aspnetcore: Blazor - BrotliCompress msbuild task duplicate processing of files - causes lock exceptions

Describe the bug

There appears to be an issue with the BrotliCompress task (and I am assuming might not be limited to the BrotliCompress task - if there are others that resolve content to process in a similar way) whereby, a single file in the project appears to be processed twice if you have a particular project entry.

This issue (duplicate entries to process) can then go on to cause an exception, because the BrotliCompress task later processes those entries (files) in parrallel - and if one parallel task doesn’t release the lock on the file before the other parallel tasks processes the duplicate entry / file, you get the msbuild failure during the dotnet publish as originally described here where more than one parallel task is trying to lock the same file.

To Reproduce

1. Create a vanilla blazor hosted wasm project.
2. Add the following entry the client (wasm) csproj file:

  <ItemGroup>
        <_ContentIncludedByDefault Remove="wwwroot\css\app.css" />
    </ItemGroup>

Do a dotnet publish -c Release -v Detailed and inspect the output, note that the app.css file appears to be processed twice by the brotli task:

 Done executing task "MakeDir".
       Using "BrotliCompress" task from assembly "C:\hostedtoolcache\windows\dotnet\sdk\5.0.102\Sdks\Microsoft.NET.Sdk.BlazorWebAssembly\targets\..\tasks\net5.0\Microsoft.NET.Sdk.BlazorWebAssembly.Tasks.dll".
       Task "BrotliCompress"
         C:\hostedtoolcache\windows\dotnet\dotnet.exe "C:\hostedtoolcache\windows\dotnet\sdk\5.0.102\Sdks\Microsoft.NET.Sdk.BlazorWebAssembly\targets\..\tools\net5.0\Microsoft.NET.Sdk.BlazorWebAssembly.Tools.dll" brotli
         -s
         D:\a\1\s\src\Foo.Client\wwwroot\appsettings.Development.json
         -o
         D:\a\1\s\src\Foo.Client\obj\Release\net5.0\compress\kMn0BpPF.br
         -s
         D:\a\1\s\src\Foo.Client\wwwroot\appsettings.json
         -o
         D:\a\1\s\src\Foo.Client\obj\Release\net5.0\compress\mnsMCpbd.br
         -s
         D:\a\1\s\src\Foo.Client\wwwroot\css\app.css
         -o
         D:\a\1\s\src\Foo.Client\obj\Release\net5.0\compress\ht+9vXXP.br
         -s
         D:\a\1\s\src\Foo.Client\wwwroot\css\app.css
         -o
         D:\a\1\s\src\Foo.Client\obj\Release\net5.0\compress\ht+9vXXP.br
         -s
         D:\a\1\s\src\Foo.Client\wwwroot\css\app.min.css

And the dotnet publish failure that happens if locks aren’t released in time:

The process cannot access the file ‘D:\a\1\s\src\Foo.Client\obj\Release\net5.0\compress\ht+9vXXP.br’ because it is being used by another process. at System.IO.FileStream.ValidateFileHandle(SafeFileHandle fileHandle) at System.IO.FileStream.CreateFileOpenHandle(FileMode mode, FileShare share, FileOptions options) at System.IO.FileStream…ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options) at System.IO.FileStream…ctor(String path, FileMode mode) at Microsoft.NET.Sdk.BlazorWebAssembly.Tools.BrotliCompressCommand.<ExecuteCoreAsync>b__16_0(Int32 i) at System.Threading.Tasks.Parallel.<>c__DisplayClass19_01.<ForWorker>b__1(RangeWorker& currentWorker, Int32 timeout, Boolean& replicationDelegateYieldedBeforeCompletion) --- End of stack trace from previous location --- at System.Threading.Tasks.Parallel.<>c__DisplayClass19_01.<ForWorker>b__1(RangeWorker& currentWorker, Int32 timeout, Boolean& replicationDelegateYieldedBeforeCompletion) at System.Threading.Tasks.TaskReplicator.Replica`1.ExecuteAction(Boolean& yieldedBeforeCompletion) at System.Threading.Tasks.TaskReplicator.Replica.Execute()

4:5>C:\hostedtoolcache\windows\dotnet\sdk\5.0.102\Sdks\Microsoft.NET.Sdk.BlazorWebAssembly\targets\Microsoft.NET.Sdk.BlazorWebAssembly.Current.targets(564,5): error MSB6006: “C:\hostedtoolcache\windows\dotnet” exited with code 1. [D:\a\1\s\src\Foo.Client\Foo.Client.csproj] Done executing task “BrotliCompress” – FAILED.

Removing this project entry fixes the problem.

Note: I am not sure why my project had this entry, but it has been upgraded over a long period of time, removing the entry seems to be a valid workaround in my case however I raise the issue as it seems like this shouldn’t be causing the issue that it does…

Exceptions (if any)

as per above

Further technical details

• ASP.NET Core version: 5.0.2
• Include the output of dotnet --info
• The IDE (VS / VS Code/ VS4Mac) you’re running on, and its version