`link_extern("libname") { … }` blocks (ADR-0085)

[10.2:1]

A link_extern item form has the shape link_extern "(" string-literal ")" "{" item* "}". The string literal names a library; the body is a sequence of body-less fn declarations.

[10.2:2]

Each fn declared inside a link_extern block is implicitly an extern declaration: the symbol resolves at link time, no body is permitted, and the call uses the C calling convention (implicit @mark(c)).

[10.2:3]

Body-less fn declarations (fn name(...) [-> type] ;) are only permitted inside a link_extern block. A body-less fn at top level is a compile-time error.

[10.2:4]

A fn declared inside a link_extern block must not carry a body. A fn with a body inside a link_extern block is a compile-time error.

[10.2:5]

The library name passed to link_extern("…") must be a non-empty string.

[10.2:6]

link_extern blocks do not nest.

[10.2:7]

link_extern("m") {
    fn sin(x: f64) -> f64;
    fn cos(x: f64) -> f64;
}

link_extern("c") {
    fn abs(x: i32) -> i32;
}

[10.2:8]

The @link_name("…") directive overrides the linker symbol name of an extern declaration. Without @link_name, the symbol equals the Gruel identifier.

[10.2:9]

Library names from every link_extern("…") block across the compilation are deduplicated and contribute a single -l<name> flag to the link command in lexicographic order.

[10.2:10]

Every fn declared inside a link_extern or static_link_extern block must carry @mark(unchecked) in its directive list (ADR-0088). Imported C symbols are unverified from the Gruel side by construction; the marker makes the call-site discipline visible — every caller must wrap the call in a checked { } block.

[10.2:11]

link_extern("m") {
    @mark(unchecked) fn sin(x: f64) -> f64;
    @mark(unchecked) fn cos(x: f64) -> f64;
}

fn compute(x: f64) -> f64 {
    checked { sin(x) + cos(x) }
}

link_extern("libname") { … } blocks (ADR-0085)

`link_extern("libname") { … }` blocks (ADR-0085)