Microsoft.Extensions.Configuration.Binder is not linker-safe

[eerhardt]

Description

The ConfigurationBinder class will recursively create objects and set properties based on an IConfiguration object. This poses a problem to make it linker-safe because the current reflection flow analysis doesn't support recursive properties. See dotnet/linker#1087. We will need this support to make this API linker-safe.

The linker could decide to trim property setters and constructors which would cause the binder to not set properties correctly.

Here are the current warnings from the linker analysis on this assembly:

F:\git\runtime2\src\libraries\Microsoft.Extensions.Configuration.Binder\src\ConfigurationBinder.cs(371,17): Trim analysis warning IL2006: Microsoft.Extensions.Configuration.ConfigurationBinder.CreateInstance(Type): The parameter 'type' of method 'Microsoft.Extensions.Configuration.ConfigurationBinder.CreateInstance(Type)' with dynamically accessed member kinds 'None' is passed into the implicit 'this' parameter of method 'System.Reflection.TypeInfo.get_DeclaredConstructors()' which requires dynamically accessed member kinds 'NonPublicConstructors | PublicConstructors'. To fix this add DynamicallyAccessedMembersAttribute to it and specify at least these member kinds 'NonPublicConstructors | PublicConstructors'.
F:\git\runtime2\src\libraries\Microsoft.Extensions.Configuration.Binder\src\ConfigurationBinder.cs(380,17): Trim analysis warning IL2006: Microsoft.Extensions.Configuration.ConfigurationBinder.CreateInstance(Type): The parameter 'type' of method 'Microsoft.Extensions.Configuration.ConfigurationBinder.CreateInstance(Type)' with dynamically accessed member kinds 'None' is passed into the parameter #0 of method 'System.Object System.Activator::CreateInstance(System.Type)' which requires dynamically accessed member kinds 'PublicParameterlessConstructor'. To fix this add DynamicallyAccessedMembersAttribute to it and specify at least these member kinds 'PublicParameterlessConstructor'.
F:\git\runtime2\src\libraries\Microsoft.Extensions.Configuration.Binder\src\ConfigurationBinder.cs(403,13): Trim analysis warning IL2006: Microsoft.Extensions.Configuration.ConfigurationBinder.BindDictionary(Object,Type,IConfiguration,BinderOptions): The parameter 'dictionaryType' of method 'Microsoft.Extensions.Configuration.ConfigurationBinder.BindDictionary(Object,Type,IConfiguration,BinderOptions)' with dynamically accessed member kinds 'None' is passed into the implicit 'this' parameter of method 'System.Reflection.TypeInfo.GetDeclaredProperty(String)' which requires dynamically accessed member kinds 'NonPublicProperties | PublicProperties'. To fix this add DynamicallyAccessedMembersAttribute to it and specify at least these member kinds 'NonPublicProperties | PublicProperties'.
F:\git\runtime2\src\libraries\Microsoft.Extensions.Configuration.Binder\src\ConfigurationBinder.cs(433,13): Trim analysis warning IL2006: Microsoft.Extensions.Configuration.ConfigurationBinder.BindCollection(Object,Type,IConfiguration,BinderOptions): The parameter 'collectionType' of method 'Microsoft.Extensions.Configuration.ConfigurationBinder.BindCollection(Object,Type,IConfiguration,BinderOptions)' with dynamically accessed member kinds 'None' is passed into the implicit 'this' parameter of method 'System.Reflection.TypeInfo.GetDeclaredMethod(String)' which requires dynamically accessed member kinds 'NonPublicMethods | PublicMethods'. To fix this add DynamicallyAccessedMembersAttribute to it and specify at least these member kinds 'NonPublicMethods | PublicMethods'.
F:\git\runtime2\src\libraries\Microsoft.Extensions.Configuration.Binder\src\ConfigurationBinder.cs(565,17): Trim analysis warning IL2006: Microsoft.Extensions.Configuration.ConfigurationBinder.GetAllProperties(TypeInfo): The parameter 'type' of method 'Microsoft.Extensions.Configuration.ConfigurationBinder.GetAllProperties(TypeInfo)' with dynamically accessed member kinds 'None' is passed into the implicit 'this' parameter of method 'System.Reflection.TypeInfo.get_DeclaredProperties()' which requires dynamically accessed member kinds 'NonPublicProperties | PublicProperties'. To fix this add DynamicallyAccessedMembersAttribute to it and specify at least these member kinds 'NonPublicProperties | PublicProperties'.

