Hot Reload unavailable

[wf-soft]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I am using the latest VS2022 17.6.0 Preview 4.0

The preview version created the BlazorServer project, and all hot reloads were invalidated without any prompt. I am unable to determine the reason

dotnet watch ⌚ File changed: C:\Users\wf-so\Downloads\HotReloadIssue45519Demo-main\HotReloadIssue45519Demo-main\TradeCars\Client\Pages\Index.razor.
dotnet watch ⌚ No hot reload changes to apply.

dotnet watch 🔥 Hot reload capabilities: Baseline AddMethodToExistingType AddStaticFieldToExistingType NewTypeDefinition ChangeCustomAttributes.
dotnet watch ⌚ File changed: C:\Users\wf-so\Downloads\HotReloadIssue45519Demo-main\HotReloadIssue45519Demo-main\TradeCars\Client\Pages\Index.razor.
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      Request starting HTTP/2 POST https://localhost:5008/_framework/blazor-hotreload application/json 2835
dotnet watch ⌚ Received 0 from browser in [Count: 1, MessageType: Binary, EndOfMessage: True].
dotnet watch ⌚ Received failed apply from delta applier.
  ❔ Do you want to restart your app - Yes (y) / No (n) / Always (a) / Never (v)?

Expected Behavior

No response

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

dotnet-sdk-7.0.203

Anything else?

No response

[szalapski]

This is a direct successor to #45519, which was closed with "Likely fixed by dotnet/sdk#31015.", but it was not fixed. I wish someone would have tested it with the provided example before deeming it "likely fixed". The test is very easy.

Here's the minimal example, the same one that was provided in #45519, now upgraded to use SDK 7.0.302

szalapski/HotReloadIssue45519Demo

Clone this and run

dotnet watch --verbose --project ./TradeCars/Server

The site should start up. You'll see Hot reload capabilities: . which portends the failure. Edit anything in Index.razor to watch hot reload fail.

Please get Hot Reload to work reliably and consistently with Blazor WebAssembly (and Blazor Server, likely the same problem), especially with changes to .razor files. This feature seems so buggy when it should "just work". It seems to work much better with non-Blazor server-side changes, e.g. to a Web API, but that's not where much productivity benefit would result.

When using dotnet watch on my Server project, with verbose logging , I get watch : Hot reload capabilities: . (not even Baseline) and, on a change, No hot reload changes to apply. (when there are). This is with .NET 7.0.5 and SDK 7.0.302 on a solution that was created with .NET 6 and recently upgraded to 7.

Starting...
dotnet watch 🔥 Hot reload capabilities: .
dotnet watch ⌚ File changed: .\MySoln\Client\Shared\MainLayout.razor.
dotnet watch ⌚ No deltas modified. Applying changes to clear diagnostics.
dotnet watch ⌚ Received 1 from browser in [Count: 1, MessageType: Binary, EndOfMessage: True].
dotnet watch ⌚ No hot reload changes to apply.
dotnet watch 🔥 Hot reload change handled in 4092.6926ms.

When running from VS (with or without debugging), I get similar output:
, or sometimes instead "Your debugged process might be corrupted and restarting it is recommended nearly always."

See also:

• Hot Reload nearly always fails, with Blazor WebAssembly and "dotnet watch" #45519 (the main one)
• .NET 6 Blazor Hot Reload fails depending on the port specified for the application Url #38029
• Hotreload doesn't work on Blazor wasm (.NET6) #38576
• Hotreload not working with .cshtml files #38809 (title says .cshtml but the same problem happens with .razor)
• CLI Hot reload Blazor wasm just doesn't work. #40587 and Remove various timeouts sdk#27699 (closed without fully fixing)
• [dotnet-watch] Hot reload capabilities are sometimes not reported for blazor-wasm #36723 (closed without fully fixing)
• Blazor WASM Hot Reload cli not working #38561 (closed without fully fixing)
• Document How to Enable Hot Reloading Using dotnet run/watch #38036 (closed without fully fixing)
• https://developercommunity.visualstudio.com/t/blazor-hot-reload-not-working/1480369 (closed without fully fixing)
• Assume basline capabilities sdk#23185 (closed as merged but no notice of what version it is fixed in)

Seems like there are a lot of others struggling too but not commenting in GitHub issues, e.g.

• https://www.reddit.com/r/Blazor/comments/10wwfpr/has_anyone_had_hotreload_randomly_stop_working/
• https://www.reddit.com/r/Blazor/comments/10kishh/blazor_united_prototype_for_from_steve_sanderson/j5r08b4/
• https://www.reddit.com/r/Blazor/comments/vaccxa/hot_reload_is_rubbish/
• https://stackoverflow.com/questions/69778272/unable-to-hot-reload-on-visual-studio-2022/74380447#74380447
• https://stackoverflow.com/questions/70005784/net-6-blazor-wasm-hot-reload-not-working/74750013
• https://learn.microsoft.com/en-us/answers/questions/908804/vs2022-blazor-server-app-hot-reload-notworking

Expected Behavior

• dotnet watch hot reload should just work. I don't want to see "No hot reload changes to apply."
• If it isn't working and thus I get "watch : Hot reload capabilities: .", I'd like to see output that tells me why in the verbose output (indeed, perhaps even in warnings).

