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Diffstat (limited to '')
| -rw-r--r-- | src/tools/rust-analyzer/crates/proc-macro-srv/src/abis/abi_1_64/proc_macro/bridge/selfless_reify.rs | 84 |
1 files changed, 0 insertions, 84 deletions
diff --git a/src/tools/rust-analyzer/crates/proc-macro-srv/src/abis/abi_1_64/proc_macro/bridge/selfless_reify.rs b/src/tools/rust-analyzer/crates/proc-macro-srv/src/abis/abi_1_64/proc_macro/bridge/selfless_reify.rs deleted file mode 100644 index 907ad256e..000000000 --- a/src/tools/rust-analyzer/crates/proc-macro-srv/src/abis/abi_1_64/proc_macro/bridge/selfless_reify.rs +++ /dev/null @@ -1,84 +0,0 @@ -//! Abstraction for creating `fn` pointers from any callable that *effectively* -//! has the equivalent of implementing `Default`, even if the compiler neither -//! provides `Default` nor allows reifying closures (i.e. creating `fn` pointers) -//! other than those with absolutely no captures. -//! -//! More specifically, for a closure-like type to be "effectively `Default`": -//! * it must be a ZST (zero-sized type): no information contained within, so -//! that `Default`'s return value (if it were implemented) is unambiguous -//! * it must be `Copy`: no captured "unique ZST tokens" or any other similar -//! types that would make duplicating values at will unsound -//! * combined with the ZST requirement, this confers a kind of "telecopy" -//! ability: similar to `Copy`, but without keeping the value around, and -//! instead "reconstructing" it (a noop given it's a ZST) when needed -//! * it must be *provably* inhabited: no captured uninhabited types or any -//! other types that cannot be constructed by the user of this abstraction -//! * the proof is a value of the closure-like type itself, in a sense the -//! "seed" for the "telecopy" process made possible by ZST + `Copy` -//! * this requirement is the only reason an abstraction limited to a specific -//! usecase is required: ZST + `Copy` can be checked with *at worst* a panic -//! at the "attempted `::default()` call" time, but that doesn't guarantee -//! that the value can be soundly created, and attempting to use the typical -//! "proof ZST token" approach leads yet again to having a ZST + `Copy` type -//! that is not proof of anything without a value (i.e. isomorphic to a -//! newtype of the type it's trying to prove the inhabitation of) -//! -//! A more flexible (and safer) solution to the general problem could exist once -//! `const`-generic parameters can have type parameters in their types: -//! -//! ```rust,ignore (needs future const-generics) -//! extern "C" fn ffi_wrapper< -//! A, R, -//! F: Fn(A) -> R, -//! const f: F, // <-- this `const`-generic is not yet allowed -//! >(arg: A) -> R { -//! f(arg) -//! } -//! ``` - -use std::mem; - -// FIXME(eddyb) this could be `trait` impls except for the `const fn` requirement. -macro_rules! define_reify_functions { - ($( - fn $name:ident $(<$($param:ident),*>)? - for $(extern $abi:tt)? fn($($arg:ident: $arg_ty:ty),*) -> $ret_ty:ty; - )+) => { - $(pub const fn $name< - $($($param,)*)? - F: Fn($($arg_ty),*) -> $ret_ty + Copy - >(f: F) -> $(extern $abi)? fn($($arg_ty),*) -> $ret_ty { - // FIXME(eddyb) describe the `F` type (e.g. via `type_name::<F>`) once panic - // formatting becomes possible in `const fn`. - assert!(mem::size_of::<F>() == 0, "selfless_reify: closure must be zero-sized"); - - $(extern $abi)? fn wrapper< - $($($param,)*)? - F: Fn($($arg_ty),*) -> $ret_ty + Copy - >($($arg: $arg_ty),*) -> $ret_ty { - let f = unsafe { - // SAFETY: `F` satisfies all criteria for "out of thin air" - // reconstructability (see module-level doc comment). - mem::MaybeUninit::<F>::uninit().assume_init() - }; - f($($arg),*) - } - let _f_proof = f; - wrapper::< - $($($param,)*)? - F - > - })+ - } -} - -define_reify_functions! { - fn _reify_to_extern_c_fn_unary<A, R> for extern "C" fn(arg: A) -> R; - - // HACK(eddyb) this abstraction is used with `for<'a> fn(BridgeConfig<'a>) - // -> T` but that doesn't work with just `reify_to_extern_c_fn_unary` - // because of the `fn` pointer type being "higher-ranked" (i.e. the - // `for<'a>` binder). - // FIXME(eddyb) try to remove the lifetime from `BridgeConfig`, that'd help. - fn reify_to_extern_c_fn_hrt_bridge<R> for extern "C" fn(bridge: super::BridgeConfig<'_>) -> R; -} |