diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml index ea6b607..f82f7f1 100644 --- a/.github/workflows/ci.yml +++ b/.github/workflows/ci.yml @@ -33,6 +33,7 @@ jobs: - 1.36.0 # Oldest supported with MaybeUninit - 1.40.0 # Oldest supported with cfg(doctest) - 1.51.0 # Oldest supported with ptr::addr_of! + - 1.65.0 # Oldest supported with stable const evaluation (sans cell) - stable - beta - nightly diff --git a/README.md b/README.md index e297b33..2df877a 100644 --- a/README.md +++ b/README.md @@ -45,12 +45,23 @@ fn main() { } ``` -## Feature flags ## +## Usage in constants ## +`memoffset` has support for compile-time `offset_of!` on rust>=1.65, or on older nightly compilers. -### Usage in constants ### -`memoffset` has **experimental** support for compile-time `offset_of!` on a nightly compiler. +### Usage on stable Rust ### +Constant evaluation is automatically enabled and avilable on stable compilers starting with rustc 1.65. -In order to use it, you must enable the `unstable_const` crate feature and several compiler features. +This is an incomplete implementation with one caveat: +Due to dependence on [`#![feature(const_refs_to_cell)]`](https://github.com/rust-lang/rust/issues/80384), you cannot get the offset of a `Cell` field in a const-context. + +This means that if need to get the offset of a cell, you'll have to remain on nightly for now. + +### Usage on recent nightlies ### + +If you're using a new-enough nightly and you require the ability to get the offset of a `Cell`, +you'll have to enable the `unstable_const` cargo feature, as well as enabling `const_refs_to_cell` in your crate root. + +Do note that `unstable_const` is an unstable feature that is set to be removed in a future version of `memoffset`. Cargo.toml: ```toml @@ -59,6 +70,14 @@ version = "0.7" features = ["unstable_const"] ``` +Your crate root: (`lib.rs`/`main.rs`) +```rust,ignore +#![feature(const_refs_to_cell)] +``` + +### Usage on older nightlies ### +In order to use it on an older nightly compiler, you must enable the `unstable_const` crate feature and several compiler features. + Your crate root: (`lib.rs`/`main.rs`) ```rust,ignore #![feature(const_ptr_offset_from, const_refs_to_cell)] diff --git a/build.rs b/build.rs index 0604c19..e18810f 100644 --- a/build.rs +++ b/build.rs @@ -19,4 +19,7 @@ fn main() { if ac.probe_rustc_version(1, 51) { println!("cargo:rustc-cfg=raw_ref_macros"); } + if ac.probe_rustc_version(1, 65) { + println!("cargo:rustc-cfg=stable_const"); + } } diff --git a/src/lib.rs b/src/lib.rs index d80ff17..72736aa 100644 --- a/src/lib.rs +++ b/src/lib.rs @@ -57,9 +57,10 @@ #![no_std] #![cfg_attr( - feature = "unstable_const", - feature(const_ptr_offset_from, const_refs_to_cell) + all(feature = "unstable_const", not(stable_const)), + feature(const_ptr_offset_from) )] +#![cfg_attr(feature = "unstable_const", feature(const_refs_to_cell))] #[macro_use] #[cfg(doctests)] diff --git a/src/offset_of.rs b/src/offset_of.rs index d070181..9ce4ae2 100644 --- a/src/offset_of.rs +++ b/src/offset_of.rs @@ -46,7 +46,7 @@ macro_rules! _memoffset__let_base_ptr { } /// Macro to compute the distance between two pointers. -#[cfg(feature = "unstable_const")] +#[cfg(any(feature = "unstable_const", stable_const))] #[macro_export] #[doc(hidden)] macro_rules! _memoffset_offset_from_unsafe { @@ -58,7 +58,7 @@ macro_rules! _memoffset_offset_from_unsafe { unsafe { (field as *const u8).offset_from(base as *const u8) as usize } }}; } -#[cfg(not(feature = "unstable_const"))] +#[cfg(not(any(feature = "unstable_const", stable_const)))] #[macro_export] #[doc(hidden)] macro_rules! _memoffset_offset_from_unsafe { @@ -312,7 +312,7 @@ mod tests { assert_eq!(f_ptr as usize + 0, raw_field_union!(f_ptr, Foo, c) as usize); } - #[cfg(feature = "unstable_const")] + #[cfg(any(feature = "unstable_const", stable_const))] #[test] fn const_offset() { #[repr(C)] @@ -337,7 +337,7 @@ mod tests { assert_eq!([0; offset_of!(Foo, b)].len(), 4); } - #[cfg(feature = "unstable_const")] + #[cfg(any(feature = "unstable_const", stable_const))] #[test] fn const_fn_offset() { const fn test_fn() -> usize {