core.traits?

[Manu]

So, druntime has core.internal.traits where a bunch of std.traits have
been mirrored to support internal machinery within druntime.
This is clear evidence that a lot of these traits are really
super-critical to doing basically anything interesting with D.
I have experience with no-phobos projects in the past where I've been
frustrated that I had to mirror all the traits I needed manually.

I suggest, a fair set of std.traits (no-brainer traits that you
basically can't live without) should be officially moved to
core.traits, so that they are always available to all D users.
Traits are pure-templates, they don't emit code, and have no impact on
the size of the druntime binary. They significantly shouldn't affect
build times unless they are instantiated.
...and they're already there in core.internal.traits.

We should move them to core.traits, and that should be their official
home. It really just makes sense. Uncontroversial low-level traits
don't belong in phobos.