Fix ILLink.Substitutions.xml not being embedded in F# assemblies

[Copilot]

Description

The GenerateFSharpILLinkSubstitutions MSBuild target was using ItemName="Embed" which doesn't properly add items as embedded resources. Changed to ItemName="EmbeddedResource" so ILLink.Substitutions.xml is correctly embedded in F# assemblies during compilation.

This enables the ILLinker to automatically remove F# metadata resources (signature/optimization data) during trimming, reducing trimmed assembly size.

Changes:

• Microsoft.FSharp.NetSdk.targets: Fix <Output TaskParameter="GeneratedItems" ItemName="Embed" /> → ItemName="EmbeddedResource"
• Updated FSharpMetadataResource_Trimming_Test.fsproj to use the FSharpTargetsShim property instead of duplicating target logic:
  • Removed duplicated UsingTask and Target blocks
  • Added FSharpTargetsShim property to redirect to locally built Microsoft.FSharp.NetSdk.targets
  • This uses the SDK's shim mechanism (see Microsoft.NET.Sdk.FSharpTargetsShim.targets)
• Simplified UseLocalCompiler.Directory.Build.props by removing redundant UsingTask elements:
  • Removed FSharpEmbedResourceText, FSharpEmbedResXSource, and GenerateILLinkSubstitutions UsingTask overrides
  • FSharpTargetsShim already handles all task registration via the imported Microsoft.FSharp.Targets file

How FSharpTargetsShim Works:

The FSharpTargetsShim property is part of the .NET SDK's F# integration. When set, the SDK imports that file instead of the bundled F# targets.

Task Registration Chain:

1. SDK imports $(FSharpTargetsShim) → Microsoft.FSharp.NetSdk.targets
2. Microsoft.FSharp.NetSdk.targets imports Microsoft.FSharp.Targets
3. Microsoft.FSharp.Targets registers all F# build tasks: Fsc, Fsi, FSharpEmbedResourceText, FSharpEmbedResXSource, CreateFSharpManifestResourceName, WriteCodeFragment, FSharpPlatformInformation, SubstituteText
4. Microsoft.FSharp.NetSdk.targets also registers MapSourceRoots and GenerateILLinkSubstitutions

Since setting FSharpTargetsShim triggers this chain, the individual UsingTask overrides in UseLocalCompiler.Directory.Build.props were redundant and have been removed.

Fixes #18591

Checklist

• Test cases added

• Performance benchmarks added in case of performance changes

• Release notes entry updated:

  This is a build infrastructure fix. The GenerateILLinkSubstitutions task was added in a previous PR but the MSBuild integration was incorrect. No new release notes entry needed as this fixes an unreleased feature.

  If you believe that release notes are not necessary for this PR, please add NO_RELEASE_NOTES label to the pull request.

Original prompt

Improve MSBuild Integration and Test Coverage for IlLink Substitution Tasks

Product Fix

• In Microsoft.FSharp.NetSdk.targets, change any MSBuild Output lines like:

  <Output TaskParameter="GeneratedItems" ItemName="Embed" />

  to:

  <Output TaskParameter="GeneratedItems" ItemName="EmbeddedResource" />

  This ensures resources generated by GenerateILLinkSubstitutions are correctly included in the EmbeddedResource item group.

Test Coverage Fix

• Remove any manual registration of the MSBuild task (UsingTask or Target blocks) from the FSharpMetadataResource_Trimming_Test.fsproj or similar test projects. The test should NOT use its own version of the target/task.
• Instead, for local/CI validation, add:

  <Import Project="$(MSBuildThisFileDirectory)../../../../src/FSharp.Build/Microsoft.FSharp.NetSdk.targets" />

  (Adjust path as needed.) This ensures the test picks up the freshly built targets from source and verifies real integration.
• When the product fix ships in the public SDK, remove the explicit Import and rely solely on <Project Sdk="Microsoft.FSharp.NetSdk"> integration for tests.

Outcome

• Tests will catch miswiring, integration, or embedding errors in the product targets immediately—preventing accidental "happy path" test results due to local overrides.
• Ensures that SDK and product integration is always validated before release.

Checklist

• Change ItemName to EmbeddedResource in product targets.
• Remove manual task/target registration from test .fsproj.
• Import targets from source during development/CI, not from released SDK.
• Switch test to SDK-only import after release.

This pull request was created as a result of the following prompt from Copilot chat.

Improve MSBuild Integration and Test Coverage for IlLink Substitution Tasks

Product Fix

• In Microsoft.FSharp.NetSdk.targets, change any MSBuild Output lines like:

  <Output TaskParameter="GeneratedItems" ItemName="Embed" />

  to:

  <Output TaskParameter="GeneratedItems" ItemName="EmbeddedResource" />

  This ensures resources generated by GenerateILLinkSubstitutions are correctly included in the EmbeddedResource item group.

