Fix calling existing ctor with MethodInvoker; share tests with invokers

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

@@ -155,7 +155,7 @@ public object Invoke(object? arg1, object? arg2, object? arg3, object? arg4)
 
         private object InvokeImpl(object? arg1, object? arg2, object? arg3, object? arg4)
         {
-            if ((_invocationFlags & (InvocationFlags.NoInvoke | InvocationFlags.ContainsStackPointers)) != 0)
+            if ((_invocationFlags & (InvocationFlags.NoInvoke | InvocationFlags.ContainsStackPointers | InvocationFlags.NoConstructorInvoke)) != 0)
             {
                 _method.ThrowNoInvokeException();
             }

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

@@ -66,7 +66,12 @@ public static MethodInvoker Create(MethodBase method)
             {
                 // This is useful for calling a constructor on an already-initialized object
                 // such as created from RuntimeHelpers.GetUninitializedObject(Type).
-                return new MethodInvoker(rci);
+                MethodInvoker invoker = new MethodInvoker(rci);
+
+                // Use the interpreted version to avoid having to generate a new method that doesn't allocate.
+                invoker._strategy = GetStrategyForUsingInterpreted();
+
+                return invoker;
             }
 
             throw new ArgumentException(SR.Argument_MustBeRuntimeMethod, nameof(method));
@@ -181,7 +186,7 @@ private MethodInvoker(MethodBase method, RuntimeType[] argumentTypes)
 
         private object? InvokeImpl(object? obj, object? arg1, object? arg2, object? arg3, object? arg4)
         {
-            if ((_invocationFlags & (InvocationFlags.NoInvoke | InvocationFlags.ContainsStackPointers)) != 0)
+            if ((_invocationFlags & (InvocationFlags.NoInvoke | InvocationFlags.ContainsStackPointers | InvocationFlags.NoConstructorInvoke)) != 0)
             {
                 ThrowForBadInvocationFlags();
             }

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

@@ -18,13 +18,14 @@ internal static void Initialize(
         {
             if (LocalAppContextSwitches.ForceInterpretedInvoke && !LocalAppContextSwitches.ForceEmitInvoke)
             {
-                // Always use the native invoke; useful for testing.
-                strategy = InvokerStrategy.StrategyDetermined_Obj4Args | InvokerStrategy.StrategyDetermined_ObjSpanArgs | InvokerStrategy.StrategyDetermined_RefArgs;
+                // Always use the native interpreted invoke.
+                // Useful for testing, to avoid startup overhead of emit, or for calling a ctor on already initialized object.
+                strategy = GetStrategyForUsingInterpreted();
             }
             else if (LocalAppContextSwitches.ForceEmitInvoke && !LocalAppContextSwitches.ForceInterpretedInvoke)
             {
                 // Always use emit invoke (if IsDynamicCodeSupported == true); useful for testing.
-                strategy = InvokerStrategy.HasBeenInvoked_Obj4Args | InvokerStrategy.HasBeenInvoked_ObjSpanArgs | InvokerStrategy.HasBeenInvoked_RefArgs;
+                strategy = GetStrategyForUsingEmit();
             }
             else
             {
@@ -69,6 +70,18 @@ internal static void Initialize(
             }
         }
 
+        internal static InvokerStrategy GetStrategyForUsingInterpreted()
+        {
+            // This causes the default strategy, which is interpreted, to always be used.
+            return InvokerStrategy.StrategyDetermined_Obj4Args | InvokerStrategy.StrategyDetermined_ObjSpanArgs | InvokerStrategy.StrategyDetermined_RefArgs;
+        }
+
+        private static InvokerStrategy GetStrategyForUsingEmit()
+        {
+            // This causes the emit strategy, if supported, to be used on the first call as well as subsequent calls.
+            return InvokerStrategy.HasBeenInvoked_Obj4Args | InvokerStrategy.HasBeenInvoked_ObjSpanArgs | InvokerStrategy.HasBeenInvoked_RefArgs;
+        }
+
         /// <summary>
         /// Confirm member invocation has an instance and is of the correct type
         /// </summary>

