Optimise GetCustomAttribute(s)

src/coreclr/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs

@@ -98,5 +98,20 @@ public static Assembly GetCallingAssembly()
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         internal static extern uint GetAssemblyCount();
+
+        internal virtual Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            // Returns an Attribute of base class/inteface attributeType on the Assembly or null if none exists.
+            // throws an AmbiguousMatchException if there are more than one defined.
+            Attribute[] attrib = Attribute.GetCustomAttributes(this, attributeType, inherit);
+
+            if (attrib == null || attrib.Length == 0)
+                return null;
+
+            if (attrib.Length == 1)
+                return attrib[0];
+
+            throw new AmbiguousMatchException(SR.RFLCT_AmbigCust);
+        }
     }
 }

src/coreclr/System.Private.CoreLib/src/System/Reflection/MdImport.cs

@@ -173,14 +173,15 @@ public static bool IsTokenOfType(int token, params MetadataTokenType[] types)
 
     internal unsafe struct MetadataEnumResult
     {
+        public const int SmallSizeLength = 16;
         // Keep the definition in sync with vm\ManagedMdImport.hpp
         private int[] largeResult;
         private int length;
-        private fixed int smallResult[16];
+        private fixed int smallResult[SmallSizeLength];
 
-        public int Length => length;
+        public readonly int Length => length;
 
-        public int this[int index]
+        public readonly int this[int index]
         {
             get
             {

src/coreclr/System.Private.CoreLib/src/System/Reflection/MemberInfo.Internal.cs

@@ -24,5 +24,18 @@ internal bool HasSameMetadataDefinitionAsCore<TOther>(MemberInfo other) where TO
 
             return true;
         }
+
+        internal virtual Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            Attribute[]? attrib = GetCustomAttributes(attributeType, inherit) as Attribute[];
+
+            if (attrib == null || attrib.Length == 0)
+                return null;
+
+            if (attrib.Length == 1)
+                return attrib[0];
+
+            throw new AmbiguousMatchException(SR.RFLCT_AmbigCust);
+        }
     }
 }

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs

@@ -277,6 +277,19 @@ public override bool IsCollectible
             return null;
         }
 
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType);
+        }
+
         // ISerializable implementation
         public override void GetObjectData(SerializationInfo info, StreamingContext context)
         {

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeConstructorInfo.cs

@@ -183,6 +183,19 @@ public override object[] GetCustomAttributes(Type attributeType, bool inherit)
             return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType);
         }
 
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType);
+        }
+
         public override bool IsDefined(Type attributeType, bool inherit)
         {
             if (attributeType == null)
@@ -253,7 +266,7 @@ public override MethodImplAttributes GetMethodImplementationFlags()
 
         internal static void CheckCanCreateInstance(Type declaringType, bool isVarArg)
         {
-            if (declaringType == null)
+            if (declaringType is null)
                 throw new ArgumentNullException(nameof(declaringType));
 
             // ctor is declared on interface class
@@ -267,7 +280,7 @@ internal static void CheckCanCreateInstance(Type declaringType, bool isVarArg)
                     SR.Format(SR.Acc_CreateAbstEx, declaringType));
 
             // ctor is on a class that contains stack pointers
-            else if (declaringType.GetRootElementType() == typeof(ArgIterator))
+            else if (ReferenceEquals(declaringType.GetRootElementType(), typeof(ArgIterator)))
                 throw new NotSupportedException();
 
             // ctor is vararg
@@ -282,7 +295,7 @@ internal static void CheckCanCreateInstance(Type declaringType, bool isVarArg)
             }
 
             // ctor is declared on System.Void
-            else if (declaringType == typeof(void))
+            else if (ReferenceEquals(declaringType, typeof(void)))
                 throw new MemberAccessException(SR.Access_Void);
         }
 

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeEventInfo.cs

@@ -89,6 +89,19 @@ public override object[] GetCustomAttributes(Type attributeType, bool inherit)
             return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType);
         }
 
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType, inherit);
+        }
+
         public override bool IsDefined(Type attributeType, bool inherit)
         {
             if (attributeType == null)

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeFieldInfo.cs

@@ -74,6 +74,19 @@ public override object[] GetCustomAttributes(Type attributeType, bool inherit)
             return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType);
         }
 
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType);
+        }
+
         public override bool IsDefined(Type attributeType, bool inherit)
         {
             if (attributeType == null)

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeMethodInfo.cs

@@ -256,6 +256,19 @@ public override object[] GetCustomAttributes(Type attributeType, bool inherit)
             return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType, inherit);
         }
 
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType, inherit);
+        }
+
         public override bool IsDefined(Type attributeType, bool inherit)
         {
             if (attributeType == null)

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs

@@ -388,6 +388,19 @@ internal bool IsTransientInternal()
             return RuntimeModule.nIsTransientInternal(new QCallModule(ref thisAsLocal));
         }
 
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType);
+        }
+
         internal MetadataImport MetadataImport => ModuleHandle.GetMetadataImport(this);
         #endregion
 

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeParameterInfo.cs

@@ -143,6 +143,25 @@ internal void SetAttributes(ParameterAttributes attributes)
         {
             AttrsImpl = attributes;
         }
+
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            if (MdToken.IsNullToken(m_tkParamDef))
+            {
+                if (!inherit || Member.MemberType != MemberTypes.Method)
+                    return null;
+            }
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType, inherit);
+        }
         #endregion
 
