An #[inline(..)] attribute was incorrectly placed on something other than a
function or method.
Example of erroneous code:
#[inline(always)]
struct Foo;
#[inline(never)]
impl Foo {
// ...
}#[inline] hints the compiler whether or not to attempt to inline a method or
function. By default, the compiler does a pretty good job of figuring this out
itself, but if you feel the need for annotations, #[inline(always)] and
#[inline(never)] can override or force the compiler’s decision.
If you wish to apply this attribute to all methods in an impl, manually annotate
each method; it is not possible to annotate the entire impl with an #[inline]
attribute.