[szalapski]

@wf-soft Can I recommend you edit the title of this issue to read:

Hot Reload nearly always fails, with Blazor and "dotnet watch"

That will get it more attention and more closely link it to #45519.

[danroth27]

Adding @phil-allen-msft @maddymontaquila and @mcumming for visibility.

[tmat]

I see this error in the browser with the latest .NET 8:

Updated repro project:
Net8.zip

 at System.Reflection.Metadata.MetadataUpdater.ApplyUpdate(Assembly assembly, ReadOnlySpan`1 metadataDelta, ReadOnlySpan`1 ilDelta, ReadOnlySpan`1 pdbDelta)
   at Microsoft.Extensions.HotReload.HotReloadAgent.ApplyDeltas(IReadOnlyList`1 deltas)
   at Microsoft.AspNetCore.Components.WebAssembly.HotReload.WebAssemblyHotReload.ApplyHotReloadDelta(String moduleIdString, Byte[] metadataDelta, Byte[] ilDelta, Byte[] pdbBytes)
   at System.Reflection.MethodInvoker.InterpretedInvoke(Object obj, IntPtr* args)
   at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr)
--- End of stack trace from previous location ---
   at Microsoft.JSInterop.Infrastructure.DotNetDispatcher.InvokeSynchronously(JSRuntime jsRuntime, DotNetInvocationInfo& callInfo, IDotNetObjectReference objectReference, String argsJson)
   at Microsoft.JSInterop.Infrastructure.DotNetDispatcher.Invoke(JSRuntime jsRuntime, DotNetInvocationInfo& invocationInfo, String argsJson)
   at Microsoft.AspNetCore.Components.WebAssembly.Services.DefaultWebAssemblyJSRuntime.InvokeDotNet(String assemblyName, String methodIdentifier, Int64 dotNetObjectId, String argsJson)
   at Microsoft.AspNetCore.Components.WebAssembly.Services.DefaultWebAssemblyJSRuntime.__Wrapper_InvokeDotNet_1772498872(JSMarshalerArgument* __arguments_buffer)
Error: The assembly can not be edited or changed.
    at yr (https://localhost:5008/_framework/dotnet.runtime.8.0.0-preview.6.23316.2.dk1nh2rbrm.js:3:35896)
    at Uo (https://localhost:5008/_framework/dotnet.runtime.8.0.0-preview.6.23316.2.dk1nh2rbrm.js:3:53691)
    at Object.<anonymous> (https://localhost:5008/_framework/dotnet.runtime.8.0.0-preview.6.23316.2.dk1nh2rbrm.js:3:52482)
    at Object.invokeDotNetFromJS (https://localhost:5008/_framework/blazor.webassembly.js:1:43350)
    at b.invokeDotNetMethod (https://localhost:5008/_framework/blazor.webassembly.js:1:3485)
    at b.invokeDotNetStaticMethod (https://localhost:5008/_framework/blazor.webassembly.js:1:3241)
    at Wt.Ye._internal.applyHotReload (https://localhost:5008/_framework/blazor.webassembly.js:1:52017)
    at https://localhost:5008/_framework/aspnetcore-browser-refresh.js:140:35
    at Array.forEach (<anonymous>)
    at applyBlazorDeltas (https://localhost:5008/_framework/aspnetcore-browser-refresh.js:138:14)
(anonymous) @ aspnetcore-browser-refresh.js:142
applyBlazorDeltas @ aspnetcore-browser-refresh.js:138
BlazorHotReloadDeltav1 @ aspnetcore-browser-refresh.js:46
connection.onmessage @ aspnetcore-browser-refresh.js:53

[tmat]

@lambdageek

[lambdageek]

@tmat I can repro that failure if I have VS Code editing the project (I have the C# Dev Kit installed). I get different results if I edit with Emacs or vim. In general The assembly can not be edited or changed. can happen if:

1. the DOTNET_MODIFIABLE_ASSEMBLIES=debug environment variable is not set in the client-side runtime
2. or the baseline assembly does not have the "optimizer disabled" attribute (essentially the assembly was compiled in Release mode, not Debug)

There's definitely something here. I'll try to get some more info

[lambdageek]

@tmat yea, I don't see that The assembly can not be edited or changed. error if I disabled the C# Dev Kit extension in VS Code

Update
If I just have ms-dotnettools.csharp (v2.0.238) enabled, I dont' have the apply update exception when I try to make changes to Client/Pages/Index.razor
If I also enable ms-dotnettools.csdevkit (v0.1.103) then I get "the assembly can not be edited or changed" if I run dotnet watch --verbose --project ./TradeCars/Server and then edit the client Index.razor page.

[tmat]

This change will communicate the error message to dotnet-watch and print it out, for easier diagnostics in future: dotnet/sdk#33471

[lambdageek]

This should improve the "assembly cannot be edited or changed" error message dotnet/runtime#87880