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A static assertion is particularly appropriate when unsafe code relies
on two types to have the same size, or on some type to have a particular
size. This is a pattern I observed in USB code, for example:
https://chromium.googlesource.com/chromiumos/platform/crosvm/+/ff7068402e6cff527a8558adf597b1596f075166/devices/src/usb/xhci/xhci_abi_schema.rs#522
EXAMPLE:
extern crate assertions;
use assertions::const_assert;
fn main() {
const_assert!(std::mem::size_of::<String>() == 24);
}
EXAMPLE THAT FAILS TO COMPILE:
extern crate assertions;
use assertions::const_assert;
fn main() {
// fails to compile:
const_assert!(std::mem::size_of::<String>() == 8);
}
FAILURE LOOKS LIKE:
error[E0271]: type mismatch resolving `<[(); 0] as assertions::Expr>::Value == assertions::True`
--> src/main.rs:5:5
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5 | const_assert!(std::mem::size_of::<String>() == 8);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `assertions::True`, found struct `assertions::False`
TEST=`cargo test` the new crate
Change-Id: I6abe36d5a6a4bd4acb1a02e3aa7c1ece5357f007
Reviewed-on: https://chromium-review.googlesource.com/1366819
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: David Tolnay <dtolnay@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
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