From fa59f6d7b27a44deafed1085a781817bf8f22c87 Mon Sep 17 00:00:00 2001
From: Jackson Schuster <36744439+jtschuster@users.noreply.github.com>
Date: Sat, 18 Jul 2026 18:09:21 -0700
Subject: [PATCH 1/5] Use Wasm runtime pack for building wasm in
 ILCompiler.ReadyToRun.Tests

---
 eng/pipelines/runtime.yml                     |  45 +++++
 .../ILCompiler.ReadyToRun.Tests.csproj        |  51 +++++-
 .../TestCases/R2RTestSuites.cs                |  11 +-
 .../TestCasesRunner/R2RResultChecker.cs       |  18 +-
 .../TestCasesRunner/R2RTestCaseCompiler.cs    |  24 +--
 .../TestCasesRunner/R2RTestRunner.cs          |  94 +++++++---
 .../TestCasesRunner/TestPaths.cs              | 169 +++---------------
 ...rosoft.NETCore.App.Runtime.CoreCLR.sfxproj |   2 +-
 8 files changed, 207 insertions(+), 207 deletions(-)

diff --git a/eng/pipelines/runtime.yml b/eng/pipelines/runtime.yml
index 77ec17437b8a1e..a122b1b40d0829 100644
--- a/eng/pipelines/runtime.yml
+++ b/eng/pipelines/runtime.yml
@@ -861,9 +861,24 @@ extends:
           jobParameters:
             timeoutInMinutes: 120
             nameSuffix: CLR_Tools_Tests
+            # Depend on the browser-wasm libraries built below so the wasm crossgen2 R2R test
+            # (ILCompiler.ReadyToRun.Tests) can compile against real browser-wasm references.
+            dependsOn:
+            - build_browser_wasm_linux_Release_CLR_Tools_Tests_WasmLibs
             buildArgs: -s clr.aot+clr.iltools+clr.corelib+clr.nativecorelib+libs.sfx+clr.toolstests+tools.cdac+tools.cdactests -c $(_BuildConfig) -test
             enablePublishTestResults: true
             testResultsFormat: 'xunit'
+            preBuildSteps:
+              # Lay the browser-wasm libraries into artifacts/bin so TestPaths' WasmRuntimePackDir
+              # resolves and the wasm R2R test compiles against real browser-wasm references.
+              - template: /eng/pipelines/common/download-artifact-step.yml
+                parameters:
+                  artifactName: CLR_Tools_Tests_WasmLibs_BuildArtifacts_browser_wasm_Release
+                  artifactFileName: CLR_Tools_Tests_WasmLibs_BuildArtifacts_browser_wasm_Release$(archiveExtension)
+                  unpackFolder: $(Build.SourcesDirectory)/artifacts/bin
+                  cleanUnpackFolder: false
+                  overwriteExistingFiles: true
+                  displayName: Browser-Wasm Libraries
             # We want to run AOT tests when illink changes because there's share code and tests from illink which are used by AOT
             condition: >-
               or(
@@ -871,6 +886,36 @@ extends:
                 eq(stageDependencies.EvaluatePaths.evaluate_paths.outputs['SetPathVars_tools_illink.containsChange'], true),
                 eq(stageDependencies.EvaluatePaths.evaluate_paths.outputs['SetPathVars_tools_cdac.containsChange'], true),
                 eq(variables['isRollingBuild'], true))
+
+      # Build the browser-wasm managed runtime pack that the CLR_Tools_Tests job uses
+      # as crossgen2 references for the wasm ReadyToRun test. Native runtime and host
+      # assets are omitted because the test only consumes managed assemblies.
+      - template: /eng/pipelines/common/platform-matrix.yml
+        parameters:
+          jobTemplate: /eng/pipelines/common/global-build-job.yml
+          buildConfig: Release
+          platforms:
+          - browser_wasm
+          jobParameters:
+            nameSuffix: CLR_Tools_Tests_WasmLibs
+            buildArgs: -s clr.corelib+libs+libs.pretest -c Release /p:IncludeStaticLibrariesInPack=false
+            timeoutInMinutes: 120
+            postBuildSteps:
+              - template: /eng/pipelines/common/upload-artifact-step.yml
+                parameters:
+                  rootFolder: $(Build.SourcesDirectory)/artifacts/bin
+                  includeRootFolder: false
+                  archiveType: $(archiveType)
+                  archiveExtension: $(archiveExtension)
+                  tarCompression: $(tarCompression)
+                  artifactName: CLR_Tools_Tests_WasmLibs_BuildArtifacts_$(osGroup)$(osSubgroup)_$(archType)_$(_BuildConfig)
+                  displayName: Browser-Wasm Libraries
+            condition: >-
+              or(
+                eq(stageDependencies.EvaluatePaths.evaluate_paths.outputs['SetPathVars_coreclr.containsChange'], true),
+                eq(stageDependencies.EvaluatePaths.evaluate_paths.outputs['SetPathVars_tools_illink.containsChange'], true),
+                eq(stageDependencies.EvaluatePaths.evaluate_paths.outputs['SetPathVars_tools_cdac.containsChange'], true),
+                eq(variables['isRollingBuild'], true))
       #
       # Build CrossDacs
       #
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
index e3f0ab6ea0cd15..14cec02ab0230e 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
@@ -12,6 +12,12 @@
     <Configurations>Debug;Release;Checked</Configurations>
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
     <TestRunnerAdditionalArguments>-notrait category=failing</TestRunnerAdditionalArguments>
+    <RequireWasmReferences Condition="'$(RequireWasmReferences)' == ''">false</RequireWasmReferences>
+    <WasmRuntimePackRoot>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'microsoft.netcore.app.runtime.browser-wasm'))</WasmRuntimePackRoot>
+    <WasmRuntimePackDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
+    <WasmRuntimePackNativeDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
+    <WasmRuntimePackDir Condition="!Exists('$(WasmRuntimePackDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/lib/$(NetCoreAppCurrent)')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
+    <WasmRuntimePackNativeDir Condition="!Exists('$(WasmRuntimePackNativeDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/native')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
   </PropertyGroup>
 
   <ItemGroup>
@@ -72,6 +78,25 @@
           SkipUnchangedFiles="true" />
   </Target>
 
+  <Target Name="ValidatePathsExist"
+          BeforeTargets="Build"
+          Condition="'$(DesignTimeBuild)' != 'true'">
+
+    <Error Condition="!Exists('$(CoreCLRArtifactsPath)\$(BuildArchitecture)\crossgen2')"
+           Text="Crossgen2 inbuild publish directory '$(CoreCLRArtifactsPath)\$(BuildArchitecture)\crossgen2' does not exist. This is a build authoring error and should be generated in the test project build." />
+    <Error Condition="!Exists('$(MicrosoftNetCoreAppRuntimePackNativeDir)')"
+           Text="Runtime pack path '$(MicrosoftNetCoreAppRuntimePackNativeDir)' does not exist." />
+    <Error Condition="!Exists('$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)')"
+           Text="Runtime pack path '$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)' does not exist." />
+
+    <Error Condition="'$(RequireWasmReferences)' == 'true' and (!Exists('$(WasmRuntimePackDir)') or !Exists('$(WasmRuntimePackNativeDir)System.Private.CoreLib.dll'))"
+           Text="The browser-wasm runtime pack was not found under '$(WasmRuntimePackRoot)'. Build and download the wasm prerequisite artifact before building this test." />
+    <Warning Condition="'$(RequireWasmReferences)' != 'true' and !Exists('$(WasmRuntimePackDir)')"
+             Text="Browser-wasm runtime pack path '$(WasmRuntimePackDir)' does not exist. Browser-wasm ReadyToRun tests will fall back to host references, which may cause unexpected failures. Generate by building the clr.corelib+libs+libs.pretest subsets for browser-wasm." />
+    <Warning Condition="'$(RequireWasmReferences)' != 'true' and !Exists('$(WasmRuntimePackNativeDir)System.Private.CoreLib.dll')"
+             Text="Browser-wasm System.Private.CoreLib.dll was not found under '$(WasmRuntimePackNativeDir)'. Browser-wasm ReadyToRun tests will fall back to host references, which may cause unexpected failures. Generate by building the clr.corelib+libs+libs.pretest subsets for browser-wasm." />
+  </Target>
+
   <!-- Test case source files are embedded as resources so we can compile them with Roslyn at test time.
        Exclude subdirectory sources from compilation since they are compiled in-memory by R2RTestCaseCompiler. -->
   <ItemGroup>
@@ -81,6 +106,7 @@
 
