[WIP] Auto-generate IlLink.Substitutions.xml to Remove F# Metadata Resources

src/FSharp.Build/FSharp.Build.fsproj

@@ -46,6 +46,7 @@
     <Compile Include="CreateFSharpManifestResourceName.fs" />
     <Compile Include="SubstituteText.fs" />
     <Compile Include="MapSourceRoots.fs" />
+    <Compile Include="GenerateILLinkSubstitutions.fs" />
     <None Include="Microsoft.FSharp.Targets" CopyToOutputDirectory="PreserveNewest" />
     <None Include="Microsoft.Portable.FSharp.Targets" CopyToOutputDirectory="PreserveNewest" />
     <None Include="Microsoft.FSharp.NetSdk.props" CopyToOutputDirectory="PreserveNewest" />

src/FSharp.Build/GenerateILLinkSubstitutions.fs

@@ -0,0 +1,84 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace FSharp.Build
+
+open System
+open System.IO
+open System.Text
+open Microsoft.Build.Framework
+open Microsoft.Build.Utilities
+
+/// <summary>
+/// MSBuild task that generates ILLink.Substitutions.xml file to remove F# metadata resources during IL linking.
+/// </summary>
+type GenerateILLinkSubstitutions() =
+    inherit Task()
+
+    /// <summary>
+    /// Assembly name to use when generating resource names to be removed.
+    /// </summary>
+    [<Required>]
+    member val AssemblyName = "" with get, set
+
+    /// <summary>
+    /// Intermediate output path for storing the generated file.
+    /// </summary>
+    [<Required>]
+    member val IntermediateOutputPath = "" with get, set
+
+    /// <summary>
+    /// Generated embedded resource items.
+    /// </summary>
+    [<Output>]
+    member val GeneratedItems = [| |] : ITaskItem[] with get, set
+
+    override this.Execute() =
+        try
+            // Define the resource prefixes that need to be removed
+            let resourcePrefixes = 
+                [| 
+                    // Signature variants
+                    yield! [| for dataType in [| "Data"; "DataB" |] do
+                               for compression in [| ""; "Compressed" |] do
+                               yield $"FSharpSignature{compression}{dataType}" |]
+
+                    // Optimization variants
+                    yield! [| for dataType in [| "Data"; "DataB" |] do
+                               for compression in [| ""; "Compressed" |] do
+                               yield $"FSharpOptimization{compression}{dataType}" |]
+
+                    // Info variants
+                    yield "FSharpOptimizationInfo"
+                    yield "FSharpSignatureInfo"
+                |]
+
+            // Generate the XML content
+            let sb = StringBuilder(4096) // pre-allocate capacity
+            sb.AppendLine("<?xml version=\"1.0\" encoding=\"utf-8\"?>") |> ignore
+            sb.AppendLine("<linker>") |> ignore
+            sb.AppendLine($"  <assembly fullname=\"{this.AssemblyName}\">") |> ignore
+
+            // Add each resource entry with proper closing tag on the same line
+            for prefix in resourcePrefixes do
+                sb.AppendLine($"    <resource name=\"{prefix}.{this.AssemblyName}\" action=\"remove\"></resource>") |> ignore
+
+            // Close assembly and linker tags
+            sb.AppendLine("  </assembly>") |> ignore
+            sb.AppendLine("</linker>") |> ignore
+
+            let xmlContent = sb.ToString()
+
+            // Create a file in the intermediate output path
+            let outputFileName = Path.Combine(this.IntermediateOutputPath, "ILLink.Substitutions.xml")
+            Directory.CreateDirectory(this.IntermediateOutputPath) |> ignore
+            File.WriteAllText(outputFileName, xmlContent)
+
+            // Create a TaskItem for the generated file
+            let item = TaskItem(outputFileName) :> ITaskItem
+            item.SetMetadata("LogicalName", "ILLink.Substitutions.xml")
+
+            this.GeneratedItems <- [| item |]
+            true
+        with ex ->
+            this.Log.LogErrorFromException(ex, true)
+            false

src/FSharp.Build/Microsoft.FSharp.NetSdk.targets

@@ -154,6 +154,18 @@ WARNING:  DO NOT MODIFY this file unless you are knowledgeable about MSBuild and
     <SourceRootMappedPathsFeatureSupported>true</SourceRootMappedPathsFeatureSupported>
   </PropertyGroup>
 
+  <!-- Register the GenerateILLinkSubstitutions task -->
+  <UsingTask TaskName="GenerateILLinkSubstitutions" AssemblyFile="$(FSharpBuildAssemblyFile)" />
+
+  <!-- Generate ILLink.Substitutions.xml to remove F# metadata resources during trimming -->
+  <Target Name="GenerateFSharpILLinkSubstitutions" BeforeTargets="CoreCompile">
+    <GenerateILLinkSubstitutions
+      AssemblyName="$(AssemblyName)"
+      IntermediateOutputPath="$(IntermediateOutputPath)">
+      <Output TaskParameter="GeneratedItems" ItemName="EmbeddedResource" />
+    </GenerateILLinkSubstitutions>
+  </Target>
+
   <!-- 
     If InitializeSourceControlInformation target isn't supported, we just continue without invoking that synchronization target. 
     We'll proceed with SourceRoot (and other source control properties) provided by the user (or blank).

