alt Hacker NewsI expect they are thinking of the "Safe C++" proposal P3390. This proposes to provide the syntax and other features needed to grant (a subset of the future) C++ the same safety properties as safe Rust via an equivalent mechanism (a borrow checker for C++ and the lifetime annotations to drive it, the destructive move, the nominative typing and so on).
Much as you might anticipate (although perhaps its designer Sean Baxter did not) this was not kindly looked upon by many C++ programmers and members of WG21 (the C++ committee)
The larger thing that "Safe C++" and the reaction to it misses is that Rust's boon is its Culture. The "Safe C++" proposal gives C++ a potential safety technology but does not and cannot gift it the accompanying Safety Culture. Government programmes to demand safety will be most effective - just as with other types of safety - if they deliver an improved culture not just technological change.
That sounds significantly more like C++ trying to be a dialect of Rust, rather than the other way around. I don't think that was the GGP's main gripe.
But more importantly, Safe C++ is just not a thing yet. People seem to discount the herculean effort that was required to properly implement the borrow checker, the thousands of little problems that needed to be solved for it to be sound, not to mention a few really, really hard problems, like variance, lifetimes in higher-kinded trait bounds, generic associated types, and how lifetimes interact with a Hindley-Milner type system in general.
Not trying to discount Safe C++'s efforts of course. I really hope they, too, succeed. I also hope they manage to find a syntax that's less... what it is now.