Make CoreCLR the default runtime for Debug builds#11169
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simonrozsival merged 8 commits intomainfrom Apr 22, 2026
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Pull request overview
This PR changes the .NET for Android SDK defaults so Debug builds no longer force UseMonoRuntime=true, which makes CoreCLR the default runtime for both Debug and Release builds (unless a project explicitly opts into MonoVM or NativeAOT).
Changes:
- Remove the Debug-only default
UseMonoRuntime=truein SDK default properties. - As a result,
_AndroidRuntimefalls back toCoreCLRwhenPublishAotis not enabled andUseMonoRuntimeisn’t explicitly set.
MSTest's VSTest bridge resolves test assembly paths via Assembly.Location, which returns empty string on CoreCLR Android with fast-deploy (assemblies are memory-mapped). This causes MSTestDiscovererHelpers.AreValidSources() to fail with NotSupportedException. Setting EmbedAssembliesIntoApk=true ensures assemblies are embedded in the APK so Assembly.Location returns a valid path. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Root Cause Analysis:
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…allback trimming (#11168) ## Summary Fixes a bug in the trimmable typemap UCO (UnmanagedCallersOnly) wrapper generator where the callback member reference used `byte` (uint8) for JNI boolean returns, but MCW-generated `n_*` callback methods use `sbyte` (int8). ## The Bug In ECMA-335 metadata, `int8` and `uint8` are different types for method signature matching. When ILLink performed its reachability analysis, it could not resolve the cross-assembly member reference from the typemap DLL to `n_*` methods in `Mono.Android.dll` because the return type did not match. ILLink then treated these `n_*` callbacks as unreachable and trimmed them. At runtime, this caused `MissingMethodException` for methods like `IHostnameVerifierInvoker.n_Verify_Ljava_lang_String_Ljavax_net_ssl_SSLSession_`, which cascaded into a SIGSEGV on a background thread. ## The Fix - Added `EncodeClrTypeForCallback()` to `JniSignatureHelper` that uses `sbyte` for JNI boolean, matching the MCW `_JniMarshal_*_B` delegate convention. - Updated `EmitUcoMethod()` in `TypeMapAssemblyEmitter` to use the callback-specific encoding when constructing the member reference to `n_*` methods. - The UCO wrapper's own method signature continues to use `byte` (correct for JNI ABI / `[UnmanagedCallersOnly]`).
Pass UseMonoRuntime=true/false via build parameters to toggle runtime. For CoreCLR, also pass EmbedAssembliesIntoApk=true as a workaround for MSTest's Assembly.Location requirement with fast-deploy. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This reverts commit 7d615b0.
DotNetCLI.Build() adds /p: via GetDefaultCommandLineArgs, but StartRun() passes parameters raw. Without /p:, dotnet run receives bare 'UseMonoRuntime=True' which breaks the command. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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| bool useMonoRuntime = runtime == AndroidRuntime.MonoVM; | ||
| var buildParameters = new List<string> { | ||
| $"UseMonoRuntime={useMonoRuntime}", | ||
| }; | ||
| if (runtime == AndroidRuntime.CoreCLR) { | ||
| // TODO: MSTest requires Assembly.Location, which returns empty with fast-deploy on CoreCLR. Remove when fast-deploy is fixed. | ||
| buildParameters.Add ("EmbedAssembliesIntoApk=true"); | ||
| } |
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Hmm, the CoreCLR test fails:
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Hmm:
- https://github.com/microsoft/testfx/blob/cba28646c410afb47d076af71c78521827a878c5/src/Platform/Microsoft.Testing.Extensions.VSTestBridge/SynchronizedSingleSessionVSTestAndTestAnywhereAdapter.cs#L152-L154
- https://github.com/microsoft/testfx/blob/cba28646c410afb47d076af71c78521827a878c5/src/Adapter/MSTestAdapter.PlatformServices/Helpers/MSTestDiscovererHelpers.cs#L13-L28
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the PR that will fix this looks solid: microsoft/testfx#7772
MSTest's VSTest bridge uses Assembly.Location to resolve test sources, which returns empty on CoreCLR Android. Assert.Ignore with link to tracking issue. See #11174 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
jonathanpeppers
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Apr 21, 2026
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I ignored the one test for now, if everything looks green, feel free to merge.
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This PR will switch the default runtime in .NET 11 P4 to CoreCLR. Both Release and Debug will now use CoreCLR.
Related to dotnet/macios#25050