The following attributes affect compile-time limits.
The recursion_limit attribute may be applied at the crate level to set the
maximum depth for potentially infinitely-recursive compile-time operations
like auto-dereference or macro expansion. It uses the MetaNameValueStr
syntax to specify the recursion depth. The default is 64.
#![recursion_limit = "4"]
macro_rules! a {
() => { a!(1) };
(1) => { a!(2) };
(2) => { a!(3) };
(3) => { a!(4) };
(4) => { };
}
// This fails to expand because it requires a recursion depth greater than 4.
a!{}The type_length_limit attribute limits the maximum size of a type
constructed during monomorphization. It is applied at the crate level, and
uses the MetaNameValueStr syntax to set the limit based on the number of
type substitutions within the type. The default value is 1048576.
#![type_length_limit = "8"]
type A = (B, B, B);
type B = (C, C, C);
struct C;
// This fails to compile because monomorphizing to
// `drop::<Option<((C, C, C), (C, C, C), (C, C, C))>>` requires more than 8
// type elements.
drop::<Option<A>>(None);