feat: Store.get_storedir()

(cherry picked from commit 6f4ba636f1e563167e6456d42c9fb6f65c9ca504)

rust/nix-store/build.rs

@@ -0,0 +1,39 @@
+fn main() {
+    // Get nix version
+    let nix_version = pkg_config::probe_library("nix-store-c").unwrap().version;
+
+    // Generate version flags
+    // Unfortunately, Rust doesn't give us a "greater than" operator in conditional
+    // compilation, so we pre-evaluate the version comparisons here, making use
+    // of the multi-valued nature of Rust cfgs.
+    let relevant_versions = vec!["2.26"];
+    let versions = relevant_versions
+        .iter()
+        .map(|v| format!("\"{}\"", v))
+        .collect::<Vec<_>>()
+        .join(",");
+
+    // Declare the known versions, so that Rust can warn about unknown versions
+    // that aren't part of `relevant_versions` yet - feel free to add entries.
+    println!(
+        "cargo:rustc-check-cfg=cfg(nix_at_least,values({}))",
+        versions
+    );
+
+    let nix_version = nix_version.split('.').collect::<Vec<&str>>();
+    let nix_version = (
+        nix_version[0].parse::<u32>().unwrap(),
+        nix_version[1].parse::<u32>().unwrap(),
+    );
+
+    for version_str in relevant_versions {
+        let version = version_str.split('.').collect::<Vec<&str>>();
+        let version = (
+            version[0].parse::<u32>().unwrap(),
+            version[1].parse::<u32>().unwrap(),
+        );
+        if nix_version >= version {
+            println!("cargo:rustc-cfg=nix_at_least=\"{}\"", version_str);
+        }
+    }
+}