   <!-- Pass build-time paths to test runtime via RuntimeHostConfigurationOption -->
   <ItemGroup>
+    <!-- Required Host-Targeting assets -->
     <RuntimeHostConfigurationOption Include="R2RTest.Crossgen2Dir">
       <Value>$(CoreCLRArtifactsPath)/$(BuildArchitecture)/crossgen2</Value>
     </RuntimeHostConfigurationOption>
@@ -90,18 +116,25 @@
     <RuntimeHostConfigurationOption Include="R2RTest.RuntimePackNativeDir">
       <Value>$(MicrosoftNetCoreAppRuntimePackNativeDir)</Value>
     </RuntimeHostConfigurationOption>
-    <RuntimeHostConfigurationOption Include="R2RTest.RefPackDir">
-      <Value>$(MicrosoftNetCoreAppRefPackRefDir)</Value>
-    </RuntimeHostConfigurationOption>
-    <RuntimeHostConfigurationOption Include="R2RTest.CoreCLRArtifactsDir">
-      <Value>$(CoreCLRArtifactsPath)</Value>
+
+    <!-- browser-wasm runtime pack paths used for validating wasm R2R compilation.
+         When absent, the wasm R2R compilation falls back to host references.
+         This could cause unexpected failures if crossgen2 expects intrinsics in
+         the wasm System.Private.CoreLib.dll that are not present in the host reference pack.
+         Thus, the RequireWasmReferences option can be used to fail the test build if the wasm
+         runtime pack is not present.
+          -->
+    <RuntimeHostConfigurationOption Include="R2RTest.RequireWasmReferences">
+      <Value>$(RequireWasmReferences)</Value>
     </RuntimeHostConfigurationOption>
-    <RuntimeHostConfigurationOption Include="R2RTest.TargetArchitecture">
-      <Value>$(TargetArchitecture)</Value>
+    <RuntimeHostConfigurationOption Include="R2RTest.WasmRuntimePackDir">
+      <Value>$(WasmRuntimePackDir)</Value>
     </RuntimeHostConfigurationOption>
-    <RuntimeHostConfigurationOption Include="R2RTest.TargetOS">
-      <Value>$(TargetOS)</Value>
+    <RuntimeHostConfigurationOption Include="R2RTest.WasmRuntimePackNativeDir">
+      <Value>$(WasmRuntimePackNativeDir)</Value>
     </RuntimeHostConfigurationOption>
+
+    <!-- Used for gating Debug-only JIT features from being tested. -->
     <RuntimeHostConfigurationOption Include="R2RTest.CoreCLRConfiguration">
       <Value>$(CoreCLRConfiguration)</Value>
     </RuntimeHostConfigurationOption>
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs
index e29a57c61cccc2..8750b3551ff007 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs
@@ -76,13 +76,10 @@ public void WasmWebcilModule()
                 new(nameof(WasmWebcilModule), [new CrossgenAssembly(wasmWebcilModule)])
                 {
                     OutputFileExtension = ".wasm",
-                    AdditionalArgs =
-                    {
-                        "--targetarch",
-                        "wasm",
-                        "--targetos",
-                        "browser",
-                    },
+                    // Reference the real browser-wasm framework assemblies when they are available
+                    // (e.g. the wasm tools-test job downloads them); otherwise the runner falls back
+                    // to host references so this test still runs everywhere.
+                    TargetRid = TargetRid.BrowserWasm,
                     Validate = Validate,
                 },
             ]));
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RResultChecker.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RResultChecker.cs
index 33b4ed1d743516..f7f11d6f5c5369 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RResultChecker.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RResultChecker.cs
@@ -1194,11 +1194,15 @@ public static bool MethodILIsPresent(string msilFilePath, string declaringType,
 /// </summary>
 internal sealed class SimpleAssemblyResolver : IAssemblyResolver
 {
-    private readonly TestPaths _paths;
+    private readonly Dictionary<string, string> _assemblyPaths;
 
-    public SimpleAssemblyResolver(TestPaths paths)
+    public SimpleAssemblyResolver(IEnumerable<string> referencePaths)
     {
-        _paths = paths;
+        _assemblyPaths = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+        foreach (string referencePath in referencePaths)
+        {
+            _assemblyPaths[Path.GetFileNameWithoutExtension(referencePath)] = referencePath;
+        }
     }
 
     public IAssemblyMetadata? FindAssembly(MetadataReader metadataReader, AssemblyReferenceHandle assemblyReferenceHandle, string parentFile)
@@ -1217,10 +1221,12 @@ public SimpleAssemblyResolver(TestPaths paths)
 
         string candidate = Path.Combine(dir, simpleName + ".dll");
         if (!File.Exists(candidate))
-            candidate = Path.Combine(_paths.RuntimePackDir, simpleName + ".dll");
+        {
+            if (!_assemblyPaths.TryGetValue(simpleName, out string? referencePath) || referencePath is null)
+                return null;
 
-        if (!File.Exists(candidate))
-            return null;
+            candidate = referencePath;
+        }
 
         return new SimpleAssemblyMetadata(candidate);
     }
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestCaseCompiler.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestCaseCompiler.cs
index 7bd12c8887fe59..cffccdf5c65b34 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestCaseCompiler.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestCaseCompiler.cs
@@ -9,6 +9,7 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.Emit;
+using Xunit.Abstractions;
 
 namespace ILCompiler.ReadyToRun.Tests.TestCasesRunner;
 
@@ -19,26 +20,13 @@ internal sealed class R2RTestCaseCompiler
 {
     private readonly List<MetadataReference> _frameworkReferences;
 
-    public R2RTestCaseCompiler(TestPaths paths)
+    public R2RTestCaseCompiler(List<string> references)
     {
         _frameworkReferences = new List<MetadataReference>();
 
-        // Add reference assemblies from the ref pack (needed for Roslyn compilation)
-        string refPackDir = paths.RefPackDir;
-        if (Directory.Exists(refPackDir))
+        foreach (string refPath in references)
         {
-            foreach (string refPath in Directory.EnumerateFiles(refPackDir, "*.dll"))
-            {
-                _frameworkReferences.Add(MetadataReference.CreateFromFile(refPath));
-            }
-        }
-        else
-        {
-            // Fallback to runtime pack implementation assemblies
-            foreach (string refPath in paths.GetFrameworkReferencePaths())
-            {
-                _frameworkReferences.Add(MetadataReference.CreateFromFile(refPath));
-            }
+            _frameworkReferences.Add(MetadataReference.CreateFromFile(refPath));
         }
     }
 
@@ -85,7 +73,7 @@ public string CompileAssembly(
             syntaxTrees,
             references,
             new CSharpCompilationOptions(outputKind)
-                .WithOptimizationLevel(OptimizationLevel.Release)
+                .WithOptimizationLevel(OptimizationLevel.Debug)
                 .WithAllowUnsafe(true)
                 .WithNullableContextOptions(NullableContextOptions.Enable));
 
@@ -97,7 +85,7 @@ public string CompileAssembly(
                 .Where(d => d.Severity == DiagnosticSeverity.Error)
                 .Select(d => d.ToString());
             throw new InvalidOperationException(
-                $"Compilation of '{assemblyName}' failed:\n{string.Join("\n", errors)}");
+                $"Compilation of '{assemblyName}' failed:\nReferences:\n{string.Join(Environment.NewLine, compilation.References.Select(r => r.Display))}\n\n{string.Join("\n", errors)}");
         }
 
         return outputPath;
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
index c6a2e26649671e..dc23a142c40946 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
@@ -11,6 +11,12 @@
 
 namespace ILCompiler.ReadyToRun.Tests.TestCasesRunner;
 
