bdukes/lockrepro

Reproduces an issue with dotnet watch and locked files

Reproduction of Source Generator File Locking Issue

When a project references a Source Generator, changes to the project while using dotnet watch can cause warning MSB3026, error MSB3027, and error MSB3021. This is due to the source generator project's output DLL being locked.

Example output

dotnet watch ⌚ File changed: .\MyExample.WidgetApi\MyExample.WidgetApi.csproj.
dotnet watch ⌚ Exited
dotnet watch 🔧 Building...
  MyExample.ThisIsASourceGenerator failed with 2 error(s) and 10 warning(s) (12.8s)
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 1 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 2 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 3 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 4 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 5 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 6 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 7 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 8 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 9 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): warning MSB3026: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.This
IsASourceGenerator.dll". Beginning retry 10 in 1000ms. The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): error MSB3027: Could not copy "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll". Exceeded retry count of 10. Failed. The file is locked by: ".NET Host (20364)"
    C:\Program Files\dotnet\sdk\8.0.300\Microsoft.Common.CurrentVersion.targets(4806,5): error MSB3021: Unable to copy file "obj\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll" to "bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll". The process cannot access the file 'I:\code\lockrepro\MyExample.ThisIsASourceGenerator\bin\Any CPU\Debug\net8.0\MyExample.ThisIsASourceGenerator.dll' because it is being used by another process.      
Build failed with 2 error(s) and 10 warning(s) in 14.1s

Repository Details

This repository contains four projects.

• MyExample.Data contains an Entity Framework Core data context
• MyExample.ThisIsASourceGenerator is a source generator which adds methods to configure the EF Core data context from MyExample.Data
• MyExample.WidgetApi is an ASP.NET Web API project which uses the EF Core data context
• MyExample.SprocketApi is an ASP.NET Web API project which does not reference these other projects

Reproduction Steps

As a convenience, run.ps1 in the root of the repository starts dotnet watch for both Web API projects. A variety of changes to the MyExample.WidgetApi will cause the above output due to file locking, whereas similar changes to MyExample.SprocketApi will not cause the issue. In a real world project, these issues have been noticed with a wide variety of code changes (which may or may not be classified as "rude"). However, the simplest reproduction is to change the version of the references NuGet packages. The reproduce.ps1 script will start dotnet watch for both projects and then cycle through commits in this repository in order to attempt to recreate the error.