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Emits the two WebAssembly tool-conventions custom sections — producers and build_id — into WebAssembly artifacts produced by the .NET toolchain for both Mono and CoreCLR.

Where the sections are emitted

Artifact	producers	build_id
dotnet.native.wasm	relocatable object merged by wasm-ld during native relink and preserved through Emscripten	managed task stamps a project-local runtime-pack copy or an already project-local relinked module
Webcil modules	appended by WebcilWasmWrapper	explicit $(WasmNativeBuildId) or per-file SHA-256 content hash
R2R Webcil	appended by WebCilObjectWriter	--wasm-native-build-id or a content hash

All paths reuse WasmCustomSectionWriter for custom-section encoding.

Workload-free build_id

$(WasmNativeBuildId) accepts a hexadecimal value and no longer forces a native relink or requires wasm-tools.

WasmStampBuildId:

1. selects the relinked module when one exists, otherwise the runtime-pack module;
2. stamps a relinked/project-local module in place;
3. copies a shared runtime-pack module to a project-local intermediate before stamping it;
4. substitutes the stamped runtime-pack copy only into the Wasm build-asset candidates, preserving standard fx/.../_framework materialization without enrolling it in normal publish copying;
5. replaces equivalent runtime-pack publish candidates with one project-local publish-stamped copy;
6. runs before static-web-asset fingerprinting, integrity calculation, compression, and bundling;
7. registers generated outputs in @(FileWrites) for clean and incrementality.

The shared runtime-pack/NuGet file is never modified. The normalized ID is also emitted into the boot configuration so runtimeBuildInfo.buildId agrees with the stamped Wasm module without a native relink.

Invalid IDs fail in the managed task before asset processing.

producers

The .NET entries are:

• language=C#
• processed-by=<Mono|CoreCLR|WebCIL>
• sdk=.NET

For native relinks, WasmEmitProducersObject contributes a small relocatable object. wasm-ld merges it with compiler-provided metadata, and -sEMIT_PRODUCERS_SECTION=1 prevents Emscripten from stripping the merged section. Set $(WasmEmitProducersSection)=false to disable it.

JavaScript exposure

runtimeBuildInfo.buildId receives the application ID through generated boot configuration. Relinked native modules may also provide the same value through their Emscripten footer; the native value takes precedence.

MSBuild properties

Property	Meaning
WasmNativeBuildId	Hexadecimal ID stamped into project-local native and Webcil Wasm artifacts. Does not force native relinking.
WasmEmitProducersSection	Emit and preserve native producers metadata. Defaults to true.

Tests

WasmMetadataSectionsTests covers:

• workload-free native runtime-pack stamping;
• explicit native-relink stamping;
• enabled and disabled native producers;
• Webcil content-hash and pinned IDs;
• invalid IDs without a workload;
• fingerprinted asset paths, publish-root hygiene, and boot configuration.

CleanTests verifies:

• the stamped runtime-pack module is materialized under fx/.../_framework;
• stamped Wasm and dotnet-producers.o are removed by clean.

Local validation

• Passed — Browser/CoreCLR baseline:

  .\build.cmd -bl -os browser -subset clr+libs+host -c Debug /p:StaticWebAssetsEnabled=false

  0 warnings, 0 errors.

• Passed — WebAssembly pack and runtime WebAssembly SDK rebuilds.

• Passed — workload-free metadata tests:

  .\dotnet.cmd build -bl /p:TargetOS=browser /p:TargetArchitecture=wasm /p:RuntimeFlavor=CoreCLR -c Debug -t:Test .\src\mono\wasm\Wasm.Build.Tests\ /p:InstallWorkloadForTesting=false /p:TestUsingWorkloads=false /p:XUnitClassName=Wasm.Build.NativeRebuild.Tests.WasmMetadataSectionsTests

  4 passed, 0 failed, 0 skipped.