+enum TargetRid
+{
+    Host,
+    BrowserWasm
+}
+
 /// <summary>
 /// Describes an assembly compiled by Roslyn as part of a test case.
 /// </summary>
@@ -94,6 +100,16 @@ internal sealed class CrossgenCompilation(string name, List<CrossgenAssembly> as
     /// </summary>
     public Action<ReadyToRunReader>? Validate { get; init; }
 
+    /// <summary>
+    /// When true, this compilation references the browser-wasm runtime pack (real wasm framework
+    /// assemblies and the wasm System.Private.CoreLib) if it is available, instead of the host
+    /// runtime pack. When the browser-wasm libs are not present the runner falls back to host
+    /// references so the test still runs (with a host-arch corelib). Set this on wasm compilations
+    /// (--targetarch wasm --targetos browser) so they reference target-matching libraries when run
+    /// in a job that downloads the browser-wasm libs.
+    /// </summary>
+    public TargetRid TargetRid { get; init; } = TargetRid.Host;
+
     public string Name => name;
 
     public bool IsComposite => Options.Contains(Crossgen2Option.Composite);
@@ -205,10 +221,18 @@ public void Run(R2RTestCase testCase)
 
             // Step 2: Run each crossgen2 compilation and validate
             var driver = new R2RDriver(_output, _paths);
-            var refPaths = BuildReferencePaths();
+            List<string> hostRefPaths = BuildReferencePaths(useWasmReferences: false);
+            List<string>? wasmRefPaths = null;
 
             foreach(var compilation in testCase.Compilations)
             {
+                List<string> refPaths = hostRefPaths;
+                if (compilation.TargetRid == TargetRid.BrowserWasm)
+                {
+                    wasmRefPaths ??= BuildReferencePaths(useWasmReferences: true);
+                    refPaths = wasmRefPaths;
+                }
+
                 string outputPath = RunCrossgenCompilation(
                     testCase.Name, compilation, driver, compilation.FilePath, refPaths, assemblyPaths);
 
@@ -216,7 +240,7 @@ public void Run(R2RTestCase testCase)
                 {
                     Assert.True(File.Exists(outputPath), $"R2R image not found: {outputPath}");
                     _output.WriteLine($"  Validating R2R image: {outputPath}");
-                    var reader = new ReadyToRunReader(new SimpleAssemblyResolver(_paths), outputPath);
+                    var reader = new ReadyToRunReader(new SimpleAssemblyResolver(refPaths), outputPath);
                     compilation.Validate(reader);
                 }
             }
@@ -234,11 +258,13 @@ public void Run(R2RTestCase testCase)
     private Dictionary<string, string> CompileAllAssemblies(
         IEnumerable<CompiledAssembly> assemblies)
     {
-        var compiler = new R2RTestCaseCompiler(_paths);
         var paths = new Dictionary<string, string>();
 
         foreach (var asm in assemblies)
         {
+            // Tests shouldn't require a platform-specific runtime/ref pack for Roslyn compilation
+            var defaultReferences = BuildReferencePaths(useWasmReferences: false);
+            var compiler = new R2RTestCaseCompiler(defaultReferences);
             var sources = asm.SourceResourceNames
                 .Select(R2RTestCaseCompiler.ReadEmbeddedSource)
                 .ToList();
@@ -252,7 +278,7 @@ private Dictionary<string, string> CompileAllAssemblies(
                 additionalReferences: asm.References.Select(r => r.FilePath).ToList(),
                 features: asm.Features.Count > 0 ? asm.Features : null);
             paths[asm.AssemblyName] = ilPath;
-            _output.WriteLine($"  Roslyn compiled '{asm.AssemblyName}' -> {ilPath}");
+            _output.WriteLine($"Roslyn compiled '{asm.AssemblyName}' -> {ilPath}");
         }
 
         return paths;
@@ -307,6 +333,13 @@ private static string RunCrossgenCompilation(
         foreach (var option in compilation.Options)
             args.Add(option.ToArg());
 
+        args.AddRange(compilation.TargetRid switch
+        {
+            TargetRid.Host => [],
+            TargetRid.BrowserWasm => ["--targetos", "browser", "--targetarch", "wasm"],
+            _ => throw new InvalidOperationException($"Unknown target RID: {compilation.TargetRid}")
+        });
+
         // Caller-supplied raw args (for options that take values, e.g. --determinism-stress=N)
         args.AddRange(compilation.AdditionalArgs);
 
@@ -335,32 +368,47 @@ private static void AddRefArgs(List<string> args, List<string> refPaths)
         }
     }
 
-    private List<string> BuildReferencePaths()
+    /// <summary>
+    /// Runtime packs are used as references for both Roslyn compilation and crossgen2 compilation. This method builds the reference paths for both.
+    /// </summary>
+    /// <param name="useWasmReferences">Whether to try to use browser-wasm references.</param>
+    private List<string> BuildReferencePaths(bool useWasmReferences)
     {
-        var paths = new List<string>();
+        List<string> paths;
 
-        paths.Add(Path.Combine(_paths.RuntimePackDir, "*.dll"));
-
-        // SPCL lives in the runtime pack native/ dir in full builds (placed by
-        // externals.csproj BinPlace during libs.pretest).  In partial CI builds
-        // that skip libs.pretest, the runtime pack layout may not exist, but the
-        // CoreCLR artifacts directory always has SPCL after clr.nativecorelib.
-        string spcl = Path.Combine(_paths.RuntimePackNativeDir, "System.Private.CoreLib.dll");
-        if (!File.Exists(spcl))
+        if (useWasmReferences)
         {
-            string fallback = Path.Combine(_paths.CoreCLRArtifactsDir, "System.Private.CoreLib.dll");
-            if (File.Exists(fallback))
+            string? wasmRuntimePackDir = _paths.WasmRuntimePackDir;
+            string? wasmCoreLibPath = _paths.WasmRuntimePackNativeDir is null
+                ? null
+                : Path.Combine(_paths.WasmRuntimePackNativeDir, "System.Private.CoreLib.dll");
+
+            if (wasmRuntimePackDir is not null && wasmCoreLibPath is not null && File.Exists(wasmCoreLibPath))
             {
-                _output.WriteLine($"[R2RTestRunner] SPCL not found at '{spcl}'; using CoreCLR artifacts fallback '{fallback}'");
-                spcl = fallback;
+                _output.WriteLine($"Using browser-wasm runtime pack references from '{wasmRuntimePackDir}'");
+                paths =
+                [
+                    ..Directory.GetFiles(wasmRuntimePackDir, "*.dll"),
+                    wasmCoreLibPath
+                ];
+                return paths;
+            }
+            else
+            {
+                Assert.False(
+                    _paths.RequireWasmReferences,
+                    "Browser-wasm framework references are required, but the browser-wasm runtime pack was not found.");
+                _output.WriteLine($"Browser-wasm runtime pack references not available. Falling back to host references.");
             }
         }
 
-        Assert.True(File.Exists(spcl),
-            $"System.Private.CoreLib.dll not found at '{spcl}'. " +
-            $"Searched RuntimePackNativeDir='{_paths.RuntimePackNativeDir}' and " +
-            $"CoreCLRArtifactsDir='{_paths.CoreCLRArtifactsDir}'");
-        paths.Add(spcl);
+        string coreLibPath = Path.Combine(_paths.RuntimePackNativeDir, "System.Private.CoreLib.dll");
+        Assert.True(File.Exists(coreLibPath), $"System.Private.CoreLib.dll not found: {coreLibPath}");
+
+        paths = [
+            ..Directory.GetFiles(_paths.RuntimePackDir, "*.dll"),
+            coreLibPath
+        ];
 
         return paths;
     }
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
index be18b5ff9aeb91..eec3b189895884 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
-using System.Collections.Generic;
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Text.RegularExpressions;
@@ -29,51 +28,10 @@ private static string GetRequiredConfig(string key)
             ?? throw new InvalidOperationException($"Missing RuntimeHostConfigurationOption '{key}'. Was the project built with the correct properties?");
     }
 
