Dotnet watch falls over frequently with "An item with the same key has already been added"

[paulguz-datapa]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Since upgrading our ASP.Net Core projects to .Net 9 (but leaving the others alone for now), we are experiencing the following error when running dotnet watch:

dotnet watch ❌ System.ArgumentException: An item with the same key has already been added. Key: 
C:\xxx\yyy\zzz\aaa\Language.csproj
   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector)
   at Microsoft.DotNet.Watcher.Tools.IncrementalMSBuildWorkspace.UpdateProjectConeAsync(String rootProjectPath, CancellationToken cancellationToken)
   at Microsoft.DotNet.Watcher.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
   at Microsoft.DotNet.Watcher.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
   at Microsoft.DotNet.Watcher.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
   at Microsoft.DotNet.Watcher.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
   at Microsoft.DotNet.Watcher.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
   at Microsoft.DotNet.Watcher.Program.RunAsync()
dotnet watch ❌ An unexpected error occurred

Language.csproj is a an assembly containing resource files.

Dotnet watch falls over at this point. It happens very frequently, making Hot Reload impossible.

Expected Behavior

Dotnet watch runs without failure

Steps To Reproduce

No response

Exceptions (if any)

System.ArgumentException: An item with the same key has already been added

.NET Version

9.0

Anything else?

This did not happen in .Net 8

[paulguz-datapa]

I also see this warning in the Command Prompt:

dotnet watch ⚠ msbuild: [Warning] Found project reference without a matching metadata reference: C:\xxx\yyy\zzz\aaa\Language.csproj

dotnet watch ⏳ Waiting for a file to change before restarting dotnet...

I don't know if the warning is related to the error in the subject of this Issue, or if the "waiting for file to change" problem is related to the warning (but it only appears after the warning occurs)

[jofford]

Also noticing this when pressing Ctrl+R to reload in the CLI. I am running an api and Blazor site simultaneously via 'dotnet watch' but wasn't a problem in .NET 8

[paulguz-datapa]

This may not be restricted to dotnet watch in the command line. I also get Hot Reload build failures when running via Visual Studio.

[paulguz-datapa]

Like @jofford, we are also have a Blazor (Wasm) project and an ASP.Net Core API project (which references the Blazor project)

[eldo-xy]

Also having this annoying issue, doing random stuff with the projects causes the watch to just crash

[paul-green]

Me too;

• Run dotnet watch
• Make a change to .razor file
• terminal says : File deleted: .(path to razor file)
• The change isn't reflected in the UI
• A few seconds later; Waiting for a file to change before restarting dotnet...
• I make another change, save it and get : System.ArgumentException: An item with the same key has already been added. Key: 5529

Then dotnet watch crashes out. This is worse than previous version which was also really flakey (sigh)

[timheuer]

@tmat should this move to dotnet/sdk?

[dbondar-dev]

Possible temporary solution is using previous dotnet version. It can be done by adding global.json file in your projects folder with previous working dotnet version:

{ "sdk": { "version": "8.0.0" } }

(https://learn.microsoft.com/en-us/dotnet/core/versions/selection#the-sdk-uses-the-latest-installed-version)

[tmat]

Anyone has a project they can share where this issue reproduces?

[limefrogyank]

Happening with my Maui hybrid app. In fact, it happened very early on and I just got used to recompiling everytime. I will try creating a project using the basic template from visual studio and see if it happens without any changes. (Tomorrow morning unless someone beats me to it.) Get Outlook for Android<https://aka.ms/AAb9ysg>

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________________________________ From: Tomáš Matoušek ***@***.***> Sent: Tuesday, December 17, 2024 6:47:47 PM To: dotnet/sdk ***@***.***> Cc: Lee McPherson ***@***.***>; Manual ***@***.***> Subject: Re: [dotnet/sdk] Dotnet watch falls over frequently with "An item with the same key has already been added" (Issue #45455) Anyone has a project they can share where this issue reproduces? — Reply to this email directly, view it on GitHub<#45455 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AB3VQSAFAH6U6BTXLW5WM6L2GDO5HAVCNFSM6AAAAABTSKFC5KVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKNJQGE4TEMZWGY>. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>