• Passed — stamped build/clean regression:

  .\dotnet.cmd build -bl /p:TargetOS=browser /p:TargetArchitecture=wasm /p:RuntimeFlavor=CoreCLR -c Debug -t:Test .\src\mono\wasm\Wasm.Build.Tests\ /p:InstallWorkloadForTesting=false /p:TestUsingWorkloads=true /p:XUnitMethodName=Wasm.Build.Tests.Blazor.CleanTests.Blazor_BuildIdStampedFile_ThenClean

  1 passed, 0 failed, 0 skipped.

• Passed — explicit CoreCLR native relink with the current targets/tasks:

  • no .wasm files at the publish root;
  • fingerprinted native module contains C#, CoreCLR, and .NET producers;
  • build_id is 1a2b3c4d5e6f7788;
  • emcc response no longer contains --build-id.

• Passed — build and publish with WasmBuildNative=false and a pinned ID:

  • no emcc/wasm-ld invocation;
  • stamped and fingerprinted modules contain the ID;
  • shared runtime-pack module hash remains unchanged.

• Passed — runtime startup under Node:

  • runtimeBuildInfo.buildId and getConfig().buildId report the normalized ID.

• Passed — incrementality:

  • identical IDs preserve Wasm and boot-config hashes/timestamps;
  • changing or removing the ID invalidates both.

• Passed — CoreCLR Browser TypeScript rollup and Mono Browser lint.

The plain full build remains independently blocked in WasmAppHost.csproj by the installed SDK reporting:

Microsoft.NET.Sdk.BlazorWeb.DotNetWatch#[.{fingerprint}]!.lib.module.js
has no matching endpoint

The same error reproduced after an MSBuild clean and while building the SDK pack directly. Disabling static-web-assets processing only for the local baseline avoids that unrelated SDK issue. The affected task assemblies, loader assets, workload-free tests, build/publish paths, clean path, and explicit relink path were validated separately as listed above.

The Mono targets parse successfully and Mono Browser lint passes. A Mono runtime build was not run locally because this worktree contains CoreCLR artifacts.

Not included / deferred

• Mutating or application-stamping the shared runtime-pack file itself.
• Registration of the .NET producer names in the WebAssembly tool-conventions repository.

Design notes: docs/design/mono/wasm-custom-sections.md.

Merged current main at 5114fa5cd78d9da73b195c2cd3b0924e5495687e in merge commit a94b7d84a6bf5bf8649181c040dedadf65e9c978. This includes the serial Helix dependency-staging fix from #136764.

Resolves #96334
Resolves #91049

Note

This PR description was updated with the assistance of GitHub Copilot.

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[Copilot]

Pull request overview

This PR prototypes emitting WebAssembly tool-conventions custom sections (producers, build_id) and surfacing a buildId value through the browser-wasm JavaScript API, wiring it through the Mono/CoreCLR relink pipelines and stamping WebCIL/R2R wasm outputs.

Changes:

• Add a reusable managed WasmCustomSectionWriter and an MSBuild task to generate a linkable wasm object contributing .NET entries to the producers section during relink.
• Plumb WasmNativeBuildId through build targets/tasks and expose runtimeBuildInfo.buildId in the JS public API surface.
• Add WBT coverage for relink/webcil metadata sections and a design doc describing the approach.

