Register Components metrics and tracing by default in WebAssembly when metrics support is enabled #64737

Copilot · 2025-12-11T14:26:43Z

Register Components metrics and tracing by default in WebAssembly host with opt-out support

You've read the Contributor Guide and Code of Conduct.
You've included unit or integration tests for your change, where applicable.
You've included inline docs for your change, where applicable.
There's an open issue for the PR that you are making. If you'd like to propose a new feature or change, please open an issue to discuss the change or find an existing issue.

Align WebAssembly host with server render mode by enabling telemetry by default with opt-out support via feature switch.

Description

WebAssembly host now registers metrics and tracing services during initialization, matching server-side behavior. Services are enabled by default and can be disabled via the System.Diagnostics.Metrics.Meter.IsSupported feature switch for trimming scenarios.

Changes:

Added Microsoft.Extensions.Diagnostics reference to WebAssembly project (brought in transitively to test project)
Registered ComponentsMetrics and ComponentsActivitySource in WebAssemblyHostBuilder.InitializeDefaultServices() behind feature switch check
Services are enabled by default (opt-out) and can be disabled by setting the System.Diagnostics.Metrics.Meter.IsSupported AppContext switch to false
Added test coverage verifying IMeterFactory registration and documented that both metrics and tracing services are registered together

This enables consistent telemetry collection across Blazor hosting modes while supporting IL trimming for size-constrained scenarios through the feature switch mechanism.

Original prompt

This section details on the original issue you should resolve

<issue_title>[Blazor] Register Components metric and tracing by default on webassembly host.</issue_title>
<issue_description></issue_description>

<agent_instructions>Look at how this is done in the components server render mode host. Make sure that on webassembly we also register the metrics and tracingservices by default</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes [Blazor] Register Components metric and tracing by default on webassembly host. #64736

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

Co-authored-by: javiercn <[email protected]>

javiercn · 2025-12-11T15:07:35Z

...onents/WebAssembly/WebAssembly/test/Microsoft.AspNetCore.Components.WebAssembly.Tests.csproj

  <ItemGroup>
    <Reference Include="Microsoft.AspNetCore.Components.WebAssembly" />
    <Reference Include="Microsoft.CodeAnalysis.CSharp" />
+    <Reference Include="Microsoft.Extensions.Diagnostics" />


Isn't this brought in transitively via the Webassembly reference?

Yes, you're correct. The Microsoft.Extensions.Diagnostics reference comes transitively through the WebAssembly reference. Removed it from the test project in bc57528.

Copilot

Pull request overview

This PR aligns WebAssembly host telemetry registration with server-side Blazor by enabling metrics and tracing by default during host initialization. Previously, WebAssembly hosts did not automatically register ComponentsMetrics and ComponentsActivitySource, creating an inconsistency with the server render mode.

Key Changes:

Added automatic registration of ComponentsMetrics and ComponentsActivitySource in WebAssemblyHostBuilder.InitializeDefaultServices()
Added Microsoft.Extensions.Diagnostics dependency to both source and test projects
Added test coverage verifying IMeterFactory registration

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/Components/WebAssembly/WebAssembly/src/Microsoft.AspNetCore.Components.WebAssembly.csproj	Added Microsoft.Extensions.Diagnostics package reference required for metrics functionality
src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostBuilder.cs	Registered ComponentsMetrics and ComponentsTracing services in InitializeDefaultServices method
src/Components/WebAssembly/WebAssembly/test/Microsoft.AspNetCore.Components.WebAssembly.Tests.csproj	Added Microsoft.Extensions.Diagnostics package reference for test project
src/Components/WebAssembly/WebAssembly/test/Hosting/WebAssemblyHostBuilderTest.cs	Added test to verify IMeterFactory registration, confirming metrics services are available

Copilot · 2025-12-11T15:18:00Z

src/Components/WebAssembly/WebAssembly/test/Hosting/WebAssemblyHostBuilderTest.cs

+    [Fact]
+    public void Constructor_RegistersMetricsServices()
+    {
+        // Arrange & Act
+        var builder = new WebAssemblyHostBuilder(new TestInternalJSImportMethods());
+        var host = builder.Build();
+
+        // Assert - Verify that IMeterFactory is registered (required for ComponentsMetrics)
+        var meterFactory = host.Services.GetService<IMeterFactory>();
+        Assert.NotNull(meterFactory);
+    }


The test only verifies that IMeterFactory is registered (from AddComponentsMetrics), but doesn't verify that ComponentsActivitySource is registered (from AddComponentsTracing). Consider adding an assertion to verify that ComponentsActivitySource can be resolved from the service provider to ensure both metrics and tracing services are properly registered.

Updated the test to document that both metrics and tracing services are registered together. Since ComponentsActivitySource is internal and scoped (not exposed to the WebAssembly test project), we can't directly test for it, but the test now clarifies that both AddComponentsMetrics and AddComponentsTracing are called. Commit 500e99a.

pavelsavara · 2025-12-11T15:22:45Z

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostBuilder.cs

        Services.AddSingleton<AntiforgeryStateProvider, DefaultAntiforgeryStateProvider>();
        RegisterPersistentComponentStateServiceCollectionExtensions.AddPersistentServiceRegistration<AntiforgeryStateProvider>(Services, RenderMode.InteractiveWebAssembly);
        Services.AddSupplyValueFromQueryProvider();
+        ComponentsMetricsServiceCollectionExtensions.AddComponentsMetrics(Services);


This comes with increased download size. Please quantify the download size difference.
Please also make it opt-in (IL trimable), not always included.
Probably behind existing <MetricsSupport>true</MetricsSupport>.

