Insurance policy in case `iter.size_hint()` lies.
Follow up to https://github.com/rust-lang/rust/pull/64949/files#r334235076.
(If the perf impact is bad we can use `debug_assert!` instead.)
The good news is that the UI tests pass locally so `iter.size_hint()` seems to be honest *thus far*.
On the other hand, with the status quo we do not have an insurance policy should that change in some case. This is problematic because a) this could possibly make some program be accepted which shouldn't, b) the compiler itself could have memory unsafety if the correctness of the iterator is assumed in `unsafe { ... }` code (even though the blame lies with the `unsafe { ... }` block in question.)
r? @RalfJung
cc @nnethercote
Use revisions to run the EFIABI in multiple configurations, compiling
for each supported UEFI platform, and checking the ABI generated in the
LLVM IR is correct.
Use no_core to make it easier to test.
Adds a new ABI for the EFIAPI calls. This ABI should reflect the latest
version of the UEFI specification at the time of commit (UEFI spec 2.8,
URL below). The specification says that for x86_64, we should follow the
win64 ABI, while on all other supported platforms (ia32, itanium, arm,
arm64 and risc-v), we should follow the C ABI.
To simplify the implementation, we will simply follow the C ABI on all
platforms except x86_64, even those technically unsupported by the UEFI
specification.
https://uefi.org/sites/default/files/resources/UEFI_Spec_2_8_final.pdf
(Or more precisely, a pair of such traits: one for `derive(PartialEq)` and one
for `derive(Eq)`.)
((The addition of the second marker trait, `StructuralEq`, is largely a hack to
work-around `fn (&T)` not implementing `PartialEq` and `Eq`; see also issue
rust-lang/rust#46989; otherwise I would just check if `Eq` is implemented.))
Note: this does not use trait fulfillment error-reporting machinery; it just
uses the trait system to determine if the ADT was tagged or not. (Nonetheless, I
have kept an `on_unimplemented` message on the new trait for structural_match
check, even though it is currently not used.)
Note also: this does *not* resolve the ICE from rust-lang/rust#65466, as noted
in a comment added in this commit. Further work is necessary to resolve that and
other problems with the structural match checking, especially to do so without
breaking stable code (adapted from test fn-ptr-is-structurally-matchable.rs):
```rust
fn r_sm_to(_: &SM) {}
fn main() {
const CFN6: Wrap<fn(&SM)> = Wrap(r_sm_to);
let input: Wrap<fn(&SM)> = Wrap(r_sm_to);
match Wrap(input) {
Wrap(CFN6) => {}
Wrap(_) => {}
};
}
```
where we would hit a problem with the strategy of unconditionally checking for
`PartialEq` because the type `for <'a> fn(&'a SM)` does not currently even
*implement* `PartialEq`.
----
added review feedback:
* use an or-pattern
* eschew `return` when tail position will do.
* don't need fresh_expansion; just add `structural_match` to appropriate `allow_internal_unstable` attributes.
also fixed example in doc comment so that it actually compiles.
