Add handling of method parameter custom attributes (#5188)

We need to apply the same rules as elsewhere to make the attributes reflectable.

src/ILCompiler.Compiler/src/Compiler/DependencyAnalysis/CustomAttributeBasedDependencyAlgorithm.cs

@@ -23,7 +23,16 @@ namespace ILCompiler.DependencyAnalysis
         {
             MetadataReader reader = method.MetadataReader;
             MethodDefinition methodDef = reader.GetMethodDefinition(method.Handle);
+
+            // Handle custom attributes on the method
             AddDependenciesDueToCustomAttributes(ref dependencies, factory, method.Module, methodDef.GetCustomAttributes());
+
+            // Handle custom attributes on method parameters
+            foreach (ParameterHandle parameterHandle in methodDef.GetParameters())
+            {
+                Parameter parameter = reader.GetParameter(parameterHandle);
+                AddDependenciesDueToCustomAttributes(ref dependencies, factory, method.Module, parameter.GetCustomAttributes());
+            }
         }
 
         public static void AddDependenciesDueToCustomAttributes(ref DependencyList dependencies, NodeFactory factory, EcmaType type)

tests/src/Simple/Reflection/Reflection.cs

@@ -9,6 +9,7 @@
 #endif
 
 using System;
+using System.Runtime.CompilerServices;
 using System.Reflection;
 
 [assembly: TestAssembly]
@@ -34,6 +35,7 @@ internal class ReflectionTest
         TestStringConstructor.Run();
         TestAssemblyAndModuleAttributes.Run();
         TestAttributeExpressions.Run();
+        TestParameterAttributes.Run();
 
         //
         // Mostly functionality tests
@@ -212,6 +214,46 @@ internal class ReflectionTest
         }
     }
 
+    class TestParameterAttributes
+    {
+#if OPTIMIZED_MODE_WITHOUT_SCANNER
+        [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
+#endif
+        public static bool Method([Parameter] ParameterType parameter)
+        {
+            return parameter == null;
+        }
+
+        public class ParameterType { }
+
+        class ParameterAttribute : Attribute
+        {
+            public ParameterAttribute([CallerMemberName] string memberName = null)
+            {
+                MemberName = memberName;
+            }
+
+            public string MemberName { get; }
+        }
+
+        public static void Run()
+        {
+            Console.WriteLine(nameof(TestParameterAttributes));
+
+            // Ensure things we reflect on are in the static callgraph
+            if (string.Empty.Length > 0)
+            {
+                Method(null);
+            }
+
+            MethodInfo method = typeof(TestParameterAttributes).GetMethod(nameof(Method));
+
+            var attribute = method.GetParameters()[0].GetCustomAttribute<ParameterAttribute>();
+            if (attribute.MemberName != nameof(Method))
+                throw new Exception();
+        }
+    }
+
     class TestAttributeExpressions
     {
         struct FirstNeverUsedType { }