use std::env; use std::process::Command; use std::str; // The rustc-cfg strings below are *not* public API. Please let us know by // opening a GitHub issue if your build environment requires some way to enable // these cfgs other than by executing our build script. fn main() { let minor = match rustc_minor_version() { Some(minor) => minor, None => return, }; // Underscore const names stabilized in Rust 1.37: // https://blog.rust-lang.org/2019/08/15/Rust-1.37.0.html#using-unnamed-const-items-for-macros if minor < 37 { println!("cargo:rustc-cfg=no_underscore_consts"); } // The ptr::addr_of! macro stabilized in Rust 1.51: // https://blog.rust-lang.org/2021/03/25/Rust-1.51.0.html#stabilized-apis if minor < 51 { println!("cargo:rustc-cfg=no_ptr_addr_of"); } } fn rustc_minor_version() -> Option { let rustc = env::var_os("RUSTC")?; let output = Command::new(rustc).arg("--version").output().ok()?; let version = str::from_utf8(&output.stdout).ok()?; let mut pieces = version.split('.'); if pieces.next() != Some("rustc 1") { return None; } pieces.next()?.parse().ok() }