Static linking (ADR-0086)

The static_link_extern("name") { … } keyword introduces a sibling form to link_extern that requests static linkage for the named library. Body grammar (items, body-less fn declarations, implicit @mark(c), @link_name overrides, empty-block permission) is identical to link_extern. The keyword is gated behind the c_ffi_extras preview feature.

A given library name cannot be declared with both link_extern (dynamic) and static_link_extern (static) linkage across the same compilation unit. Mixed declarations are rejected with a compile-time diagnostic.

On ELF targets, a static-linked library contributes -Wl,-Bstatic -l<name> -Wl,-Bdynamic to the linker line. Static libraries are emitted in lex-sorted order ahead of dynamic ones; the closing -Wl,-Bdynamic ensures libc and the Gruel runtime remain dynamic.

On Mach-O targets, a static-linked library contributes -Wl,-search_paths_first -l<name>. macOS ld has no -Bstatic/-Bdynamic toggle; -search_paths_first causes the linker to scan a search directory for lib<name>.a before lib<name>.dylib. If only a .dylib is present, the link succeeds dynamically — same outcome as the ELF dynamic fallback. A diagnostic warning is reserved for this fallback but is not emitted in this revision.

static_link_extern blocks may not nest. Mixing static_link_extern inside link_extern (or vice versa) is rejected with the same LinkExternNested diagnostic ADR-0085 introduced for link_extern nesting. 
static_link_extern("foo") {
    fn foo_init() -> c_int;
}

link_extern("c") { // dynamic, unchanged from ADR-0085
    fn write(fd: c_int, buf: Ptr(u8), n: usize) -> isize;
}