[dotnet] Don't claim dynamic code is unsupported when using CoreCLR. Fixes #26430 by rolfbjarne · Pull Request #26468 · dotnet/macios

rolfbjarne · 2026-08-25T14:59:44Z

The $(DynamicCodeSupport) default dates back to when Mono was the only runtime for iOS/tvOS/Mac Catalyst: it was set to false unless the Mono interpreter was enabled. Neither $(MtouchInterpreter) nor $(UseInterpreter) mean anything for CoreCLR, so on .NET 11 - where CoreCLR is the default runtime - we ended up claiming that dynamic code isn't supported even though it is.

That makes ILLink substitute RuntimeFeature.IsDynamicCodeSupported with false in the trimmed System.Private.CoreLib, which in turn breaks libraries that use this feature switch to detect NativeAOT. Entity Framework Core for instance throws "Model building is not supported when publishing with NativeAOT. Use a compiled model." in plain Debug builds.

So only default to false when dynamic code really isn't available:

NativeAOT.
Mono without the interpreter on iOS/tvOS/Mac Catalyst.

In every other case we leave the property alone and let dotnet/sdk pick its default (which is true).

Note that this comes at a size cost, since System.Reflection.Emit is now kept alive: a stock Mac Catalyst app in Release goes from ~21 MB to ~39 MB. Anybody who doesn't need dynamic code can opt out with <DynamicCodeSupport>false</DynamicCodeSupport>.

Fixes #26430

🤖 Pull request created by Copilot

…out the interpreter. The $(DynamicCodeSupport) default was computed with Mono-era logic: "if the interpreter isn't enabled, everything is AOT-compiled, so there's no dynamic code". Neither $(MtouchInterpreter) nor $(UseInterpreter) has any effect on CoreCLR, so on .NET 11 - where CoreCLR is the default runtime - the condition always evaluated to true, and every iOS/tvOS/Mac Catalyst app claimed that dynamic code isn't supported. That value ends up as the 'System.Runtime.CompilerServices.RuntimeFeature.IsDynamicCodeSupported' feature switch, which ILLink then substitutes into System.Private.CoreLib as a constant 'false'. This isn't just cosmetic: * Reflection.Emit throws PlatformNotSupportedException even though CoreCLR supports it just fine. * Entity Framework Core uses the feature switch to detect NativeAOT, so any DbContext fails with "Model building is not supported when publishing with NativeAOT. Use a compiled model." in a plain Debug build. So only default $(DynamicCodeSupport) to false when actually using Mono without the interpreter, and otherwise leave the property alone and let dotnet/sdk apply its default (which is 'true'). Note that this means dynamic code paths can no longer be trimmed away, which makes apps bigger (a stock Mac Catalyst app in Release went from 21.5 MB to 39 MB in a local test). Apps that don't need dynamic code can get the previous behavior - and size - back by setting <DynamicCodeSupport>false</DynamicCodeSupport>. Also add a test for the new behavior, and move the GetRuntimeHostConfigurationOption helper to TestBaseClass so it can be shared. Fixes #26430 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: da66ea8b-c45e-4f8b-88dd-ce3d6be3123a

The $(DynamicCodeSupport) default dates back to when Mono was the only runtime for iOS/tvOS/Mac Catalyst: it was set to 'false' unless the Mono interpreter was enabled. Neither $(MtouchInterpreter) nor $(UseInterpreter) mean anything for CoreCLR, so on .NET 11 - where CoreCLR is the default runtime - we ended up claiming that dynamic code isn't supported even though it is. That makes ILLink substitute RuntimeFeature.IsDynamicCodeSupported with 'false' in the trimmed System.Private.CoreLib, which in turn breaks libraries that use this feature switch to detect NativeAOT. Entity Framework Core for instance throws "Model building is not supported when publishing with NativeAOT" in plain Debug builds. So only default to 'false' when dynamic code really isn't available: * NativeAOT. * Mono without the interpreter on iOS/tvOS/Mac Catalyst. In every other case we leave the property alone and let dotnet/sdk pick its default (which is 'true'). Fixes #26430 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: da66ea8b-c45e-4f8b-88dd-ce3d6be3123a

Copilot

Pull request overview

Updates DynamicCodeSupport defaults so CoreCLR is not treated as lacking dynamic code, while preserving false for NativeAOT and non-interpreted Mono.

Changes:

Refines runtime-specific dynamic-code defaults.
Adds regression tests.
Updates size and preserved-API baselines.