-    /// <summary>
-    /// Tries to find an existing directory by swapping the build configuration path segment
-    /// (Debug, Release, Checked) in the path. Returns the first match, or the original
-    /// path if no fallback exists.
-    /// </summary>
-    private string ProbeConfigFallback(string dir)
+    private static string? GetOptionalConfig(string key)
     {
-        if (Directory.Exists(dir))
-            return dir;
-
-        foreach (string fallbackConfig in new[] { "Release", "Checked", "Debug" })
-        {
-            string fallback = Regex.Replace(
-                dir, @"(?<=[/\\])(Debug|Release|Checked)(?=[/\\])", fallbackConfig);
-            if (fallback != dir && Directory.Exists(fallback))
-            {
-                _output.WriteLine($"[TestPaths] '{dir}' not found; falling back to '{fallback}'");
-                return fallback;
-            }
-        }
-
-        return dir;
-    }
-
-    /// <summary>
-    /// Like <see cref="ProbeConfigFallback"/> but for paths where the configuration name
-    /// is embedded in a dot-delimited segment (e.g. <c>linux.x64.Checked</c>).
-    /// </summary>
-    private string ProbeDottedConfigFallback(string dir)
-    {
-        if (Directory.Exists(dir))
-            return dir;
-
-        foreach (string fallbackConfig in new[] { "Checked", "Release", "Debug" })
-        {
-            string fallback = Regex.Replace(
-                dir, @"\.(Debug|Release|Checked)([/\\])", $".{fallbackConfig}$2");
-            if (fallback != dir && Directory.Exists(fallback))
-            {
-                _output.WriteLine($"[TestPaths] '{dir}' not found; falling back to '{fallback}'");
-                return fallback;
-            }
-        }
-
-        return dir;
+        string? value = AppContext.GetData(key) as string;
+        return string.IsNullOrEmpty(value) ? null : value;
     }
 
     /// <summary>
@@ -81,24 +39,9 @@ private string ProbeDottedConfigFallback(string dir)
     /// e.g. artifacts/bin/coreclr/linux.x64.Checked/x64/crossgen2/
     /// Falls back to Checked or Release if the configured path doesn't exist.
     /// </summary>
-    public string Crossgen2Dir
-    {
-        get
-        {
-            string dir = GetRequiredConfig("R2RTest.Crossgen2Dir");
-            if (!File.Exists(Path.Combine(dir, Crossgen2ExeName)))
-            {
-                string fallback = ProbeDottedConfigFallback(dir);
-                if (File.Exists(Path.Combine(fallback, Crossgen2ExeName)))
-                    return fallback;
-            }
+    public string Crossgen2Dir => GetRequiredConfig("R2RTest.Crossgen2Dir");
 
-            return dir;
-        }
-    }
-
-    private static string Crossgen2ExeName =>
-        RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "crossgen2.exe" : "crossgen2";
+    private static string Crossgen2ExeName => RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "crossgen2.exe" : "crossgen2";
 
     /// <summary>
     /// Path to the self-contained crossgen2 executable (from crossgen2_inbuild).
@@ -106,97 +49,37 @@ public string Crossgen2Dir
     public string Crossgen2Exe => Path.Combine(Crossgen2Dir, Crossgen2ExeName);
 
     /// <summary>
-    /// Path to the runtime pack managed assemblies directory.
-    /// e.g. artifacts/bin/microsoft.netcore.app.runtime.linux-x64/Release/runtimes/linux-x64/lib/net11.0/
-    /// Falls back to a different build configuration if the path doesn't exist.
-    /// </summary>
-    public string RuntimePackDir
-    {
-        get
-        {
-            string dir = GetRequiredConfig("R2RTest.RuntimePackDir");
-            return ProbeConfigFallback(dir);
-        }
-    }
-
-    /// <summary>
-    /// Path to the runtime pack native directory (contains System.Private.CoreLib.dll and native runtime).
-    /// e.g. artifacts/bin/microsoft.netcore.app.runtime.linux-x64/Release/runtimes/linux-x64/native/
-    /// Falls back to a different build configuration if the path doesn't exist.
+    /// Path to the host runtime pack managed assemblies directory.
     /// </summary>
-    public string RuntimePackNativeDir
-    {
-        get
-        {
-            string dir = GetRequiredConfig("R2RTest.RuntimePackNativeDir");
-            return ProbeConfigFallback(dir);
-        }
-    }
+    public string RuntimePackDir => GetRequiredConfig("R2RTest.RuntimePackDir");
 
     /// <summary>
-    /// Path to the CoreCLR artifacts directory (contains native bits like corerun).
-    /// e.g. artifacts/bin/coreclr/linux.x64.Checked/
-    /// Falls back to Checked or Release if the configured path doesn't exist.
+    /// Path to the host runtime pack native directory.
     /// </summary>
-    public string CoreCLRArtifactsDir
-    {
-        get
-        {
-            string dir = GetRequiredConfig("R2RTest.CoreCLRArtifactsDir");
-            return ProbeDottedConfigFallback(dir);
-        }
-    }
-
-    public static string TargetArchitecture => GetRequiredConfig("R2RTest.TargetArchitecture");
-    public static string TargetOS => GetRequiredConfig("R2RTest.TargetOS");
-    public static string CoreCLRConfiguration => GetRequiredConfig("R2RTest.CoreCLRConfiguration");
-    public static bool IsReleaseCoreCLR => string.Equals(CoreCLRConfiguration, "Release", StringComparison.OrdinalIgnoreCase);
-    public static bool IsNotReleaseCoreCLR => !IsReleaseCoreCLR;
+    public string RuntimePackNativeDir => GetRequiredConfig("R2RTest.RuntimePackNativeDir");
 
     /// <summary>
-    /// Path to the reference assembly pack (for Roslyn compilation).
-    /// e.g. artifacts/bin/microsoft.netcore.app.ref/ref/net11.0/
+    /// Path to the browser-wasm runtime pack managed assemblies directory, or <c>null</c> when the
+    /// browser-wasm runtime pack has not been built/downloaded (e.g. in the default linux-x64 tools
+    /// test job). When present, the wasm crossgen2 compilation references these real browser-wasm
+    /// framework assemblies instead of the host runtime pack.
+    /// e.g. artifacts/bin/microsoft.netcore.app.runtime.browser-wasm/Release/runtimes/browser-wasm/lib/net11.0/
     /// </summary>
-    public string RefPackDir
-    {
-        get
-        {
-            string dir = GetRequiredConfig("R2RTest.RefPackDir");
-            if (!Directory.Exists(dir))
-            {
-                // Try the artifacts/bin/ref/net* fallback
-                string artifactsBin = Path.GetFullPath(Path.Combine(CoreCLRArtifactsDir, "..", ".."));
-                string refDir = Path.Combine(artifactsBin, "ref");
-                if (Directory.Exists(refDir))
-                {
-                    foreach (string subDir in Directory.GetDirectories(refDir, "net*"))
-                    {
-                        if (File.Exists(Path.Combine(subDir, "System.Runtime.dll")))
-                        {
-                            _output.WriteLine($"[TestPaths] '{dir}' not found; falling back to '{subDir}'");
-                            return subDir;
-                        }
-                    }
-                }
-            }
-
-            return dir;
-        }
-    }
+    public string? WasmRuntimePackDir => GetOptionalConfig("R2RTest.WasmRuntimePackDir");
 
