#[ctor] from a (static) library not applied if library not imported with use

[peter-lyons-kehl]

Thanks Matt for rust-ctor.

Situation:

• a (static) library crate (let's call it static_library here) uses #[ctor], and
• that (static) library doesn't have any public items. Instead, its only purpose is to run its functionality at start (with #[ctor]), and
• a consumer binary imports/declares that (static) library in its Cargo.toml's [dependencies], but it doesn't have use static_library; nor #[allow(unused)] use static_library;, then
• the function(s) in static_library marked with #[ctor] are not run (at least not on x64 Linux).

If the binary has use static_library; or #[allow(unused)] use static_library; then the #[ctor] function(s) from static_library are run as expected.

• static library: always-abort > src/lib.rs
• consumer binary: always-abort > tests-as-binary/import-forgotten/src/main.rs

Such a use is probably rare, so this may not need any action/investigation, and a note in documentation may be enough.

FYI: I've tried with #[constructor(65535)] of static_init crate (current 1.0.3) instead of rust-ctor, and it has the same problem/limitation. Without use (of the static library) functions marked with #[constructor(...)] are not run.

Even when I use static_init's #[dynamic(drop)] together with #[used], expressions that generate initial values of such statics is not run (again, if I don't use the static library).

(I may migrate always-abort to depend on static_init instead of ctor, but there are no emotions here. Thank you for ctor.)