[wasm] Embed HotReload in WebAssembly SDK by maraf · Pull Request #52710 · dotnet/sdk

maraf · 2026-01-28T16:35:54Z

Replace a PackageReference with content shipped inside of the SDK.
It requires to manually reference the dll and define a StaticWebAsset for JSInitializer.

The HotReload project for WebAssembly is pinned to net10.0 as we don't need to multi-target yet.
Baselines tests have a new token ${WebAssemblySdkPath} pointing to WebAssembly SDK inside .NET SDK

Fixes #49877
Fixes #52686
Fixes dotnet/aspnetcore#65261

maraf · 2026-01-29T12:42:13Z

src/WasmSdk/Sdk/Sdk.targets

+  <Target Name="_ImplicitlyReferenceHotReload" BeforeTargets="ResolveProjectStaticWebAssets" AfterTargets="ResolveStaticWebAssetsConfiguration" Condition="'$(_WasmEnableHotReload)' == 'true'">
+    <PropertyGroup>
+      <_WasmHotReloadRoot>$([MSBuild]::NormalizeDirectory($(MSBuildThisFileDirectory), '..', 'hotreload'))</_WasmHotReloadRoot>
+      <_WasmHotReloadDllPath Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(TargetFrameworkVersion)', '10.0'))">net10.0</_WasmHotReloadDllPath>


@tmat Do you prefer to multi-target the dll or pin it to .NET 10?

Let's pin to .NET 10 until we need runtime features that need higher version. It's simpler and reduces SDK size.

Also, let's target release/10.0.3xx branch instead of main.

I would rather land it on main and backport it to 10. We are testing some scenarios only on main in runtime and I have some unpleasant memories when changes arrived there later due to delayed forward flow in SDK

...ols/HotReloadAgent.WebAssembly.Browser/Microsoft.DotNet.HotReload.WebAssembly.Browser.csproj

src/WasmSdk/Tasks/Microsoft.NET.Sdk.WebAssembly.Tasks.csproj

tmat · 2026-01-30T17:16:37Z

src/WasmSdk/Tasks/Microsoft.NET.Sdk.WebAssembly.Tasks.csproj

@@ -35,18 +35,22 @@
  </PropertyGroup>

  <PropertyGroup>
-    <TargetFrameworks>$(SdkTargetFramework);net472</TargetFrameworks>
+    <!-- We are not using the assembly anywhere -->
+    <TargetFrameworks>$(SdkTargetFramework)</TargetFrameworks>


Shouldn't this be TargetFramework (singular)?

Hmm. For some reason it doesn't produce a correct layout - the output SDK folder contains just the dll

tmat · 2026-01-30T17:20:55Z

src/WasmSdk/Tasks/Microsoft.NET.Sdk.WebAssembly.Tasks.csproj

-      <Pack>true</Pack>
-      <PackagePath>targets</PackagePath>
-    </AdditionalContent>
+    <ProjectReference Include="..\..\BuiltInTools\HotReloadAgent.WebAssembly.Browser\Microsoft.DotNet.HotReload.WebAssembly.Browser.csproj">


I think setting metadata of the ProjectReference like so and removing the <AdditionalContent> below would work

<OutputItemType>AdditionalContent</OutputItemType> <ReferenceOutputAssembly>false</ReferenceOutputAssembly> <Pack>true</Pack> <PackagePath>hotreload</PackagePath>

