This turned up as part of #3170. When constructing an `undef` value to
return in the error case, we were trying to get the element type of the
Rust-level value being indexed instead of the underlying array; when
indexing a slice, that's not an array and the LLVM assertion failure
reflects this.
The regression test is a lightly altered copy of `const-array-oob.rs`.
This lint warning was originally intended to help against misuse of the old Rust
`int` and `uint` types in FFI bindings where the Rust `int` was not equal to the
C `int`. This confusion no longer exists (as Rust's types are now `isize` and
`usize`), and as a result the need for this lint has become much less over time.
Additionally, starting with [the RFC for libc][rfc] it's likely that `isize` and
`usize` will be quite common in FFI bindings (e.g. they're the definition of
`size_t` and `ssize_t` on many platforms).
[rfc]: https://github.com/rust-lang/rfcs/pull/1291
This commit disables these lints to instead consider `isize` and `usize` valid
types to have in FFI signatures.
Part of #28710
Landing pads during stage0 are now enabled by defaullt. Since this has its downsides and upsides either way, I made it possible to change the option through configure.
I had to fix a few things. Notable changes:
1. I removed the MIR support for constants, instead falling back to the existing `ConstVal`. I still think we ought to reform how we handle constants, but it's not clear to me that the approach I was taking is correct, and anyway I think we ought to do it separately.
2. I adjusted how we handle bindings in matches: we now *declare* all the bindings up front, rather than doing it as we encounter them. This is not only simpler, since we don't have to check if a binding has already been declared, it avoids ICEs if any of the arms turn out to be unreachable.
3. I do MIR construction *after* `check_match`, because it detects various broken cases. I'd like for `check_match` to be subsumed by MIR construction, but we can do that as a separate PR (if indeed it makes sense).
I did a crater run and found no regressions in the wild: https://gist.github.com/nikomatsakis/0038f90e10c8ad00f2f8
and track which arms are reached (though in fact we don't make use of
this right now -- we might later if we absorb the checking of patterns
into MIR, as I would like)
