Fix circular init in AOT equality comparer causing NRE on Mono#16615
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akoeplinger merged 1 commit intodotnet:mainfrom Mar 20, 2026
Merged
Fix circular init in AOT equality comparer causing NRE on Mono#16615akoeplinger merged 1 commit intodotnet:mainfrom
akoeplinger merged 1 commit intodotnet:mainfrom
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…/WASM The defaultComparer field in AssertEqualityComparer (AOT path) eagerly creates AssertEqualityComparerAdapter<object>(AssertEqualityComparer<object>()). This triggers AssertEqualityComparer<object>'s static initializer, which reads DefaultInnerComparer = GetDefaultInnerComparer(typeof(object)), which reads back defaultComparer — before it has been assigned. On Mono/WASM, this causes DefaultInnerComparer to be permanently null. When comparing ValueTuple elements via IStructuralEquatable.Equals, the null comparer is passed through, causing NullReferenceException inside ValueTuple's implementation. Fix by removing the cached static field and creating a new instance per call, matching the non-AOT (reflection) path's behavior. The re-entrant type initialization resolves correctly because the second access to AssertEqualityComparer<object>'s cctor is a no-op (already in progress on the same thread), so the instance constructor runs without re-triggering the static initializer. By the time the outer call returns, DefaultInnerComparer has been assigned. Verified on both CoreCLR and Mono runtimes. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
akoeplinger
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agocke
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The defaultComparer field in AssertEqualityComparer (AOT path) eagerly creates AssertEqualityComparerAdapter<object>, which triggers AssertEqualityComparer<object>'s static initializer. That initializer reads defaultComparer back via GetDefaultInnerComparer before the field has been assigned. On Mono/WASM this results in DefaultInnerComparer being permanently null, leading to NullReferenceException when comparing value types via IStructuralEquatable. Fix by creating a new instance on each call, matching the non-AOT reflection path behavior. Port of dotnet/arcade#16615 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
bradwilson
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Mar 20, 2026
The defaultComparer field in AssertEqualityComparer (AOT path) eagerly creates AssertEqualityComparerAdapter<object>, which triggers AssertEqualityComparer<object>'s static initializer. That initializer reads defaultComparer back via GetDefaultInnerComparer before the field has been assigned. On Mono/WASM this results in DefaultInnerComparer being permanently null, leading to NullReferenceException when comparing value types via IStructuralEquatable. Fix by creating a new instance on each call, matching the non-AOT reflection path behavior. Port of dotnet/arcade#16615 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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The defaultComparer field in AssertEqualityComparer (AOT path) eagerly
creates AssertEqualityComparerAdapter(AssertEqualityComparer()).
This triggers AssertEqualityComparer's static initializer, which reads
DefaultInnerComparer = GetDefaultInnerComparer(typeof(object)), which reads
back defaultComparer — before it has been assigned. On Mono/WASM, this causes
DefaultInnerComparer to be permanently null. When comparing ValueTuple
elements via IStructuralEquatable.Equals, the null comparer is passed through,
causing NullReferenceException inside ValueTuple's implementation.
Fix by removing the cached static field and creating a new instance per call,
matching the non-AOT (reflection) path's behavior. The re-entrant type
initialization resolves correctly because the second access to
AssertEqualityComparer's cctor is a no-op (already in progress on the
same thread), so the instance constructor runs without re-triggering the
static initializer. By the time the outer call returns, DefaultInnerComparer
has been assigned.