It add items to the AdditionalContent, but the PackagePath metadata is ignored

maraf · 2026-01-30T21:53:28Z

Relevant test failure log

/datadisks/disk1/work/C4900A2F/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk.StaticWebAssets/targets/Microsoft.NET.Sdk.StaticWebAssets.JSModules.targets(215,3): error MSB4018: The "FilterStaticWebAssetEndpoints" task failed unexpectedly. [/datadisks/disk1/work/C4900A2F/t/dotnetSdkTests.qFYAxAdO/Publish_Hosti---AC2D7A92/BlazorMultipleApps.Server/BlazorMultipleApps.Server.csproj]
/datadisks/disk1/work/C4900A2F/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk.StaticWebAssets/targets/Microsoft.NET.Sdk.StaticWebAssets.JSModules.targets(215,3): error MSB4018: System.ArgumentException: An item with the same key has already been added. Key: /datadisks/disk1/work/C4900A2F/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk.WebAssembly/hotreload/net10.0/wwwroot/Microsoft.DotNet.HotReload.WebAssembly.Browser.lib.module.js [/datadisks/disk1/work/C4900A2F/t/dotnetSdkTests.qFYAxAdO/Publish_Hosti---AC2D7A92/BlazorMultipleApps.Server/BlazorMultipleApps.Server.csproj]
/datadisks/disk1/work/C4900A2F/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk.StaticWebAssets/targets/Microsoft.NET.Sdk.StaticWebAssets.JSModules.targets(215,3): error MSB4018:    at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value) [/datadisks/disk1/work/C4900A2F/t/dotnetSdkTests.qFYAxAdO/Publish_Hosti---AC2D7A92/BlazorMultipleApps.Server/BlazorMultipleApps.Server.csproj]
/datadisks/disk1/work/C4900A2F/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk.StaticWebAssets/targets/Microsoft.NET.Sdk.StaticWebAssets.JSModules.targets(215,3): error MSB4018:    at Microsoft.AspNetCore.StaticWebAssets.Tasks.StaticWebAsset.ToAssetDictionary(ITaskItem[] candidateAssets, Boolean validate) in /_/src/StaticWebAssetsSdk/Tasks/Data/StaticWebAsset.cs:line 1237 [/datadisks/disk1/work/C4900A2F/t/dotnetSdkTests.qFYAxAdO/Publish_Hosti---AC2D7A92/BlazorMultipleApps.Server/BlazorMultipleApps.Server.csproj]
/datadisks/disk1/work/C4900A2F/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk.StaticWebAssets/targets/Microsoft.NET.Sdk.StaticWebAssets.JSModules.targets(215,3): error MSB4018:    at Microsoft.AspNetCore.StaticWebAssets.Tasks.FilterStaticWebAssetEndpoints.Execute() in /_/src/StaticWebAssetsSdk/Tasks/FilterStaticWebAssetEndpoints.cs:line 35 [/datadisks/disk1/work/C4900A2F/t/dotnetSdkTests.qFYAxAdO/Publish_Hosti---AC2D7A92/BlazorMultipleApps.Server/BlazorMultipleApps.Server.csproj]
/datadisks/disk1/work/C4900A2F/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk.StaticWebAssets/targets/Microsoft.NET.Sdk.StaticWebAssets.JSModules.targets(215,3): error MSB4018:    at Microsoft.Build.BackEnd.TaskExecutionHost.Execute() [/datadisks/disk1/work/C4900A2F/t/dotnetSdkTests.qFYAxAdO/Publish_Hosti---AC2D7A92/BlazorMultipleApps.Server/BlazorMultipleApps.Server.csproj]
/datadisks/disk1/work/C4900A2F/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk.StaticWebAssets/targets/Microsoft.NET.Sdk.StaticWebAssets.JSModules.targets(215,3): error MSB4018:    at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(TaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask) [/datadisks/disk1/work/C4900A2F/t/dotnetSdkTests.qFYAxAdO/Publish_Hosti---AC2D7A92/BlazorMultipleApps.Server/BlazorMultipleApps.Server.csproj]
StdErr:

maraf · 2026-01-30T22:22:35Z

@javiercn How to handle when there two endpoints pointing to a single source file?

two-endpoints-pointing-to-the-same-source-file.zip

javiercn · 2026-02-02T11:24:49Z

@maraf

@javiercn How to handle when there two endpoints pointing to a single source file?
[two-endpoints-pointing-to-the-same-source-file.zip](https://github.com/user-attachments/files/24975041/two-endpoints-pointing-to-the-same-source-file.zip)

I would start tracing back where the endpoint is originated. Does it come from a referenced project? (Seems to be a FirstApp and SecondApp). Is there a potential bug on FilterStaticWebAssetEndpoints? https://github.com/dotnet/sdk/blob/main/src/StaticWebAssetsSdk/Tasks/FilterStaticWebAssetEndpoints.cs#L35

I imagine that what's different here is that the assets on a package get deduplicated, while the assets you are injecting manually on each app aren't getting de-duplicated.

