Method binding by name with Type.DefaultBinder.BindToMethod fails with specific condition

[calbonaler]

Description

Type.DefaultBinder.BindToMethod throws IndexOutOfRangeException with the following conditions.

• All the arguments are specified by name.
• Some methods to bind have any unspecified parameters before the specified one.
• All the unspecified parameters have default values.

Reproduction Steps

1. Define the following class and method.

public static class Sample
{
	public static void SampleMethod(string param1, int param2 = 0, bool param3 = false) { }
}

2. Bind to the above method with specifying parameter param1 and param3.

var methods = typeof(Sample).GetMethods();
var methodArgs = new object?[] { "value", true };
var method = Type.DefaultBinder.BindToMethod(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static, methods, ref methodArgs, null, null, new[] { "param1", "param3" }, out var _);

3. IndexOutOfRangeException is thrown at the last line of the above code.

Expected behavior

For example, C# compiler can compile the following code.

Sample.SampleMethod(param1: "value", param3: true);

So I expect that the binding succeeds and no exceptions are thrown.

Actual behavior

IndexOutOfRangeException is thrown and the binding fails.

Regression?

I reproduced this issue on the following platforms:

• .NET Core 3.1
• .NET Framework 4.8

Known Workarounds

No response

Configuration

• Runtime: .NET 6.0
• OS: Windows 10 (x64) Home 21H1

I don't think this issue is specific to the configuration.

Other information

No response

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Issue Details

---

Description

Type.DefaultBinder.BindToMethod throws IndexOutOfRangeException with the following conditions.

• All the arguments are specified by name.
• Some methods to bind have any unspecified parameters before the specified one.
• All the unspecified parameters have default values.

Reproduction Steps

1. Define the following class and method.

public static class Sample
{
	public static void SampleMethod(string param1, int param2 = 0, bool param3 = false) { }
}

2. Bind to the above method with specifying parameter param1 and param3.

var methods = typeof(Sample).GetMethods();
var methodArgs = new object?[] { "value", true };
var method = Type.DefaultBinder.BindToMethod(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static, methods, ref methodArgs, null, null, new[] { "param1", "param3" }, out var _);

3. IndexOutOfRangeException is thrown at the last line of the above code.

Expected behavior

For example, C# compiler can compile the following code.

Sample.SampleMethod(param1: "value", param3: true);

So I expect that the binding succeeds and no exceptions are thrown.

Actual behavior

IndexOutOfRangeException is thrown and the binding fails.

Regression?

I reproduced this issue on the following platforms:

• .NET Core 3.1
• .NET Framework 4.8

Known Workarounds

No response

Configuration

• Runtime: .NET 6.0
• OS: Windows 10 (x64) Home 21H1

I don't think this issue is specific to the configuration.

Other information

No response

Author:	calbonaler
Assignees:	-
Labels:	area-System.Reflection, untriaged
Milestone:	-

[steveharter]

This does appear to be a bug; the binding mechanism is supposed to account for parameter names and default values. Even if not supported, IndexOutOfRangeException should not be thrown.