[comex]

You mean that Miri catches it at runtime, right? If so, that hardly demonstrates anything about the difficulty or lack thereof of fixing rustc’s type checker, since Miri is not a type checker and doesn’t know anything about “lifetimes” in the usual sense.

I agree that this isn’t a “fundamental design flaw in the language”, but Miri is irrelevant to proving that.

[pcwalton]

Yes. I'm not saying that Miri demonstrates anything other than that it's not a language issue.

[comex]

I’m not sure it even demonstrates that. For comparison, C’s inability to prevent undefined behavior at compile time definitely is a fundamental weakness of the language. Yet C has its own tools that, like Miri, can detect most undefined behavior at runtime in exchange for a drastic performance cost. (tis-interpreter is probably the closest analogy, though of course you also have ASan and Valgrind.)

Or to put it another way, the reason that Rust’s implied bounds issue is not a fundamental language issue is that it almost certainly can be fixed without massive backwards compatibility breakage or language alterations, whereas making C safe would require such breakage and alterations. But Miri tells us nothing about that.