feat: Enable Nix 2.33 APIs for pre-release testing/validation

Pre-release versions (2.33.0pre) now enable 2.33 APIs, allowing development
and integration testing before the stable release. Tests remain disabled for
2.33 until stable to avoid blocking on unrelated pre-release issues.

nix-bindings-util/src/lib.rs

@@ -2,3 +2,4 @@ pub mod context;
 pub mod settings;
 #[macro_use]
 pub mod string_return;
+pub mod nix_version;

nix-bindings-util/src/nix_version.rs

@@ -0,0 +1,101 @@
+//! Nix version parsing and conditional compilation support.
+
+/// Emit [`cargo:rustc-cfg`] directives for Nix version-based conditional compilation.
+///
+/// Call from build.rs with the Nix version and desired version gates.
+///
+/// [`cargo:rustc-cfg`]: https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-cfg
+///
+/// # Example
+///
+/// ```
+/// use nix_bindings_util::nix_version::emit_version_cfg;
+/// # // Stub pkg_config so that we can render a full usage example
+/// # mod pkg_config { pub fn probe_library(_: &str) -> Result<Library, ()> { Ok(Library { version: "2.33.0pre".into() }) }
+/// #   pub struct Library { pub version: String } }
+///
+/// let nix_version = pkg_config::probe_library("nix-store-c").unwrap().version;
+/// emit_version_cfg(&nix_version, &["2.26", "2.33.0pre", "2.33"]);
+/// ```
+///
+/// Emits `nix_at_least="2.26"` and `nix_at_least="2.33.0pre"` for version 2.33.0pre,
+/// usable as `#[cfg(nix_at_least = "2.26")]`.
+pub fn emit_version_cfg(nix_version: &str, relevant_versions: &[&str]) {
+    // Declare the known versions for cargo check-cfg
+    let versions = relevant_versions
+        .iter()
+        .map(|v| format!("\"{}\"", v))
+        .collect::<Vec<_>>()
+        .join(",");
+
+    println!(
+        "cargo:rustc-check-cfg=cfg(nix_at_least,values({}))",
+        versions
+    );
+
+    let nix_version = parse_version(nix_version);
+
+    for version_str in relevant_versions {
+        let version = parse_version(version_str);
+        if nix_version >= version {
+            println!("cargo:rustc-cfg=nix_at_least=\"{}\"", version_str);
+        }
+    }
+}
+
+/// Parse a Nix version string into a comparable tuple `(major, minor, patch)`.
+///
+/// Pre-release versions (containing `"pre"`) get patch = -1, sorting before stable releases.
+/// Omitted patch defaults to 0.
+///
+/// # Examples
+///
+/// ```
+/// use nix_bindings_util::nix_version::parse_version;
+///
+/// assert_eq!(parse_version("2.26"), (2, 26, 0));
+/// assert_eq!(parse_version("2.33.0pre"), (2, 33, -1));
+/// assert_eq!(parse_version("2.33"), (2, 33, 0));
+/// assert_eq!(parse_version("2.33.1"), (2, 33, 1));
+///
+/// // Pre-release versions sort before stable
+/// assert!(parse_version("2.33.0pre") < parse_version("2.33"));
+/// ```
+pub fn parse_version(version_str: &str) -> (u32, u32, i32) {
+    let parts = version_str.split('.').collect::<Vec<&str>>();
+    let major = parts[0].parse::<u32>().unwrap();
+    let minor = parts[1].parse::<u32>().unwrap();
+    let patch = if parts.get(2).map_or(false, |s| s.contains("pre")) {
+        -1i32
+    } else {
+        parts
+            .get(2)
+            .and_then(|s| s.parse::<i32>().ok())
+            .unwrap_or(0)
+    };
+    (major, minor, patch)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_version() {
+        assert_eq!(parse_version("2.26"), (2, 26, 0));
+        assert_eq!(parse_version("2.33.0pre"), (2, 33, -1));
+        assert_eq!(parse_version("2.33"), (2, 33, 0));
+        assert_eq!(parse_version("2.33.1"), (2, 33, 1));
+    }
+
+    #[test]
+    fn test_version_ordering() {
+        // Pre-release versions should sort before stable
+        assert!(parse_version("2.33.0pre") < parse_version("2.33"));
+        assert!(parse_version("2.33.0pre") < parse_version("2.33.0"));
+
+        // Normal version ordering
+        assert!(parse_version("2.26") < parse_version("2.33"));
+        assert!(parse_version("2.33") < parse_version("2.33.1"));
+    }
+}