chore: checkpoint before Python removal

vendor/zmij/build.rs

@@ -0,0 +1,38 @@
+use std::env;
+use std::ffi::OsString;
+use std::process::{self, Command};
+use std::str;
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    let rustc = rustc_minor_version().unwrap_or(u32::MAX);
+
+    if rustc >= 80 {
+        println!("cargo:rustc-check-cfg=cfg(exhaustive)");
+        println!("cargo:rustc-check-cfg=cfg(zmij_no_select_unpredictable)");
+    }
+
+    if rustc < 88 {
+        // https://doc.rust-lang.org/std/hint/fn.select_unpredictable.html
+        println!("cargo:rustc-cfg=zmij_no_select_unpredictable");
+    }
+}
+
+fn rustc_minor_version() -> Option<u32> {
+    let rustc = cargo_env_var("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()
+}
+
+fn cargo_env_var(key: &str) -> OsString {
+    env::var_os(key).unwrap_or_else(|| {
+        eprintln!("Environment variable ${key} is not set during execution of build script");
+        process::exit(1);
+    })
+}