Don't assert decompiled local types match the signature

[siegfriedpammer]

Problem

DebugInfoGenerator.HandleMethodBody asserted, for every local variable, that its decompiled type is equivalent to the metadata local-signature type at the same slot:

Debug.Assert(v.Index < types.Length && NormalizeTypeVisitor.TypeErasure.EquivalentTypes(v.Type, types[v.Index.Value]));

This aborts portable-PDB generation (Debug builds) for ordinary inputs — e.g. any method containing a fixed statement, and async state machines — surfaced while generating PDBs for real assemblies such as System.Net.Requests.dll.

Why the type check is wrong

The type equivalence holds when the variables are first read from IL, but not afterwards:

• Variable splitting gives a single IL slot several variables with different (refined) types; the signature type matches at most one.
• Pinned-region locals are modeled as pointers (int*), while the signature types the slot as int& pinned.
• Generic-context type-parameter identity differs (e.g. ReadOnlySpan<``0> vs ReadOnlySpan<0>` in local functions / iterators).

Empirically, ~32% of CoreLib's qualifying locals mismatch across these classes; neither a size nor an IsCompatibleTypeForMemoryAccess comparison covers them.

Why it cannot affect debugging

AddLocalVariable writes only the slot index and name to the PDB — never the type, which the debugger reads from the metadata signature directly. And the slot index is correct by construction: it is the IL ldloc/stloc operand, assigned from the signature slot when the variable is created (ILReader.InitLocalVariables) and copied verbatim by SplitVariables; ILVariable.Index is never reassigned. A wrong index is ruled out structurally.

Fix

Drop the type-equivalence check; keep only the (trivially-true, documented) index bound as a guard against a future regression in index assignment.

Test

Adds TestCases/PdbGen/PinnedLocalSlot.il — a minimal fixed statement whose pinned local is int& pinned in metadata but int* after decompilation — and a PdbGenerationTestRunner.PinnedLocalSlot test that runs DebugInfoGenerator over it and asserts it does not throw. Fails (asserts) before the fix, passes after; full PdbGen fixture stays green.

🤖 Generated with Claude Code