     /// <summary>
-    /// Returns the target triple string for crossgen2 (e.g. "linux-x64").
+    /// Path to the browser-wasm runtime pack native directory (contains the wasm
+    /// System.Private.CoreLib.dll), or <c>null</c> when not available.
+    /// e.g. artifacts/bin/microsoft.netcore.app.runtime.browser-wasm/Release/runtimes/browser-wasm/native/
     /// </summary>
-    public static string TargetTriple => $"{TargetOS.ToLowerInvariant()}-{TargetArchitecture.ToLowerInvariant()}";
+    public string? WasmRuntimePackNativeDir => GetOptionalConfig("R2RTest.WasmRuntimePackNativeDir");
 
-    /// <summary>
-    /// Returns all framework reference assembly paths (*.dll in the runtime pack).
-    /// </summary>
-    public IEnumerable<string> GetFrameworkReferencePaths()
-    {
-        if (!Directory.Exists(RuntimePackDir))
-            throw new DirectoryNotFoundException($"Runtime pack directory not found: {RuntimePackDir}");
+    public bool RequireWasmReferences => string.Equals(
+        GetOptionalConfig("R2RTest.RequireWasmReferences"),
+        bool.TrueString,
+        StringComparison.OrdinalIgnoreCase);
 
-        return Directory.EnumerateFiles(RuntimePackDir, "*.dll");
-    }
+    public static string CoreCLRConfiguration => GetRequiredConfig("R2RTest.CoreCLRConfiguration");
+    public static bool IsReleaseCoreCLR => string.Equals(CoreCLRConfiguration, "Release", StringComparison.OrdinalIgnoreCase);
+    public static bool IsNotReleaseCoreCLR => !IsReleaseCoreCLR;
 }
diff --git a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj
index 45a5d877f608a9..61dcef292c508d 100644
--- a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj
+++ b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.CoreCLR.sfxproj
@@ -15,7 +15,7 @@
     <UseTemplatedPlatformManifest>true</UseTemplatedPlatformManifest>
     <UseRidGraph>true</UseRidGraph>
     <!-- WASM CoreCLR ships static libs in the runtime pack so apps can relink with emcc. -->
-    <IncludeStaticLibrariesInPack Condition="'$(TargetOS)' == 'browser' or '$(TargetOS)' == 'wasi'">true</IncludeStaticLibrariesInPack>
+    <IncludeStaticLibrariesInPack Condition="'$(IncludeStaticLibrariesInPack)' == '' and ('$(TargetOS)' == 'browser' or '$(TargetOS)' == 'wasi')">true</IncludeStaticLibrariesInPack>
   </PropertyGroup>
 
   <ItemGroup>

From 4f17299b5e9f48777b19a709e259fcdb663a3175 Mon Sep 17 00:00:00 2001
From: Jackson Schuster <36744439+jtschuster@users.noreply.github.com>
Date: Sat, 18 Jul 2026 18:11:37 -0700
Subject: [PATCH 2/5] Clean up ILCompiler.ReadyToRun.Tests.csproj

- Use CopyAllJitLibrariesToAotCompilerOutput=true instead of copying ourselves.
- Set crossgenDir based on crossgen2_inbuild.csproj output items
- Reorder properties and items to keep related items close to each other
---
 .../ILCompiler.ReadyToRun.Tests.csproj        | 139 +++++++-----------
 1 file changed, 55 insertions(+), 84 deletions(-)

diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
index 14cec02ab0230e..9c2ff4fdf2e558 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
@@ -13,11 +13,6 @@
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
     <TestRunnerAdditionalArguments>-notrait category=failing</TestRunnerAdditionalArguments>
     <RequireWasmReferences Condition="'$(RequireWasmReferences)' == ''">false</RequireWasmReferences>
-    <WasmRuntimePackRoot>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'microsoft.netcore.app.runtime.browser-wasm'))</WasmRuntimePackRoot>
-    <WasmRuntimePackDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
-    <WasmRuntimePackNativeDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
-    <WasmRuntimePackDir Condition="!Exists('$(WasmRuntimePackDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/lib/$(NetCoreAppCurrent)')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
-    <WasmRuntimePackNativeDir Condition="!Exists('$(WasmRuntimePackNativeDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/native')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
   </PropertyGroup>
 
   <ItemGroup>
@@ -25,57 +20,33 @@
     <PackageReference Include="Microsoft.DotNet.XUnitExtensions" Version="$(MicrosoftDotNetXUnitExtensionsVersion)" />
   </ItemGroup>
 
+  <!-- Test case source files are embedded as resources so we can compile them with Roslyn at test time.
+       Exclude subdirectory sources from compilation since they are compiled in-memory by R2RTestCaseCompiler. -->
+  <ItemGroup>
+    <Compile Remove="TestCases/*/**/*.cs" />
+    <EmbeddedResource Include="TestCases/**/*.cs" LogicalName="%(RecursiveDir)%(Filename)%(Extension)" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="../ILCompiler.Reflection.ReadyToRun/ILCompiler.Reflection.ReadyToRun.csproj" />
-    <ProjectReference Include="../crossgen2/crossgen2_inbuild.csproj" ReferenceOutputAssembly="false">
-      <!-- crossgen2 is a CoreCLR artifact, so publish it in the CoreCLR configuration. This keeps it
-           alongside the other CoreCLR artifacts the test consumes (System.Private.CoreLib, the JITs)
-           even when this test project is built in a different configuration than CoreCLR was (e.g.
-           CoreCLR built Release via 'clr -rc release', but the test built/run as Debug). Mirrors the
-           CoreLib SetConfiguration pattern in eng/references.targets. -->
-      <SetConfiguration Condition="'$(Configuration)' == '$(CoreCLRConfiguration)'">CopyAllJitLibrariesToAotCompilerOutput=true</SetConfiguration>
-      <SetConfiguration Condition="'$(Configuration)' != '$(CoreCLRConfiguration)'">Configuration=$(CoreCLRConfiguration);CopyAllJitLibrariesToAotCompilerOutput=true</SetConfiguration>
+    <ProjectReference Include="../crossgen2/crossgen2_inbuild.csproj" ReferenceOutputAssembly="false" OutputItemType="Crossgen2InbuildOutputItems">
+      <SetConfiguration>Configuration=$(CoreCLRConfiguration);CopyAllJitLibrariesToAotCompilerOutput=true</SetConfiguration>
     </ProjectReference>
   </ItemGroup>
 