         #region Constructor
@@ -502,9 +521,12 @@ public override Type[] GetOptionalCustomModifiers()
         public override object[] GetCustomAttributes(bool inherit)
         {
             if (MdToken.IsNullToken(m_tkParamDef))
-                return Array.Empty<object>();
+            {
+                if (!inherit || Member.MemberType != MemberTypes.Method)
+                    return Array.Empty<object>();
+            }
 
-            return CustomAttribute.GetCustomAttributes(this, (typeof(object) as RuntimeType)!);
+            return CustomAttribute.GetCustomAttributes(this, (typeof(object) as RuntimeType)!, inherit);
         }
 
         public override object[] GetCustomAttributes(Type attributeType, bool inherit)
@@ -513,14 +535,17 @@ public override object[] GetCustomAttributes(Type attributeType, bool inherit)
                 throw new ArgumentNullException(nameof(attributeType));
 
             if (MdToken.IsNullToken(m_tkParamDef))
-                return Array.Empty<object>();
+            {
+                if (!inherit || Member.MemberType != MemberTypes.Method)
+                    return Array.Empty<object>();
+            }
 
             RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
 
             if (attributeRuntimeType == null)
                 throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
 
-            return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType);
+            return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType, inherit);
         }
 
         public override bool IsDefined(Type attributeType, bool inherit)

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimePropertyInfo.cs

@@ -134,7 +134,7 @@ public override string ToString()
         #region ICustomAttributeProvider
         public override object[] GetCustomAttributes(bool inherit)
         {
-            return CustomAttribute.GetCustomAttributes(this, (typeof(object) as RuntimeType)!);
+            return CustomAttribute.GetCustomAttributes(this, (typeof(object) as RuntimeType)!, inherit);
         }
 
         public override object[] GetCustomAttributes(Type attributeType, bool inherit)
@@ -147,7 +147,20 @@ public override object[] GetCustomAttributes(Type attributeType, bool inherit)
             if (attributeRuntimeType == null)
                 throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
 
-            return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType);
+            return CustomAttribute.GetCustomAttributes(this, attributeRuntimeType, inherit);
+        }
+
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType, inherit);
         }
 
         public override bool IsDefined(Type attributeType, bool inherit)

src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs

@@ -69,7 +69,7 @@ public ListBuilder(int capacity)
                 _capacity = capacity;
             }
 
-            public T this[int index]
+            public readonly T this[int index]
             {
                 get
                 {
@@ -104,7 +104,7 @@ public void CopyTo(object[] array, int index)
                 Array.Copy(_items!, 0, array, index, _count);
             }
 
-            public int Count => _count;
+            public readonly int Count => _count;
 
             public void Add(T item)
             {
@@ -1870,6 +1870,32 @@ internal FieldInfo GetField(RuntimeFieldHandleInternal field)
             return retval;
         }
 
+        internal override Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            if (attributeType == null)
+                throw new ArgumentNullException(nameof(attributeType));
+
+            RuntimeType? attributeRuntimeType = attributeType.UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(attributeType));
+
+            return CustomAttribute.GetCustomAttribute(this, attributeRuntimeType, inherit);
+        }
+
+        internal override AttributeUsageAttribute GetAttributeUsageAttribute()
+        {
+            if (!this.IsSubclassOf(typeof(Attribute)))
+                throw new ArgumentException(SR.Argument_MustHaveAttributeBaseClass);
+
+            RuntimeType? attributeRuntimeType = typeof(AttributeUsageAttribute).UnderlyingSystemType as RuntimeType;
+
+            if (attributeRuntimeType == null)
+                throw new ArgumentException(SR.Arg_MustBeType, nameof(Attribute));
+
+            return CustomAttribute.GetAttributeUsage(this);
+        }
+
         internal object? GenericCache
         {
             get => CacheIfExists?.GenericCache;

src/coreclr/System.Private.CoreLib/src/System/Type.CoreCLR.cs

@@ -105,5 +105,21 @@ internal virtual RuntimeTypeHandle GetTypeHandleInternal()
         // Exists to faciliate code sharing between CoreCLR and CoreRT.
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal bool IsRuntimeImplemented() => this is RuntimeType;
+
+        internal virtual AttributeUsageAttribute GetAttributeUsageAttribute()
+        {
+            if (!this.IsSubclassOf(typeof(Attribute)))
+                throw new ArgumentException(SR.Argument_MustHaveAttributeBaseClass);
+
+            Attribute[]? attrib = GetCustomAttributes(typeof(AttributeUsageAttribute), false) as Attribute[];
+
+            if (attrib == null || attrib.Length == 0)
+                return AttributeUsageAttribute.Default;
+
+            if (attrib.Length == 1)
+                return (AttributeUsageAttribute)attrib[0];
+
+            throw new FormatException(SR.Format(SR.Format_AttributeUsage, this));
+        }
     }
 }

src/libraries/System.Private.CoreLib/src/System/Reflection/Module.cs

@@ -189,5 +189,20 @@ private static bool FilterTypeNameImpl(Type cls, object filterCriteria, StringCo
 
             return cls.Name.Equals(str, comparison);
         }
+
+        internal virtual Attribute? GetCustomAttribute(Type attributeType, bool inherit)
+        {
+            // Returns an Attribute of base class/interface attributeType on the Module or null if none exists.
+            // throws an AmbiguousMatchException if there are more than one defined.
+            Attribute[] attrib = Attribute.GetCustomAttributes(this, attributeType, inherit);
+
+            if (attrib == null || attrib.Length == 0)
+                return null;
+
+            if (attrib.Length == 1)
+                return attrib[0];
+
+            throw new AmbiguousMatchException(SR.RFLCT_AmbigCust);
+        }
     }
 }