Fix NullReferenceException in DestroyStructure for blittable types

[Copilot]

Description

BoxedLayoutTypeMarshaler<T> (introduced in #126621) routes DestroyStructure for blittable value types through StructureMarshaler<T>.Free, which unconditionally called NativeMemory.Clear(ptr, size) even when FreeCore was a no-op. Passing an invalid pointer like (IntPtr)1 — the longstanding test pattern for "blittable types should be a no-op" — faults at address 1, manifesting as a NullReferenceException on Android.

Changes

• StructureMarshaler<T>: Added a s_isBlittable static field (initialized once via Marshal.HasLayout). Free() now skips both FreeCore and NativeMemory.Clear for blittable types. For non-blittable types (array marshaling path via NonBlittableStructureArrayFree), the JIT generates a FreeCore IL stub that frees native sub-structures; NativeMemory.Clear still follows to prevent double-free.

• LayoutClassMarshaler<T>.Methods: Added IsBlittable property using the existing s_nativeSizeForBlittableTypes field (non-zero ⟺ blittable). Access to IsBlittable is wrapped in a GetIsBlittable() method that follows the same [MethodImpl(MethodImplOptions.NoInlining)] + try/catch (TypeInitializationException) pattern used by all other Methods accessors, ensuring TypeLoadException is surfaced instead of TypeInitializationException on recursive native layout failures. Free() is now a no-op for blittable reference types — same fix, same reasoning.

Testing

Existing DestroyStructure_Blittable_Success test covers the regression. Full System.Runtime.InteropServices.Tests suite: 2549 passed, 0 failed.

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[am11]

Failure seems related https://helix.dot.net/api/2019-06-17/jobs/ac25ae7c-952e-4650-900f-5f3fcb70ec27/workitems/Interop/consol

Test FAIL: Xunit.Sdk.ThrowsException: Assert.Throws() Failure: Exception type was not an exact match
Expected: typeof(System.TypeLoadException)
Actual:   typeof(System.TypeInitializationException)
   at Xunit.Assert.ThrowsImpl(Type exceptionType, Exception exception, Func`2 inspector) in /_/src/arcade/src/Microsoft.DotNet.XUnitAssert/src/ExceptionAsserts.cs:line 509
   at MarshalArrayAsField.LPArray.Test.RunTest2(String report)
   at MarshalArrayAsField.LPArray.Test.TestEntryPoint()
Xunit.Sdk.EqualException: Assert.Equal() Failure: Values differ
Expected: 100
Actual:   101
   at Xunit.Assert.Equal[T](T expected, T actual, IEqualityComparer`1 comparer) in /_/src/arcade/src/Microsoft.DotNet.XUnitAssert/src/EqualityAsserts.cs:line 102
   at Program.<<Main>$>g__TestExecutor41|0_42(StreamWriter tempLogSw, StreamWriter statsCsvSw, <>c__DisplayClass0_0&)
21:55:07.441 Failed test: global::MarshalArrayAsField.LPArray.Test.TestEntryPoint()
21:55:07.446 Running test: global::MarshalArrayAsParam.Default.ArrayMarshal.TestMarshalByVal_NoAttributes()
ByVal marshaling CLR array as c-style-array no attributes

[jkoritzinsky]

@copilot Please wrap the access to IsBlittable in a no-inline property that does the same try-catch-rethrow pattern as all other accessors to the Methods subclass.

[Copilot]

Done in 844dcd8. Added a GetIsBlittable() method with the same try/catch (TypeInitializationException)/ExceptionDispatchInfo.Capture(...).Throw() pattern and a [MethodImpl(MethodImplOptions.NoInlining)] local CallIsBlittable() function accessing Methods.IsBlittable, matching all other accessors in the class.

[Copilot]

Pull request overview

Fixes a crash in Marshal.DestroyStructure for blittable layout types by avoiding NativeMemory.Clear on potentially invalid pointers (e.g., (IntPtr)1), and preserves the existing “unwrap TypeInitializationException” behavior for blittable detection in the layout-class marshaler.

Changes:

• Skip FreeCore/NativeMemory.Clear in StructureMarshaler<T>.Free when T is blittable (computed once via Marshal.HasLayout).
• Add Methods.IsBlittable + GetIsBlittable() wrapper in LayoutClassMarshaler<T> and make Free a no-op for blittable layout classes.
• Keep NativeMemory.Clear for non-blittable types to prevent double-free after nested cleanup.