Comment by aw1621107

> There are crucial issues, namely that there is no spec and there is only one implementation. I don't know why Linus is ok with this.

I can try to provide a (weak) steelman argument:

Strictly speaking, neither the lack of a spec nor a single implementation have been blockers for Linux's use of stuff, either now or in the past. Non-standard GCC extensions and flags aren't exactly rare in the kernel, and Linus has been perfectly fine with the single non-standard implementation of those. Linus has also stated in the past (paraphrasing) that what works in practice is more important than what standards dictate [0]. Perhaps Linus feels that what Rust does in practice is good enough, especially given its (currently) limited role in the kernel.

Granted, not having a spec for individual flags/features is not equivalent to not having a spec for the language, so it's not the strongest argument as I said. I do think there's a point nestled in there though - perhaps what happens on the ground is the most important factor. It probably helps that there is work being done on both the spec and multiple implementation fronts.

[0]: https://lkml.org/lkml/2018/6/5/769