, Func`4 body, Action`1 localFinally)
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.DefineStaticWebAssetEndpoints.Execute()
         at Microsoft.Build.BackEnd.TaskExecutionHost.Execute()
         at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(TaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask)

Build failed with 1 error(s) in 1.0s

Further technical details

.NET SDK:
 Version:           9.0.300
 Commit:            15606fe0a8
 Workload version:  9.0.300-manifests.87b8cca8
 MSBuild version:   17.14.5+edd3bbf37

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.26100
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\9.0.300\

.NET workloads installed:
 [wasm-tools]
   Installation Source: VS 17.14.36109.1
   Manifest Version:    9.0.5/9.0.100
   Manifest Path:       c:\program files\dotnet\sdk-manifests\9.0.100\microsoft.net.workload.mono.toolchain.current\9.0.5\WorkloadManifest.json
   Install Type:              Msi

Configured to use loose manifests when installing new manifests.

Host:
  Version:      9.0.5
  Architecture: x64
  Commit:       e36e4d1a8f

.NET SDKs installed:
  9.0.204 [C:\Program Files\dotnet\sdk]
  9.0.300 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 8.0.16 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 9.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 8.0.16 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 9.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 8.0.16 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 9.0.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  x86   [C:\Program Files (x86)\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
  Not set

global.json file:
  Not found

[PerseusTheGreat]

Under similar circumstances, I am encountering similar errors across all my ASP.NET Core Razor Class Libraries that include MVC .cshtml files. The errors seem to be associated with each <link> to static files, such as .css, within _Layout.cshtml. It appears that the new .NET 9.0 static asset delivery optimization treats all .cshtml files as if they were Blazor .razor components!"

[baronfel]

Cc @javiercn

[javiercn]

@MRT-77 can you provide a binlog/repro so that we can take a look?

[aminmashayekhi]

I just created a new Blazor Web App in Visual Studio with default settings and ran it, but the error occurred!

[MRT-77]

R: @javiercn
As I mentioned earlier, you can easily check this error by using visual studio blazor project templates or the dotnet new blazorwasm -o _MyCleanApp --framework net9.0 command. No extra code is needed.

[hyspdrt]

I think this might be related to blazor/razor component error, but only on non-windows

#49038

[itoledo]

rolling back to 9.0.204 using global.json allows it to compile. also with plain asp.net core web site, not only with blazor. Happens to me in Windows.

[MRT-77]

I was curious so I tested it on Ubuntu 24.04 LTS WSL2 and the build was completed without errors.

install instruction:

wget https://dot.net/v1/dotnet-install.sh -O dotnet-install.sh
chmod +x dotnet-install.sh
./dotnet-install.sh --version 9.0.300 --install-dir $HOME/dotnet

dotnet build output:

Restore complete (0.4s)
  _MyCleanApp succeeded (4.2s) → bin/Debug/net9.0/wwwroot

Build succeeded in 4.9s

[aminmashayekhi]

same issue with dotnet build and just one custom css in new asp.net core web app (razor pages):

