You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
94 lines
3.4 KiB
94 lines
3.4 KiB
4 months ago
|
# proc-macro2
|
||
|
|
|
||
|
|
[](https://github.com/alexcrichton/proc-macro2/actions)
|
||
|
|
[](https://crates.io/crates/proc-macro2)
|
||
|
|
[](https://docs.rs/proc-macro2)
|
||
|
|
|
||
|
|
A wrapper around the procedural macro API of the compiler's `proc_macro` crate.
|
||
|
|
This library serves two purposes:
|
||
|
|
|
||
|
|
- **Bring proc-macro-like functionality to other contexts like build.rs and
|
||
|
|
main.rs.** Types from `proc_macro` are entirely specific to procedural macros
|
||
|
|
and cannot ever exist in code outside of a procedural macro. Meanwhile
|
||
|
|
`proc_macro2` types may exist anywhere including non-macro code. By developing
|
||
|
|
foundational libraries like [syn] and [quote] against `proc_macro2` rather
|
||
|
|
than `proc_macro`, the procedural macro ecosystem becomes easily applicable to
|
||
|
|
many other use cases and we avoid reimplementing non-macro equivalents of
|
||
|
|
those libraries.
|
||
|
|
|
||
|
|
- **Make procedural macros unit testable.** As a consequence of being specific
|
||
|
|
to procedural macros, nothing that uses `proc_macro` can be executed from a
|
||
|
|
unit test. In order for helper libraries or components of a macro to be
|
||
|
|
testable in isolation, they must be implemented using `proc_macro2`.
|
||
|
|
|
||
|
|
[syn]: https://github.com/dtolnay/syn
|
||
|
|
[quote]: https://github.com/dtolnay/quote
|
||
|
|
|
||
|
|
## Usage
|
||
|
|
|
||
|
|
```toml
|
||
|
|
[dependencies]
|
||
|
|
proc-macro2 = "1.0"
|
||
|
|
```
|
||
|
|
|
||
|
|
The skeleton of a typical procedural macro typically looks like this:
|
||
|
|
|
||
|
|
```rust
|
||
|
|
extern crate proc_macro;
|
||
|
|
|
||
|
|
#[proc_macro_derive(MyDerive)]
|
||
|
|
pub fn my_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
|
||
|
|
let input = proc_macro2::TokenStream::from(input);
|
||
|
|
|
||
|
|
let output: proc_macro2::TokenStream = {
|
||
|
|
/* transform input */
|
||
|
|
};
|
||
|
|
|
||
|
|
proc_macro::TokenStream::from(output)
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
If parsing with [Syn], you'll use [`parse_macro_input!`] instead to propagate
|
||
|
|
parse errors correctly back to the compiler when parsing fails.
|
||
|
|
|
||
|
|
[`parse_macro_input!`]: https://docs.rs/syn/1.0/syn/macro.parse_macro_input.html
|
||
|
|
|
||
|
|
## Unstable features
|
||
|
|
|
||
|
|
The default feature set of proc-macro2 tracks the most recent stable compiler
|
||
|
|
API. Functionality in `proc_macro` that is not yet stable is not exposed by
|
||
|
|
proc-macro2 by default.
|
||
|
|
|
||
|
|
To opt into the additional APIs available in the most recent nightly compiler,
|
||
|
|
the `procmacro2_semver_exempt` config flag must be passed to rustc. We will
|
||
|
|
polyfill those nightly-only APIs back to Rust 1.31.0. As these are unstable APIs
|
||
|
|
that track the nightly compiler, minor versions of proc-macro2 may make breaking
|
||
|
|
changes to them at any time.
|
||
|
|
|
||
|
|
```
|
||
|
|
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.
|
||
|
|
|
||
|
|
Semver exempt methods are marked as such in the proc-macro2 documentation.
|
||
|
|
|
||
|
|
<br>
|
||
|
|
|
||
|
|
#### License
|
||
|
|
|
||
|
|
<sup>
|
||
|
|
Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
|
||
|
|
2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
|
||
|
|
</sup>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
|
||
|
|
<sub>
|
||
|
|
Unless you explicitly state otherwise, any contribution intentionally submitted
|
||
|
|
for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
|
||
|
|
be dual licensed as above, without any additional terms or conditions.
|
||
|
|
</sub>
|