What's the exact scenario this targets, multiple apps being referenced by a host app? If so, it should technically be the host app providing the hot reload script, not the referenced apps (the asset should be marked as project so that it doesn't flow to the consuming apps).

lewing · 2026-02-05T02:34:26Z

current version is #52816

@maraf

…et10.0 Two issues introduced by review feedback commits: 1. OutputItemType=AdditionalContent on ProjectReference doesn't flow PackagePath metadata to the created items (confirmed by @maraf in PR dotnet#52710). Restored the explicit AdditionalContent glob from that was working in the green commit. 2. HotReload csproj TFM changed from net10.0 to but Sdk.targets hardcodes _WasmHotReloadTfm=net10.0. Per @tmat's guidance in PR dotnet#52710: pin to net10.0 until higher version needed. The ProjectReference still has SkipGetTargetFrameworkProperties, ReferenceOutputAssembly=false, and UndefineProperties for net472 compatibility as @tmat requested.

maraf added 4 commits January 19, 2026 13:04

Fix test assets

7ec7aa6

Remove dependency on Package for running tests

415a97b

Embed HotReload in WasmSDK

1d61ff1

Reference embedded HotReload

c777ede

maraf self-assigned this Jan 28, 2026

maraf added the Area-WasmSdk label Jan 28, 2026

maraf added 2 commits January 28, 2026 18:14

Define SWA for JSInitializer

366479c

Fix content root

43ca45c

maraf changed the title ~~Embed HotReload in WebAssembly SDK~~ [wasm] Embed HotReload in WebAssembly SDK Jan 29, 2026

Don't pack the package

9b27e95

maraf commented Jan 29, 2026

View reviewed changes

build-analysis bot mentioned this pull request Jan 29, 2026

dotnet-watch tests failing #40006

Open

More properties

0b699ca

tmat mentioned this pull request Jan 29, 2026

Pin hot reaload wasm browser package version #52733

Closed

tmat reviewed Jan 29, 2026

View reviewed changes

...ols/HotReloadAgent.WebAssembly.Browser/Microsoft.DotNet.HotReload.WebAssembly.Browser.csproj Show resolved Hide resolved

tmat reviewed Jan 29, 2026

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src/WasmSdk/Tasks/Microsoft.NET.Sdk.WebAssembly.Tasks.csproj Show resolved Hide resolved

maraf added 8 commits January 30, 2026 09:14

Feedback

a5c04c4

Copy JS part through project reference

db3697d

Fix

724f7f0

ProjectReference with manual asset copy

438b349

Fix

d1eb14f

Fix

b0b6233

Refactor

d7a29f0

Baselines

c8bb76b

tmat reviewed Jan 30, 2026

View reviewed changes

maraf added 2 commits January 30, 2026 20:27

Merge branch 'main' into maraf/WasmHotReloadEmbed

66273f1

Don't add .nuget as package source

09dcf66

Fix double slash

a16649e

lewing mentioned this pull request Feb 3, 2026

Fix hotreload duplicate assets #52816

Merged

This was referenced Feb 6, 2026

[release/11.0.1xx-preview1] Backport #52816 #52879

Closed

[release/10.0.3xx] Backport #52816 #52881

Merged

lewing closed this Feb 7, 2026

maraf deleted the maraf/WasmHotReloadEmbed branch February 10, 2026 12:10

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maraf commented Jan 30, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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