Make guard against unmatchable matchers less strict to enable user-based wildcard matching

CHANGELOG.md

@@ -15,6 +15,7 @@ and `Setup(x => x.GetFooAsync(It.IsAny<string>()).Result).Throws((string s) => n
 
 #### Fixed
 
+* The guard against unmatchable matchers (added in #900) was too strict; relaxed it to enable an alternative user-code shorthand `_` for `It.IsAny<>()` (@adamfk, #1199)
 * mock.Protected() setup methods fail when argument is of type Expression (@tonyhallett, #1189)
 * Parameter is invalid in Protected().SetupSet() ... VerifySet (@tonyhallett, #1186)
 

src/Moq/MatcherFactory.cs

@@ -95,14 +95,30 @@ public static Pair<IMatcher, Expression> CreateMatcher(Expression argument, Para
 				var convertExpression = (UnaryExpression)argument;
 				if (convertExpression.Method?.Name == "op_Implicit")
 				{
-					if (!parameter.ParameterType.IsAssignableFrom(convertExpression.Operand.Type) && convertExpression.Operand.IsMatch(out _))
+					if (convertExpression.Operand.IsMatch(out var match))
 					{
-						throw new ArgumentException(
-							string.Format(
-								Resources.ArgumentMatcherWillNeverMatch,
-								convertExpression.Operand.ToStringFixed(),
-								convertExpression.Operand.Type.GetFormattedName(),
-								parameter.ParameterType.GetFormattedName()));
+						Type matchedValuesType;
+
+						if (match.GetType().IsGenericType)
+						{
+							// If match type is `Match<int>`, matchedValuesType set to `int`
+							// Fix for https://github.com/moq/moq4/issues/1199
+							matchedValuesType = match.GetType().GenericTypeArguments[0];
+						}
+						else
+						{
+							matchedValuesType = convertExpression.Operand.Type;
+						}
+
+						if (!matchedValuesType.IsAssignableFrom(parameter.ParameterType))
+						{
+							throw new ArgumentException(
+								string.Format(
+									Resources.ArgumentMatcherWillNeverMatch,
+									convertExpression.Operand.ToStringFixed(),
+									convertExpression.Operand.Type.GetFormattedName(),
+									parameter.ParameterType.GetFormattedName()));
+						}
 					}
 				}
 			}

tests/Moq.Tests/Matchers/Wildcard.cs

@@ -0,0 +1,202 @@
+using Xunit;
+using System;
+
+/// <summary>
+/// Tests for https://github.com/moq/moq4/issues/1199
+/// </summary>
+
+namespace Moq.Tests.Matchers.Wildcard
+{
+	using static AutoIsAny;   // note using static to simplify syntax
+
+	/// <summary>
+	/// Helper class provided by user
+	/// </summary>
+	public abstract class AutoIsAny
+	{
+		public static AnyValue _
+		{
+			get
+			{
+				It.IsAny<object>();
+				return new AnyValue();
+			}
+		}
+	}
+
+	/// <summary>
+	/// Helper class provided by user. Interfaces implemented via IDE auto explicit interface implementation
+	/// or Roslyn analyzer/code fix.
+	/// </summary>
+	public class AnyValue : ISomeService
+	{
+		int ISomeService.Calc(int a, int b, int c, int d)
+		{
+			throw new NotImplementedException();
+		}
+
+		int ISomeService.DoSomething(ISomeService a, GearId b, int c)
+		{
+			throw new NotImplementedException();
+		}
+
+		int ISomeService.Echo(int a)
+		{
+			throw new NotImplementedException();
+		}
+
+		int ISomeService.UseAnimal(Animal a)
+		{
+			throw new NotImplementedException();
+		}
+
+		int ISomeService.UseDolphin(Dolphin a)
+		{
+			throw new NotImplementedException();
+		}
+
+		int ISomeService.UseInterface(ISomeService a)
+		{
+			throw new NotImplementedException();
+		}
+
+		public static implicit operator int(AnyValue _) => default;
+		public static implicit operator byte(AnyValue _) => default;
+		public static implicit operator GearId(AnyValue _) => default;
+		public static implicit operator Animal(AnyValue _) => default;
+		public static implicit operator Dolphin(AnyValue _) => default;
+	}
+
+
+	public class Tests
+	{
+		Mock<ISomeService> mock;
+		ISomeService obj;
+
+		public Tests()
+		{
+			mock = new Mock<ISomeService>();
+			obj = mock.Object;
+		}
+
+		[Fact]
+		public void Echo_1Primitive()
+		{
+			mock.Setup(obj => obj.Echo(_)).Returns(777);
+			Assert.Equal(777, obj.Echo(1));
+		}
+
+		[Fact]
+		public void Calc_4Primitives()
+		{
+			mock.Setup(obj => obj.Calc(_, _, _, _)).Returns(999);
+			Assert.Equal(999, obj.Calc(1, 2, 3, 4));
+		}
+
+		[Fact]
+		public void UseInterface()
+		{
+			mock.Setup(obj => obj.UseInterface(_)).Returns(555);
+			Assert.Equal(555, obj.UseInterface(null));
+
+			var realService = new SomeService();
+			Assert.Equal(555, obj.UseInterface(realService));
+		}
+
+		[Fact]
+		public void DoSomething_MixedTypes()
+		{
+			mock.Setup(obj => obj.DoSomething(_, _, _)).Returns(444);
+			Assert.Equal(444, obj.DoSomething(null, GearId.Neutral, 1));
+		}
+
+		[Fact]
+		public void UseAnimal()
+		{
+			mock.Setup(obj => obj.UseAnimal(_)).Returns(777);
+			Assert.Equal(777, obj.UseAnimal(new Animal()));
+			Assert.Equal(777, obj.UseAnimal(new Dolphin()));
+		}
+
+		[Fact]
+		public void UseDolphin()
+		{
+			mock.Setup(obj => obj.UseDolphin(_)).Returns(888);
+			Assert.Equal(888, obj.UseDolphin(new Dolphin()));
+		}
+	}
+
+
+	/// <summary>
+	/// Example enum
+	/// </summary>
+	public enum GearId
+	{
+		Reverse,
+		Neutral,
+		Gear1,
+	}
+
+
+	/// <summary>
+	/// Example interface
+	/// </summary>
+	public interface ISomeService
+	{
+		int Echo(int a);
+		int Calc(int a, int b, int c, int d);
+		int UseInterface(ISomeService a);
+		int DoSomething(ISomeService a, GearId b, int c);
+		int UseAnimal(Animal a);
+		int UseDolphin(Dolphin a);
+	}
+
+
+	/// <summary>
+	/// just a class that implements interface
+	/// </summary>
+	public class SomeService : ISomeService
+	{
+		public int Calc(int a, int b, int c, int d)
+		{
+			throw new NotImplementedException();
+		}
+
+		public int DoSomething(ISomeService a, GearId b, int c)
+		{
+			throw new NotImplementedException();
+		}
+
+		public int Echo(int a)
+		{
+			throw new NotImplementedException();
+		}
+
+		public int UseAnimal(Animal a)
+		{
+			throw new NotImplementedException();
+		}
+
+		public int UseDolphin(Dolphin a)
+		{
+			throw new NotImplementedException();
+		}
+
+		public int UseInterface(ISomeService a)
+		{
+			throw new NotImplementedException();
+		}
+	}
+
+
+	public class Animal
+	{
+
+	}
+
+
+	public class Dolphin : Animal
+	{
+
+	}
+}