Regression?

No - this API has never been linker-safe.

Repro

Here's a simple application that doesn't work after being fully trimmed:

using Microsoft.Extensions.Configuration;
using System;
using System.Collections.Generic;

namespace ConsoleApp1
{
    class Program
    {
        static int Main(string[] args)
        {
            var dic = new Dictionary<string, string>
            {
                {"Section:Integer", "-2"},
                {"Section:Boolean", "TRUe"},
                {"Section:Nested:Integer", "11"},
                {"Section:Virtual", "Sup"}
            };
            var configurationBuilder = new ConfigurationBuilder();
            configurationBuilder.AddInMemoryCollection(dic);
            var config = configurationBuilder.Build();

            var options = config.Get<ConfigurationInterfaceOptions>();

            var childOptions = options.Section.Get<DerivedOptions>();

            Assert.True(childOptions.Boolean);
            Assert.Equal(-2, childOptions.Integer);
            Assert.Equal(11, childOptions.Nested.Integer);
            Assert.Equal("Derived:Sup", childOptions.Virtual);

            Assert.Equal("Section", options.Section.Key);
            Assert.Equal("Section", options.Section.Path);
            Assert.Null(options.Section.Value);

            return 100;
        }
    }

    public class ComplexOptions
    {
        public ComplexOptions()
        {
            Nested = new NestedOptions();
            Virtual = "complex";
        }

        public NestedOptions Nested { get; set; }
        public int Integer { get; set; }
        public bool Boolean { get; set; }
        public virtual string Virtual { get; set; }
    }

    public class NestedOptions
    {
        public int Integer { get; set; }
    }

    public class DerivedOptions : ComplexOptions
    {
        public override string Virtual
        {
            get
            {
                return base.Virtual;
            }
            set
            {
                base.Virtual = "Derived:" + value;
            }
        }
    }

    public class ConfigurationInterfaceOptions
    {
        public IConfigurationSection Section { get; set; }
    }

    internal class Assert
    {
        internal static void Equal<T>(T left, T right) where T : IEquatable<T>
        {
            if (!EqualityComparer<T>.Default.Equals(left, right)) throw new Exception();
        }

        internal static void Null(string value)
        {
            if (value is object) throw new Exception();
        }

        internal static void True(bool boolean)
        {
            if (!boolean) throw new Exception();
        }
    }
}

Running that application after trimming throws:

Unhandled exception. System.InvalidOperationException: Cannot create instance of type 'ConsoleApp1.ConfigurationInterfaceOptions' because it is missing a public parameterless constructor.
   at Microsoft.Extensions.Configuration.ConfigurationBinder.CreateInstance(Type type)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.BindInstance(Type type, Object instance, IConfiguration config, BinderOptions options)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.Get(IConfiguration configuration, Type type, Action`1 configureOptions)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.Get[T](IConfiguration configuration, Action`1 configureOptions)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.Get[T](IConfiguration configuration)
   at ConsoleApp1.Program.Main(String[] args) in F:\DotNetTest\HelloWorld\Program.cs:line 19

After forcing the linker to keep that constructor, I start getting:

Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'configuration')
   at Microsoft.Extensions.Configuration.ConfigurationBinder.Get[T](IConfiguration configuration, Action`1 configureOptions)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.Get[T](IConfiguration configuration)
   at ConsoleApp1.Program.Main(String[] args) in F:\DotNetTest\HelloWorld\Program.cs:line 30

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[layomia]

This will be solved by #44493.