I hold the argument that if the Rust compiler produces unsound behavior for safe Rust, then the compiler needs to be fixed.
As I see it, in either case, the program can be fixed, or the compiler can be fixed. The only difference as I see it is that the C++ spec does not expect the compiler to be fixed.
Did I misunderstand your post?
- either that the claims are paired as you say (the second one implying that the program cannot be fixed),
- or that the claims are completely distinct, that simply state the desirable state of things.
Using the second interpretation, the corollaries would be:
- there is (typically) no reasonable fix for the C++ compiler that would address the UB. Therefore to fix the UB all C++ programs exhibiting the same need to be fixed, which is hard, as the compiler will keep accepting them.
- once the Rust compiler is fixed, then all safe Rust programs exploiting the bug must now be fixed, or the compiler will reject them.
What I would sign under would be the second interpretation, not the first one. But I intentionally also selected the particular ambiguous form due to the cutesy, albeit misleading, symmetry of the statements.