Expose build identity in version output

build.rs

@@ -0,0 +1,26 @@
+use std::process::Command;
+
+fn git(args: &[&str]) -> Option<String> {
+    let output = Command::new("git").args(args).output().ok()?;
+    if !output.status.success() {
+        return None;
+    }
+    let text = String::from_utf8(output.stdout).ok()?;
+    Some(text.trim().to_string())
+}
+
+fn main() {
+    println!("cargo:rerun-if-changed=.git/HEAD");
+    println!("cargo:rerun-if-changed=.git/index");
+
+    let hash = git(&["rev-parse", "--short=12", "HEAD"]).unwrap_or_else(|| "unknown".into());
+    let date = git(&["show", "-s", "--format=%cs", "HEAD"]).unwrap_or_else(|| "unknown".into());
+    let dirty = Command::new("git")
+        .args(["diff", "--quiet", "--ignore-submodules", "--"])
+        .status()
+        .map(|status| if status.success() { "" } else { "+dirty" })
+        .unwrap_or("");
+
+    println!("cargo:rustc-env=DOSH_GIT_HASH={hash}{dirty}");
+    println!("cargo:rustc-env=DOSH_COMMIT_DATE={date}");
+}