| commit | d7568e53327c614200ccf5d4b61bbbc62e566780 | [log] [tgz] |
|---|---|---|
| author | David Tolnay <dtolnay@gmail.com> | Sun Nov 11 15:23:32 2018 -0800 |
| committer | David Tolnay <dtolnay@gmail.com> | Sun Nov 11 15:23:35 2018 -0800 |
| tree | 5e561de789059e5341753c38bc3c15fca3025b42 | |
| parent | c239f03ca8a4259cb8d164d7e8a5fe18e7e38be2 [diff] |
Work around when built as a dependency in docs.rs
Our build script has:
if cfg!(procmacro2_semver_exempt) {
println!("cargo:rustc-cfg=super_unstable");
}
But when proc-macro2 is built as a dependency of another crate in docs.rs, we
are seeing the builder invoke rustc with `--cfg super_unstable` but without
`--cfg procmacro2_semver_exempt`. The super_unstable flag is only set on that
one line, so procmacro2_semver_exempt should have also been set. Hopefully this
change will result in both flags being passed.
We will need to figure out how to set unstable flags only when building our own
docs.rs docs, not when building proc-macro2 as a dependency of a different
crate.
proc-macro2
A small shim over the proc_macro crate in the compiler intended to multiplex the stable interface as of 1.15.0 and the interface as of 1.30.0.
New features added in Rust 1.30.0 include:
- Span information on tokens
- No need to go in/out through strings
- Structured input/output
Libraries ported to proc_macro2 can retain support for older compilers while continuing to get all the nice benefits of using a 1.30.0+ compiler.
Usage
This crate compiles on all 1.15.0+ stable compilers and usage looks like:
[dependencies] proc-macro2 = "0.4"
followed by
extern crate proc_macro; extern crate proc_macro2; #[proc_macro_derive(MyDerive)] pub fn my_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream { let input: proc_macro2::TokenStream = input.into(); let output: proc_macro2::TokenStream = { /* transform input */ }; output.into() }
The 1.30.0 compiler is automatically detected and its interfaces are used when available.
Unstable Features
proc-macro2 supports exporting some methods from proc_macro which are currently highly unstable, and are not stabilized in the first pass of proc_macro stabilizations. These features are not exported by default. Minor versions of proc-macro2 may make breaking changes to them at any time.
To enable these features, the procmacro2_semver_exempt config flag must be passed to rustc.
RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo build
Note that this must not only be done for your crate, but for any crate that depends on your crate. This infectious nature is intentional, as it serves as a reminder that you are outside of the normal semver guarantees.
License
This project is licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Serde by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.