Don't assert decompiled local types match the signature

DebugInfoGenerator asserted that every local variable's decompiled type
is equivalent to the metadata local-signature type at its slot. That
holds at IL-read time but not afterwards: variable splitting gives one
slot several typed variables, pinned-region locals are modeled as
pointers (int* vs int& pinned), and generic-context type-parameter
identity differs. The assertion therefore aborted PDB generation (Debug
builds) for ordinary inputs such as any method with a fixed statement.

The type is never written to the PDB - only the slot index and name are -
so the mismatch cannot affect the debugging experience. The slot index,
the only emitted value, is correct by construction: it is the IL
ldloc/stloc operand, sourced from the signature slot when the variable is
created and copied verbatim by SplitVariables; it is never reassigned.
Keep only the index-bound check and document why the type is not verified.

Assisted-by: Claude:claude-opus-4-8:Claude Code

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -164,6 +164,7 @@
   <ItemGroup>
     <None Include="TestCases\PdbGen\*.cs" />
     <None Include="TestCases\PdbGen\PinnedRegionWarning.il" />
+    <None Include="TestCases\PdbGen\PinnedLocalSlot.il" />
   </ItemGroup>
 
   <ItemGroup>

ICSharpCode.Decompiler.Tests/PdbGenerationTestRunner.cs

@@ -336,6 +336,29 @@ namespace ICSharpCode.Decompiler.Tests
 			Assert.DoesNotThrow(() => decompiler.CreateSequencePoints(syntaxTree));
 		}
 
+		[Test]
+		public async Task PinnedLocalSlot()
+		{
+			// The decompiler models a pinned-region local as a pointer (int*), which never matches the
+			// metadata local signature type (int& pinned). The slot index is still faithful to the IL,
+			// and the type is never written to the PDB, so generating debug info must not assert on the
+			// type difference.
+			string ilFile = Path.Combine(TestCasePath, nameof(PinnedLocalSlot) + ".il");
+			string peFileName = await Tester.AssembleIL(ilFile, AssemblerOptions.Library);
+
+			var module = new PEFile(peFileName);
+			var resolver = new UniversalAssemblyResolver(peFileName, false,
+				module.Metadata.DetectTargetFrameworkId(), null, PEStreamOptions.PrefetchEntireImage);
+			var decompiler = new CSharpDecompiler(module, resolver, new DecompilerSettings());
+
+			var syntaxTree = decompiler.DecompileType(new Decompiler.TypeSystem.FullTypeName("C"));
+
+			Assert.DoesNotThrow(() => {
+				var debugInfo = new Decompiler.DebugInfo.DebugInfoGenerator(decompiler.TypeSystem);
+				syntaxTree.AcceptVisitor(debugInfo);
+			});
+		}
+
 		private class TestProgressReporter : IProgress<DecompilationProgress>
 		{
 			private Action<DecompilationProgress> reportFunc;

ICSharpCode.Decompiler.Tests/TestCases/PdbGen/PinnedLocalSlot.il

@@ -0,0 +1,34 @@
+// A simple pinned pointer (fixed statement). The metadata local signature types the slot as
+// `int32& pinned`, but the decompiler models a pinned-region local as a pointer (`int*`). The two
+// never match, yet the slot index is faithful to the IL ldloc/stloc operand, so PDB generation
+// must not assert on the type difference. Regression fixture for that assertion.
+.assembly extern System.Runtime { }
+.assembly PinnedLocalSlot { }
+.module PinnedLocalSlot.dll
+
+.class public auto ansi beforefieldinit C extends [System.Runtime]System.Object
+{
+  .method public hidebysig instance int32 M(int32[] a) cil managed
+  {
+    .maxstack 2
+    .locals ( [0] int32& pinned p )
+    ldarg.1
+    ldc.i4.0
+    ldelema [System.Runtime]System.Int32
+    stloc.0
+    ldloc.0
+    ldind.i4
+    ldc.i4.0
+    conv.u
+    stloc.0
+    ret
+  }
+
+  .method public hidebysig specialname rtspecialname instance void .ctor() cil managed
+  {
+    .maxstack 1
+    ldarg.0
+    call instance void [System.Runtime]System.Object::.ctor()
+    ret
+  }
+}

ICSharpCode.Decompiler/DebugInfo/DebugInfoGenerator.cs

@@ -253,7 +253,14 @@ namespace ICSharpCode.Decompiler.DebugInfo
 					if (v.Index != null && v.Kind.IsLocal())
 					{
 #if DEBUG
-						Debug.Assert(v.Index < types.Length && NormalizeTypeVisitor.TypeErasure.EquivalentTypes(v.Type, types[v.Index.Value]));
+						// The index is the IL ldloc/stloc operand, which indexes the local signature
+						// directly: ILReader creates one variable per signature slot, and SplitVariables
+						// copies that index. It is therefore correct by construction. The variable type
+						// is intentionally not checked against the signature - it is never written to the
+						// PDB (only the slot index and name are), and it legitimately diverges after
+						// variable splitting (one slot, several typed variables), for pinned-region locals
+						// modeled as pointers, and through generic-context type-parameter identity.
+						Debug.Assert(v.Index < types.Length);
 #endif
 						localVariables.Add(v);
 					}