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Fix DWARF debug info generation for uninstantiated types #122599

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Fix DWARF debug info generation for uninstantiated types #122599

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84e10fb
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Copilot Dec 16, 2025
8641bf6
Remove guard that prevents DWARF debug info for uninstantiated types
Copilot Dec 16, 2025
261f7b0
Remove unused hasInstanceFields variable
Copilot Dec 16, 2025
cbda4cc
Clean up comments by removing commented-out code
Copilot Dec 16, 2025
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8 changes: 5 additions & 3 deletions src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/UserDefinedTypeDescriptor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -594,7 +594,6 @@ private uint GetClassTypeIndex(TypeDesc type, bool needsCompleteType)
bool hasNonGcStatics = NodeFactory.MetadataManager.HasNonGcStaticBase(defType);
bool hasGcStatics = NodeFactory.MetadataManager.HasGcStaticBase(defType);
bool hasThreadStatics = NodeFactory.MetadataManager.HasThreadStaticBase(defType);
bool hasInstanceFields = defType.IsValueType || NodeFactory.MetadataManager.HasConstructedEEType(defType);

bool isCanonical = defType.IsCanonicalSubtype(CanonicalFormKind.Any);

Expand Down Expand Up @@ -622,8 +621,11 @@ private uint GetClassTypeIndex(TypeDesc type, bool needsCompleteType)
}
else
{
if (!hasInstanceFields)
continue;
// Allow instance fields to be emitted even for types that are never instantiated.
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@MichalStrehovsky MichalStrehovsky Dec 17, 2025

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Doing this is problematic because we're going to be looking at layout of types that we didn't look at before (no constructed type means we never had to calculate type size or look at instance fields). If there's a problem with the type (e.g. has an instance field of a type that doesn't resolve because e.g. NuGet was a mismatched version), we're likely to crash here a couple lines down. We had crashes like that before, this is what the code around line 636 is dealing with.

I'm going to ask about the motivation in the original issue. Right now I'm leaning toward By Design/Won't fix on this.

// This ensures DWARF debug info is generated for all type fields, which is
// important for debugging scenarios where types are referenced but not constructed.
// Previously, a guard would skip instance fields when hasInstanceFields was false,
// preventing debug info generation for types like: var nullObj = (MyClass)null;
}

LayoutInt fieldOffset = fieldDesc.Offset;
Expand Down