src/libraries/System.Reflection/tests/ConstructorCommonTests.cs

@@ -0,0 +1,167 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Linq;
+using Xunit;
+
+namespace System.Reflection.Tests
+{
+    /// <summary>
+    /// These tests are shared with ConstructorInfo.Invoke and ConstructorInvoker.Invoke by using
+    /// the abstract Invoke(...) methods below.
+    /// </summary>
+    public abstract class ConstructorCommonTests
+    {
+        public abstract object Invoke(ConstructorInfo constructorInfo, object?[]? parameters);
+
+        protected abstract bool IsExceptionWrapped { get; }
+
+        /// <summary>
+        /// Invoke constructor on an existing instance. Should return null.
+        /// </summary>
+        public abstract object? Invoke(ConstructorInfo constructorInfo, object obj, object?[]? parameters);
+
+        public static ConstructorInfo[] GetConstructors(Type type)
+        {
+            return type.GetTypeInfo().DeclaredConstructors.ToArray();
+        }
+
+        [Fact]
+        public void SimpleInvoke()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWith3Constructors));
+            Assert.Equal(3, constructors.Length);
+            ClassWith3Constructors obj = (ClassWith3Constructors)Invoke(constructors[0], null);
+            Assert.NotNull(obj);
+        }
+
+        [Fact]
+        [ActiveIssue("https://github.com/mono/mono/issues/15024", TestRuntimes.Mono)]
+        public void Invoke_StaticConstructor_ThrowsMemberAccessException()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWithStaticConstructor));
+            Assert.Equal(1, constructors.Length);
+            Assert.Throws<MemberAccessException>(() => Invoke(constructors[0], new object[0]));
+        }
+
+        [Fact]
+        public void Invoke_OneDimensionalArray()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(object[]));
+            int[] arraylength = { 1, 2, 99, 65535 };
+
+            // Try to invoke Array ctors with different lengths
+            foreach (int length in arraylength)
+            {
+                // Create big Array with elements
+                object[] arr = (object[])Invoke(constructors[0], new object[] { length });
+                Assert.Equal(arr.Length, length);
+            }
+        }
+
+        [Fact]
+        public void Invoke_OneDimensionalArray_NegativeLengths_ThrowsOverflowException()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(object[]));
+            int[] arraylength = new int[] { -1, -2, -99 };
+            // Try to invoke Array ctors with different lengths
+            foreach (int length in arraylength)
+            {
+                // Create big Array with elements
+                if (IsExceptionWrapped)
+                {
+                    Exception ex = Assert.Throws<TargetInvocationException>(() => Invoke(constructors[0], new object[] { length }));
+                    Assert.IsType<OverflowException>(ex.InnerException);
+                }
+                else
+                {
+                    Assert.Throws<OverflowException>(() => Invoke(constructors[0], new object[] { length }));
+                }
+            }
+        }
+
+        [Fact]
+        public void Invoke_OneParameter()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWith3Constructors));
+            ClassWith3Constructors obj = (ClassWith3Constructors)Invoke(constructors[1], new object[] { 100 });
+            Assert.Equal(100, obj.intValue);
+        }
+
+        [Fact]
+        public void Invoke_TwoParameters()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWith3Constructors));
+            ClassWith3Constructors obj = (ClassWith3Constructors)Invoke(constructors[2], new object[] { 101, "hello" });
+            Assert.Equal(101, obj.intValue);
+            Assert.Equal("hello", obj.stringValue);
+        }
+
+        [Fact]
+        public void Invoke_NoParameters_ThowsTargetParameterCountException()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWith3Constructors));
+            Assert.Throws<TargetParameterCountException>(() => Invoke(constructors[2], new object[0]));
+        }
+
+        [Fact]
+        public void Invoke_ParameterMismatch_ThrowsTargetParameterCountException()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWith3Constructors));
+            Assert.Throws<TargetParameterCountException>(() => (ClassWith3Constructors)Invoke(constructors[2], new object[] { 121 }));
+        }
+
+        [Fact]
+        public void Invoke_ParameterWrongType_ThrowsArgumentException()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWith3Constructors));
+            AssertExtensions.Throws<ArgumentException>(null, () => (ClassWith3Constructors)Invoke(constructors[1], new object[] { "hello" }));
+        }
+
+        [Fact]
+        public void Invoke_ExistingInstance()
+        {
+            // Should not produce a second object.
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWith3Constructors));
+            ClassWith3Constructors obj1 = new ClassWith3Constructors(100, "hello");
+            ClassWith3Constructors obj2 = (ClassWith3Constructors)Invoke(constructors[2], obj1, new object[] { 999, "initialized" });
+            Assert.Null(obj2);
+            Assert.Equal(999, obj1.intValue);
+            Assert.Equal("initialized", obj1.stringValue);
+        }
+
+        [Fact]
+        public void Invoke_NullForObj()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWith3Constructors));
+            Assert.Throws<TargetException>(() => Invoke(constructors[2], obj: null, new object[] { 999, "initialized" }));
+        }
+
+        [Fact]
+        [ActiveIssue("https://github.com/mono/mono/issues/15026", TestRuntimes.Mono)]
+        public void Invoke_AbstractClass_ThrowsMemberAccessException()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ConstructorInfoAbstractBase));
+            Assert.Throws<MemberAccessException>(() => (ConstructorInfoAbstractBase)Invoke(constructors[0], new object[0]));
+        }
+
+        [Fact]
+        public void Invoke_SubClass()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ConstructorInfoDerived));
+            ConstructorInfoDerived obj = null;
+            obj = (ConstructorInfoDerived)Invoke(constructors[0], new object[] { });
+            Assert.NotNull(obj);
+        }
+
+        [Fact]
+        public void Invoke_Struct()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(StructWith1Constructor));
+            StructWith1Constructor obj;
+            obj = (StructWith1Constructor)Invoke(constructors[0], new object[] { 1, 2 });
+            Assert.Equal(1, obj.x);
+            Assert.Equal(2, obj.y);
+        }
+    }
+}