#proc-macro2 #syn


Apply parser functions to proc-macro2 token streams

4 stable releases

3.0.4 Aug 26, 2023
2.0.3 Nov 9, 2020
1.0.3 Nov 9, 2020
1.0.2 Nov 8, 2020
1.0.0 May 11, 2020

#63 in Procedural macros

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Used in 5 crates (3 directly)


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This library provides a call2 function that sits somewhere in-between syn's parse2 and ParseBuffer::call: It lets you conveniently apply a parser function to a proc-macro2 token stream, for example from a quote!.


Please use cargo-edit to always add the latest version of this library:

cargo add call2-for-syn


use call2_for_syn::{call2_allow_incomplete, call2_strict};
use quote::quote;
use syn::{ext::IdentExt as _, Ident, Token};
use unquote::unquote;

let (now, is) = call2_strict(
    quote!(Now is...),
    |input| {
        let now: Ident = input.parse()?;
        let is: Ident = input.parse()?;
        // input.parse::<Token![!]>()?;
        syn::Result::Ok((now, is))
).unwrap_err().parsed.unwrap(); // Use ? here in a real program.

assert_eq!(format!("{}", now), "Now");
assert_eq!(format!("{}", is), "is");

let (a, good, time) = call2_strict(
    quote!(...a good time...),
    |input| {
        let a: Ident;
        let good: Ident;
        let time: Ident;
        unquote!(input, ... #a #good #time ...);
        syn::Result::Ok((a, good, time))
).unwrap().unwrap(); // Use ? here in a real program.

assert_eq!(format!("{}", a), "a");
assert_eq!(format!("{}", good), "good");
assert_eq!(format!("{}", time), "time");

let (r#for, parsing) = call2_allow_incomplete(
    quote!(for parsing!),
    |input| {
        let r#for = input.call(Ident::parse_any)?;
        let parsing: Ident = input.parse()?;
        // input.parse::<Token![!]>()?;
        syn::Result::Ok((r#for, parsing))
).unwrap(); // Use ? here in a real program.

assert_eq!(format!("{}", r#for), "for");
assert_eq!(format!("{}", parsing), "parsing");


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

See CONTRIBUTING for more information.

Code of Conduct



call2-for-syn strictly follows Semantic Versioning 2.0.0 with the following exceptions:

  • The minor version will not reset to 0 on major version changes (except for v1).
    Consider it the global feature level.
  • The patch version will not reset to 0 on major or minor version changes (except for v0.1 and v1).
    Consider it the global patch level.

This includes the Rust version requirement specified above.
Earlier Rust versions may be compatible, but this can change with minor or patch releases.

Which versions are affected by features and patches can be determined from the respective headings in CHANGELOG.md.

Note that dependencies of this crate may have a more lenient MSRV policy! Please use cargo +nightly update -Z minimal-versions in your automation if you don't generate Cargo.lock manually (or as necessary) and require support for a compiler older than current stable.


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