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 println!("cargo:rerun-if-changed=build.rs"); 10 11 let minor = match rustc_minor_version() { 12 Some(minor) => minor, 13 None => return, 14 }; 15 16 // Underscore const names stabilized in Rust 1.37: 17 // https://blog.rust-lang.org/2019/08/15/Rust-1.37.0.html#using-unnamed-const-items-for-macros 18 if minor < 37 { 19 println!("cargo:rustc-cfg=no_underscore_consts"); 20 } 21 22 // The ptr::addr_of! macro stabilized in Rust 1.51: 23 // https://blog.rust-lang.org/2021/03/25/Rust-1.51.0.html#stabilized-apis 24 if minor < 51 { 25 println!("cargo:rustc-cfg=no_ptr_addr_of"); 26 } 27 } 28 rustc_minor_version() -> Option<u32>29fn rustc_minor_version() -> Option<u32> { 30 let rustc = env::var_os("RUSTC")?; 31 let output = Command::new(rustc).arg("--version").output().ok()?; 32 let version = str::from_utf8(&output.stdout).ok()?; 33 let mut pieces = version.split('.'); 34 if pieces.next() != Some("rustc 1") { 35 return None; 36 } 37 pieces.next()?.parse().ok() 38 } 39