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Ensure that the argument to static_assert is a bool #55945

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Nov 23, 2018
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Ensure that the argument to static_assert is a bool #55945

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3 changes: 2 additions & 1 deletion src/librustc_data_structures/macros.rs
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Expand Up @@ -11,11 +11,12 @@
/// A simple static assertion macro. The first argument should be a unique
/// ALL_CAPS identifier that describes the condition.
#[macro_export]
#[allow_internal_unstable]
macro_rules! static_assert {
($name:ident: $test:expr) => {
// Use the bool to access an array such that if the bool is false, the access
// is out-of-bounds.
#[allow(dead_code)]
static $name: () = [()][!$test as usize];
static $name: () = [()][!($test: bool) as usize];
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You could use #[allow_internal_unstable] instead, maybe?
Also, has the const _ = ...; proposal been implemented?

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Also, has the const _ = ...; proposal been implemented?

It has been implemented, but it does not cope well with allow_internal_unstable, because the crate using static_assert won't have the feature for _ items enabled, thus causing an error about item with name _ being declared multiple times

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I'm very confused, how could that even happen?!

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I don't know, I presume it's because we now do have multiple items with the name _, but the multiple items with same name check doesn't know about allow_internal_unstable and thus assumes the relevant feature gate (for _ names) isn't active.

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But the implementation should be using gensym so that should be impossible?

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@oli-obk No, because that won't preserve the association. Anyway, gensyms are just an implementation hack, you don't actually need a name for these items.

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@oli-obk oli-obk Nov 16, 2018 •
edited
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I can refactor AST and HIR to have Option<Symbol> for their items' names

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That seems overkill for now, and also, we can move this into an issue and land a simpler version of this patch.

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by simpler you mean keeping the actual names for the assert items?

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yeah

}
}