Fix Issue 19226 - std.typecons.Nullable(T, T nullValue) doesn't fully handle non-self-equal nullValue

[n8sh]

Nullable(T, T nullValue) special-cases floating point numbers but this doesn't account for all types where nullValue != nullValue. For instance:

https://run.dlang.io/is/hiLncI

struct S
{
    float f;
}

void main()
{
    import std.typecons : Nullable;

    alias N = Nullable!(S, S.init);
    assert(N(S.init).isNull); // Fails!
}

[dlang-bot]

Thanks for your pull request, @n8sh!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	19226	normal	std.typecons.Nullable(T, T nullValue) doesn't fully handle non-self-equal nullValue

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + phobos#6693"

[schveiguy]

Is this different/related to #6583?

[schveiguy]

Oh nevermind, this isn't about opEquals.

[n8sh]

It is related though since opEquals requires we know how to properly check isNull.

[n8sh]

Opened bug report https://issues.dlang.org/show_bug.cgi?id=19227 S.init is S.init failing for struct with float member.

[schveiguy]

Is there a codegen bug on Linux 32-bit? Seems odd that the test case would only fail on that platform.

[n8sh]

It seems like this must be a bug.

[n8sh]

Q: Why is there the seemingly-extraneous __traits(isFloating, T)?
A: So this patch doesn't change the behavior of Nullable!(double, -0.0).

[n8sh]

The wrong code generation on 32-bit linux was still happening last I checked so I expect this not to go through.

[12345swordy]

3 days have been passed already.

[wilzbach]

The wrong code generation on 32-bit linux was still happening last I checked so I expect this not to go through.

Yup, it's still there.

[n8sh]

I've been unable to replicate the Linux_32 / Linux_64_32 problem locally so far so I'm unable to tell what the problem is or make a useful bug report.

[n8sh]

I am changing the test case for this PR. Whatever is wrong with 32-bit linux is a separate issue.