1 use core::str::from_utf8_unchecked;
2
3 use proc_macro2::TokenStream;
4 use uuid::adapter::Simple;
5 use uuid::Uuid;
6
7 use quote::format_ident;
8 use quote::quote;
9 use quote::ToTokens;
10
generate_caster(ty: &impl ToTokens, trait_: &impl ToTokens, sync: bool) -> TokenStream11 pub fn generate_caster(ty: &impl ToTokens, trait_: &impl ToTokens, sync: bool) -> TokenStream {
12 let mut fn_buf = [0u8; FN_BUF_LEN];
13 let fn_ident = format_ident!("{}", new_fn_name(&mut fn_buf));
14 // 生成从dyn trait转换为具体类型结构体ty的caster
15 let new_caster = if sync {
16 quote! {
17 ::intertrait::Caster::<dyn #trait_>::new_sync(
18 |from| from.downcast_ref::<#ty>().unwrap(),
19 |from| from.downcast_mut::<#ty>().unwrap(),
20 |from| from.downcast::<#ty>().unwrap(),
21 |from| from.downcast::<#ty>().unwrap(),
22 |from| from.downcast::<#ty>().unwrap()
23 )
24 }
25 } else {
26 quote! {
27 ::intertrait::Caster::<dyn #trait_>::new(
28 |from| from.downcast_ref::<#ty>().unwrap(),
29 |from| from.downcast_mut::<#ty>().unwrap(),
30 |from| from.downcast::<#ty>().unwrap(),
31 |from| from.downcast::<#ty>().unwrap(),
32 )
33 }
34 };
35
36 // 由于过程宏是在预编译期执行的，这里的target_os是linux。
37 // 编译完成的proc macro会交给下一阶段进行编译，因此，#[cfg(target_os)]会在下一阶段生效。
38 // 我们必须在预处理阶段把两种代码的token stream都生成出来，然后在下一阶段选择性地使用其中一种。
39 quote! {
40
41 #[cfg(not(target_os = "none"))]
42 #[::linkme::distributed_slice(::intertrait::CASTERS)]
43 fn #fn_ident() -> (::std::any::TypeId, ::intertrait::BoxedCaster) {
44 (::std::any::TypeId::of::<#ty>(), Box::new(#new_caster))
45 }
46
47 #[cfg(target_os = "none")]
48 #[::linkme::distributed_slice(::intertrait::CASTERS)]
49 fn #fn_ident() -> (::core::any::TypeId, ::intertrait::BoxedCaster) {
50 (::core::any::TypeId::of::<#ty>(), alloc::boxed::Box::new(#new_caster))
51 }
52 }
53 }
54
55 const FN_PREFIX: &[u8] = b"__";
56 const FN_BUF_LEN: usize = FN_PREFIX.len() + Simple::LENGTH;
57
new_fn_name(buf: &mut [u8]) -> &str58 fn new_fn_name(buf: &mut [u8]) -> &str {
59 buf[..FN_PREFIX.len()].copy_from_slice(FN_PREFIX);
60 Uuid::new_v4()
61 .to_simple()
62 .encode_lower(&mut buf[FN_PREFIX.len()..]);
63 unsafe { from_utf8_unchecked(&buf[..FN_BUF_LEN]) }
64 }
65