1 files changed, 38 insertions, 0 deletions
diff --git a/build.rs b/build.rs
new file mode 100644
index 0000000..1249dab
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,38 @@
+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() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    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<u32> {
+    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()
+}