Reviewed changes

Copilot reviewed 8 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Summary
`tests/dotnet/UnitTests/expected/TVOS-CoreCLR-R2R-size.txt`	Updates tvOS CoreCLR R2R size baseline.
`tests/dotnet/UnitTests/expected/TVOS-CoreCLR-Interpreter-size.txt`	Updates tvOS CoreCLR interpreter size baseline.
`tests/dotnet/UnitTests/expected/MacCatalyst-CoreCLR-R2R-size.txt`	Updates Mac Catalyst CoreCLR R2R size baseline.
`tests/dotnet/UnitTests/expected/MacCatalyst-CoreCLR-Interpreter-size.txt`	Updates Mac Catalyst CoreCLR interpreter size baseline.
`tests/dotnet/UnitTests/expected/iOS-CoreCLR-R2R-size.txt`	Updates iOS CoreCLR R2R size baseline.
`tests/dotnet/UnitTests/expected/iOS-CoreCLR-Interpreter-size.txt`	Updates iOS CoreCLR interpreter size baseline.
`tests/dotnet/UnitTests/expected/iOS-CoreCLR-Interpreter-preservedapis.txt`	Records newly preserved dynamic-code APIs.
`tests/dotnet/UnitTests/DynamicCodeSupportTest.cs`	Adds dynamic-code configuration regression tests.
`dotnet/targets/Xamarin.Shared.Sdk.targets`	Adjusts runtime-aware defaults; coverage is missing for non-interpreted Mono without an interpreter.

Suppressed comments (3)

dotnet/targets/Xamarin.Shared.Sdk.targets:173

💡 Documentation — This makes DynamicCodeSupport a meaningful user-facing override, with a substantial app-size tradeoff when left enabled, but docs/building-apps/build-properties.md has no entry for it while documenting adjacent feature-switch properties such as DynamicRegistrationSupported, MtouchInterpreter, and UseInterpreter. Please document the platform/runtime defaults and the false opt-out so users can make this size-versus-dynamic-code choice intentionally.

		<DynamicCodeSupport Condition="'$(DynamicCodeSupport)' == '' And '$(_UseNativeAot)' == 'true'">false</DynamicCodeSupport>
		<DynamicCodeSupport Condition="'$(DynamicCodeSupport)' == '' And '$(UseMonoRuntime)' == 'true' And ( '$(MtouchInterpreter)' == '' And '$(UseInterpreter)' != 'true' ) And ('$(_PlatformName)' == 'iOS' Or '$(_PlatformName)' == 'tvOS' Or '$(_PlatformName)' == 'MacCatalyst')">false</DynamicCodeSupport>

tests/dotnet/UnitTests/DynamicCodeSupportTest.cs:74

⚠️ Test coverage — Treating a missing DynamicCodeSupport property as "true" means this test passes even if the SDK default becomes false (or the feature switch is never emitted); the helper therefore does not verify the effective value it claims to return. Validate the generated feature-switch/runtime value instead, or make the SDK-default behavior an explicit assertion.

			if (!BinLog.TryFindPropertyValue (binLogPath, "DynamicCodeSupport", out var value) || string.IsNullOrEmpty (value))
				return "true";

tests/dotnet/UnitTests/DynamicCodeSupportTest.cs:13

⚠️ Testing — This new matrix never sets UseMonoRuntime=true, so the changed Mono-specific default at Xamarin.Shared.Sdk.targets:173 is not exercised: neither Mono without an interpreter (expected false) nor Mono with MtouchInterpreter/UseInterpreter (expected true) is covered. Please add those cases so a regression in the legacy Mono behavior cannot pass while the CoreCLR and NativeAOT tests remain green.

		public void SupportedWithCoreCLR (ApplePlatform platform, string runtimeIdentifiers)

 		<!-- This should be set by dotnet/sdk instead, once https://github.com/dotnet/sdk/issues/25392 gets resolved.  -->
-		<DynamicCodeSupport Condition="'$(DynamicCodeSupport)' == '' And ( '$(MtouchInterpreter)' == '' And '$(UseInterpreter)' != 'true' ) And ('$(_PlatformName)' == 'iOS' Or '$(_PlatformName)' == 'tvOS' Or '$(_PlatformName)' == 'MacCatalyst')">false</DynamicCodeSupport>
+		<DynamicCodeSupport Condition="'$(DynamicCodeSupport)' == '' And '$(_UseNativeAot)' == 'true'">false</DynamicCodeSupport>
+		<DynamicCodeSupport Condition="'$(DynamicCodeSupport)' == '' And '$(UseMonoRuntime)' == 'true' And ( '$(MtouchInterpreter)' == '' And '$(UseInterpreter)' != 'true' ) And ('$(_PlatformName)' == 'iOS' Or '$(_PlatformName)' == 'tvOS' Or '$(_PlatformName)' == 'MacCatalyst')">false</DynamicCodeSupport>


vs-mobiletools-engineering-service2 · 2026-08-25T15:37:17Z

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vs-mobiletools-engineering-service2 · 2026-08-25T18:10:23Z

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rolfbjarne and others added 3 commits August 25, 2026 12:33

[tests] Update expected sizes.

282dbf5

Copilot AI lite review requested due to automatic review settings August 25, 2026 14:59

rolfbjarne requested a review from dalexsoto as a code owner August 25, 2026 14:59

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[net11.0][Mac Catalyst][CoreCLR] EF Core fails in Debug because dynamic code is reported unsupported #26430

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[dotnet] Don't claim dynamic code is unsupported when using CoreCLR. Fixes #26430 - #26468

[dotnet] Don't claim dynamic code is unsupported when using CoreCLR. Fixes #26430#26468
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