1 use std::env; 2 use std::process::Command; 3 use std::str; 4 5 // The rustc-cfg strings below are *not* public API. Please let us know by 6 // opening a GitHub issue if your build environment requires some way to enable 7 // these cfgs other than by executing our build script. main()8fn main() { 9 let minor = match rustc_minor_version() { 10 Some(minor) => minor, 11 None => return, 12 }; 13 14 // Function-like procedural macros in expressions, patterns, and statements 15 // stabilized in Rust 1.45: 16 // https://blog.rust-lang.org/2020/07/16/Rust-1.45.0.html#stabilizing-function-like-procedural-macros-in-expressions-patterns-and-statements 17 if minor < 45 { 18 println!("cargo:rustc-cfg=need_proc_macro_hack"); 19 } 20 } 21 rustc_minor_version() -> Option<u32>22fn rustc_minor_version() -> Option<u32> { 23 let rustc = env::var_os("RUSTC")?; 24 let output = Command::new(rustc).arg("--version").output().ok()?; 25 let version = str::from_utf8(&output.stdout).ok()?; 26 let mut pieces = version.split('.'); 27 if pieces.next() != Some("rustc 1") { 28 return None; 29 } 30 pieces.next()?.parse().ok() 31 } 32