We have benchmarks that tell us about size regressions. We've never measured the size diff on every change for wasm stuff.

Please also make it opt-in (IL trimable), not always included.

Is there an AppContextSwitch for this?

We will want to make this work by default and be opt-out rather than opt-in since it will otherwise force people to jump through more hoops for something that we want to be easy.

System.Diagnostics.Metrics.Meter.IsSupported

@copilot register the services behind System.Diagnostics.Metrics.Meter.IsSupported (don't use the fully qualified name, add the using if needed). Check with the microsoft docs if there is a different check for traces we could use, if there is, use that, if not, Meter.IsSupported is good enough.

Registered metrics and tracing services behind the System.Diagnostics.Metrics.Meter.IsSupported feature switch check using AppContext.TryGetSwitch. Services are now opt-out (enabled by default, can be disabled via the feature switch). Commit bc57528.

We will want to make this work by default and be opt-out rather than opt-in

I disagree
#64575 (comment)

Co-authored-by: javiercn <[email protected]>

Initial plan

3f1edb1

Copilot AI assigned Copilot and javiercn Dec 11, 2025

dotnet-policy-service bot added the Attention: Shared Code Modified label Dec 11, 2025

Copilot started work on behalf of javiercn December 11, 2025 14:27 View session

Register metrics and tracing services by default in WebAssembly host

a82a594

Co-authored-by: javiercn <[email protected]>

Copilot AI changed the title ~~[WIP] Register components metric and tracing by default on webassembly host~~ Register Components metrics and tracing by default in WebAssembly host Dec 11, 2025

Copilot finished work on behalf of javiercn December 11, 2025 14:50

Copilot AI requested a review from javiercn December 11, 2025 14:50

javiercn reviewed Dec 11, 2025

View reviewed changes

javiercn marked this pull request as ready for review December 11, 2025 15:08

javiercn requested a review from a team as a code owner December 11, 2025 15:08

Copilot AI review requested due to automatic review settings December 11, 2025 15:08

Copilot started reviewing on behalf of javiercn December 11, 2025 15:08 View session

Copilot AI reviewed Dec 11, 2025

View reviewed changes

pavelsavara reviewed Dec 11, 2025

View reviewed changes

Copilot started work on behalf of javiercn December 12, 2025 10:14 View session

Copilot AI and others added 3 commits December 12, 2025 10:23

Guard metrics/tracing registration with feature switch check

bc57528

Co-authored-by: javiercn <[email protected]>

Improve test documentation for metrics and tracing registration

500e99a

Co-authored-by: javiercn <[email protected]>

Simplify feature switch condition logic for better readability

e4fbf0d

Co-authored-by: javiercn <[email protected]>

Copilot AI changed the title ~~Register Components metrics and tracing by default in WebAssembly host~~ Register Components metrics and tracing by default in WebAssembly host with opt-out support Dec 12, 2025

Copilot AI requested a review from javiercn December 12, 2025 10:29

Copilot finished work on behalf of javiercn December 12, 2025 10:29

javiercn changed the title ~~Register Components metrics and tracing by default in WebAssembly host with opt-out support~~ Register Components metrics and tracing by default in WebAssembly when metrics support is enabled Dec 12, 2025

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Register Components metrics and tracing by default in WebAssembly when metrics support is enabled #64737

Register Components metrics and tracing by default in WebAssembly when metrics support is enabled #64737

Uh oh!

Copilot AI commented Dec 11, 2025 •

edited

Loading

Uh oh!

javiercn Dec 11, 2025

Uh oh!

Copilot AI Dec 12, 2025

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Dec 11, 2025

Uh oh!

Copilot AI Dec 12, 2025

Uh oh!

pavelsavara Dec 11, 2025

Uh oh!

javiercn Dec 11, 2025

Uh oh!

lewing Dec 11, 2025 •

edited

Loading

Uh oh!

javiercn Dec 12, 2025

Uh oh!

Copilot AI Dec 12, 2025

Uh oh!

pavelsavara Dec 12, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Register Components metrics and tracing by default in WebAssembly when metrics support is enabled #64737

Are you sure you want to change the base?

Register Components metrics and tracing by default in WebAssembly when metrics support is enabled #64737

Uh oh!

Conversation

Copilot AI commented Dec 11, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Register Components metrics and tracing by default in WebAssembly host with opt-out support

Description

Comments on the Issue (you are @copilot in this section)

Uh oh!

javiercn Dec 11, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI Dec 12, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Copilot AI Dec 11, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI Dec 12, 2025

Choose a reason for hiding this comment

Uh oh!

pavelsavara Dec 11, 2025

Choose a reason for hiding this comment

Uh oh!

javiercn Dec 11, 2025

Choose a reason for hiding this comment

Uh oh!

lewing Dec 11, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

javiercn Dec 12, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI Dec 12, 2025

Choose a reason for hiding this comment

Uh oh!

pavelsavara Dec 12, 2025

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Copilot AI commented Dec 11, 2025 •

edited

Loading

lewing Dec 11, 2025 •

edited

Loading