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Diffstat (limited to 'rustversion/src/lib.rs')
| -rw-r--r-- | rustversion/src/lib.rs | 254 |
1 files changed, 254 insertions, 0 deletions
diff --git a/rustversion/src/lib.rs b/rustversion/src/lib.rs new file mode 100644 index 0000000..cf8ed21 --- /dev/null +++ b/rustversion/src/lib.rs @@ -0,0 +1,254 @@ +//! This crate provides macros for conditional compilation according to rustc +//! compiler version, analogous to [`#[cfg(...)]`][cfg] and +//! [`#[cfg_attr(...)]`][cfg_attr]. +//! +//! [cfg]: https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute +//! [cfg_attr]: https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg_attr-attribute +//! +//! <br> +//! +//! # Selectors +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::stable]</code></b> +//! —<br> +//! True on any stable compiler. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::stable(1.34)]</code></b> +//! —<br> +//! True on exactly the specified stable compiler. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::beta]</code></b> +//! —<br> +//! True on any beta compiler. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::nightly]</code></b> +//! —<br> +//! True on any nightly compiler or dev build. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::nightly(2019-01-01)]</code></b> +//! —<br> +//! True on exactly one nightly. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::since(1.34)]</code></b> +//! —<br> +//! True on that stable release and any later compiler, including beta and +//! nightly. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::since(2019-01-01)]</code></b> +//! —<br> +//! True on that nightly and all newer ones. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::before(</code></b><i>version or date</i><b><code>)]</code></b> +//! —<br> +//! Negative of <i>#[rustversion::since(...)]</i>. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::not(</code></b><i>selector</i><b><code>)]</code></b> +//! —<br> +//! Negative of any selector; for example <i>#[rustversion::not(nightly)]</i>. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::any(</code></b><i>selectors...</i><b><code>)]</code></b> +//! —<br> +//! True if any of the comma-separated selectors is true; for example +//! <i>#[rustversion::any(stable, beta)]</i>. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::all(</code></b><i>selectors...</i><b><code>)]</code></b> +//! —<br> +//! True if all of the comma-separated selectors are true; for example +//! <i>#[rustversion::all(since(1.31), before(1.34))]</i>. +//! </p> +//! +//! - <p style="margin-left:50px;text-indent:-50px"> +//! <b><code>#[rustversion::attr(</code></b><i>selector</i><b><code>, </code></b><i>attribute</i><b><code>)]</code></b> +//! —<br> +//! For conditional inclusion of attributes; analogous to +//! <code>cfg_attr</code>. +//! </p> +//! +//! <br> +//! +//! # Use cases +//! +//! Providing additional trait impls as types are stabilized in the standard library +//! without breaking compatibility with older compilers; in this case Pin\<P\> +//! stabilized in [Rust 1.33][pin]: +//! +//! [pin]: https://blog.rust-lang.org/2019/02/28/Rust-1.33.0.html#pinning +//! +//! ``` +//! # trait MyTrait {} +//! # +//! #[rustversion::since(1.33)] +//! use std::pin::Pin; +//! +//! #[rustversion::since(1.33)] +//! impl<P: MyTrait> MyTrait for Pin<P> { +//! /* ... */ +//! } +//! ``` +//! +//! Similar but for language features; the ability to control alignment greater than +//! 1 of packed structs was stabilized in [Rust 1.33][packed]. +//! +//! [packed]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1330-2019-02-28 +//! +//! ``` +//! #[rustversion::attr(before(1.33), repr(packed))] +//! #[rustversion::attr(since(1.33), repr(packed(2)))] +//! struct Six(i16, i32); +//! +//! fn main() { +//! println!("{}", std::mem::align_of::<Six>()); +//! } +//! ``` +//! +//! Augmenting code with `const` as const impls are stabilized in the standard +//! library. This use of `const` as an attribute is recognized as a special case +//! by the rustversion::attr macro. +//! +//! ``` +//! use std::time::Duration; +//! +//! #[rustversion::attr(since(1.32), const)] +//! fn duration_as_days(dur: Duration) -> u64 { +//! dur.as_secs() / 60 / 60 / 24 +//! } +//! ``` +//! +//! <br> + +extern crate proc_macro; + +mod attr; +mod bound; +mod date; +mod expr; +mod rustc; +mod time; +mod version; + +use crate::attr::Then; +use crate::expr::Expr; +use proc_macro::TokenStream; +use proc_macro2::{Ident, Span, TokenStream as TokenStream2}; +use quote::quote; +use syn::{parse_macro_input, ItemFn, Result}; + +#[proc_macro_attribute] +pub fn stable(args: TokenStream, input: TokenStream) -> TokenStream { + cfg("stable", args, input) +} + +#[proc_macro_attribute] +pub fn beta(args: TokenStream, input: TokenStream) -> TokenStream { + cfg("beta", args, input) +} + +#[proc_macro_attribute] +pub fn nightly(args: TokenStream, input: TokenStream) -> TokenStream { + cfg("nightly", args, input) +} + +#[proc_macro_attribute] +pub fn since(args: TokenStream, input: TokenStream) -> TokenStream { + cfg("since", args, input) +} + +#[proc_macro_attribute] +pub fn before(args: TokenStream, input: TokenStream) -> TokenStream { + cfg("before", args, input) +} + +#[proc_macro_attribute] +pub fn not(args: TokenStream, input: TokenStream) -> TokenStream { + cfg("not", args, input) +} + +#[proc_macro_attribute] +pub fn any(args: TokenStream, input: TokenStream) -> TokenStream { + cfg("any", args, input) +} + +#[proc_macro_attribute] +pub fn all(args: TokenStream, input: TokenStream) -> TokenStream { + cfg("all", args, input) +} + +fn cfg(top: &str, args: TokenStream, input: TokenStream) -> TokenStream { + match try_cfg(top, args, input) { + Ok(tokens) => tokens, + Err(err) => TokenStream::from(err.to_compile_error()), + } +} + +fn try_cfg(top: &str, args: TokenStream, input: TokenStream) -> Result<TokenStream> { + let args = TokenStream2::from(args); + let top = Ident::new(top, Span::call_site()); + + let mut full_args = quote!(#top); + if !args.is_empty() { + full_args.extend(quote!((#args))); + } + + let expr: Expr = syn::parse2(full_args)?; + let version = rustc::version()?; + + if expr.eval(version) { + Ok(input) + } else { + Ok(TokenStream::new()) + } +} + +#[proc_macro_attribute] +pub fn attr(args: TokenStream, input: TokenStream) -> TokenStream { + let args = parse_macro_input!(args as attr::Args); + + match try_attr(args, input) { + Ok(tokens) => tokens, + Err(err) => TokenStream::from(err.to_compile_error()), + } +} + +fn try_attr(args: attr::Args, input: TokenStream) -> Result<TokenStream> { + let version = rustc::version()?; + + if !args.condition.eval(version) { + return Ok(input); + } + + match args.then { + Then::Const(const_token) => { + let mut input: ItemFn = syn::parse(input)?; + input.sig.constness = Some(const_token); + Ok(TokenStream::from(quote!(#input))) + } + Then::Attribute(then) => { + let input = TokenStream2::from(input); + Ok(TokenStream::from(quote! { + #[cfg_attr(all(), #then)] + #input + })) + } + } +} |