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ToStr, Encodable and Decodable are not marked as such, since they're
already expensive, and lead to large methods, so inlining will bloat the
metadata & the binaries.
This means that something like
#[deriving(Eq)]
struct A { x: int }
creates an instance like
#[doc = "Automatically derived."]
impl ::std::cmp::Eq for A {
#[inline]
fn eq(&self, __arg_0: &A) -> ::bool {
match *__arg_0 {
A{x: ref __self_1_0} =>
match *self {
A{x: ref __self_0_0} => true && __self_0_0.eq(__self_1_0)
}
}
}
#[inline]
fn ne(&self, __arg_0: &A) -> ::bool {
match *__arg_0 {
A{x: ref __self_1_0} =>
match *self {
A{x: ref __self_0_0} => false || __self_0_0.ne(__self_1_0)
}
}
}
}
(The change being the `#[inline]` attributes.)
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This rearranges the deriving code so that #[deriving] a trait on a field
that doesn't implement that trait will point to the field in question,
e.g.
struct NotEq; // doesn't implement Eq
#[deriving(Eq)]
struct Foo {
ok: int,
also_ok: ~str,
bad: NotEq // error points here.
}
Unfortunately, this means the error is disconnected from the `deriving`
itself but there's no current way to pass that information through to
rustc except via the spans, at the moment.
Fixes #7724.
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