Fix #354: NullReferenceException expanding "Read By" node when variable is referenced from an async method.

ILSpy/TreeNodes/Analyzer/Helpers.cs

@@ -68,11 +68,24 @@ namespace ICSharpCode.ILSpy.TreeNodes.Analyzer
 
 			return typeUsage ?? method;
 		}
+		
+		/// <summary>
+		/// Given a compiler-generated type, returns the method where that type is used.
+		/// Used to detect the 'parent method' for a lambda/iterator/async state machine.
+		/// </summary>
 		public static MethodDefinition GetOriginalCodeLocation(TypeDefinition type)
 		{
 			if (type != null && type.DeclaringType != null && type.IsCompilerGenerated()) {
-				MethodDefinition constructor = GetTypeConstructor(type);
+				if (type.IsValueType) {
-				return FindMethodUsageInType(type.DeclaringType, constructor);
+					// Value types might not have any constructor; but they must be stored in a local var
+					// because 'initobj' (or 'call .ctor') expects a managed ref.
+					return FindVariableOfTypeUsageInType(type.DeclaringType, type);
+				} else {
+					MethodDefinition constructor = GetTypeConstructor(type);
+					if (constructor == null)
+						return null;
+					return FindMethodUsageInType(type.DeclaringType, constructor);
+				}
 			}
 			return null;
 		}
@@ -106,5 +119,26 @@ namespace ICSharpCode.ILSpy.TreeNodes.Analyzer
 			}
 			return null;
 		}
+		
+		private static MethodDefinition FindVariableOfTypeUsageInType(TypeDefinition type, TypeDefinition variableType)
+		{
+			foreach (MethodDefinition method in type.Methods) {
+				bool found = false;
+				if (!method.HasBody)
+					continue;
+				foreach (var v in method.Body.Variables) {
+					if (v.VariableType.ResolveWithinSameModule() == variableType) {
+						found = true;
+						break;
+					}
+				}
+
+				method.Body = null;
+
+				if (found)
+					return method;
+			}
+			return null;
+		}
 	}
 }