Fix InvalidOperationException in GetImplementingProperty with explicit interface implementations

[Copilot]

When a class explicitly implements an interface property (e.g., string IStringId.Id => Id.ToString()) while also having a property with the same name (public int Id), GetImplementingProperty throws InvalidOperationException: Sequence contains no matching element.

Changes

• TypeExtensions.cs: Replace .First() with .FirstOrDefault() ?? propertyInfo to gracefully handle cases where the implementing property isn't found in the derived type's property list
• TypeExtensionTests.cs: Add unit test coverage for explicit interface implementation scenarios
• ExplicitInterfaceImplementationTests.cs: Add functional tests to validate the fix works correctly with EF Core queries (Select and Where operations)
• ProjectionExpressionGeneratorTests.cs: Add generator test to verify source generation handles explicit interface implementations correctly

Example

public interface IStringId { string Id { get; } }

public class Item : IStringId
{
    public int Id { get; set; }
    string IStringId.Id => Id.ToString();  // Explicit implementation
}

// Previously threw InvalidOperationException, now works correctly
var property = typeof(Item).GetImplementingProperty(typeof(IStringId).GetProperty("Id"));

Testing

• ✅ All 161 tests pass (24 unit tests, 67 functional tests, 71 generator tests)
• ✅ Unit tests verify the fix at the TypeExtensions level
• ✅ Functional tests validate the fix works in real EF Core query scenarios
• ✅ Generator test confirms source generation works correctly with explicit interface implementations

Original prompt

Fix this issue :

Two properties with same name causes GetImplementingProperty to throw System.InvalidOperationException: Sequence contains no matching element

Simplification of my setup:

public interface IStringId { string Id { get; } }

public class Item
{
public int Id { get; set ; }
string IStringId.Id => Id.ToString();
}

public Task GetItem(string id) => db.Items.FirstOrDefaultAsync(x => x.Id == id);

GetItem method throws InvalidOperationException when UseProjectables() is called, but works fine otherwise.

I see that TypeExtensions.GetConcreteProperty is called with propertyInfo being the string Id property from IStringId

DeclaringType is an interface, so it calls GetImplementingProperty, but it's looking for a property that isn't declared on this class, so this .First throws the InvalidOperationException:

        return derivedProperties.First(propertyInfo.GetMethod == accessor
            ? p => p.GetMethod == implementingAccessor
            : p => p.SetMethod == implementingAccessor);

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[PhenX]

@copilot Please also add functional and generator tests in there respective projects

[Copilot]

@copilot Please also add functional and generator tests in there respective projects

Added functional and generator tests as requested in commit 201cabe.

Functional tests (ExplicitInterfaceImplementationTests.cs):

• ProjectOverExplicitInterfaceImplementation - Tests Select queries
• FilterOnExplicitInterfaceImplementation - Tests Where queries

Generator test (ProjectionExpressionGeneratorTests.cs):

• ExplicitInterfaceImplementation - Verifies source generation for explicit interface implementations

All 161 tests pass (24 unit tests, 67 functional tests, 71 generator tests).