logging - Why ASP.NET Core DI knows how to resolve ILogger<T>, but not ILogger?

Question

If class T contains dependency on ILogger, dependency is resolved:

public class Foo
{
    private ILogger _logger;

    public Foo(ILogger<Foo> logger)
    {
        _logger = logger;
    }
}

but the following does not work, as logger will be null:

public class Foo
{
    private ILogger _logger;

    public Foo(ILogger logger)
    {
        _logger = logger;
    }
}

Answer 1

Logging adds the following services to DI

services.TryAdd(ServiceDescriptor.Singleton<ILoggerFactory, LoggerFactory>());
services.TryAdd(ServiceDescriptor.Singleton(typeof(ILogger<>), typeof(Logger<>)));

and Logger<> depends on ILoggerFactory from DI.

For your second scenario you would need to inject ILoggerFactory instead of ILogger.

public Foo(ILoggerFactory loggerFactory)
{
    _logger = loggerFactory.CreateLogger("logger name here");
}