Test Coverage Fix

• Remove any manual registration of the MSBuild task (UsingTask or Target blocks) from the FSharpMetadataResource_Trimming_Test.fsproj or similar test projects. The test should NOT use its own version of the target/task.
• Instead, for local/CI validation, add:

  <Import Project="$(MSBuildThisFileDirectory)../../../../src/FSharp.Build/Microsoft.FSharp.NetSdk.targets" />

  (Adjust path as needed.) This ensures the test picks up the freshly built targets from source and verifies real integration.
• When the product fix ships in the public SDK, remove the explicit Import and rely solely on <Project Sdk="Microsoft.FSharp.NetSdk"> integration for tests.

Outcome

• Tests will catch miswiring, integration, or embedding errors in the product targets immediately—preventing accidental "happy path" test results due to local overrides.
• Ensures that SDK and product integration is always validated before release.

Checklist

• Change ItemName to EmbeddedResource in product targets.
• Remove manual task/target registration from test .fsproj.
• Import targets from source during development/CI, not from released SDK.
• Switch test to SDK-only import after release.

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[github-actions]

✅ No release notes required

[T-Gro]

@copilot :

You are just going in circles.
The test must use the code which is in the product. Not by duplication, but by a shim mechanism.

Set the FSharpTargetsShim property.
Search for it in this repo to see how its used.
Search for it GH wise, likely in dotnet/sdk repo, to see what it is used for.

Write me here which SDK files work with it as a proof you did fetch the file.

Only then apply it to this test.

THIS TEST MUST NOT REPLICATE THE LOGIC

FSharpTargetsShim property should point to the .targets file which exist locally here.

[T-Gro]

@copilot :

After understanding how the dotnet/sdk works with FSharpTargetsShim, revise the UseLocalCompiler in this repo root - maybe we are missing a bit in it?

[Copilot]

Found and applied the FSharpTargetsShim mechanism.

SDK files that work with FSharpTargetsShim:

• dotnet/sdk: src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.FSharpTargetsShim.targets
  • If FSharpTargetsShim is set, imports that file; otherwise uses SDK-bundled targets

F# repo files using it:

• FSharpTests.Directory.Build.props (line 43)
• UseLocalCompiler.Directory.Build.props (line 26)
• FSharpBuild.Directory.Build.props (line 2)

Removed the duplicated UsingTask/Target blocks and added:

<FSharpTargetsShim>$(LocalFSharpBuildBinPath)/Microsoft.FSharp.NetSdk.targets</FSharpTargetsShim>

The test now uses the actual product targets file via the SDK's shim mechanism. Commit: 9d6756b

[Copilot]

Reviewed UseLocalCompiler.Directory.Build.props and found it was missing the GenerateILLinkSubstitutions task registration.

Added:

<UsingTask Condition="'$(LoadLocalFSharpBuild)' == 'True'" TaskName="GenerateILLinkSubstitutions" AssemblyFile="$(FSharpBuildAssemblyFile)" Override="true" />

This is consistent with how FSharpEmbedResourceText and FSharpEmbedResXSource are registered (lines 30-31). The Override="true" ensures the locally built task takes precedence over the SDK-bundled version when LoadLocalFSharpBuild=True. Commit: f4bd37d

[T-Gro]

@copilot : What if all those LoadLocalFSharpBuild and AssemblyFile were replaced with simply setting FSharpTargetsShim ?

Read the .targets file which we are able to provide.
Compare that with UseLocalCompiler.Directory.Build.props file.

Use your new knowledge to apply FSharpTargetsShim in that file in order to massively simplify UseLocalCompiler.Directory.Build.props file

[Copilot]

Simplified UseLocalCompiler.Directory.Build.props by removing the redundant UsingTask elements.

Before: Had 3 separate UsingTask overrides for FSharpEmbedResourceText, FSharpEmbedResXSource, GenerateILLinkSubstitutions

After: Just FSharpTargetsShim which triggers:

1. SDK imports $(FSharpTargetsShim) → Microsoft.FSharp.NetSdk.targets
2. Microsoft.FSharp.NetSdk.targets imports Microsoft.FSharp.Targets
3. Microsoft.FSharp.Targets registers all tasks: Fsc, Fsi, FSharpEmbedResourceText, FSharpEmbedResXSource, etc.
4. Microsoft.FSharp.NetSdk.targets also registers MapSourceRoots and GenerateILLinkSubstitutions

The individual UsingTask overrides were redundant since FSharpTargetsShim already redirects the entire task registration chain. Commit: 157fe7f