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 // Underscore const names stabilized in Rust 1.37: 15 // https://blog.rust-lang.org/2019/08/15/Rust-1.37.0.html#using-unnamed-const-items-for-macros 16 if minor >= 37 { 17 println!("cargo:rustc-cfg=underscore_consts"); 18 } 19 20 // The ptr::addr_of! macro stabilized in Rust 1.51: 21 // https://blog.rust-lang.org/2021/03/25/Rust-1.51.0.html#stabilized-apis 22 if minor >= 51 { 23 println!("cargo:rustc-cfg=ptr_addr_of"); 24 } 25 } 26 rustc_minor_version() -> Option<u32>27fn rustc_minor_version() -> Option<u32> { 28 let rustc = env::var_os("RUSTC")?; 29 let output = Command::new(rustc).arg("--version").output().ok()?; 30 let version = str::from_utf8(&output.stdout).ok()?; 31 let mut pieces = version.split('.'); 32 if pieces.next() != Some("rustc 1") { 33 return None; 34 } 35 pieces.next()?.parse().ok() 36 } 37