Reviewed changes

Copilot reviewed 38 out of 42 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/tasks/WasmAppBuilder/WebcilConverter.cs	Exposes build-id/version passthrough to Webcil converter.
src/tasks/WasmAppBuilder/WasmEmitProducersObject.cs	New task writing producers wasm object for linker merge.
src/tasks/Microsoft.NET.WebAssembly.Webcil/WebcilWasmWrapper.cs	Appends producers/build_id to wrapped WebCIL wasm.
src/tasks/Microsoft.NET.WebAssembly.Webcil/WebcilConverter.cs	Wires metadata options into wrapper output.
src/tasks/Microsoft.NET.WebAssembly.Webcil/Microsoft.NET.WebAssembly.Webcil.csproj	Links shared custom-section writer into task assembly.
src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/ConvertDllsToWebCil.cs	Passes build-id/product version into WebCIL conversion.
src/native/rollup.config.defines.js	Adds buildId rollup constant from env.
src/native/libs/System.Native.Browser/native/index.ts	Overrides runtimeBuildInfo.buildId from relinked native module.
src/native/libs/System.Native.Browser/libSystem.Native.Browser.footer.js	Exposes WASM_BUILD_ID via $DOTNET during emcc link.
src/native/libs/Common/JavaScript/types/public-api.ts	Extends public RuntimeAPI typing with buildId.
src/native/libs/Common/JavaScript/types/ems-ambient.ts	Adds buildId to emscripten ambient DOTNET shape.
src/native/libs/Common/JavaScript/loader/index.ts	Seeds runtimeBuildInfo.buildId from rollup constant.
src/native/libs/Common/JavaScript/loader/dotnet.d.ts	Updates generated public typings for buildId.
src/mono/wasm/Wasm.Build.Tests/NativeRebuildTests/WasmMetadataSectionsTests.cs	New tests validating producers/build_id emission.
src/mono/wasm/build/WasmApp.Common.targets	Forces native relink when WasmNativeBuildId is set.
src/mono/sample/wasm/Directory.Build.targets	Propagates WasmNativeBuildId through nested builds.
src/mono/sample/wasm/browser-advanced/Wasm.Advanced.Sample.csproj	Sample configuration updates (currently problematic).
src/mono/nuget/Microsoft.NET.Workload.Mono.Toolchain.Current.Manifest/WorkloadManifest.targets.in	Treats WasmNativeBuildId as relink-triggering.
src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets	Passes build-id/version into ConvertDllsToWebCIL task.
src/mono/browser/runtime/types/internal.ts	Adds buildId to emscriptenBuildOptions typing.
src/mono/browser/runtime/types/index.ts	Extends runtime API typing with buildId.
src/mono/browser/runtime/rollup.config.js	Adds buildId constant in mono runtime rollup config.
src/mono/browser/runtime/loader/globals.ts	Formatting-only changes.
src/mono/browser/runtime/loader/assets.ts	Formatting-only changes.
src/mono/browser/runtime/globals.ts	Copies buildId from relinked module into runtimeBuildInfo.
src/mono/browser/runtime/exports.ts	Seeds runtimeBuildInfo.buildId from rollup constant.
src/mono/browser/runtime/es6/dotnet.es6.lib.js	Plumbs WASM_BUILD_ID into emcc-evaluated options blob.
src/mono/browser/runtime/dotnet.d.ts	Updates generated public typings for buildId.
src/mono/browser/build/BrowserWasmApp.targets	Mono relink: emits producers object + build-id linker/env wiring.
src/mono/browser/build/BrowserWasmApp.CoreCLR.targets	CoreCLR relink: emits producers object + build-id linker/env wiring.
src/mono/browser/browser.proj	Treats WasmNativeBuildId as runtime-pack defaultable property.
src/coreclr/tools/Common/Wasm/WasmCustomSectionWriter.cs	New encoder/merger for producers/build_id custom sections.
src/coreclr/tools/Common/Compiler/ObjectWriter/WasmObjectWriter.cs	Stamps producers/build_id into R2R webcil wasm output.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj	Links shared custom-section writer into ILC tool.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCodegenCompilationBuilder.cs	Plumbs wasm build-id option through compilation pipeline.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCodegenCompilation.cs	Carries wasm build-id into object emission.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/CodeGen/ReadyToRunObjectWriter.cs	Passes wasm build-id through to WasmObjectWriter.
src/coreclr/tools/aot/crossgen2/Properties/Resources.resx	Adds help text for new crossgen2 option.
src/coreclr/tools/aot/crossgen2/Program.cs	Wires new option into ReadyToRun builder.
src/coreclr/tools/aot/crossgen2/Crossgen2RootCommand.cs	Adds --wasm-native-build-id option.
src/coreclr/hosts/corerun/wasm/libCorerun.extpost.js	Adds buildId field to corerun runtimeBuildInfo.
docs/design/mono/wasm-custom-sections.md	Design doc describing custom section strategy and properties.

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