-  <!-- HACK: We run runtime.proj inline to build the wasm JIT and then Copy it directly into
-       crossgen2_inbuild's publish dir. This is hacky for two reasons:
-         1. crossgen2_inbuild's <Content> glob for clrjits is evaluated at project-load time,
-            before this target runs, so on a clean tree the glob misses the freshly installed
-            JITs and the direct Copy is the only thing that reliably gets the file there.
-         2. We reach into another project's publish dir instead of flowing outputs through the
-            ProjectReference protocol.
-       Ideally this would be replaced by a proper ProjectReference setup where the wasm JIT and
-       crossgen2's other dependencies flow into our own output dir via GetCopyToOutputDirectoryItems,
-       and R2RTest.Crossgen2Dir points at the test's bin dir instead of crossgen2_inbuild's publish dir.
-
-       In cross builds JITs land in $(CoreCLRArtifactsPath)$(BuildArchitecture)/; we mirror
-       eng/Subsets.props's cross-tool stanza so install/read paths agree.
-       Hooks into ResolveProjectReferences so it fires for `dotnet build` (and CI's `build.sh -test`,
-       which builds before testing). `dotnet build /t:test` alone won't trigger it. -->
-  <PropertyGroup>
-    <_BuildJitsCrossArch Condition="'$(CrossBuild)' == 'true' or '$(BuildArchitecture)' != '$(TargetArchitecture)' or '$(HostOS)' != '$(TargetOS)' or '$(EnableNativeSanitizers)' != ''">true</_BuildJitsCrossArch>
-    <_BuildJitsProperties>ClrAllJitsSubset=true;ClrWasmJitSubset=true;Configuration=$(CoreCLRConfiguration)</_BuildJitsProperties>
-    <_BuildJitsProperties Condition="!$([MSBuild]::IsOsPlatform(Windows))">$(_BuildJitsProperties);Ninja=true</_BuildJitsProperties>
-    <_BuildJitsProperties Condition="'$(_BuildJitsCrossArch)' == 'true'">$(_BuildJitsProperties);HostArchitecture=$(BuildArchitecture);HostCrossOS=$(HostOS);CrossBuild=false;BuildSubdirectory=$(BuildArchitecture);CMakeArgs=$(CMakeArgs) -DCLR_CROSS_COMPONENTS_BUILD=1;PgoInstrument=false;NoPgoOptimize=true</_BuildJitsProperties>
-  </PropertyGroup>
-
+  <!-- The JITs must be built before crossgen2_inbuild so that they can be copied to the output directory -->
   <Target Name="BuildAllJitsForReadyToRunTests"
           BeforeTargets="ResolveProjectReferences"
           Condition="'$(DesignTimeBuild)' != 'true'">
+    <PropertyGroup>
+      <_BuildJitsCrossArch Condition="'$(CrossBuild)' == 'true' or '$(BuildArchitecture)' != '$(TargetArchitecture)' or '$(HostOS)' != '$(TargetOS)' or '$(EnableNativeSanitizers)' != ''">true</_BuildJitsCrossArch>
+      <_BuildJitsProperties>ClrAllJitsSubset=true;ClrWasmJitSubset=true;Configuration=$(CoreCLRConfiguration)</_BuildJitsProperties>
+      <_BuildJitsProperties Condition="!$([MSBuild]::IsOsPlatform(Windows))">$(_BuildJitsProperties);Ninja=true</_BuildJitsProperties>
+      <_BuildJitsProperties Condition="'$(_BuildJitsCrossArch)' == 'true'">$(_BuildJitsProperties);HostArchitecture=$(BuildArchitecture);HostCrossOS=$(HostOS);CrossBuild=false;BuildSubdirectory=$(BuildArchitecture);CMakeArgs=$(CMakeArgs) -DCLR_CROSS_COMPONENTS_BUILD=1;PgoInstrument=false;NoPgoOptimize=true</_BuildJitsProperties>
+    </PropertyGroup>
     <MSBuild Projects="$(CoreClrProjectRoot)runtime.proj"
              Targets="Build"
              Properties="$(_BuildJitsProperties)" />
-
-    <PropertyGroup>
-      <_WasmJitCrossHostArchSubdir Condition="'$(_BuildJitsCrossArch)' == 'true'">$(BuildArchitecture)/</_WasmJitCrossHostArchSubdir>
-      <_WasmJitFileName>$(HostLibPrefix)clrjit_universal_wasm_$(BuildArchitecture)$(HostLibSuffix)</_WasmJitFileName>
-      <_WasmJitSourcePath>$(CoreCLRArtifactsPath)$(_WasmJitCrossHostArchSubdir)$(_WasmJitFileName)</_WasmJitSourcePath>
-      <_Crossgen2InbuildPublishDir>$(CoreCLRArtifactsPath)$(BuildArchitecture)/crossgen2/</_Crossgen2InbuildPublishDir>
-    </PropertyGroup>
-    <Copy SourceFiles="$(_WasmJitSourcePath)"
-          DestinationFolder="$(_Crossgen2InbuildPublishDir)"
-          SkipUnchangedFiles="true" />
   </Target>
 
   <Target Name="ValidatePathsExist"
@@ -89,6 +60,7 @@
     <Error Condition="!Exists('$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)')"
            Text="Runtime pack path '$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)' does not exist." />
 
+    <!-- Wasm runtime pack is not strictly required for local builds, but is enforced in CI with RequireWasmReferences -->
     <Error Condition="'$(RequireWasmReferences)' == 'true' and (!Exists('$(WasmRuntimePackDir)') or !Exists('$(WasmRuntimePackNativeDir)System.Private.CoreLib.dll'))"
            Text="The browser-wasm runtime pack was not found under '$(WasmRuntimePackRoot)'. Build and download the wasm prerequisite artifact before building this test." />
     <Warning Condition="'$(RequireWasmReferences)' != 'true' and !Exists('$(WasmRuntimePackDir)')"
@@ -97,47 +69,46 @@
              Text="Browser-wasm System.Private.CoreLib.dll was not found under '$(WasmRuntimePackNativeDir)'. Browser-wasm ReadyToRun tests will fall back to host references, which may cause unexpected failures. Generate by building the clr.corelib+libs+libs.pretest subsets for browser-wasm." />
   </Target>
 
-  <!-- Test case source files are embedded as resources so we can compile them with Roslyn at test time.
-       Exclude subdirectory sources from compilation since they are compiled in-memory by R2RTestCaseCompiler. -->
-  <ItemGroup>
-    <Compile Remove="TestCases/*/**/*.cs" />
-    <EmbeddedResource Include="TestCases/**/*.cs" LogicalName="%(RecursiveDir)%(Filename)%(Extension)" />
-  </ItemGroup>
+  <!-- RuntimeConfiguration values that depend on build output paths must be set in a target -->
+  <Target Name="SetRuntimeConfigurationOptions"
+          BeforeTargets="GenerateBuildRuntimeConfigurationFiles"
+          Condition="'$(DesignTimeBuild)' != 'true'">
 
-  <!-- Pass build-time paths to test runtime via RuntimeHostConfigurationOption -->
-  <ItemGroup>
-    <!-- Required Host-Targeting assets -->
-    <RuntimeHostConfigurationOption Include="R2RTest.Crossgen2Dir">
-      <Value>$(CoreCLRArtifactsPath)/$(BuildArchitecture)/crossgen2</Value>
-    </RuntimeHostConfigurationOption>
-    <RuntimeHostConfigurationOption Include="R2RTest.RuntimePackDir">
-      <Value>$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)</Value>
-    </RuntimeHostConfigurationOption>
-    <RuntimeHostConfigurationOption Include="R2RTest.RuntimePackNativeDir">
-      <Value>$(MicrosoftNetCoreAppRuntimePackNativeDir)</Value>
-    </RuntimeHostConfigurationOption>
+    <PropertyGroup>
+      <WasmRuntimePackRoot>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'microsoft.netcore.app.runtime.browser-wasm'))</WasmRuntimePackRoot>
+      <WasmRuntimePackDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
+      <WasmRuntimePackNativeDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
+      <WasmRuntimePackDir Condition="!Exists('$(WasmRuntimePackDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/lib/$(NetCoreAppCurrent)')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
+      <WasmRuntimePackNativeDir Condition="!Exists('$(WasmRuntimePackNativeDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/native')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
+    </PropertyGroup>
 
-    <!-- browser-wasm runtime pack paths used for validating wasm R2R compilation.
-         When absent, the wasm R2R compilation falls back to host references.
-         This could cause unexpected failures if crossgen2 expects intrinsics in
-         the wasm System.Private.CoreLib.dll that are not present in the host reference pack.
-         Thus, the RequireWasmReferences option can be used to fail the test build if the wasm
-         runtime pack is not present.
-          -->
-    <RuntimeHostConfigurationOption Include="R2RTest.RequireWasmReferences">
-      <Value>$(RequireWasmReferences)</Value>
-    </RuntimeHostConfigurationOption>
-    <RuntimeHostConfigurationOption Include="R2RTest.WasmRuntimePackDir">
-      <Value>$(WasmRuntimePackDir)</Value>
-    </RuntimeHostConfigurationOption>
-    <RuntimeHostConfigurationOption Include="R2RTest.WasmRuntimePackNativeDir">
-      <Value>$(WasmRuntimePackNativeDir)</Value>
-    </RuntimeHostConfigurationOption>
+    <ItemGroup>
+      <RuntimeHostConfigurationOption Include="R2RTest.Crossgen2Dir">
+        <Value>@(Crossgen2InbuildOutputItems->WithMetadataValue('Filename', 'crossgen2')->WithMetadataValue('Extension', '$(ExeSuffix)')->'%(RootDir)%(Directory)')</Value>
+      </RuntimeHostConfigurationOption>
+      <RuntimeHostConfigurationOption Include="R2RTest.RuntimePackDir">
+        <Value>$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)</Value>
+      </RuntimeHostConfigurationOption>
+      <RuntimeHostConfigurationOption Include="R2RTest.RuntimePackNativeDir">
+        <Value>$(MicrosoftNetCoreAppRuntimePackNativeDir)</Value>
+      </RuntimeHostConfigurationOption>
 
