NullabilityInfoContext.Create throws IndexOutOfRangeException

[ropufu]

Description

NullabilityInfoContext will throw IndexOutOfRangeException when calling Create method on certain Dictionary-valued properties in generic classes. Seems to happen when the TValue of the dictionary is a generic class with one type parameter coinciding with the type parameter of the class that defines the property.

Reproduction Steps

// .NET 6.0 LTS Console App project with default settings (nullability context enabled).
using System.Reflection;

Foo<int>? bar = new();
NullabilityInfoContext context = new();
PropertyInfo x = bar.GetType().GetProperty(nameof(bar.Bad))!;
// The next line will throw.
NullabilityInfo info = context.Create(x);
Console.WriteLine(info.ReadState);

public class Foo<T>
{
    public Dictionary<int, List<T>>? Bad { get; set; }
    public Dictionary<int, IEquatable<T>>? AlsoBad { get; set; }
    public Dictionary<int, List<int>>? Good { get; set; }
    public Dictionary<int, T>? AlsoGood { get; set; }
}

Expected behavior

Program should successfully terminate with Nullable displayed on the console.

Actual behavior

Line NullabilityInfo info = context.Create(x); throws a System.IndexOutOfRangeException.

   at System.Reflection.NullabilityInfoContext.CheckGenericParameters(NullabilityInfo nullability, MemberInfo metaMember, Type metaType)
   at System.Reflection.NullabilityInfoContext.TryLoadGenericMetaTypeNullability(MemberInfo memberInfo, NullabilityInfo nullability)
   at System.Reflection.NullabilityInfoContext.GetNullabilityInfo(MemberInfo memberInfo, Type type, IList`1 customAttributes, Int32 index)
   at System.Reflection.NullabilityInfoContext.GetNullabilityInfo(MemberInfo memberInfo, Type type, IList`1 customAttributes, Int32 index)
   at System.Reflection.NullabilityInfoContext.Create(PropertyInfo propertyInfo)

Regression?

No response

Known Workarounds

No response

Configuration

This is a vanilla .NET 6.0 Long-term Support "Console App" project created in Visual Studio 2022 on a Windows 11 machine. Fails in both Debug and Release mode when targeting "Any CPU".

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
</Project>

Other information

No response

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Issue Details

---

Description

NullabilityInfoContext will throw IndexOutOfRangeException when calling Create method on certain Dictionary-valued properties in generic classes. Seems to happen when the TValue of the dictionary is a generic class with one type parameter coinciding with the type parameter of the class that defines the property.

Reproduction Steps

// .NET 6.0 LTS Console App project with default settings (nullability context enabled).
using System.Reflection;

Foo<int>? bar = new();
NullabilityInfoContext context = new();
PropertyInfo x = bar.GetType().GetProperty(nameof(bar.Bad))!;
// The next line will throw.
NullabilityInfo info = context.Create(x);
Console.WriteLine(info.ReadState);

public class Foo<T>
{
    public Dictionary<int, List<T>>? Bad { get; set; }
    public Dictionary<int, IEquatable<T>>? AlsoBad { get; set; }
    public Dictionary<int, List<int>>? Good { get; set; }
    public Dictionary<int, T>? AlsoGood { get; set; }
}

Expected behavior

Program should successfully terminate with Nullable displayed on the console.

Actual behavior

Line NullabilityInfo info = context.Create(x); throws a System.IndexOutOfRangeException.

   at System.Reflection.NullabilityInfoContext.CheckGenericParameters(NullabilityInfo nullability, MemberInfo metaMember, Type metaType)
   at System.Reflection.NullabilityInfoContext.TryLoadGenericMetaTypeNullability(MemberInfo memberInfo, NullabilityInfo nullability)
   at System.Reflection.NullabilityInfoContext.GetNullabilityInfo(MemberInfo memberInfo, Type type, IList`1 customAttributes, Int32 index)
   at System.Reflection.NullabilityInfoContext.GetNullabilityInfo(MemberInfo memberInfo, Type type, IList`1 customAttributes, Int32 index)
   at System.Reflection.NullabilityInfoContext.Create(PropertyInfo propertyInfo)

Regression?