tests/AheadOfTime/Trimming/FSharpMetadataResource_Trimming_Test/FSharpMetadataResource_Trimming_Test.fsproj

@@ -0,0 +1,40 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFrameworks>net9.0</TargetFrameworks>
+    <LangVersion>preview</LangVersion>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <DisableImplicitFSharpCoreReference>true</DisableImplicitFSharpCoreReference>
+    <DisableImplicitNuGetFallbackFolder>true</DisableImplicitNuGetFallbackFolder>
+    <DisableImplicitLibraryPacksFolder>true</DisableImplicitLibraryPacksFolder>
+    <PublishTrimmed>true</PublishTrimmed>
+    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <DotnetFscCompilerPath>$(MSBuildThisFileDirectory)../../../../artifacts/bin/fsc/Release/net9.0/fsc.dll</DotnetFscCompilerPath>
+    <Fsc_DotNET_DotnetFscCompilerPath>$(MSBuildThisFileDirectory)../../../../artifacts/bin/fsc/Release/net9.0/fsc.dll</Fsc_DotNET_DotnetFscCompilerPath>
+    <FSharpBuildAssemblyFile>$(MSBuildThisFileDirectory)../../../../artifacts/bin/FSharp.Build/Release/net9.0/FSharp.Build.dll</FSharpBuildAssemblyFile>
+    <FSharpPreferNetFrameworkTools>False</FSharpPreferNetFrameworkTools>
+    <FSharpPrefer64BitTools>True</FSharpPrefer64BitTools>
+  </PropertyGroup>
+
+  <!-- Import the custom targets file directly from the repository to use the latest version -->
+  <Import Project="$(MSBuildThisFileDirectory)../../../../src/FSharp.Build/Microsoft.FSharp.NetSdk.props" />
+  <Import Project="$(MSBuildThisFileDirectory)../../../../src/FSharp.Build/Microsoft.FSharp.NetSdk.targets" />
+
+  <ItemGroup>
+    <Compile Include="..\Program.fs" />
+  </ItemGroup>
+
+  <Import Project="$(MSBuildThisFileDirectory)../../../../eng/Versions.props" />
+
+  <ItemGroup>
+      <PackageReference Include="FSharp.Core" Version="$(FSharpCorePreviewPackageVersionValue)"/>
+  </ItemGroup>
+
+</Project>

tests/AheadOfTime/Trimming/check.ps1

@@ -33,7 +33,11 @@ function CheckTrim($root, $tfm, $outputfile, $expected_len) {
     # Checking that the trimmed outputfile binary is of expected size (needs adjustments if test is updated).
     $file = Get-Item (Join-Path $PSScriptRoot "${root}\bin\release\${tfm}\win-x64\publish\${outputfile}")
     $file_len = $file.Length
-    if (-not ($expected_len -eq -1 -or $file_len -eq $expected_len))
+    if ($expected_len -eq -1)
+    {
+        Write-Host "Actual ${tfm} - trimmed ${outputfile} length: ${file_len} Bytes (expected length is placeholder -1, update test with this actual value)"
+    }
+    elseif ($file_len -ne $expected_len)
     {
         Write-Error "Test failed with unexpected ${tfm}  -  trimmed ${outputfile} length:`nExpected:`n`t${expected_len} Bytes`nActual:`n`t${file_len} Bytes`nEither codegen or trimming logic have changed. Please investigate and update expected dll size or report an issue." -ErrorAction Stop
     }
@@ -42,8 +46,12 @@ function CheckTrim($root, $tfm, $outputfile, $expected_len) {
 # NOTE: Trimming now errors out on desktop TFMs, as shown below:
 # error NETSDK1124: Trimming assemblies requires .NET Core 3.0 or higher.
 
-# Check net7.0 trimmed assemblies
+# Check net9.0 trimmed assemblies
 CheckTrim -root "SelfContained_Trimming_Test" -tfm "net9.0" -outputfile "FSharp.Core.dll" -expected_len 300032
 
-# Check net8.0 trimmed assemblies
+# Check net9.0 trimmed assemblies with static linked FSharpCore
 CheckTrim -root "StaticLinkedFSharpCore_Trimming_Test" -tfm "net9.0" -outputfile "StaticLinkedFSharpCore_Trimming_Test.dll" -expected_len 9154048
+
+# Check net9.0 trimmed assemblies with F# metadata resources removed
+CheckTrim -root "FSharpMetadataResource_Trimming_Test" -tfm "net9.0" -outputfile "FSharpMetadataResource_Trimming_Test.dll" -expected_len -1
+