-    <!-- Used for gating Debug-only JIT features from being tested. -->
-    <RuntimeHostConfigurationOption Include="R2RTest.CoreCLRConfiguration">
-      <Value>$(CoreCLRConfiguration)</Value>
-    </RuntimeHostConfigurationOption>
-  </ItemGroup>
+      <RuntimeHostConfigurationOption Include="R2RTest.RequireWasmReferences">
+        <Value>$(RequireWasmReferences)</Value>
+      </RuntimeHostConfigurationOption>
+      <RuntimeHostConfigurationOption Include="R2RTest.WasmRuntimePackDir">
+        <Value>$(WasmRuntimePackDir)</Value>
+      </RuntimeHostConfigurationOption>
+      <RuntimeHostConfigurationOption Include="R2RTest.WasmRuntimePackNativeDir">
+        <Value>$(WasmRuntimePackNativeDir)</Value>
+      </RuntimeHostConfigurationOption>
+
+      <!-- Used for gating Debug-only JIT features from being tested. -->
+      <RuntimeHostConfigurationOption Include="R2RTest.CoreCLRConfiguration">
+        <Value>$(CoreCLRConfiguration)</Value>
+      </RuntimeHostConfigurationOption>
+    </ItemGroup>
+
+  </Target>
 
 </Project>

From 898d14be4ef04bcfb6b9b49966d39551e763451f Mon Sep 17 00:00:00 2001
From: Jackson Schuster <36744439+jtschuster@users.noreply.github.com>
Date: Sat, 18 Jul 2026 18:32:00 -0700
Subject: [PATCH 3/5] Cleanup

---
 .../TestCases/R2RTestSuites.cs                      | 13 +++++++++----
 .../TestCasesRunner/R2RDriver.cs                    |  2 --
 .../TestCasesRunner/R2RTestCaseCompiler.cs          |  3 +--
 .../TestCasesRunner/R2RTestRunner.cs                | 10 ++--------
 .../TestCasesRunner/TestPaths.cs                    |  1 +
 5 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs
index 8750b3551ff007..4c92350b7fe581 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCases/R2RTestSuites.cs
@@ -150,7 +150,12 @@ static void Validate(ReadyToRunReader reader)
         }
     }
 
-    [Fact]
+    // Note: The arm tests compile for an arm32 target, but they are compiled with the host Corelib. If there are
+    // load-bearing dependencies in the arm32 corelib (that aren't present in the host corelib) that crossgen2 requires,
+    // these tests may fail. Wasm tests are similar, but since it doesn't require a special cross-build setup, they use
+    // a wasm corelib in CI. arm32 tests could be similarly set up, but it hasn't been done yet.
+
+    [ConditionalFact(typeof(TestPaths), nameof(TestPaths.ArmOnHostOSSupported))]
     public void ArmThumbBitRelocationTargets()
     {
         var inlineableLib = new CompiledAssembly
@@ -174,7 +179,7 @@ public void ArmThumbBitRelocationTargets()
                     new CrossgenAssembly(inlineableLib) { Kind = Crossgen2InputKind.Reference },
                 ])
                 {
-                    Options = [Crossgen2Option.TargetArchArm],
+                    TargetRid = TargetRid.HostArm,
                     Validate = Validate,
                 },
             ]));
@@ -187,7 +192,7 @@ static void Validate(ReadyToRunReader reader)
     }
 
     // JitStressProcedureSplitting is only available in Debug/Checked JIT builds.
-    [ConditionalFact(typeof(TestPaths), nameof(TestPaths.IsNotReleaseCoreCLR))]
+    [ConditionalFact(typeof(TestPaths), nameof(TestPaths.IsNotReleaseCoreCLR), nameof(TestPaths.ArmOnHostOSSupported))]
     public void ArmThumbBitHotColdRuntimeFunctions()
     {
         var hotColdSplitting = new CompiledAssembly
@@ -201,9 +206,9 @@ public void ArmThumbBitHotColdRuntimeFunctions()
             [
                 new(nameof(ArmThumbBitHotColdRuntimeFunctions), [new CrossgenAssembly(hotColdSplitting)])
                 {
+                    TargetRid = TargetRid.HostArm,
                     Options =
                     [
-                        Crossgen2Option.TargetArchArm,
                         Crossgen2Option.Optimize,
                         Crossgen2Option.HotColdSplitting,
                     ],
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RDriver.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RDriver.cs
index a359f7bfa45d05..c598f917dc0787 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RDriver.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RDriver.cs
@@ -32,7 +32,6 @@ internal enum Crossgen2Option
     InputBubble,
     HotColdSplitting,
     Optimize,
-    TargetArchArm,
     StripILBodies,
 }
 
@@ -59,7 +58,6 @@ internal static class Crossgen2OptionsExtensions
         Crossgen2Option.InputBubble => $"--input-bubble",
         Crossgen2Option.HotColdSplitting => $"--hot-cold-splitting",
         Crossgen2Option.Optimize => $"--optimize",
-        Crossgen2Option.TargetArchArm => $"--targetarch:arm",
         Crossgen2Option.StripILBodies => $"--strip-il-bodies",
         _ => throw new ArgumentOutOfRangeException(nameof(kind)),
     };
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestCaseCompiler.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestCaseCompiler.cs
index cffccdf5c65b34..816801c96cdc6c 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestCaseCompiler.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestCaseCompiler.cs
@@ -9,7 +9,6 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.Emit;
-using Xunit.Abstractions;
 
 namespace ILCompiler.ReadyToRun.Tests.TestCasesRunner;
 
@@ -85,7 +84,7 @@ public string CompileAssembly(
                 .Where(d => d.Severity == DiagnosticSeverity.Error)
                 .Select(d => d.ToString());
             throw new InvalidOperationException(
-                $"Compilation of '{assemblyName}' failed:\nReferences:\n{string.Join(Environment.NewLine, compilation.References.Select(r => r.Display))}\n\n{string.Join("\n", errors)}");
+                $"Compilation of '{assemblyName}' failed:\n{string.Join("\n", errors)}");
         }
 
         return outputPath;
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
index dc23a142c40946..769cdad89c2773 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
@@ -14,6 +14,7 @@ namespace ILCompiler.ReadyToRun.Tests.TestCasesRunner;
 enum TargetRid
 {
     Host,
+    HostArm,
     BrowserWasm
 }
 
@@ -100,14 +101,6 @@ internal sealed class CrossgenCompilation(string name, List<CrossgenAssembly> as
     /// </summary>
     public Action<ReadyToRunReader>? Validate { get; init; }
 
-    /// <summary>
-    /// When true, this compilation references the browser-wasm runtime pack (real wasm framework
-    /// assemblies and the wasm System.Private.CoreLib) if it is available, instead of the host
-    /// runtime pack. When the browser-wasm libs are not present the runner falls back to host
-    /// references so the test still runs (with a host-arch corelib). Set this on wasm compilations
-    /// (--targetarch wasm --targetos browser) so they reference target-matching libraries when run
-    /// in a job that downloads the browser-wasm libs.
-    /// </summary>
     public TargetRid TargetRid { get; init; } = TargetRid.Host;
 
     public string Name => name;
@@ -336,6 +329,7 @@ private static string RunCrossgenCompilation(
         args.AddRange(compilation.TargetRid switch
         {
             TargetRid.Host => [],
+            TargetRid.HostArm => ["--targetarch", "arm"],
             TargetRid.BrowserWasm => ["--targetos", "browser", "--targetarch", "wasm"],
             _ => throw new InvalidOperationException($"Unknown target RID: {compilation.TargetRid}")
         });
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
index eec3b189895884..4947a4604dd50a 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
@@ -82,4 +82,5 @@ private static string GetRequiredConfig(string key)
     public static string CoreCLRConfiguration => GetRequiredConfig("R2RTest.CoreCLRConfiguration");
     public static bool IsReleaseCoreCLR => string.Equals(CoreCLRConfiguration, "Release", StringComparison.OrdinalIgnoreCase);
     public static bool IsNotReleaseCoreCLR => !IsReleaseCoreCLR;
+    public static bool ArmOnHostOSSupported => RuntimeInformation.IsOSPlatform(OSPlatform.Linux);
 }

