From 75fcf55d9a1425ac32c61e25dd6166d68b9cce1c Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Fri, 12 Jun 2026 17:28:24 +0200
Subject: [PATCH] [wasm] Re-enable System.Formats.Nrbf tests on browser CoreCLR

The System.Formats.Nrbf.Tests suite was excluded on browser-wasm +
CoreCLR because test discovery crashed with a FileNotFoundException for
System.Runtime.Serialization.Formatters, Version=11.0.0.0.

Root cause: for a self-contained browser-wasm app, @(ReferenceCopyLocalPaths)
contains two copies of System.Runtime.Serialization.Formatters - the shared
framework's non-functional 8.1.0.0 stub (from the runtime pack) and the
functional 11.0.0.0 build the test references app-local. The WebAssembly SDK
task ComputeWasmBuildAssets dedupes webcil bundle candidates by relative path
on a first-wins, version-blind basis, so the 8.1.0.0 stub got bundled into
_framework and shadowed the app-local 11.0.0.0 copy. xunit discovery then
materializes [InlineData(FormatterTypeStyle.X)] attribute blobs, triggering an
Assembly.Load of the 11.0.0.0 build, which is not present - aborting discovery.

Unlike desktop (framework-dependent deployment, or single-file publish whose
bundler consumes the already version-resolved ResolvedFileToPublish set), the
wasm webcil bundle is assembled at build time from candidates that are not
version-conflict-resolved against ProjectReferences.

Fix: add a CoreCLR-wasm target that applies copy-local-wins semantics before
the bundle candidates are gathered - it drops runtime-pack copy-local
assemblies that are shadowed by a same-named app-local copy. Apps without an
app-local copy of a framework assembly are unaffected.

With the fix the bundled Formatters webcil is the functional 11.0.0.0 build,
discovery finds 153 test cases (was 6) and the suite passes; the ReadTests
hierarchy correctly skips on browser since BinaryFormatter is unsupported there.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/libraries/tests.proj                      |  2 --
 .../build/BrowserWasmApp.CoreCLR.targets      | 34 +++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/src/libraries/tests.proj b/src/libraries/tests.proj
index 4de29857494251..3a733a0604e79f 100644
--- a/src/libraries/tests.proj
+++ b/src/libraries/tests.proj
@@ -185,8 +185,6 @@
 
   <!-- https://github.com/dotnet/runtime/issues/125495 - These tests are disabled on browser/CoreCLR because of crashes and test failures. -->
   <ItemGroup Condition="'$(TargetOS)' == 'browser' and '$(RuntimeFlavor)' == 'CoreCLR' and '$(RunDisabledWasmTests)' != 'true'">
-    <!-- test failures -->
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Formats.Nrbf\tests\System.Formats.Nrbf.Tests.csproj" />
     <!-- long running suites -->
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Linq\tests\System.Linq.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Memory\tests\System.Memory.Tests.csproj" />
diff --git a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
index e94f759abc4f69..b83bf16ec25a33 100644
--- a/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
+++ b/src/mono/browser/build/BrowserWasmApp.CoreCLR.targets
@@ -178,6 +178,40 @@
                      '$(WasmBuildingForNestedPublish)' != 'true' and
                      '$(UsingBrowserRuntimeWorkload)' != 'true'" />
 
+  <!-- ======================== Prefer app-local assemblies over runtime-pack copies ========================
+
+    For a self-contained browser-wasm app, @(ReferenceCopyLocalPaths) can contain two copies of the
+    same assembly: the runtime-pack copy (under $(MicrosoftNetCoreAppRuntimePackDir)) and an app-local
+    copy referenced out-of-band at a different version. ComputeWasmBuildAssets dedupes the webcil bundle
+    candidates by relative path (first-wins, version-blind), so the runtime-pack copy can shadow the
+    app-local one in _framework. The canonical case is System.Runtime.Serialization.Formatters: the
+    shared framework ships a non-functional 8.1.0.0 stub while the app references the functional 11.0.0.0
+    build, so an Assembly.Load for 11.0.0.0 then fails with FileNotFoundException.
+
+    Resolve it the way a self-contained app loads assemblies (copy-local wins): drop runtime-pack copies
+    shadowed by a same-named app-local copy before the candidates are gathered. Apps without an app-local
+    copy of a framework assembly are unaffected.
+  -->
+  <Target Name="_CoreCLRPreferAppLocalAssembliesOverRuntimePack"
+          BeforeTargets="_ComputeWasmBuildCandidates;_GatherWasmFilesToBuild"
+          Condition="'$(IsBrowserWasmProject)' == 'true' and '$(MicrosoftNetCoreAppRuntimePackDir)' != ''">
+    <ItemGroup>
+      <!-- App-local (non-runtime-pack) managed assemblies copied next to the app. -->
+      <_CoreCLRAppLocalAssembly Include="@(ReferenceCopyLocalPaths)"
+                                Condition="'%(Extension)' == '.dll' and !$([System.String]::Copy('%(FullPath)').StartsWith('$(MicrosoftNetCoreAppRuntimePackDir)'))" />
+    </ItemGroup>
+    <PropertyGroup>
+      <_CoreCLRAppLocalAssemblyNames>;@(_CoreCLRAppLocalAssembly->'%(FileName)%(Extension)');</_CoreCLRAppLocalAssemblyNames>
+    </PropertyGroup>
+    <ItemGroup>
+      <!-- Drop runtime-pack copies shadowed by a same-named app-local assembly. -->
+      <ReferenceCopyLocalPaths Remove="@(ReferenceCopyLocalPaths)"
+                               Condition="'%(Extension)' == '.dll'
+                                          and $([System.String]::Copy('%(FullPath)').StartsWith('$(MicrosoftNetCoreAppRuntimePackDir)'))
+                                          and $(_CoreCLRAppLocalAssemblyNames.Contains(';%(FileName)%(Extension);'))" />
+    </ItemGroup>
+  </Target>
+
   <!-- ======================== Core Orchestrator ======================== -->
 
   <PropertyGroup>