No response

Known Workarounds

No response

Configuration

This is a vanilla .NET 6.0 Long-term Support "Console App" project created in Visual Studio 2022 on a Windows 11 machine. Fails in both Debug and Release mode when targeting "Any CPU".

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
</Project>

Other information

No response

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

[ropufu]

Here are some more cases that will fail, this time without referencing lists or dictionaries.

class Foo<T>
{
    // Nesting 1-inside-2.
    public Two<int, One<T>>? Bad1 { get; set; }
    // Order does not matter.
    public Two<One<T>, int>? Bad2 { get; set; }
    // Nesting 1-inside-3.
    public Three<int, int, One<T>>? Bad3 { get; set; }
    // Nesting 2-inside-3.
    public Three<int, int, Two<T, T>>? Bad4 { get; set; }
}

class Three<T, U, V> { }
class Two<T, U> { }
class One<T> { }

[danmoseley]

Thanks for the report @ropufu . Any interest in debugging a bit, or offering a fix?

[ropufu]

I'll give it a shot :^) However, I'm very new to creating PR and almost hopeless at git. So this will take me a while to read through all relevant instructions.

[danmoseley]

Sure - take your time and let me know if you get stuck. There are pretty good workflow instructions though.

[am11]

Nice report, @ropufu. I can reproduce it with net7.0 as well. A quick fix is to change this line:

runtime/src/libraries/System.Private.CoreLib/src/System/Reflection/NullabilityInfoContext.cs

Line 462 in a9f9745

for (int i = 0; i < genericArguments.Length; i++)

as for (int i = 0; i < genericArguments.Length && i < nullability.GenericTypeArguments.Length; i++) . However, I think it is not the right fix as nullability.GenericTypeArguments should account for same number of generic arguments as metadata.GetGenericArguments() so the checks will run for each nested argument as well, right?

using System.Reflection;

Foo<int> bar = new();
NullabilityInfoContext context = new();

PropertyInfo x0 = bar.GetType().GetProperty(nameof(bar.Prop0))!;
NullabilityInfo info0 = context.Create(x0); // fine

PropertyInfo x1 = bar.GetType().GetProperty(nameof(bar.Prop1))!;
NullabilityInfo info1 = context.Create(x1); // throws IOoRE

class Foo<T>
{
    public Two<int, T> Prop0 { get; set; }
    public Two<int, One<T>> Prop1 { get; set; }
}

class Two<T, U> { }
class One<T> { }

@madelson, do you remember seeing this case while working on #64143?

[madelson]

@am11 I don't recall running into this. I'm surprised that the test cases don't cover this given that the repro seems fairly simple.

However, I think it is not the right fix as nullability.GenericTypeArguments should account for same number of generic arguments as metadata.GetGenericArguments()

Agreed. We need to figure out why these differ.

I'd be happy to take this if @ropufu doesn't end up wanting to.

[buyaa-n]

I'll give it a shot

Hello @ropufu? Are you still working on it? It better to be fixed within 7.0 preview 7 and not many days left

[ropufu]

Thank you for the nudge. I wasn't for a while: I could not follow the Contributing/Workflow guidelines to set up debugging for the issue in conjunction with System.Private.CoreLib back then... and I still can't.

If there is a deadline for me to aim at--that would be helpful (assuming that leaves you folks enough time to crack it if I fail). And if you have other references (like a minimal example/walkthrough how to set up a debuggable project in VS that targets the preview .NET) that would be most welcome. My apologies for not speaking up the first time I could not do it.

[buyaa-n]

After building clr+libs+libs.tests as mentioned in the Contributing/Workflow guidelines you could be able to add tests into https://github.com/dotnet/runtime/blob/main/src/libraries/System.Runtime/tests/System/Reflection/NullabilityInfoContextTests.cs and debug from that System.Runtime which references code in System.Private.CoreLib

If there is a deadline for me to aim at--that would be helpful

The preview 7 deadline is next Monday, so if you could do the fix within this week

[ropufu]

@buyaa-n Thank you so much for your help. Right to the point. Saved me a lot of frustration and pain. Thank you!

I think I managed to get the thing fixed. Reflection tests look good; I'll try to get the proper submission done in an hour or two. My only concern is that I am not so fluent in the NullabilityInfoContext class as to understand all of the potential ramifications of my change (although I don't think there should be any).