Nullable reference types support

[andrewvk]

Feel free to apply changes from previous PR.

[andrewvk]

One more interesting point. R# automatically removes its own CanBeNull markup when adding "?" to a type. @NN---

[NN---]

I paid attention to that:) As I said my concern is old ReSharper versions without good NRT support.

[NN---]

@andrewvk So, do we agree that all ReSharper nullability attributes will be replaced with .NET nullability attributes ?

[NN---]

@andrewvk Can we merge what we have now ?

[andrewvk]

There is some issue with nullability and autogenerated code. By default, C# compiler treat all generated code as #nullable disabled, regardless of project settings. In that case you should specify #nullable enabled explicitly. I fixed this in base T4 template, but did not rerun all templates. So, after I did it we still have hundreds of nullability warnings and errors (see last commit).

[NN---]

Ok. I can fix that too. There is some problem with build time limit . Is there any solution for this ?

[andrewvk]

If there is one, I don't know it :(

[NN---]

I think GitHub actions can handle this. Need to try.

[NN---]

@andrewvk in my project I added NAssert.NotNull which tells compiler to make variable non nullable and avoid useless ! . Do you think it worth adding it?

[andrewvk]

Can you explain in more detail what you mean by that? In any case, using ! in most cases is definitely not the best option.

[NN---]

This assertion makes this code compiling

string? f();
void g(string) {}

string? a = f();
NAssert.NotNull(a);

// a here is not null
g(a); // OK

using System.Diagnostics.CodeAnalysis;
using NUnit.Framework;

namespace Tests
{
    public static class NAssert
    {
#pragma warning disable CS8777 // Parameter must have a non-null value when exiting.
        // The warning is due to fact we do not check for null and throw directly.

        #region NotNull

        /// <summary>
        /// Verifies that the object that is passed in is not equal to <see langword="null" />. Returns without throwing an
        /// exception when inside a multiple assert block.
        /// </summary>
        /// <param name="anObject">The object that is to be tested</param>
        /// <param name="message">The message to display in case of failure</param>
        /// <param name="args">Array of objects to be used in formatting the message</param>
        public static void NotNull([NotNull] object? anObject, string message, params object?[]? args)
        {
            Assert.NotNull(anObject, message, args);
        }

        /// <summary>
        /// Verifies that the object that is passed in is not equal to <see langword="null" />. Returns without throwing an
        /// exception when inside a multiple assert block.
        /// </summary>
        /// <param name="anObject">The object that is to be tested</param>
        public static void NotNull([NotNull] object? anObject)
        {
            Assert.NotNull(anObject);
        }

        #endregion

#pragma warning restore CS8777 // Parameter must have a non-null value when exiting.
    }
}

[NN---]

Btw, IDictionary doesn't require "TKey : notnull" according to sources. https://github.com/dotnet/runtime/blob/master/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IDictionary.cs

It means adding this constraint is not correct.

[andrewvk]

You mean that NUnit still doesn't have a NotNull attribute markup? Yeah, that's pretty weird. Of course, in this case it's worth adding your own variant.

[andrewvk]

[NN---]

Yeah. I tried to reproduce this in a separate project but everything compiled. Probably it requires this constraint only for specific framework. Currently everything compiles but not in appveyor:( I’ll check how to improve it.

[andrewvk]

Core 3.0 library Core 5.0 library Shall we try to hide it under a compiler directive?

[andrewvk]

`#if NETCOREAPP3_1 where TKey : notnull

endif`

Build OK

[NN---]

It is better to not introduce additional constraint if possble

[NN---]

Fixed recursion and now the build works :) @andrewvk Is there anything left in PR ?