Do not promote extern statics - #2302
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Reference update for rust-lang/rust#157641: a borrow of an extern static is never eligible for constant promotion, even when the reference itself is never read from.
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| r[destructors.scope.const-promotion.extern-static] | ||
| A borrow of an [`extern` static] cannot be promoted, even if the resulting reference is never read from. | ||
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| ```rust,compile_fail | ||
| unsafe extern "C" { | ||
| static X: i32; | ||
| } | ||
| static mut FOO: *const &i32 = [unsafe { &X }].as_ptr(); | ||
| ``` | ||
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If the error produced has an error code, we'll want to add that to the infostring line.
Probably we also want to add some comments to this example to help make clear what's going on. And maybe it's worth adding an admonition that mentions the theory behind why this is rejected (see, e.g., what I wrote in rust-lang/rust#157641 (comment)).
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Reference update for rust-lang/rust#157641: a borrow of an extern static cannot be promoted, even when the reference is never read from.