PS D:\source\WebApplication4\WebApplication4> dotnet build
Restore complete (0/3s)
  WebApplication4 failed with 1 error(s) (0/2s)
    C:\Program Files\dotnet\sdk\9.0.300\Sdks\Microsoft.NET.Sdk.StaticWebAssets\targets\Microsoft.NET.Sdk.StaticWebAssets.targets(693,5): error MSB4018:
      The "DefineStaticWebAssetEndpoints" task failed unexpectedly.
      System.AggregateException: One or more errors occurred. (Last write time for 'D:\source\WebApplication4\WebApplica
      tion4\wwwroot\css\request-page.css' is not defined.) (Last write time for 'D:\source\WebApplication4\WebApplicatio
      n4\wwwroot\images\banner3.svg' is not defined.)
       ---> System.InvalidOperationException: Last write time for 'D:\source\WebApplication4\WebApplication4\wwwroot\css
      \request-page.css' is not defined.
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.StaticWebAsset.Validate()
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.StaticWebAsset.FromTaskItem(ITaskItem item)
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.DefineStaticWebAssetEndpoints.ParallelWorker.Process(Int32 i, Par
      allelLoopState _)
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.DefineStaticWebAssetEndpoints.<>c.<Execute>b__16_2(Int32 i, Paral
      lelLoopState loop, ParallelWorker state)
         at System.Threading.Tasks.Parallel.<>c__DisplayClass19_0`2.<ForWorker>b__1(RangeWorker& currentWorker, Int64 ti
      meout, Boolean& replicationDelegateYieldedBeforeCompletion)
      --- End of stack trace from previous location ---
         at System.Threading.Tasks.Parallel.<>c__DisplayClass19_0`2.<ForWorker>b__1(RangeWorker& currentWorker, Int64 ti
      meout, Boolean& replicationDelegateYieldedBeforeCompletion)
         at System.Threading.Tasks.TaskReplicator.Replica.Execute()
         --- End of inner exception stack trace ---
         at System.Threading.Tasks.TaskReplicator.Run[TState](ReplicatableUserAction`1 action, ParallelOptions options,
      Boolean stopOnFirstFailure)
         at System.Threading.Tasks.Parallel.ForWorker[TLocal,TInt](TInt fromInclusive, TInt toExclusive, ParallelOptions
       parallelOptions, Action`1 body, Action`2 bodyWithState, Func`4 bodyWithLocal, Func`1 localInit, Action`1 localFin
      ally)
      --- End of stack trace from previous location ---
         at System.Threading.Tasks.Parallel.ForWorker[TLocal,TInt](TInt fromInclusive, TInt toExclusive, ParallelOptions
       parallelOptions, Action`1 body, Action`2 bodyWithState, Func`4 bodyWithLocal, Func`1 localInit, Action`1 localFin
      ally)
         at System.Threading.Tasks.Parallel.For[TLocal](Int32 fromInclusive, Int32 toExclusive, Func`1 localInit, Func`4
       body, Action`1 localFinally)
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.DefineStaticWebAssetEndpoints.Execute()
         at Microsoft.Build.BackEnd.TaskExecutionHost.Execute()
         at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(TaskExecutionHost taskExecutionHost, TaskLogging
      Context taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask)
       ---> (Inner Exception #1) System.InvalidOperationException: Last write time for 'D:\source\WebApplication4\WebApp
      lication4\wwwroot\images\banner3.svg' is not defined.
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.StaticWebAsset.Validate()
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.StaticWebAsset.FromTaskItem(ITaskItem item)
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.DefineStaticWebAssetEndpoints.ParallelWorker.Process(Int32 i, Par
      allelLoopState _)
         at Microsoft.AspNetCore.StaticWebAssets.Tasks.DefineStaticWebAssetEndpoints.<>c.<Execute>b__16_2(Int32 i, Paral
      lelLoopState loop, ParallelWorker state)
         at System.Threading.Tasks.Parallel.<>c__DisplayClass19_0`2.<ForWorker>b__1(RangeWorker& currentWorker, Int64 ti
      meout, Boolean& replicationDelegateYieldedBeforeCompletion)
      --- End of stack trace from previous location ---
         at System.Threading.Tasks.Parallel.<>c__DisplayClass19_0`2.<ForWorker>b__1(RangeWorker& currentWorker, Int64 ti
      meout, Boolean& replicationDelegateYieldedBeforeCompletion)
         at System.Threading.Tasks.TaskReplicator.Replica.Execute()<---


Build failed with 1 error(s) in 1/2s

[csarigul]

@javiercn
I also faced with variety of those StaticWebAssets issues.
In the end, I found out it's simply static caching issue cause by StaticWebAssets.

Running dotnet clean or using Visual Studio's Clean Solution does not remove the StaticAsset cache file (rpswa.dswa.cache.json) located in the obj directory.

Workaround:
Simply remove "obj" folder under project, than it should compiled fine.

Especially, when you checkout to another branch and you had different web assets, then you must delete "obj" folder once again. Otherwise, you will face "xxx.js" is not defined ... etc.

Hopefully, it would be patched in future

I also created an issue about it :
#49082

[PerseusTheGreat]

#49101

[MRT-77]

Now I upgraded Visual Studio to the latest version but this error still exists in the new version .NET SDK 9.0.301.