Add build script to make git version available in code

Signed-off-by: pep <pep@bouah.net>

build.rs

@@ -0,0 +1,41 @@
+// Copyright (C) 2026-2099 The crate authors.
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU Affero General Public License as published by the
+// Free Software Foundation, either version 3 of the License, or (at your
+// option) any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License
+// for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+use std::env;
+use std::fs;
+use std::path::Path;
+
+use git2::Repository;
+
+fn main() {
+	let oid = {
+		match Repository::open(".") {
+			Ok(repo) => {
+				let head = repo.head().unwrap();
+				format!("{}", repo.refname_to_id(head.name().unwrap()).unwrap())
+			}
+			Err(e) => {
+				println!("cargo::warning={}", e);
+				String::new()
+			}
+		}
+	};
+
+	let out_dir = env::var_os("OUT_DIR").unwrap();
+	let dest_path = Path::new(&out_dir).join("GIT_COMMIT");
+	fs::write(&dest_path, oid).unwrap();
+
+	println!("cargo::rerun-if-changed=build.rs");
+}