From 08fc40a5d8fcf5bda8f392f8ea00e1f0c25b7295 Mon Sep 17 00:00:00 2001
From: Jackson Schuster <36744439+jtschuster@users.noreply.github.com>
Date: Mon, 20 Jul 2026 09:07:50 -0700
Subject: [PATCH 4/5] Address copilot feedback

---
 .../ILCompiler.ReadyToRun.Tests.csproj         | 18 ++++++++++--------
 .../TestCasesRunner/R2RTestRunner.cs           |  6 +++---
 .../TestCasesRunner/TestPaths.cs               |  1 -
 3 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
index 9c2ff4fdf2e558..7d99e13fac1471 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/ILCompiler.ReadyToRun.Tests.csproj
@@ -34,8 +34,18 @@
     </ProjectReference>
   </ItemGroup>
 
+  <PropertyGroup>
+    <WasmRuntimePackRoot>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'microsoft.netcore.app.runtime.browser-wasm'))</WasmRuntimePackRoot>
+    <WasmRuntimePackDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
+    <WasmRuntimePackNativeDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
+    <WasmRuntimePackDir Condition="!Exists('$(WasmRuntimePackDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/lib/$(NetCoreAppCurrent)')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
+    <WasmRuntimePackNativeDir Condition="!Exists('$(WasmRuntimePackNativeDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/native')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
+  </PropertyGroup>
+
+
   <!-- The JITs must be built before crossgen2_inbuild so that they can be copied to the output directory -->
   <Target Name="BuildAllJitsForReadyToRunTests"
+          DependsOnTargets=""
           BeforeTargets="ResolveProjectReferences"
           Condition="'$(DesignTimeBuild)' != 'true'">
     <PropertyGroup>
@@ -74,14 +84,6 @@
           BeforeTargets="GenerateBuildRuntimeConfigurationFiles"
           Condition="'$(DesignTimeBuild)' != 'true'">
 
-    <PropertyGroup>
-      <WasmRuntimePackRoot>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'microsoft.netcore.app.runtime.browser-wasm'))</WasmRuntimePackRoot>
-      <WasmRuntimePackDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
-      <WasmRuntimePackNativeDir>$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', '$(LibrariesConfiguration)', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
-      <WasmRuntimePackDir Condition="!Exists('$(WasmRuntimePackDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/lib/$(NetCoreAppCurrent)')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'lib', '$(NetCoreAppCurrent)'))</WasmRuntimePackDir>
-      <WasmRuntimePackNativeDir Condition="!Exists('$(WasmRuntimePackNativeDir)') and Exists('$(WasmRuntimePackRoot)Release/runtimes/browser-wasm/native')">$([MSBuild]::NormalizeDirectory('$(WasmRuntimePackRoot)', 'Release', 'runtimes', 'browser-wasm', 'native'))</WasmRuntimePackNativeDir>
-    </PropertyGroup>
-
     <ItemGroup>
       <RuntimeHostConfigurationOption Include="R2RTest.Crossgen2Dir">
         <Value>@(Crossgen2InbuildOutputItems->WithMetadataValue('Filename', 'crossgen2')->WithMetadataValue('Extension', '$(ExeSuffix)')->'%(RootDir)%(Directory)')</Value>
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
index 769cdad89c2773..850bf53ffc0750 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
@@ -253,11 +253,11 @@ private Dictionary<string, string> CompileAllAssemblies(
     {
         var paths = new Dictionary<string, string>();
 
+        // Tests shouldn't require a platform-specific runtime/ref pack for Roslyn compilation
+        var defaultReferences = BuildReferencePaths(useWasmReferences: false);
+        var compiler = new R2RTestCaseCompiler(defaultReferences);
         foreach (var asm in assemblies)
         {
-            // Tests shouldn't require a platform-specific runtime/ref pack for Roslyn compilation
-            var defaultReferences = BuildReferencePaths(useWasmReferences: false);
-            var compiler = new R2RTestCaseCompiler(defaultReferences);
             var sources = asm.SourceResourceNames
                 .Select(R2RTestCaseCompiler.ReadEmbeddedSource)
                 .ToList();
diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
index 4947a4604dd50a..71661567fe2daf 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/TestPaths.cs
@@ -37,7 +37,6 @@ private static string GetRequiredConfig(string key)
     /// <summary>
     /// Path to the crossgen2 output directory (contains the self-contained crossgen2 executable and clrjit).
     /// e.g. artifacts/bin/coreclr/linux.x64.Checked/x64/crossgen2/
-    /// Falls back to Checked or Release if the configured path doesn't exist.
     /// </summary>
     public string Crossgen2Dir => GetRequiredConfig("R2RTest.Crossgen2Dir");
 

From 7e40733b9c8cd0c7f00e32825e438411df6cda41 Mon Sep 17 00:00:00 2001
From: Jackson Schuster <36744439+jtschuster@users.noreply.github.com>
Date: Mon, 20 Jul 2026 14:05:33 -0700
Subject: [PATCH 5/5] Check runtime pack dir exists before enumerating

---
 .../TestCasesRunner/R2RTestRunner.cs                        | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
index 850bf53ffc0750..e8c1704bd3fd58 100644
--- a/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
+++ b/src/coreclr/tools/aot/ILCompiler.ReadyToRun.Tests/TestCasesRunner/R2RTestRunner.cs
@@ -365,7 +365,7 @@ private static void AddRefArgs(List<string> args, List<string> refPaths)
     /// <summary>
     /// Runtime packs are used as references for both Roslyn compilation and crossgen2 compilation. This method builds the reference paths for both.
     /// </summary>
-    /// <param name="useWasmReferences">Whether to try to use browser-wasm references.</param>
+    /// <param name="useWasmReferences">Whether to try to use browser-wasm references. The host references are used as a fallback if browser-wasm references are not available.</param>
     private List<string> BuildReferencePaths(bool useWasmReferences)
     {
         List<string> paths;
@@ -377,7 +377,8 @@ private List<string> BuildReferencePaths(bool useWasmReferences)
                 ? null
                 : Path.Combine(_paths.WasmRuntimePackNativeDir, "System.Private.CoreLib.dll");
 
-            if (wasmRuntimePackDir is not null && wasmCoreLibPath is not null && File.Exists(wasmCoreLibPath))
+            if (wasmRuntimePackDir is not null && wasmCoreLibPath is not null
+                && File.Exists(wasmCoreLibPath) && Directory.Exists(wasmRuntimePackDir))
             {
                 _output.WriteLine($"Using browser-wasm runtime pack references from '{wasmRuntimePackDir}'");
                 paths =
@@ -398,6 +399,7 @@ private List<string> BuildReferencePaths(bool useWasmReferences)
 
         string coreLibPath = Path.Combine(_paths.RuntimePackNativeDir, "System.Private.CoreLib.dll");
         Assert.True(File.Exists(coreLibPath), $"System.Private.CoreLib.dll not found: {coreLibPath}");
+        Assert.True(Directory.Exists(_paths.RuntimePackDir), $"Runtime pack directory not found: {_paths.RuntimePackDir}");
 
         paths = [
             ..Directory.GetFiles(_paths.RuntimePackDir, "*.dll"),